Avoid deep recursion in serialization write-buffer test

The "many small structural writes exceed the write buffer" subcase built
a 1100-deep nested array and dumped it to force >1024 consecutive
single-character writes through put_char (exercising the write buffer's
flush-when-full branch). dump() recurses per nesting level, so on MSVC
debug builds (smaller default stack, larger frames) this overflowed the
stack and crashed test-serialization; Linux/macOS have enough headroom to
hide it.

Replace the nesting with a flat array of 500 empty strings. Each element
emits '"', '"', ',' via put_char, so the dump is a long run of
single-character writes (1501 bytes > the 1024-byte buffer) at nesting
depth two, hitting the same flush branch without deep recursion. Library
code is unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XAYM1qhSA2FDaDcGfPW3fG
Signed-off-by: Niels Lohmann <mail@nlohmann.me>

.github/SECURITY.md

@@ -15,14 +15,6 @@ guidance.
 
 For vulnerabilities in third-party dependencies or modules, please report them directly to the respective maintainers.
 
-## Unofficial packages
-
-This project does not publish an official npm package. The npm package
-[`nlohmann-json`](https://www.npmjs.com/package/nlohmann-json) (or similarly named packages) is not maintained or
-endorsed by this project. See the
-[package managers documentation](https://json.nlohmann.me/integration/package_managers/#npm) for supported
-integration options.
-
 ## Additional Resources
 
 - Explore security-related topics and contribute to tools and projects through

.github/workflows/check_amalgamation.yml

@@ -39,14 +39,14 @@ jobs:
           egress-policy: audit
 
       - name: Checkout pull request
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           path: main
           ref: ${{ github.event.pull_request.head.sha }}
           persist-credentials: false
 
       - name: Checkout tools
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           path: tools
           ref: develop

.github/workflows/codeql-analysis.yml

@@ -32,20 +32,20 @@ jobs:
         egress-policy: audit
 
     - name: Checkout repository
-      uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
       with:
         persist-credentials: false
 
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL
-      uses: github/codeql-action/init@7188fc363630916deb702c7fdcf4e481b751f97a # v4.37.1
+      uses: github/codeql-action/init@99df26d4f13ea111d4ec1a7dddef6063f76b97e9 # v4.37.0
       with:
         languages: c-cpp
 
     # Autobuild attempts to build any compiled languages  (C/C++, C#, or Java).
     # If this step fails, then you should remove it and run the build manually (see below)
     - name: Autobuild
-      uses: github/codeql-action/autobuild@7188fc363630916deb702c7fdcf4e481b751f97a # v4.37.1
+      uses: github/codeql-action/autobuild@99df26d4f13ea111d4ec1a7dddef6063f76b97e9 # v4.37.0
 
     - name: Perform CodeQL Analysis
-      uses: github/codeql-action/analyze@7188fc363630916deb702c7fdcf4e481b751f97a # v4.37.1
+      uses: github/codeql-action/analyze@99df26d4f13ea111d4ec1a7dddef6063f76b97e9 # v4.37.0

.github/workflows/dependency-review.yml

@@ -22,7 +22,7 @@ jobs:
           egress-policy: audit
 
       - name: 'Checkout Repository'
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: 'Dependency Review'

.github/workflows/flawfinder.yml

@@ -32,7 +32,7 @@ jobs:
           egress-policy: audit
 
       - name: Checkout code
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
 
@@ -43,6 +43,6 @@ jobs:
           output: 'flawfinder_results.sarif'
 
       - name: Upload analysis results to GitHub Security tab
-        uses: github/codeql-action/upload-sarif@7188fc363630916deb702c7fdcf4e481b751f97a # v4.37.1
+        uses: github/codeql-action/upload-sarif@99df26d4f13ea111d4ec1a7dddef6063f76b97e9 # v4.37.0
         with:
           sarif_file: ${{github.workspace}}/flawfinder_results.sarif

.github/workflows/macos.yml

@@ -26,7 +26,7 @@ jobs:
       DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
 
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Run CMake
@@ -45,7 +45,7 @@ jobs:
       DEVELOPER_DIR: /Applications/Xcode_${{ matrix.xcode }}.app/Contents/Developer
 
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Run CMake
@@ -62,7 +62,7 @@ jobs:
         standard: [11, 14, 17, 20, 23, 26]
 
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Run CMake

.github/workflows/publish_documentation.yml

@@ -31,7 +31,7 @@ jobs:
         with:
           egress-policy: audit
 
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
 
       - name: Install virtual environment
         run: make install_venv -C docs/mkdocs

.github/workflows/scorecards.yml

@@ -41,7 +41,7 @@ jobs:
           egress-policy: audit
 
       - name: "Checkout code"
-        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
 
@@ -76,6 +76,6 @@ jobs:
 
       # Upload the results to GitHub's code scanning dashboard.
       - name: "Upload to code-scanning"
-        uses: github/codeql-action/upload-sarif@7188fc363630916deb702c7fdcf4e481b751f97a # v4.37.1
+        uses: github/codeql-action/upload-sarif@99df26d4f13ea111d4ec1a7dddef6063f76b97e9 # v4.37.0
         with:
           sarif_file: results.sarif

.github/workflows/semgrep.yml

@@ -37,7 +37,7 @@ jobs:
           egress-policy: audit
 
       # Checkout project source
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
 
@@ -61,7 +61,7 @@ jobs:
 
       # Upload SARIF file generated in previous step
       - name: Upload SARIF file
-        uses: github/codeql-action/upload-sarif@7188fc363630916deb702c7fdcf4e481b751f97a # v4.37.1
+        uses: github/codeql-action/upload-sarif@99df26d4f13ea111d4ec1a7dddef6063f76b97e9 # v4.37.0
         with:
           sarif_file: semgrep.sarif
         if: always()

.github/workflows/ubuntu.yml

@@ -21,11 +21,11 @@ jobs:
     runs-on: ubuntu-latest
     container: gcc:latest
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -43,11 +43,11 @@ jobs:
         run: |
           wget -q -O - "https://github.com/facebook/infer/releases/download/v1.3.0/infer-linux-x86_64-v1.3.0.tar.xz" | sudo tar -C /opt -xJ
           sudo ln -s /opt/infer-linux-x86_64-v1.3.0/bin/infer /usr/local/bin/infer
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -66,11 +66,11 @@ jobs:
 
       - name: Install Valgrind
         run: sudo apt-get update ; sudo apt-get install -y valgrind
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -85,11 +85,11 @@ jobs:
     steps:
       - name: Install git, clang-tools, iwyu (ci_single_binaries), and unzip
         run: apt-get update ; apt-get install -y git clang-tools iwyu unzip
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -104,11 +104,11 @@ jobs:
     steps:
       - name: Install build-essential
         run: apt-get update ; apt-get install -y build-essential unzip wget git libssl-dev
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -122,7 +122,7 @@ jobs:
         with:
           egress-policy: audit
 
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Install dependencies and de_DE locale
@@ -163,15 +163,7 @@ jobs:
           export DEBIAN_FRONTEND=noninteractive
           apt-get update
           apt-get install -y --no-install-recommends software-properties-common ca-certificates gnupg make git
-          # add-apt-repository resolves the PPA through the Launchpad API,
+          add-apt-repository -y ppa:ubuntu-toolchain-r/test
-          # which intermittently times out or fails the team lookup (the plain
-          # "deb ..." sources below never hit Launchpad and never flake).
-          # Retry with backoff so a transient Launchpad blip does not fail CI.
-          for attempt in 1 2 3 4 5; do
-            add-apt-repository -y ppa:ubuntu-toolchain-r/test && break
-            echo "::warning::add-apt-repository ppa:ubuntu-toolchain-r/test failed (attempt ${attempt}/5); retrying"
-            sleep $((attempt * 10))
-          done
           apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ bionic main"
           apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ bionic universe"
           apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ xenial main"
@@ -180,11 +172,11 @@ jobs:
           apt-add-repository -y "deb http://archive.ubuntu.com/ubuntu/ xenial-updates universe"
           apt-get update
           apt-get install -y --no-install-recommends g++-${{ matrix.compiler }}
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: CXX=g++-${{ matrix.compiler }} cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -198,11 +190,11 @@ jobs:
         compiler: ['7', '8', '9', '10', '11', '12', '13', '14', '15', 'latest']
     container: gcc:${{ matrix.compiler }}
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -215,11 +207,11 @@ jobs:
         compiler: ['3.4', '3.5', '3.6', '3.7', '3.8', '3.9', '4', '5', '6', '7', '8', '9', '10', '11', '12', '13', '14', '15-bullseye', '16', '17', '18', '19', '20', 'latest']
     container: silkeh/clang:${{ matrix.compiler }}
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Set env FORCE_STDCPPFS_FLAG for clang 7 / 8 / 9 / 10
         run: echo "JSON_FORCED_GLOBAL_COMPILE_OPTIONS=-DJSON_HAS_FILESYSTEM=0;-DJSON_HAS_EXPERIMENTAL_FILESYSTEM=0" >> "$GITHUB_ENV"
         if: ${{ matrix.compiler == '7' || matrix.compiler == '8' || matrix.compiler == '9' || matrix.compiler == '10' }}
@@ -235,11 +227,11 @@ jobs:
       matrix:
         standard: [11, 14, 17, 20, 23, 26]
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -255,11 +247,11 @@ jobs:
     steps:
       - name: Install git and unzip
         run: apt-get update ; apt-get install -y git unzip
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build with libc++
@@ -282,11 +274,11 @@ jobs:
         cuda: ['11.8.0', '12.1.1', '12.6.3']
     container: nvidia/cuda:${{ matrix.cuda }}-devel-ubuntu22.04
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -299,14 +291,14 @@ jobs:
     runs-on: ubuntu-latest
     container: ${{ matrix.container }}
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       # The module test uses `import std;`, which needs CMake's experimental
       # import-std support. Its opt-in token is CMake-version-specific, so pin
       # CMake to the version whose token is set in tests/module_cpp20/CMakeLists.txt.
       - name: Get pinned CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
         with:
           cmakeVersion: 4.3.4
       # Clang: the std library module is provided by libc++ (the image's libstdc++
@@ -328,11 +320,11 @@ jobs:
     # Intel's own last officially published image that still includes it.
     container: intel/oneapi-hpckit:2023.2.1-devel-ubuntu22.04
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -345,9 +337,9 @@ jobs:
     runs-on: ubuntu-latest
     container: intel/oneapi-hpckit:latest
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -357,9 +349,9 @@ jobs:
     runs-on: ubuntu-latest
     container: nvcr.io/nvidia/nvhpc:25.5-devel-cuda12.9-ubuntu22.04
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DJSON_CI=On
       - name: Build
@@ -375,11 +367,11 @@ jobs:
 
       - name: Install emscripten
         uses: mymindstorm/setup-emsdk@4528d102f7230f0e7b276855c01ea1159be0e984 # v16
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Run CMake
         run: cmake -S . -B build -DCMAKE_TOOLCHAIN_FILE=$EMSDK/upstream/emscripten/cmake/Modules/Platform/Emscripten.cmake -GNinja
       - name: Build
@@ -396,7 +388,7 @@ jobs:
         with:
           egress-policy: audit
 
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Run CMake

.github/workflows/windows.yml

@@ -24,7 +24,7 @@ jobs:
         architecture: [x64, x86]
 
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Set up MinGW
@@ -49,7 +49,7 @@ jobs:
     runs-on: windows-2022
 
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Set extra CXX_FLAGS for latest std_version
@@ -86,9 +86,9 @@ jobs:
     runs-on: windows-2025
 
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
       - name: Get latest CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
       - name: Set extra CXX_FLAGS for latest std_version
         # /wd5285 silences C5285 emitted by the bundled third-party doctest.h, which
         # specializes std::tuple (newly diagnosed by the VS2026 v145 toolset)
@@ -122,7 +122,7 @@ jobs:
     runs-on: windows-11-arm
 
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
       - name: Run CMake (Release)
         run: cmake -S . -B build -G "Visual Studio 17 2022" -A ARM64 -DJSON_BuildTests=On -DCMAKE_CXX_FLAGS="/W4 /WX"
         if: matrix.build_type == 'Release'
@@ -143,7 +143,7 @@ jobs:
         version: [11.0.1, 12.0.1, 13.0.1, 14.0.6, 15.0.7, 16.0.6, 18.1.8, 19.1.7, 20.1.8]
 
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Install Clang
@@ -173,7 +173,7 @@ jobs:
         architecture: [Win32, x64]
 
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       - name: Run CMake
@@ -186,14 +186,14 @@ jobs:
   ci_module_cpp20:
     runs-on: windows-2022
     steps:
-      - uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+      - uses: actions/checkout@9c091bb21b7c1c1d1991bb908d89e4e9dddfe3e0 # v7.0.0
         with:
           persist-credentials: false
       # The module test uses `import std;`, which needs CMake's experimental
       # import-std support. Its opt-in token is CMake-version-specific, so pin
       # CMake to the version whose token is set in tests/module_cpp20/CMakeLists.txt.
       - name: Get pinned CMake and ninja
-        uses: lukka/get-cmake@e6906078ebd1ccb8ce51ab4626ac46a1b5a517e3 # v4.4.0
+        uses: lukka/get-cmake@f5b8fbb4d77cec1acc5a5f9f0df4beffaf5d98d9 # v4.3.4
         with:
           cmakeVersion: 4.3.4
       - name: Run CMake (Debug)

README.md

@@ -90,6 +90,7 @@ You can sponsor this library at [GitHub Sponsors](https://github.com/sponsors/nl
 - [Steve Sperandeo](https://github.com/homer6)
 - [Robert Jefe Lindstädt](https://github.com/eljefedelrodeodeljefe)
 - [Steve Wagner](https://github.com/ciroque)
+- [Lion Yang](https://github.com/LionNatsu)
 
 ### Further support
 

docs/mkdocs/docs/api/basic_json/dump.md

@@ -43,17 +43,6 @@ Strong guarantee: if an exception is thrown, there are no changes to any JSON va
 Throws [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) if a string stored inside the JSON value
 is not UTF-8 encoded and `error_handler` is set to `strict`
 
-!!! warning "Serializing untrusted input"
-
-    When serializing values that may contain invalid or untrusted UTF-8 (e.g., bytes taken directly from network
-    input), `dump()` throws [`type_error.316`](../../home/exceptions.md#jsonexceptiontype_error316) in the default
-    `strict` mode. To serialize such data without throwing, pass
-    [`error_handler_t::replace`](error_handler_t.md) (substitutes U+FFFD) or
-    [`error_handler_t::ignore`](error_handler_t.md). Callers that serialize untrusted input on a crash-sensitive path
-    should either choose a non-strict error handler or wrap `dump()` in a `#!cpp try`/`#!cpp catch`.
-
-    See the [FAQ](../../home/faq.md#serializing-untrusted-or-invalid-utf-8) for details.
-
 ## Complexity
 
 Linear.

docs/mkdocs/docs/api/basic_json/to_bson.md

@@ -40,9 +40,6 @@ Strong guarantee: if an exception is thrown, there are no changes in the JSON va
   is not an object; example: `"to serialize to BSON, top-level type must be object, but is string"`
 - Throws [`out_of_range.409`](../../home/exceptions.md#jsonexceptionout_of_range409) if a key in the JSON object contains
   a null byte (code point U+0000); example: `"BSON key cannot contain code point U+0000 (at byte 2)"`
-- Throws [`out_of_range.412`](../../home/exceptions.md#jsonexceptionout_of_range412) if the length of a document, array,
-  string, or binary value exceeds the range of the 32-bit BSON length field; example:
-  `"BSON length 2147483661 exceeds maximum of 2147483647"`
 
 ## Complexity
 

docs/mkdocs/docs/api/macros/index.md

@@ -24,6 +24,7 @@ header. See also the [macro overview page](../../features/macros.md).
 - [**JSON_NO_IO**](json_no_io.md) - switch off functions relying on certain C++ I/O headers
 - [**JSON_SKIP_UNSUPPORTED_COMPILER_CHECK**](json_skip_unsupported_compiler_check.md) - do not warn about unsupported compilers
 - [**JSON_USE_GLOBAL_UDLS**](json_use_global_udls.md) - place user-defined string literals (UDLs) into the global namespace
+- [**JSON_USE_SIMDUTF**](json_use_simdutf.md) - use the simdutf library to accelerate UTF-8 validation
 
 ## Library version
 

docs/mkdocs/docs/api/macros/json_use_simdutf.md

@@ -0,0 +1,52 @@
+# JSON_USE_SIMDUTF
+
+```cpp
+#define JSON_USE_SIMDUTF
+```
+
+When defined, the parser validates the UTF-8 content of JSON strings that come from a **contiguous byte input**
+(`std::string`, `std::vector<char>`/`<std::uint8_t>`, string literals, `const char*` ranges, …) using the
+[simdutf](https://github.com/simdutf/simdutf) library instead of the built-in scalar validator. On text with many
+non-ASCII characters (e.g. CJK or emoji) this can validate several times faster.
+
+This is an **opt-in external dependency**. The library itself remains header-only and its behavior is unchanged: the
+same input is accepted or rejected either way, and every parse error is reported at the same position with the same
+message (simdutf is only used to fast-path *valid* runs; anything it flags falls back to the scalar path so the exact
+diagnostic is preserved). Streaming inputs (files, `std::istream`, wide strings, user-defined adapters) always use the
+scalar path.
+
+When `JSON_USE_SIMDUTF` is defined you must make the `simdutf.h` header available on the include path and link the
+simdutf library. When it is not defined, no simdutf header is included and there is no dependency.
+
+## Default definition
+
+By default, `#!cpp JSON_USE_SIMDUTF` is not defined and the portable C++11 scalar validator is used.
+
+```cpp
+#undef JSON_USE_SIMDUTF
+```
+
+## Examples
+
+??? example
+
+    The code below enables the simdutf backend for UTF-8 validation.
+
+    ```cpp
+    #define JSON_USE_SIMDUTF 1
+    #include <simdutf.h>
+    #include <nlohmann/json.hpp>
+
+    ...
+    ```
+
+    The project must also link against simdutf, e.g. with CMake:
+
+    ```cmake
+    target_compile_definitions(your_target PRIVATE JSON_USE_SIMDUTF)
+    target_link_libraries(your_target PRIVATE simdutf::simdutf)
+    ```
+
+## Version history
+
+- Added in version 3.12.1.

docs/mkdocs/docs/home/exceptions.md

@@ -898,22 +898,6 @@ A JSON Patch `add` operation cannot be applied because the target location's par
 
     This exception was added in version 3.13.0. Before that, this situation hit an internal assertion (aborting the program in debug builds) or was silently ignored when assertions were disabled.
 
-### json.exception.out_of_range.412
-
-BSON stores the length of documents, arrays, strings, and binary values in a signed 32-bit integer. This exception is thrown when a value is too large to be described by such a length field.
-
-!!! failure "Example message"
-
-    ```
-    BSON length 2147483661 exceeds maximum of 2147483647
-    ```
-
-!!! note
-
-    This exception was added in version 3.13.0. Before that, the length was silently truncated, and
-    [`to_bson`](../api/basic_json/to_bson.md) produced documents with negative length prefixes that
-    [`from_bson`](../api/basic_json/from_bson.md) rejected.
-
 ## Further exceptions
 
 This exception is thrown in case of errors that cannot be classified with the

docs/mkdocs/docs/home/faq.md

@@ -194,27 +194,6 @@ The library uses `std::numeric_limits<number_float_t>::digits10` (15 for IEEE `d
 
 See [this section](../features/types/number_handling.md#number-serialization) on the library's number handling for more information.
 
-### Serializing untrusted or invalid UTF-8
-
-!!! question "Questions"
-
-    - Why does `dump()` throw when I serialize data that came from the network?
-    - Is CVE-2024-34363 a vulnerability in this library?
-
-Crashes reported against this library that stem from an uncaught
-[`type_error.316`](exceptions.md#jsonexceptiontype_error316) while serializing unvalidated input (e.g.,
-CVE-2024-34363) are a usage issue, not a library vulnerability:
-[`dump()`](../api/basic_json/dump.md) throws in its default `strict` mode because
-[RFC 8259](https://datatracker.ietf.org/doc/html/rfc8259#section-8.1) requires JSON text to be valid UTF-8.
-
-The recommended pattern is to pass a non-strict [`error_handler`](../api/basic_json/error_handler_t.md) or to handle the
-exception:
-
-```cpp
-// replace invalid sequences with U+FFFD instead of throwing
-const auto s = j.dump(-1, ' ', false, json::error_handler_t::replace);
-```
-
 ### Using JSON values with `std::format` or `fmt`
 
 !!! question

docs/mkdocs/docs/home/sponsors.md

@@ -14,5 +14,6 @@ You can sponsor this library at [GitHub Sponsors](https://github.com/sponsors/nl
 - [Steve Sperandeo](https://github.com/homer6)
 - [Robert Jefe Lindstädt](https://github.com/eljefedelrodeodeljefe)
 - [Steve Wagner](https://github.com/ciroque)
+- [Lion Yang](https://github.com/LionNatsu)
 
 Thanks everyone!

docs/mkdocs/docs/integration/package_managers.md

@@ -930,12 +930,6 @@ If you are using [CocoaPods](https://cocoapods.org), you can use the library by
 to your podfile (see [an example](https://bitbucket.org/benman/nlohmann_json-cocoapod/src/master/)). Please file issues
 [here](https://bitbucket.org/benman/nlohmann_json-cocoapod/issues?status=new&status=open).
 
-## npm
-
-This project does not publish an official [npm](https://www.npmjs.com) package. The npm package
-[`nlohmann-json`](https://www.npmjs.com/package/nlohmann-json) (or similarly named packages) is not maintained or
-endorsed by this project. Use one of the package managers listed above, or integrate the single header directly.
-
 ## ESP-IDF and PlatformIO
 
 There is no official package published to the [ESP-IDF Component Registry](https://components.espressif.com) or the

docs/mkdocs/mkdocs.yml

@@ -296,6 +296,7 @@ nav:
           - 'JSON_USE_GLOBAL_UDLS': api/macros/json_use_global_udls.md
           - 'JSON_USE_IMPLICIT_CONVERSIONS': api/macros/json_use_implicit_conversions.md
           - 'JSON_USE_LEGACY_DISCARDED_VALUE_COMPARISON': api/macros/json_use_legacy_discarded_value_comparison.md
+          - 'JSON_USE_SIMDUTF': api/macros/json_use_simdutf.md
           - 'NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_INTRUSIVE_ONLY_SERIALIZE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_DERIVED_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_derived_type.md
           - 'NLOHMANN_DEFINE_TYPE_INTRUSIVE, NLOHMANN_DEFINE_TYPE_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_type_intrusive.md
           - 'NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_WITH_DEFAULT, NLOHMANN_DEFINE_TYPE_NON_INTRUSIVE_ONLY_SERIALIZE': api/macros/nlohmann_define_type_non_intrusive.md

docs/mkdocs/requirements.txt

@@ -2,7 +2,7 @@ wheel==0.47.0
 
 mkdocs==1.6.1                                       # documentation framework
 mkdocs-git-revision-date-localized-plugin==1.5.3    # plugin "git-revision-date-localized"
-mkdocs-material==9.7.7                             # theme for mkdocs
+mkdocs-material==9.7.6                             # theme for mkdocs
 mkdocs-material-extensions==1.3.1                   # extensions
 mkdocs-minify-plugin==0.8.0                         # plugin "minify"
 mkdocs-redirects==1.2.3                             # plugin "redirects"

include/nlohmann/detail/input/binary_reader.hpp

@@ -163,39 +163,12 @@ class binary_reader
     // BSON //
     //////////
 
-    /*!
-    @brief Validate a BSON document's declared size against the bytes read.
-
-    A BSON document starts with an int32 that counts its own total length in
-    bytes, including that prefix and the trailing 0x00. The reader is driven
-    by the terminator rather than the declared length, so without this check a
-    nested document could declare a length that disagrees with where its
-    terminator actually falls and quietly hand the bytes in between to the
-    enclosing document. A well-formed document is at least 5 bytes (the prefix
-    plus the terminator); the equality also rejects those impossible sizes,
-    since at least 5 bytes are always consumed.
-
-    @param[in] document_start  value of chars_read before the size prefix
-    @param[in] document_size   the declared document size
-    @return whether the declared size matches the number of bytes read
-    */
-    bool check_bson_document_size(const std::size_t document_start, const std::int32_t document_size)
-    {
-        if (JSON_HEDLEY_UNLIKELY(document_size < 0 || static_cast<std::size_t>(document_size) != chars_read - document_start))
-        {
-            return sax->parse_error(chars_read, get_token_string(), parse_error::create(112, chars_read,
-                                    exception_message(input_format_t::bson, concat("document size ", std::to_string(document_size), " does not match the number of bytes read (", std::to_string(chars_read - document_start), ")"), "document"), nullptr));
-        }
-        return true;
-    }
-
     /*!
     @brief Reads in a BSON-object and passes it to the SAX-parser.
     @return whether a valid BSON-value was passed to the SAX parser
     */
     bool parse_bson_internal()
     {
-        const std::size_t document_start = chars_read;
         std::int32_t document_size{};
         get_number<std::int32_t, true>(input_format_t::bson, document_size);
 
@@ -209,11 +182,6 @@ class binary_reader
             return false;
         }
 
-        if (JSON_HEDLEY_UNLIKELY(!check_bson_document_size(document_start, document_size)))
-        {
-            return false;
-        }
-
         return sax->end_object();
     }
 
@@ -429,7 +397,6 @@ class binary_reader
     */
     bool parse_bson_array()
     {
-        const std::size_t document_start = chars_read;
         std::int32_t document_size{};
         get_number<std::int32_t, true>(input_format_t::bson, document_size);
 
@@ -443,11 +410,6 @@ class binary_reader
             return false;
         }
 
-        if (JSON_HEDLEY_UNLIKELY(!check_bson_document_size(document_start, document_size)))
-        {
-            return false;
-        }
-
         return sax->end_array();
     }
 
@@ -1884,29 +1846,6 @@ class binary_reader
         return get_ubjson_value(get_char ? get_ignore_noop() : current);
     }
 
-    /*!
-    @brief reject a negative UBJSON/BJData string length
-
-    String and key lengths are written with signed integer markers (i, I, l,
-    L). A negative value is malformed; without this check get_string() would
-    silently treat it as an empty string and leave the following bytes to be
-    misread as the next value. This mirrors the non-negative check the
-    optimized-container count path already performs in get_ubjson_size_value.
-
-    @param[in] len  the string length read from the input
-    @return whether the length is valid (non-negative)
-    */
-    template<typename NumberType>
-    bool check_ubjson_string_length(const NumberType len)
-    {
-        if (JSON_HEDLEY_UNLIKELY(len < 0))
-        {
-            return sax->parse_error(chars_read, get_token_string(), parse_error::create(113, chars_read,
-                                    exception_message(input_format, "string length must not be negative", "string"), nullptr));
-        }
-        return true;
-    }
-
     /*!
     @brief reads a UBJSON string
 
@@ -1944,25 +1883,25 @@ class binary_reader
             case 'i':
             {
                 std::int8_t len{};
-                return get_number(input_format, len) && check_ubjson_string_length(len) && get_string(input_format, len, result);
+                return get_number(input_format, len) && get_string(input_format, len, result);
             }
 
             case 'I':
             {
                 std::int16_t len{};
-                return get_number(input_format, len) && check_ubjson_string_length(len) && get_string(input_format, len, result);
+                return get_number(input_format, len) && get_string(input_format, len, result);
             }
 
             case 'l':
             {
                 std::int32_t len{};
-                return get_number(input_format, len) && check_ubjson_string_length(len) && get_string(input_format, len, result);
+                return get_number(input_format, len) && get_string(input_format, len, result);
             }
 
             case 'L':
             {
                 std::int64_t len{};
-                return get_number(input_format, len) && check_ubjson_string_length(len) && get_string(input_format, len, result);
+                return get_number(input_format, len) && get_string(input_format, len, result);
             }
 
             case 'u':

include/nlohmann/detail/input/input_adapters.hpp

@@ -231,6 +231,33 @@ class iterator_input_adapter
         std::is_same<IteratorType, SentinelType>::value && std::is_pointer<IteratorType>::value;
 #endif
 
+  public:
+    // Whether the remaining input is a single contiguous block of 1-byte
+    // elements that the lexer can inspect directly (used for the SWAR string
+    // fast path). Restricted to same-type iterator/sentinel pairs so that plain
+    // std::distance/std::advance are well-defined in all standards.
+    static constexpr bool supports_bulk_scan =
+        iterator_is_contiguous && std::is_same<IteratorType, SentinelType>::value && sizeof(char_type) == 1;
+
+    // Pointer to the next unread element; only valid when bulk_remaining() > 0.
+    const char_type* bulk_data() const
+    {
+        return &*current;
+    }
+
+    // Number of unread elements available as one contiguous block.
+    std::size_t bulk_remaining() const
+    {
+        return static_cast<std::size_t>(std::distance(current, end));
+    }
+
+    // Consume @a n elements previously inspected via bulk_data().
+    void bulk_skip(std::size_t n)
+    {
+        std::advance(current, static_cast<typename std::iterator_traits<IteratorType>::difference_type>(n));
+    }
+
+  private:
     // contiguous fast path: bulk copy the remaining range with std::memcpy
     template<class T>
     std::size_t get_elements_impl(T* dest, std::size_t count, std::true_type /*contiguous*/)
@@ -566,6 +593,24 @@ typename iterator_input_adapter_factory<IteratorType, SentinelType>::adapter_typ
     return factory_type::create(first, last);
 }
 
+// Detect a container that stores its elements contiguously as single bytes
+// (std::string, std::vector<char/unsigned char>, std::array<char, N>,
+// std::string_view, ...). Such inputs are wrapped in a pointer-based adapter so
+// they benefit from the contiguous fast paths (bulk string scanning, memcpy for
+// binary formats) in every C++ standard - not only in C++20, where the standard
+// library iterators model std::contiguous_iterator and are detected directly.
+template<typename ContainerType, typename = void>
+struct is_contiguous_byte_container : std::false_type {};
+
+template<typename ContainerType>
+struct is_contiguous_byte_container < ContainerType, void_t <
+decltype(std::declval<const ContainerType&>().data()),
+decltype(std::declval<const ContainerType&>().size()) >>
+            : std::integral_constant < bool,
+        std::is_pointer<decltype(std::declval<const ContainerType&>().data())>::value&&
+        std::is_integral<typename std::remove_pointer<decltype(std::declval<const ContainerType&>().data())>::type>::value&&
+        sizeof(typename std::remove_pointer<decltype(std::declval<const ContainerType&>().data())>::type) == 1 > {};
+
 // Convenience shorthand from container to iterator
 // Enables ADL on begin(container) and end(container)
 // Encloses the using declarations in namespace for not to leak them to outside scope
@@ -593,12 +638,32 @@ struct container_input_adapter_factory< ContainerType,
 
 }  // namespace container_input_adapter_factory_impl
 
-template<typename ContainerType>
+// General container path (iterator-based). Contiguous single-byte containers
-typename container_input_adapter_factory_impl::container_input_adapter_factory<ContainerType>::adapter_type input_adapter(ContainerType&& container)
+// are excluded here and routed through the pointer-based overload below.
+template < typename ContainerType,
+           enable_if_t < !is_contiguous_byte_container<ContainerType>::value, int > = 0 >
+typename container_input_adapter_factory_impl::container_input_adapter_factory<ContainerType>::adapter_type input_adapter(ContainerType && container)
 {
     return container_input_adapter_factory_impl::container_input_adapter_factory<ContainerType>::create(std::forward<ContainerType>(container));
 }
 
+// Contiguous single-byte containers (std::string, std::vector<char>, ...) are
+// wrapped in a pointer-based adapter so the contiguous fast paths apply in every
+// standard. The pointer keeps the container's own element type (const char* for
+// std::string, const std::uint8_t* for std::vector<std::uint8_t>, ...), so the
+// resulting char_type - and therefore the parsing behavior - is byte-for-byte
+// identical to the iterator-based path; only the raw pointer additionally
+// enables the bulk fast paths. The container outlives the adapter for the whole
+// parse (temporaries live until the end of the full expression), exactly as the
+// iterators it replaces did.
+template < typename ContainerType,
+           enable_if_t < is_contiguous_byte_container<ContainerType>::value, int > = 0 >
+auto input_adapter(const ContainerType& container)
+-> decltype(input_adapter(container.data(), container.data() + container.size()))
+{
+    return input_adapter(container.data(), container.data() + container.size());
+}
+
 // specialization for std::string
 using string_input_adapter_type = decltype(input_adapter(std::declval<std::string>()));
 

include/nlohmann/detail/input/lexer.hpp

@@ -19,7 +19,9 @@
 #include <vector> // vector
 
 #include <nlohmann/detail/input/input_adapters.hpp>
+#include <nlohmann/detail/input/number_parse.hpp>
 #include <nlohmann/detail/input/position_t.hpp>
+#include <nlohmann/detail/input/string_scan.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/meta/type_traits.hpp>
 
@@ -125,6 +127,25 @@ constexpr bool input_adapter_supports_seek(std::false_type /*detected*/)
     return false;
 }
 
+// Detect whether an input adapter exposes a contiguous byte block that the
+// lexer can scan directly (see iterator_input_adapter::supports_bulk_scan).
+// Adapters without the flag - file, stream, wide-string, user-defined - fall
+// back to the character-at-a-time string scanner.
+template<typename InputAdapterType>
+using detect_supports_bulk_scan = decltype(InputAdapterType::supports_bulk_scan);
+
+template<typename InputAdapterType>
+constexpr bool input_adapter_supports_bulk_scan(std::true_type /*detected*/)
+{
+    return InputAdapterType::supports_bulk_scan;
+}
+
+template<typename InputAdapterType>
+constexpr bool input_adapter_supports_bulk_scan(std::false_type /*detected*/)
+{
+    return false;
+}
+
 /*!
 @brief lexical analysis
 
@@ -146,6 +167,14 @@ class lexer : public lexer_base<BasicJsonType>
     static constexpr bool lazy_token_string =
         input_adapter_supports_seek<InputAdapterType>(is_detected<detect_supports_seek, InputAdapterType> {});
 
+    /// whether string scanning may bulk-consume runs of ordinary characters
+    /// directly from a contiguous input buffer (SWAR fast path). This requires
+    /// the token to be reconstructible lazily (lazy_token_string), so bypassing
+    /// the per-character capture in get() cannot lose error diagnostics.
+    static constexpr bool bulk_scan =
+        lazy_token_string
+        && input_adapter_supports_bulk_scan<InputAdapterType>(is_detected<detect_supports_bulk_scan, InputAdapterType> {});
+
   public:
     using token_type = typename lexer_base<BasicJsonType>::token_type;
 
@@ -265,6 +294,40 @@ class lexer : public lexer_base<BasicJsonType>
         return true;
     }
 
+    /// contiguous input: bulk-append the run of ordinary characters and complete
+    /// well-formed UTF-8 sequences starting at the current read position, leaving
+    /// the first byte that needs individual handling (the closing quote, an
+    /// escape, a control character, or an ill-formed UTF-8 byte) for get()
+    void scan_string_bulk(std::true_type /*bulk*/)
+    {
+        // a pending unget must be consumed through the normal path first
+        if (next_unget)
+        {
+            return;
+        }
+        const std::size_t remaining = ia.bulk_remaining();
+        if (remaining == 0)
+        {
+            return;
+        }
+        const auto* const data = reinterpret_cast<const unsigned char*>(ia.bulk_data());
+
+        const std::size_t pos = string_bulk_run(data, remaining);
+        if (pos == 0)
+        {
+            return;
+        }
+        token_buffer.append(reinterpret_cast<const typename string_t::value_type*>(data), pos);
+        ia.bulk_skip(pos);
+        // the run contains no newline (all bytes < 0x20 are treated as special),
+        // so only the flat character counters advance
+        position.chars_read_total += pos;
+        position.chars_read_current_line += pos;
+    }
+
+    /// streaming input: no bulk fast path
+    void scan_string_bulk(std::false_type /*bulk*/) const noexcept {}
+
     /*!
     @brief scan a string literal
 
@@ -290,6 +353,10 @@ class lexer : public lexer_base<BasicJsonType>
 
         while (true)
         {
+            // bulk-consume ordinary characters from contiguous input, then
+            // handle the next special byte through the switch below
+            scan_string_bulk(std::integral_constant<bool, bulk_scan> {});
+
             // get the next character
             switch (get())
             {
@@ -1279,45 +1346,56 @@ scan_number_done:
         // we are done scanning a number)
         unget();
 
-        char* endptr = nullptr; // NOLINT(misc-const-correctness,cppcoreguidelines-pro-type-vararg,hicpp-vararg)
+        return convert_number(number_type);
-        errno = 0;
+    }
 
-        // try to parse integers first and fall back to floats
+    /*!
+    @brief convert the number text in token_buffer to its value and token type
+
+    The digit sequence in token_buffer has already been validated (by the
+    scan_number() state machine or by the contiguous fast path) and holds the
+    locale decimal point in place of '.'. Integers are parsed first and fall
+    back to floating point on overflow. This is shared so both scanners produce
+    identical results.
+    */
+    token_type convert_number(token_type number_type)
+    {
+        const char* const num_begin = token_buffer.data();
+        const char* const num_end = num_begin + token_buffer.size();
+
+        // try to parse integers first and fall back to floats; the digit
+        // sequence has already been validated, so a dedicated parser can avoid
+        // the locale/errno overhead of strtoull
         if (number_type == token_type::value_unsigned)
         {
-            const auto x = std::strtoull(token_buffer.data(), &endptr, 10);
+            if (parse_integer_unsigned(num_begin, num_end, value_unsigned))
-
-            // we checked the number format before
-            JSON_ASSERT(endptr == token_buffer.data() + token_buffer.size());
-
-            if (errno != ERANGE)
-            {
-                value_unsigned = static_cast<number_unsigned_t>(x);
-                if (value_unsigned == x)
             {
                 return token_type::value_unsigned;
             }
         }
-        }
         else if (number_type == token_type::value_integer)
         {
-            const auto x = std::strtoll(token_buffer.data(), &endptr, 10);
+            if (parse_integer_signed(num_begin, num_end, value_integer))
-
-            // we checked the number format before
-            JSON_ASSERT(endptr == token_buffer.data() + token_buffer.size());
-
-            if (errno != ERANGE)
-            {
-                value_integer = static_cast<number_integer_t>(x);
-                if (value_integer == x)
             {
                 return token_type::value_integer;
             }
         }
-        }
 
         // this code is reached if we parse a floating-point number or if an
-        // integer conversion above failed
+        // integer conversion above overflowed. Prefer std::from_chars
+        // (Eisel-Lemire, locale-independent, correctly rounded) when available;
+        // otherwise the exact Clinger fast path (double only); otherwise the
+        // locale-aware strtof/strtod.
+        if (parse_float_from_chars(num_begin, num_end, value_float))
+        {
+            return token_type::value_float;
+        }
+        if (parse_float_fast(num_begin, num_end, decimal_point_char, value_float))
+        {
+            return token_type::value_float;
+        }
+
+        char* endptr = nullptr; // NOLINT(misc-const-correctness,cppcoreguidelines-pro-type-vararg,hicpp-vararg)
         strtof(value_float, token_buffer.data(), &endptr);
 
         // we checked the number format before
@@ -1326,6 +1404,130 @@ scan_number_done:
         return token_type::value_float;
     }
 
+    /*!
+    @brief contiguous fast path for scanning a number
+
+    Parses the whole number token straight from the input buffer, avoiding the
+    per-character get()/add() of scan_number(). On success it fills token_buffer
+    (with the locale decimal point substituted, as scan_number() does) and
+    returns the token type. On anything it does not fully recognize as a
+    well-formed number it makes no state change and returns
+    token_type::uninitialized, so the caller falls back to scan_number(), which
+    then produces the exact diagnostic. @a current is the first digit or the
+    leading minus (already read); the remaining bytes are taken from the adapter.
+    */
+    token_type scan_number_bulk_contiguous()
+    {
+        // a pending unget offsets the buffer position from current; fall back
+        if (next_unget)
+        {
+            return token_type::uninitialized;
+        }
+        const std::size_t rem = ia.bulk_remaining();
+        if (rem == 0)
+        {
+            // the first digit is the last input byte; let scan_number() finish
+            return token_type::uninitialized;
+        }
+        // the byte before the next unread one is current (contiguous input)
+        const char* const data = reinterpret_cast<const char*>(ia.bulk_data()) - 1;
+        const std::size_t avail = rem + 1;
+
+        // validate + classify the number extent (mirrors scan_number()'s grammar)
+        std::size_t i = 0;
+        std::size_t dot_index = std::string::npos;
+        token_type number_type = token_type::value_unsigned;
+        if (data[0] == '-')
+        {
+            number_type = token_type::value_integer;
+            i = 1;
+            if (i >= avail)
+            {
+                return token_type::uninitialized;
+            }
+        }
+        if (data[i] == '0')
+        {
+            ++i;
+        }
+        else if (data[i] >= '1' && data[i] <= '9')
+        {
+            ++i;
+            while (i < avail && data[i] >= '0' && data[i] <= '9')
+            {
+                ++i;
+            }
+        }
+        else
+        {
+            return token_type::uninitialized;
+        }
+        if (i < avail && data[i] == '.')
+        {
+            number_type = token_type::value_float;
+            dot_index = i;
+            ++i;
+            if (i >= avail || !(data[i] >= '0' && data[i] <= '9'))
+            {
+                return token_type::uninitialized;
+            }
+            while (i < avail && data[i] >= '0' && data[i] <= '9')
+            {
+                ++i;
+            }
+        }
+        if (i < avail && (data[i] == 'e' || data[i] == 'E'))
+        {
+            number_type = token_type::value_float;
+            ++i;
+            if (i < avail && (data[i] == '+' || data[i] == '-'))
+            {
+                ++i;
+            }
+            if (i >= avail || !(data[i] >= '0' && data[i] <= '9'))
+            {
+                return token_type::uninitialized;
+            }
+            while (i < avail && data[i] >= '0' && data[i] <= '9')
+            {
+                ++i;
+            }
+        }
+        const std::size_t len = i;
+
+        // materialize the token exactly as scan_number() would, substituting the
+        // locale decimal point so convert_number()'s strtof fallback stays valid.
+        // reset() already cleared token_buffer, so append() fills it (assign() is
+        // avoided because custom string_t types need not provide it)
+        reset();
+        token_buffer.append(reinterpret_cast<const typename string_t::value_type*>(data), len);
+        if (dot_index != std::string::npos)
+        {
+            token_buffer[dot_index] = static_cast<typename string_t::value_type>(decimal_point_char);
+            decimal_point_position = dot_index;
+        }
+
+        // consume the remaining bytes of the number (current was already read)
+        ia.bulk_skip(len - 1);
+        position.chars_read_total += (len - 1);
+        position.chars_read_current_line += (len - 1);
+
+        return convert_number(number_type);
+    }
+
+    /// contiguous input: try the number fast path, else the byte-path scanner
+    token_type scan_number_dispatch(std::true_type /*bulk*/)
+    {
+        const token_type t = scan_number_bulk_contiguous();
+        return (t != token_type::uninitialized) ? t : scan_number();
+    }
+
+    /// streaming input: always use the byte-path scanner
+    token_type scan_number_dispatch(std::false_type /*bulk*/)
+    {
+        return scan_number();
+    }
+
     /*!
     @param[in] literal_text  the literal text to expect
     @param[in] length        the length of the passed literal text
@@ -1680,7 +1882,7 @@ scan_number_done:
             case '7':
             case '8':
             case '9':
-                return scan_number();
+                return scan_number_dispatch(std::integral_constant<bool, bulk_scan> {});
 
             // end of input (the null byte is needed when parsing from
             // string literals)

include/nlohmann/detail/input/number_parse.hpp

@@ -0,0 +1,302 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <array> // array
+#include <cfloat> // FLT_EVAL_METHOD
+#include <cstddef> // size_t
+#include <cstdint> // int64_t, uint64_t
+#include <limits> // numeric_limits
+
+#include <nlohmann/detail/macro_scope.hpp>
+
+// std::from_chars lives in <charconv>, but being in C++17 mode does not
+// guarantee the header exists: GCC 7 sets __cplusplus to C++17 yet ships no
+// <charconv> (added in GCC 8; floating-point support in GCC 11). Guard the
+// include with __has_include so such toolchains fall back to the scalar path.
+#if defined(JSON_HAS_CPP_17) && defined(__has_include)
+    #if __has_include(<charconv>)
+        #include <charconv> // from_chars (only used when __cpp_lib_to_chars is defined)
+        #include <system_error> // errc
+    #endif
+#endif
+
+// This file contains the value-conversion helpers used by the lexer to turn an
+// already-validated number token into a value, without the locale/errno
+// overhead of std::strtoull/std::strtod. They are free functions so the lexer
+// stays focused on scanning; see lexer::convert_number().
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+namespace detail
+{
+
+/*!
+@brief fast integer parser for an already-validated unsigned integer
+
+The number scanner has already checked that [first, last) is a valid JSON
+integer, so this only needs to accumulate the digits and detect overflow. This
+avoids the locale/errno machinery of std::strtoull, which dominates
+integer-heavy inputs.
+
+@param[in]  first   pointer to the first character (a digit)
+@param[in]  last    pointer past the last character
+@param[out] value   the parsed value on success
+@return true if the value fit into @a NumberUnsignedType; false on overflow, in
+        which case the caller falls back to floating-point parsing (matching the
+        previous std::strtoull behavior)
+*/
+template<typename NumberUnsignedType>
+bool parse_integer_unsigned(const char* first, const char* last, NumberUnsignedType& value) noexcept
+{
+    // accumulate in the widest unsigned type used by the previous strtoull
+    // path so the overflow behavior is unchanged for custom number types
+    std::uint64_t x = 0;
+    constexpr std::uint64_t cutoff = (std::numeric_limits<std::uint64_t>::max)() / 10u;
+    constexpr std::uint64_t cutlim = (std::numeric_limits<std::uint64_t>::max)() % 10u;
+    for (const char* p = first; p != last; ++p)
+    {
+        const auto digit = static_cast<std::uint64_t>(static_cast<unsigned char>(*p) - static_cast<unsigned char>('0'));
+        if (JSON_HEDLEY_UNLIKELY(x > cutoff || (x == cutoff && digit > cutlim)))
+        {
+            return false;
+        }
+        x = (x * 10u) + digit;
+    }
+    value = static_cast<NumberUnsignedType>(x);
+    // reject values that do not round-trip into a narrower NumberUnsignedType
+    return static_cast<std::uint64_t>(value) == x;
+}
+
+/*!
+@brief fast integer parser for an already-validated negative integer
+
+@param[in]  first   pointer to the leading '-'
+@param[in]  last    pointer past the last character
+@param[out] value   the parsed (negative) value on success
+@return true on success; false on overflow (caller falls back to float)
+*/
+template<typename NumberIntegerType>
+bool parse_integer_signed(const char* first, const char* last, NumberIntegerType& value) noexcept
+{
+    // the state machine only reaches the signed path via a leading '-'
+    JSON_ASSERT(first != last && *first == '-');
+    std::uint64_t magnitude = 0;
+    // |INT64_MIN| == INT64_MAX + 1; this is the largest admissible magnitude
+    constexpr std::uint64_t limit = static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()) + 1u;
+    for (const char* p = first + 1; p != last; ++p)
+    {
+        const auto digit = static_cast<std::uint64_t>(static_cast<unsigned char>(*p) - static_cast<unsigned char>('0'));
+        if (JSON_HEDLEY_UNLIKELY(magnitude > (limit - digit) / 10u))
+        {
+            return false;
+        }
+        magnitude = (magnitude * 10u) + digit;
+    }
+    const std::int64_t x = (magnitude == limit)
+                           ? (std::numeric_limits<std::int64_t>::min)()
+                           : -static_cast<std::int64_t>(magnitude);
+    value = static_cast<NumberIntegerType>(x);
+    // reject values that do not round-trip into a narrower NumberIntegerType
+    return static_cast<std::int64_t>(value) == x;
+}
+
+/*!
+@brief exact fast path for parsing a `double` (Clinger's algorithm)
+
+For the common case - at most 19 significant digits, a decimal exponent in
+[-22, 22], and a significand below 2^53 - the value equals significand *
+10^exp computed in IEEE-754 double arithmetic, which is exact under
+round-to-nearest because both operands are exactly representable. This is the
+same fast path used by fast_float/simdjson; the general cases are left to
+std::strtod. The parser only activates for number_float_t == double; float and
+long double keep the std::strtof/std::strtold paths (see the templated overload
+below).
+
+@param[in]  first          pointer to the first character of the number
+@param[in]  last           pointer past the last character
+@param[in]  decimal_point  the (locale-dependent) decimal point character
+@param[out] out            the parsed value on success
+@return true if the value was parsed exactly; false to fall back to strtod
+*/
+template<typename DecimalPointType>
+bool parse_float_fast(const char* first, const char* last, DecimalPointType decimal_point, double& out) noexcept
+{
+#if defined(FLT_EVAL_METHOD) && FLT_EVAL_METHOD != 0
+    // Clinger's fast path is only exact when double operations are evaluated in
+    // true double precision. On platforms that keep intermediates in extended
+    // precision (e.g. the x87 FPU on 32-bit x86, where FLT_EVAL_METHOD == 2) the
+    // single significand * 10^scale step is double-rounded and can be 1 ULP off,
+    // so decline and let the caller fall back to the correctly-rounded
+    // std::from_chars / std::strtod path.
+    static_cast<void>(first);
+    static_cast<void>(last);
+    static_cast<void>(decimal_point);
+    static_cast<void>(out);
+    return false;
+#else
+    static const std::array<double, 23> powers_of_ten =
+    {
+        {
+            1e0, 1e1, 1e2, 1e3, 1e4, 1e5, 1e6, 1e7, 1e8, 1e9, 1e10, 1e11,
+            1e12, 1e13, 1e14, 1e15, 1e16, 1e17, 1e18, 1e19, 1e20, 1e21, 1e22
+        }
+    };
+
+    const char* p = first;
+    bool negative = false;
+    if (p != last && (*p == '-' || *p == '+'))
+    {
+        negative = (*p == '-');
+        ++p;
+    }
+
+    std::uint64_t significand = 0;
+    int num_digits = 0;
+    int fractional_digits = 0;
+    bool seen_dot = false;
+    bool any_digit = false;
+    for (; p != last; ++p)
+    {
+        const char c = *p;
+        if (c >= '0' && c <= '9')
+        {
+            any_digit = true;
+            if (JSON_HEDLEY_UNLIKELY(num_digits >= 19))
+            {
+                return false; // significand may not fit into uint64_t
+            }
+            significand = (significand * 10u) + static_cast<std::uint64_t>(c - '0');
+            ++num_digits;
+            fractional_digits += static_cast<int>(seen_dot);
+        }
+        else if (static_cast<DecimalPointType>(c) == decimal_point)
+        {
+            if (JSON_HEDLEY_UNLIKELY(seen_dot))
+            {
+                return false;
+            }
+            seen_dot = true;
+        }
+        else if (c == 'e' || c == 'E')
+        {
+            ++p;
+            break;
+        }
+        else
+        {
+            return false;
+        }
+    }
+    if (JSON_HEDLEY_UNLIKELY(!any_digit))
+    {
+        return false;
+    }
+
+    int exponent = 0;
+    if (p != last) // an exponent part remains
+    {
+        bool exp_negative = false;
+        if (p != last && (*p == '-' || *p == '+'))
+        {
+            exp_negative = (*p == '-');
+            ++p;
+        }
+        bool any_exp_digit = false;
+        for (; p != last; ++p)
+        {
+            if (JSON_HEDLEY_UNLIKELY(*p < '0' || *p > '9'))
+            {
+                return false;
+            }
+            exponent = (exponent * 10) + (*p - '0');
+            any_exp_digit = true;
+            if (JSON_HEDLEY_UNLIKELY(exponent > 9999))
+            {
+                return false;
+            }
+        }
+        if (JSON_HEDLEY_UNLIKELY(!any_exp_digit))
+        {
+            return false;
+        }
+        if (exp_negative)
+        {
+            exponent = -exponent;
+        }
+    }
+
+    const int scale = exponent - fractional_digits;
+    if (JSON_HEDLEY_UNLIKELY(significand >= (static_cast<std::uint64_t>(1) << 53)))
+    {
+        return false; // significand not exactly representable as double
+    }
+
+    auto result = static_cast<double>(significand);
+    if (scale >= 0)
+    {
+        if (JSON_HEDLEY_UNLIKELY(scale > 22))
+        {
+            return false;
+        }
+        result *= powers_of_ten[static_cast<std::size_t>(scale)];
+    }
+    else
+    {
+        if (JSON_HEDLEY_UNLIKELY(-scale > 22))
+        {
+            return false;
+        }
+        result /= powers_of_ten[static_cast<std::size_t>(-scale)];
+    }
+    out = negative ? -result : result;
+    return true;
+#endif
+}
+
+/// fast float path is only exact for `double`; decline for float/long double
+template<typename DecimalPointType, typename FloatType>
+bool parse_float_fast(const char* /*first*/, const char* /*last*/, DecimalPointType /*decimal_point*/, FloatType& /*out*/) noexcept
+{
+    return false;
+}
+
+/*!
+@brief parse a float with std::from_chars (Eisel-Lemire) when available
+
+std::from_chars is locale-independent, correctly rounded, and - via the
+Eisel-Lemire algorithm in modern standard libraries - much faster than strtod
+over the whole value range (not just the Clinger subset). It is used only when
+__cpp_lib_to_chars indicates full floating-point support and only when it
+consumes the entire token ([first, last)); a partial parse means the buffer
+uses a non-'.' locale decimal point, in which case the caller falls back to the
+locale-aware path. An under-/overflow (result_out_of_range) also declines, so
+the caller's strtod fallback supplies the well-defined ±inf/0 result the parser
+expects (side-stepping the P4168 divergence between implementations).
+
+@return true if the value was parsed exactly and fully; false to fall back
+*/
+template<typename FloatType>
+bool parse_float_from_chars(const char* first, const char* last, FloatType& out) noexcept
+{
+    // JSON_HAS_CPP_17 must gate the use as well as the <charconv> include above:
+    // some standard libraries (e.g. libstdc++ 15) define __cpp_lib_to_chars even
+    // in C++14 mode, where <charconv> is not included.
+#if defined(JSON_HAS_CPP_17) && defined(__cpp_lib_to_chars)
+    const auto result = std::from_chars(first, last, out);
+    return result.ec == std::errc() && result.ptr == last;
+#else
+    static_cast<void>(first);
+    static_cast<void>(last);
+    static_cast<void>(out);
+    return false;
+#endif
+}
+
+}  // namespace detail
+NLOHMANN_JSON_NAMESPACE_END

include/nlohmann/detail/input/string_scan.hpp

@@ -0,0 +1,289 @@
+//     __ _____ _____ _____
+//  __|  |   __|     |   | |  JSON for Modern C++
+// |  |  |__   |  |  | | | |  version 3.12.0
+// |_____|_____|_____|_|___|  https://github.com/nlohmann/json
+//
+// SPDX-FileCopyrightText: 2013-2026 Niels Lohmann <https://nlohmann.me>
+// SPDX-License-Identifier: MIT
+
+#pragma once
+
+#include <cstddef> // size_t
+#include <cstdint> // uint64_t
+#include <cstring> // memcpy
+
+#if defined(JSON_USE_SIMDUTF)
+    // Optional SIMD backend for bulk UTF-8 validation. This is an opt-in
+    // external dependency: nlohmann/json itself stays header-only and the C++11
+    // scalar validator below is always available; defining JSON_USE_SIMDUTF
+    // additionally requires the simdutf headers on the include path and linking
+    // the simdutf library. See string_bulk_run().
+    #include <simdutf.h>
+#endif
+
+#include <nlohmann/detail/macro_scope.hpp>
+
+// This file contains the byte-level string-scanning helpers used by the lexer's
+// contiguous fast path. They operate purely on raw bytes (no dependency on the
+// lexer's template parameters) so they are free functions, keeping the lexer
+// itself focused on the state machine; see lexer::scan_string_bulk().
+
+NLOHMANN_JSON_NAMESPACE_BEGIN
+namespace detail
+{
+
+// classify a single byte as needing individual string handling: the closing
+// quote, an escape, a control character, or a non-ASCII (UTF-8)
+// lead/continuation byte. Ordinary bytes (0x20..0x7F except '"' and '\\') are
+// copied verbatim, which the bulk scanner does 8 bytes at a time.
+inline bool is_string_special(unsigned char c) noexcept
+{
+    return c == '\"' || c == '\\' || c < 0x20u || c >= 0x80u;
+}
+
+// SWAR helper: return a word whose high bit is set in every byte of @a v that
+// is_string_special(); zero if the 8 bytes are all ordinary.
+inline std::uint64_t swar_string_special(std::uint64_t v) noexcept
+{
+    constexpr std::uint64_t ones = 0x0101010101010101ull;
+    constexpr std::uint64_t high = 0x8080808080808080ull;
+    const std::uint64_t q = v ^ 0x2222222222222222ull; // '"'  (0x22)
+    const std::uint64_t b = v ^ 0x5C5C5C5C5C5C5C5Cull; // '\\' (0x5C)
+    const std::uint64_t has_quote     = (q - ones) & ~q & high;
+    const std::uint64_t has_backslash = (b - ones) & ~b & high;
+    const std::uint64_t has_control   = (v - 0x2020202020202020ull) & ~v & high; // < 0x20
+    const std::uint64_t has_non_ascii = v & high;                                // >= 0x80
+    return has_quote | has_backslash | has_control | has_non_ascii;
+}
+
+// return the index of the first is_string_special() byte in [data, data+n), or
+// n if every byte is ordinary; scans 8 bytes at a time
+inline std::size_t find_string_special(const unsigned char* data, std::size_t n) noexcept
+{
+    std::size_t i = 0;
+    for (; i + 8 <= n; i += 8)
+    {
+        std::uint64_t word = 0;
+        std::memcpy(&word, data + i, sizeof(word));
+        if (swar_string_special(word) != 0)
+        {
+            // a special byte is in this word; locate it (endian-agnostic)
+            for (std::size_t j = 0; j < 8; ++j)
+            {
+                if (is_string_special(data[i + j]))
+                {
+                    return i + j;
+                }
+            }
+        }
+    }
+    for (; i < n; ++i)
+    {
+        if (is_string_special(data[i]))
+        {
+            return i;
+        }
+    }
+    return n;
+}
+
+// classify a byte as one the serializer must NOT copy verbatim when
+// ensure_ascii is requested: the closing quote, an escape, a control character
+// (< 0x20), DEL (0x7F), or any non-ASCII byte (>= 0x80). Everything else -
+// printable ASCII except '"' and '\\' - is emitted unchanged. Note this differs
+// from is_string_special() only in that 0x7F is also a stop (it is escaped as
+// \u007f under ensure_ascii).
+inline bool is_ascii_copyable(unsigned char c) noexcept
+{
+    return c >= 0x20u && c < 0x7Fu && c != '\"' && c != '\\';
+}
+
+// return the index of the first byte in [data, data+n) that is NOT
+// is_ascii_copyable(), or n if every byte can be copied verbatim; scans 8 bytes
+// at a time. Used by the serializer's ensure_ascii fast path.
+inline std::size_t find_ascii_copyable_run(const unsigned char* data, std::size_t n) noexcept
+{
+    constexpr std::uint64_t ones = 0x0101010101010101ull;
+    constexpr std::uint64_t high = 0x8080808080808080ull;
+    std::size_t i = 0;
+    for (; i + 8 <= n; i += 8)
+    {
+        std::uint64_t v = 0;
+        std::memcpy(&v, data + i, sizeof(v));
+        const std::uint64_t q = v ^ 0x2222222222222222ull; // '"'  (0x22)
+        const std::uint64_t b = v ^ 0x5C5C5C5C5C5C5C5Cull; // '\\' (0x5C)
+        const std::uint64_t d = v ^ 0x7F7F7F7F7F7F7F7Full; // DEL  (0x7F)
+        const std::uint64_t stop = ((q - ones) & ~q & high)   // == '"'
+                                   | ((b - ones) & ~b & high)  // == '\\'
+                                   | ((d - ones) & ~d & high)  // == 0x7F
+                                   | ((v - 0x2020202020202020ull) & ~v & high) // < 0x20
+                                   | (v & high);               // >= 0x80
+        if (stop != 0)
+        {
+            for (std::size_t j = 0; j < 8; ++j)
+            {
+                if (!is_ascii_copyable(data[i + j]))
+                {
+                    return i + j;
+                }
+            }
+        }
+    }
+    for (; i < n; ++i)
+    {
+        if (!is_ascii_copyable(data[i]))
+        {
+            return i;
+        }
+    }
+    return n;
+}
+
+// Validate one UTF-8 sequence at the front of [data, data+avail). Returns its
+// length (2..4) only when the bytes form a *well-formed* sequence using exactly
+// the same ranges as scan_string()'s per-byte switch, so the bulk path accepts
+// precisely what the byte path accepts. Returns 0 for anything that is invalid,
+// incomplete, or that the byte path must diagnose (the caller then defers to
+// that path, keeping error messages unchanged). Lead bytes < 0x80 are handled
+// by the caller and never passed here.
+inline std::size_t validate_one_utf8(const unsigned char* data, std::size_t avail) noexcept
+{
+    const unsigned char c0 = data[0];
+    if (c0 >= 0xC2 && c0 <= 0xDF)  // U+0080..U+07FF
+    {
+        if (avail >= 2 && data[1] >= 0x80 && data[1] <= 0xBF)
+        {
+            return 2;
+        }
+    }
+    else if (c0 == 0xE0)  // U+0800..U+0FFF
+    {
+        if (avail >= 3 && data[1] >= 0xA0 && data[1] <= 0xBF && data[2] >= 0x80 && data[2] <= 0xBF)
+        {
+            return 3;
+        }
+    }
+    else if ((c0 >= 0xE1 && c0 <= 0xEC) || c0 == 0xEE || c0 == 0xEF)  // U+1000..U+CFFF, U+E000..U+FFFF
+    {
+        if (avail >= 3 && data[1] >= 0x80 && data[1] <= 0xBF && data[2] >= 0x80 && data[2] <= 0xBF)
+        {
+            return 3;
+        }
+    }
+    else if (c0 == 0xED)  // U+D000..U+D7FF (excludes surrogates)
+    {
+        if (avail >= 3 && data[1] >= 0x80 && data[1] <= 0x9F && data[2] >= 0x80 && data[2] <= 0xBF)
+        {
+            return 3;
+        }
+    }
+    else if (c0 == 0xF0)  // U+10000..U+3FFFF
+    {
+        if (avail >= 4 && data[1] >= 0x90 && data[1] <= 0xBF && data[2] >= 0x80 && data[2] <= 0xBF && data[3] >= 0x80 && data[3] <= 0xBF)
+        {
+            return 4;
+        }
+    }
+    else if (c0 >= 0xF1 && c0 <= 0xF3)  // U+40000..U+FFFFF
+    {
+        if (avail >= 4 && data[1] >= 0x80 && data[1] <= 0xBF && data[2] >= 0x80 && data[2] <= 0xBF && data[3] >= 0x80 && data[3] <= 0xBF)
+        {
+            return 4;
+        }
+    }
+    else if (c0 == 0xF4)  // U+100000..U+10FFFF
+    {
+        if (avail >= 4 && data[1] >= 0x80 && data[1] <= 0x8F && data[2] >= 0x80 && data[2] <= 0xBF && data[3] >= 0x80 && data[3] <= 0xBF)
+        {
+            return 4;
+        }
+    }
+    return 0; // invalid, incomplete, or must be diagnosed by the byte path
+}
+
+// Scalar (C++11) computation of the bulk run length: the number of leading
+// bytes in [data, data+n) that are ordinary ASCII or complete well-formed UTF-8
+// sequences, stopping before the first byte that needs individual handling (the
+// closing quote, an escape, a control character, or an ill-formed/truncated
+// sequence). ASCII is skipped 8 bytes at a time.
+inline std::size_t scalar_string_bulk_run(const unsigned char* data, std::size_t n) noexcept
+{
+    std::size_t pos = 0;
+    while (pos < n)
+    {
+        pos += find_string_special(data + pos, n - pos);
+        if (pos >= n || data[pos] < 0x80u)
+        {
+            break; // end of buffer, or a quote/escape/control byte
+        }
+        const std::size_t seq = validate_one_utf8(data + pos, n - pos);
+        if (seq == 0)
+        {
+            break; // ill-formed or truncated: let the byte path diagnose it
+        }
+        pos += seq;
+    }
+    return pos;
+}
+
+#if defined(JSON_USE_SIMDUTF)
+// Index of the first quote/escape/control byte in [data, data+n) (non-ASCII
+// bytes are *not* stops here - the whole run is handed to simdutf), or n.
+inline std::size_t find_string_delimiter(const unsigned char* data, std::size_t n) noexcept
+{
+    constexpr std::uint64_t ones = 0x0101010101010101ull;
+    constexpr std::uint64_t high = 0x8080808080808080ull;
+    std::size_t i = 0;
+    for (; i + 8 <= n; i += 8)
+    {
+        std::uint64_t v = 0;
+        std::memcpy(&v, data + i, sizeof(v));
+        const std::uint64_t q = v ^ 0x2222222222222222ull;
+        const std::uint64_t b = v ^ 0x5C5C5C5C5C5C5C5Cull;
+        const std::uint64_t hit = ((q - ones) & ~q & high)
+                                  | ((b - ones) & ~b & high)
+                                  | ((v - 0x2020202020202020ull) & ~v & high);
+        if (hit != 0)
+        {
+            for (std::size_t j = 0; j < 8; ++j)
+            {
+                const unsigned char c = data[i + j];
+                if (c == '\"' || c == '\\' || c < 0x20u)
+                {
+                    return i + j;
+                }
+            }
+        }
+    }
+    for (; i < n; ++i)
+    {
+        const unsigned char c = data[i];
+        if (c == '\"' || c == '\\' || c < 0x20u)
+        {
+            return i;
+        }
+    }
+    return n;
+}
+#endif
+
+// Backend-dispatched bulk run length. With JSON_USE_SIMDUTF the run up to the
+// next delimiter is validated in one shot by simdutf; on the rare failure the
+// scalar helper recomputes the exact valid prefix so the byte path still
+// produces the precise diagnostic. Without it, the pure scalar path is used.
+inline std::size_t string_bulk_run(const unsigned char* data, std::size_t n) noexcept
+{
+#if defined(JSON_USE_SIMDUTF)
+    const std::size_t run = find_string_delimiter(data, n);
+    if (run != 0 && simdutf::validate_utf8(reinterpret_cast<const char*>(data), run))
+    {
+        return run;
+    }
+    return scalar_string_bulk_run(data, n);
+#else
+    return scalar_string_bulk_run(data, n);
+#endif
+}
+
+}  // namespace detail
+NLOHMANN_JSON_NAMESPACE_END

include/nlohmann/detail/output/binary_writer.hpp

@@ -979,28 +979,13 @@ class binary_writer
         return /*id*/ 1ul + name.size() + /*zero-terminator*/1u;
     }
 
-    /*!
-    @brief Checks that @a size fits into the 32-bit length field used by BSON
-    @return The size as a signed 32-bit integer
-    @throw out_of_range.412 if @a size exceeds the range of std::int32_t
-    */
-    static std::int32_t to_bson_length(const std::size_t size)
-    {
-        if (JSON_HEDLEY_UNLIKELY(!value_in_range_of<std::int32_t>(size)))
-        {
-            JSON_THROW(out_of_range::create(412, concat("BSON length ", std::to_string(size), " exceeds maximum of ", std::to_string((std::numeric_limits<std::int32_t>::max)())), nullptr));
-        }
-
-        return static_cast<std::int32_t>(size);
-    }
-
     /*!
     @brief Writes the given @a element_type and @a name to the output adapter
     */
     void write_bson_entry_header(const string_t& name,
                                  const std::uint8_t element_type)
     {
-        oa->write_character(to_char_type(element_type));
+        oa->write_character(to_char_type(element_type)); // boolean
         oa->write_characters(
             reinterpret_cast<const CharType*>(name.c_str()),
             name.size() + 1u);
@@ -1042,7 +1027,7 @@ class binary_writer
     {
         write_bson_entry_header(name, 0x02);
 
-        write_number<std::int32_t>(to_bson_length(value.size() + 1ul), true);
+        write_number<std::int32_t>(static_cast<std::int32_t>(value.size() + 1ul), true);
         oa->write_characters(
             reinterpret_cast<const CharType*>(value.c_str()),
             value.size() + 1);
@@ -1085,7 +1070,7 @@ class binary_writer
     }
 
     /*!
-    @return The size of the BSON-encoded unsigned integer @a value
+    @return The size of the BSON-encoded unsigned integer in @a j
     */
     static constexpr std::size_t calc_bson_unsigned_size(const std::uint64_t value) noexcept
     {
@@ -1098,22 +1083,22 @@ class binary_writer
     @brief Writes a BSON element with key @a name and unsigned @a value
     */
     void write_bson_unsigned(const string_t& name,
-                             const std::uint64_t value)
+                             const BasicJsonType& j)
     {
-        if (value <= static_cast<std::uint64_t>((std::numeric_limits<std::int32_t>::max)()))
+        if (j.m_data.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::int32_t>::max)()))
         {
             write_bson_entry_header(name, 0x10 /* int32 */);
-            write_number<std::int32_t>(static_cast<std::int32_t>(value), true);
+            write_number<std::int32_t>(static_cast<std::int32_t>(j.m_data.m_value.number_unsigned), true);
         }
-        else if (value <= static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()))
+        else if (j.m_data.m_value.number_unsigned <= static_cast<std::uint64_t>((std::numeric_limits<std::int64_t>::max)()))
         {
             write_bson_entry_header(name, 0x12 /* int64 */);
-            write_number<std::int64_t>(static_cast<std::int64_t>(value), true);
+            write_number<std::int64_t>(static_cast<std::int64_t>(j.m_data.m_value.number_unsigned), true);
         }
         else
         {
             write_bson_entry_header(name, 0x11 /* uint64 */);
-            write_number<std::uint64_t>(value, true);
+            write_number<std::uint64_t>(static_cast<std::uint64_t>(j.m_data.m_value.number_unsigned), true);
         }
     }
 
@@ -1157,7 +1142,7 @@ class binary_writer
                           const typename BasicJsonType::array_t& value)
     {
         write_bson_entry_header(name, 0x04); // array
-        write_number<std::int32_t>(to_bson_length(calc_bson_array_size(value)), true);
+        write_number<std::int32_t>(static_cast<std::int32_t>(calc_bson_array_size(value)), true);
 
         std::size_t array_index = 0ul;
 
@@ -1177,7 +1162,7 @@ class binary_writer
     {
         write_bson_entry_header(name, 0x05);
 
-        write_number<std::int32_t>(to_bson_length(value.size()), true);
+        write_number<std::int32_t>(static_cast<std::int32_t>(value.size()), true);
         write_number(value.has_subtype() ? static_cast<std::uint8_t>(value.subtype()) : static_cast<std::uint8_t>(0x00));
 
         oa->write_characters(reinterpret_cast<const CharType*>(value.data()), value.size());
@@ -1259,7 +1244,7 @@ class binary_writer
                 return write_bson_integer(name, j.m_data.m_value.number_integer);
 
             case value_t::number_unsigned:
-                return write_bson_unsigned(name, j.m_data.m_value.number_unsigned);
+                return write_bson_unsigned(name, j);
 
             case value_t::string:
                 return write_bson_string(name, *j.m_data.m_value.string);
@@ -1299,7 +1284,7 @@ class binary_writer
     */
     void write_bson_object(const typename BasicJsonType::object_t& value)
     {
-        write_number<std::int32_t>(to_bson_length(calc_bson_object_size(value)), true);
+        write_number<std::int32_t>(static_cast<std::int32_t>(calc_bson_object_size(value)), true);
 
         for (const auto& el : value)
         {

include/nlohmann/detail/output/serializer.hpp

@@ -16,6 +16,7 @@
 #include <cstddef> // size_t, ptrdiff_t
 #include <cstdint> // uint8_t
 #include <cstdio> // snprintf
+#include <cstring> // memcpy
 #include <limits> // numeric_limits
 #include <string> // string, char_traits
 #include <iomanip> // setfill, setw
@@ -24,6 +25,7 @@
 
 #include <nlohmann/detail/conversions/to_chars.hpp>
 #include <nlohmann/detail/exceptions.hpp>
+#include <nlohmann/detail/input/string_scan.hpp>
 #include <nlohmann/detail/macro_scope.hpp>
 #include <nlohmann/detail/meta/cpp_future.hpp>
 #include <nlohmann/detail/output/binary_writer.hpp>
@@ -109,6 +111,25 @@ class serializer
               const bool ensure_ascii,
               const unsigned int indent_step,
               const unsigned int current_indent = 0)
+    {
+        dump_internal(val, pretty_print, ensure_ascii, indent_step, current_indent);
+        flush();
+    }
+
+  JSON_PRIVATE_UNLESS_TESTED:
+    /*!
+    @brief recursive worker for @ref dump
+
+    Identical in behavior to the historical @ref dump, but writes into the
+    serializer's internal @ref write_buffer instead of issuing a virtual call
+    per token. The public @ref dump wraps this and flushes the buffer once the
+    top-level value has been serialized.
+    */
+    void dump_internal(const BasicJsonType& val,
+                       const bool pretty_print,
+                       const bool ensure_ascii,
+                       const unsigned int indent_step,
+                       const unsigned int current_indent = 0)
     {
         switch (val.m_data.m_type)
         {
@@ -116,13 +137,13 @@ class serializer
             {
                 if (val.m_data.m_value.object->empty())
                 {
-                    o->write_characters("{}", 2);
+                    put_chars("{}", 2);
                     return;
                 }
 
                 if (pretty_print)
                 {
-                    o->write_characters("{\n", 2);
+                    put_chars("{\n", 2);
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
@@ -135,51 +156,51 @@ class serializer
                     auto i = val.m_data.m_value.object->cbegin();
                     for (std::size_t cnt = 0; cnt < val.m_data.m_value.object->size() - 1; ++cnt, ++i)
                     {
-                        o->write_characters(indent_string.c_str(), new_indent);
+                        put_chars(indent_string.c_str(), new_indent);
-                        o->write_character('\"');
+                        put_char('\"');
                         dump_escaped(i->first, ensure_ascii);
-                        o->write_characters("\": ", 3);
+                        put_chars("\": ", 3);
-                        dump(i->second, true, ensure_ascii, indent_step, new_indent);
+                        dump_internal(i->second, true, ensure_ascii, indent_step, new_indent);
-                        o->write_characters(",\n", 2);
+                        put_chars(",\n", 2);
                     }
 
                     // last element
                     JSON_ASSERT(i != val.m_data.m_value.object->cend());
                     JSON_ASSERT(std::next(i) == val.m_data.m_value.object->cend());
-                    o->write_characters(indent_string.c_str(), new_indent);
+                    put_chars(indent_string.c_str(), new_indent);
-                    o->write_character('\"');
+                    put_char('\"');
                     dump_escaped(i->first, ensure_ascii);
-                    o->write_characters("\": ", 3);
+                    put_chars("\": ", 3);
-                    dump(i->second, true, ensure_ascii, indent_step, new_indent);
+                    dump_internal(i->second, true, ensure_ascii, indent_step, new_indent);
 
-                    o->write_character('\n');
+                    put_char('\n');
-                    o->write_characters(indent_string.c_str(), current_indent);
+                    put_chars(indent_string.c_str(), current_indent);
-                    o->write_character('}');
+                    put_char('}');
                 }
                 else
                 {
-                    o->write_character('{');
+                    put_char('{');
 
                     // first n-1 elements
                     auto i = val.m_data.m_value.object->cbegin();
                     for (std::size_t cnt = 0; cnt < val.m_data.m_value.object->size() - 1; ++cnt, ++i)
                     {
-                        o->write_character('\"');
+                        put_char('\"');
                         dump_escaped(i->first, ensure_ascii);
-                        o->write_characters("\":", 2);
+                        put_chars("\":", 2);
-                        dump(i->second, false, ensure_ascii, indent_step, current_indent);
+                        dump_internal(i->second, false, ensure_ascii, indent_step, current_indent);
-                        o->write_character(',');
+                        put_char(',');
                     }
 
                     // last element
                     JSON_ASSERT(i != val.m_data.m_value.object->cend());
                     JSON_ASSERT(std::next(i) == val.m_data.m_value.object->cend());
-                    o->write_character('\"');
+                    put_char('\"');
                     dump_escaped(i->first, ensure_ascii);
-                    o->write_characters("\":", 2);
+                    put_chars("\":", 2);
-                    dump(i->second, false, ensure_ascii, indent_step, current_indent);
+                    dump_internal(i->second, false, ensure_ascii, indent_step, current_indent);
 
-                    o->write_character('}');
+                    put_char('}');
                 }
 
                 return;
@@ -189,13 +210,13 @@ class serializer
             {
                 if (val.m_data.m_value.array->empty())
                 {
-                    o->write_characters("[]", 2);
+                    put_chars("[]", 2);
                     return;
                 }
 
                 if (pretty_print)
                 {
-                    o->write_characters("[\n", 2);
+                    put_chars("[\n", 2);
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
@@ -208,37 +229,37 @@ class serializer
                     for (auto i = val.m_data.m_value.array->cbegin();
                             i != val.m_data.m_value.array->cend() - 1; ++i)
                     {
-                        o->write_characters(indent_string.c_str(), new_indent);
+                        put_chars(indent_string.c_str(), new_indent);
-                        dump(*i, true, ensure_ascii, indent_step, new_indent);
+                        dump_internal(*i, true, ensure_ascii, indent_step, new_indent);
-                        o->write_characters(",\n", 2);
+                        put_chars(",\n", 2);
                     }
 
                     // last element
                     JSON_ASSERT(!val.m_data.m_value.array->empty());
-                    o->write_characters(indent_string.c_str(), new_indent);
+                    put_chars(indent_string.c_str(), new_indent);
-                    dump(val.m_data.m_value.array->back(), true, ensure_ascii, indent_step, new_indent);
+                    dump_internal(val.m_data.m_value.array->back(), true, ensure_ascii, indent_step, new_indent);
 
-                    o->write_character('\n');
+                    put_char('\n');
-                    o->write_characters(indent_string.c_str(), current_indent);
+                    put_chars(indent_string.c_str(), current_indent);
-                    o->write_character(']');
+                    put_char(']');
                 }
                 else
                 {
-                    o->write_character('[');
+                    put_char('[');
 
                     // first n-1 elements
                     for (auto i = val.m_data.m_value.array->cbegin();
                             i != val.m_data.m_value.array->cend() - 1; ++i)
                     {
-                        dump(*i, false, ensure_ascii, indent_step, current_indent);
+                        dump_internal(*i, false, ensure_ascii, indent_step, current_indent);
-                        o->write_character(',');
+                        put_char(',');
                     }
 
                     // last element
                     JSON_ASSERT(!val.m_data.m_value.array->empty());
-                    dump(val.m_data.m_value.array->back(), false, ensure_ascii, indent_step, current_indent);
+                    dump_internal(val.m_data.m_value.array->back(), false, ensure_ascii, indent_step, current_indent);
 
-                    o->write_character(']');
+                    put_char(']');
                 }
 
                 return;
@@ -246,9 +267,9 @@ class serializer
 
             case value_t::string:
             {
-                o->write_character('\"');
+                put_char('\"');
                 dump_escaped(*val.m_data.m_value.string, ensure_ascii);
-                o->write_character('\"');
+                put_char('\"');
                 return;
             }
 
@@ -256,7 +277,7 @@ class serializer
             {
                 if (pretty_print)
                 {
-                    o->write_characters("{\n", 2);
+                    put_chars("{\n", 2);
 
                     // variable to hold indentation for recursive calls
                     const auto new_indent = current_indent + indent_step;
@@ -265,9 +286,9 @@ class serializer
                         indent_string.resize(indent_string.size() * 2, ' ');
                     }
 
-                    o->write_characters(indent_string.c_str(), new_indent);
+                    put_chars(indent_string.c_str(), new_indent);
 
-                    o->write_characters("\"bytes\": [", 10);
+                    put_chars("\"bytes\": [", 10);
 
                     if (!val.m_data.m_value.binary->empty())
                     {
@@ -275,30 +296,30 @@ class serializer
                                 i != val.m_data.m_value.binary->cend() - 1; ++i)
                         {
                             dump_integer(*i);
-                            o->write_characters(", ", 2);
+                            put_chars(", ", 2);
                         }
                         dump_integer(val.m_data.m_value.binary->back());
                     }
 
-                    o->write_characters("],\n", 3);
+                    put_chars("],\n", 3);
-                    o->write_characters(indent_string.c_str(), new_indent);
+                    put_chars(indent_string.c_str(), new_indent);
 
-                    o->write_characters("\"subtype\": ", 11);
+                    put_chars("\"subtype\": ", 11);
                     if (val.m_data.m_value.binary->has_subtype())
                     {
                         dump_integer(val.m_data.m_value.binary->subtype());
                     }
                     else
                     {
-                        o->write_characters("null", 4);
+                        put_chars("null", 4);
                     }
-                    o->write_character('\n');
+                    put_char('\n');
-                    o->write_characters(indent_string.c_str(), current_indent);
+                    put_chars(indent_string.c_str(), current_indent);
-                    o->write_character('}');
+                    put_char('}');
                 }
                 else
                 {
-                    o->write_characters("{\"bytes\":[", 10);
+                    put_chars("{\"bytes\":[", 10);
 
                     if (!val.m_data.m_value.binary->empty())
                     {
@@ -306,20 +327,20 @@ class serializer
                                 i != val.m_data.m_value.binary->cend() - 1; ++i)
                         {
                             dump_integer(*i);
-                            o->write_character(',');
+                            put_char(',');
                         }
                         dump_integer(val.m_data.m_value.binary->back());
                     }
 
-                    o->write_characters("],\"subtype\":", 12);
+                    put_chars("],\"subtype\":", 12);
                     if (val.m_data.m_value.binary->has_subtype())
                     {
                         dump_integer(val.m_data.m_value.binary->subtype());
-                        o->write_character('}');
+                        put_char('}');
                     }
                     else
                     {
-                        o->write_characters("null}", 5);
+                        put_chars("null}", 5);
                     }
                 }
                 return;
@@ -329,11 +350,11 @@ class serializer
             {
                 if (val.m_data.m_value.boolean)
                 {
-                    o->write_characters("true", 4);
+                    put_chars("true", 4);
                 }
                 else
                 {
-                    o->write_characters("false", 5);
+                    put_chars("false", 5);
                 }
                 return;
             }
@@ -358,13 +379,13 @@ class serializer
 
             case value_t::discarded:
             {
-                o->write_characters("<discarded>", 11);
+                put_chars("<discarded>", 11);
                 return;
             }
 
             case value_t::null:
             {
-                o->write_characters("null", 4);
+                put_chars("null", 4);
                 return;
             }
 
@@ -400,6 +421,45 @@ class serializer
 
         for (std::size_t i = 0; i < s.size(); ++i)
         {
+            // Fast path: at a character boundary (state == UTF8_ACCEPT),
+            // bulk-copy the longest run of bytes that need no escaping using a
+            // SWAR scanner shared with the lexer's contiguous path. The scanner
+            // stops exactly at the first byte dump_escaped would handle
+            // individually, so that byte is left to the byte-at-a-time path
+            // below, keeping escaping output and error diagnostics unchanged.
+            //
+            // - ensure_ascii == false: string_bulk_run() copies ordinary bytes
+            //   and complete well-formed UTF-8, stopping at a quote, backslash,
+            //   control character (< 0x20), or ill-formed/truncated sequence.
+            // - ensure_ascii == true: only printable ASCII may be copied
+            //   verbatim; find_ascii_copyable_run() additionally stops at 0x7F
+            //   and every non-ASCII byte (>= 0x80), which must be \u-escaped.
+            if (state == UTF8_ACCEPT)
+            {
+                const auto* const data = reinterpret_cast<const unsigned char*>(s.data());
+                const std::size_t run = ensure_ascii
+                                        ? find_ascii_copyable_run(data + i, s.size() - i)
+                                        : string_bulk_run(data + i, s.size() - i);
+                if (run != 0)
+                {
+                    // emit any bytes still pending in string_buffer first to
+                    // preserve output order, then write the run directly
+                    if (bytes != 0)
+                    {
+                        put_chars(string_buffer.data(), bytes);
+                        bytes = 0;
+                    }
+                    put_chars(s.data() + i, run);
+                    bytes_after_last_accept = 0;
+                    undumped_chars = 0;
+                    i += run;
+                    if (i >= s.size())
+                    {
+                        break;
+                    }
+                }
+            }
+
             const auto byte = static_cast<std::uint8_t>(s[i]);
 
             switch (decode(state, codepoint, byte))
@@ -488,7 +548,7 @@ class serializer
                     // written ("\uxxxx\uxxxx\0") for one code point
                     if (string_buffer.size() - bytes < 13)
                     {
-                        o->write_characters(string_buffer.data(), bytes);
+                        put_chars(string_buffer.data(), bytes);
                         bytes = 0;
                     }
 
@@ -547,7 +607,7 @@ class serializer
                                 // written ("\uxxxx\uxxxx\0") for one code point
                                 if (string_buffer.size() - bytes < 13)
                                 {
-                                    o->write_characters(string_buffer.data(), bytes);
+                                    put_chars(string_buffer.data(), bytes);
                                     bytes = 0;
                                 }
 
@@ -586,7 +646,7 @@ class serializer
             // write buffer
             if (bytes > 0)
             {
-                o->write_characters(string_buffer.data(), bytes);
+                put_chars(string_buffer.data(), bytes);
             }
         }
         else
@@ -602,22 +662,22 @@ class serializer
                 case error_handler_t::ignore:
                 {
                     // write all accepted bytes
-                    o->write_characters(string_buffer.data(), bytes_after_last_accept);
+                    put_chars(string_buffer.data(), bytes_after_last_accept);
                     break;
                 }
 
                 case error_handler_t::replace:
                 {
                     // write all accepted bytes
-                    o->write_characters(string_buffer.data(), bytes_after_last_accept);
+                    put_chars(string_buffer.data(), bytes_after_last_accept);
                     // add a replacement character
                     if (ensure_ascii)
                     {
-                        o->write_characters("\\ufffd", 6);
+                        put_chars("\\ufffd", 6);
                     }
                     else
                     {
-                        o->write_characters("\xEF\xBF\xBD", 3);
+                        put_chars("\xEF\xBF\xBD", 3);
                     }
                     break;
                 }
@@ -628,6 +688,66 @@ class serializer
         }
     }
 
+  private:
+    /*!
+    @brief append a single character to the write buffer
+
+    Structural characters ('{', '"', ',', ...) previously went straight to the
+    output adapter, one virtual call each. Buffering them and flushing in bulk
+    turns those many indirect calls into a single memcpy plus an occasional
+    flush, which dominates the cost of serializing object/array-heavy values.
+    */
+    void put_char(char c)
+    {
+        if (JSON_HEDLEY_UNLIKELY(write_buffer_pos == write_buffer.size()))
+        {
+            flush();
+        }
+        write_buffer[write_buffer_pos++] = c;
+    }
+
+    /*!
+    @brief append @a length characters to the write buffer
+
+    Runs that do not fit the buffer are written straight through the output
+    adapter (after flushing what is pending), so large string/number payloads
+    are not copied an extra time.
+    */
+    JSON_HEDLEY_NON_NULL(2)
+    void put_chars(const char* s, std::size_t length)
+    {
+        if (JSON_HEDLEY_UNLIKELY(length >= write_buffer.size()))
+        {
+            flush();
+            o->write_characters(s, length);
+            return;
+        }
+        if (JSON_HEDLEY_UNLIKELY(write_buffer_pos + length > write_buffer.size()))
+        {
+            flush();
+        }
+        std::memcpy(write_buffer.data() + write_buffer_pos, s, length);
+        write_buffer_pos += length;
+    }
+
+  JSON_PRIVATE_UNLESS_TESTED:
+    /*!
+    @brief flush the write buffer to the output adapter
+
+    Writing zero characters is a well-defined no-op for every output adapter, so
+    the buffered length is passed through unconditionally (no empty-guard branch
+    to leave uncovered).
+
+    @note dump_escaped() and dump_integer()/dump_float() write into the internal
+    write buffer; callers that invoke them directly (rather than through the
+    public dump()) must call flush() before inspecting the output.
+    */
+    void flush()
+    {
+        o->write_characters(write_buffer.data(), write_buffer_pos);
+        write_buffer_pos = 0;
+    }
+
   private:
     /*!
     @brief count digits
@@ -752,7 +872,7 @@ class serializer
         // special case for "0"
         if (x == 0)
         {
-            o->write_character('0');
+            put_char('0');
             return;
         }
 
@@ -805,7 +925,7 @@ class serializer
             *(--buffer_ptr) = static_cast<char>('0' + abs_value);
         }
 
-        o->write_characters(number_buffer.data(), n_chars);
+        put_chars(number_buffer.data(), n_chars);
     }
 
     /*!
@@ -821,7 +941,7 @@ class serializer
         // NaN / inf
         if (!std::isfinite(x))
         {
-            o->write_characters("null", 4);
+            put_chars("null", 4);
             return;
         }
 
@@ -842,7 +962,7 @@ class serializer
         auto* begin = number_buffer.data();
         auto* end = ::nlohmann::detail::to_chars(begin, begin + number_buffer.size(), x);
 
-        o->write_characters(begin, static_cast<size_t>(end - begin));
+        put_chars(begin, static_cast<size_t>(end - begin));
     }
 
     JSON_HEDLEY_NON_NULL(1)
@@ -893,7 +1013,7 @@ class serializer
             }
         }
 
-        o->write_characters(number_buffer.data(), static_cast<std::size_t>(len));
+        put_chars(number_buffer.data(), static_cast<std::size_t>(len));
 
         // determine if we need to append ".0"
         const bool value_is_int_like =
@@ -905,7 +1025,7 @@ class serializer
 
         if (value_is_int_like)
         {
-            o->write_characters(".0", 2);
+            put_chars(".0", 2);
         }
     }
 
@@ -1015,6 +1135,12 @@ class serializer
 
     /// error_handler how to react on decoding errors
     const error_handler_t error_handler;
+
+    /// buffer collecting output before it is flushed to the output adapter, so
+    /// that the many small structural writes become few bulk writes
+    std::array<char, 1024> write_buffer{{}};
+    /// number of valid bytes currently held in @ref write_buffer
+    std::size_t write_buffer_pos = 0;
 };
 
 }  // namespace detail

tests/src/unit-bjdata.cpp

@@ -2721,19 +2721,6 @@ TEST_CASE("BJData")
                 CHECK_THROWS_WITH_AS(_ = json::from_bjdata(v), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing BJData string: expected length type specification (U, i, u, I, m, l, M, L); last byte: 0x31", json::parse_error&);
             }
 
-            SECTION("negative length")
-            {
-                json _;
-
-                std::vector<uint8_t> const vi = {'S', 'i', 0xFF};
-                CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vi), "[json.exception.parse_error.113] parse error at byte 3: syntax error while parsing BJData string: string length must not be negative", json::parse_error&);
-                CHECK(json::from_bjdata(vi, true, false).is_discarded());
-
-                std::vector<uint8_t> const vl = {'S', 'l', 0xFF, 0xFF, 0xFF, 0xFF};
-                CHECK_THROWS_WITH_AS(_ = json::from_bjdata(vl), "[json.exception.parse_error.113] parse error at byte 6: syntax error while parsing BJData string: string length must not be negative", json::parse_error&);
-                CHECK(json::from_bjdata(vl, true, false).is_discarded());
-            }
-
             SECTION("parse bjdata markers in ubjson")
             {
                 // create a single-character string for all number types

tests/src/unit-bson.cpp

@@ -11,35 +11,12 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
-#include <cstdint>
 #include <fstream>
 #include <limits>
 #include <sstream>
-#include <vector>
 #include "make_test_data_available.hpp"
 #include "test_utils.hpp"
 
-namespace
-{
-// a binary container that reports a size beyond INT32_MAX without allocating
-// that much memory, so the BSON length overflow can be tested cheaply
-class huge_binary_t : public std::vector<std::uint8_t>
-{
-  public:
-    using std::vector<std::uint8_t>::vector;
-
-    size_type size() const noexcept // NOLINT(readability-convert-member-functions-to-static)
-    {
-        // one byte more than the BSON length field can represent
-        return static_cast<size_type>((std::numeric_limits<std::int32_t>::max)()) + 1;
-    }
-};
-
-using huge_binary_json = nlohmann::basic_json <
-                         std::map, std::vector, std::string, bool, std::int64_t, std::uint64_t,
-                         double, std::allocator, nlohmann::adl_serializer, huge_binary_t, void >;
-} // namespace
-
 TEST_CASE("BSON")
 {
     SECTION("individual values not supported")
@@ -103,14 +80,6 @@ TEST_CASE("BSON")
 #endif
     }
 
-    SECTION("lengths exceeding INT32_MAX cannot be serialized to BSON")
-    {
-        huge_binary_json j;
-        j["b"] = huge_binary_json::binary(huge_binary_t{});
-
-        CHECK_THROWS_WITH_AS(huge_binary_json::to_bson(j), "[json.exception.out_of_range.412] BSON length 2147483661 exceeds maximum of 2147483647", huge_binary_json::out_of_range&);
-    }
-
     SECTION("string length must be at least 1")
     {
         // from https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=11175
@@ -885,62 +854,6 @@ TEST_CASE("Unsupported BSON input")
     CHECK(!json::sax_parse(bson, &scp, json::input_format_t::bson));
 }
 
-TEST_CASE("BSON document size mismatch")
-{
-    json _;
-
-    SECTION("top-level document declaring more bytes than it contains")
-    {
-        // empty object, but the length prefix claims 6 bytes instead of 5
-        std::vector<std::uint8_t> const input = {0x06, 0x00, 0x00, 0x00, 0x00};
-        CHECK_THROWS_WITH_AS(_ = json::from_bson(input), "[json.exception.parse_error.112] parse error at byte 5: syntax error while parsing BSON document: document size 6 does not match the number of bytes read (5)", json::parse_error&);
-        CHECK(json::from_bson(input, true, false).is_discarded());
-    }
-
-    SECTION("top-level document with a negative size")
-    {
-        std::vector<std::uint8_t> const input = {0xFF, 0xFF, 0xFF, 0xFF, 0x00};
-        CHECK_THROWS_WITH_AS(_ = json::from_bson(input), "[json.exception.parse_error.112] parse error at byte 5: syntax error while parsing BSON document: document size -1 does not match the number of bytes read (5)", json::parse_error&);
-        CHECK(json::from_bson(input, true, false).is_discarded());
-    }
-
-    SECTION("embedded document whose size disagrees with its terminator")
-    {
-        // the embedded document "d" declares 0x7FFFFFFF bytes but its 0x00
-        // terminator falls right after {"a":null}; the length prefix would
-        // otherwise let the following "h" element be read as a member of the
-        // enclosing document instead of "d"
-        std::vector<std::uint8_t> const input =
-        {
-            0x00, 0x00, 0x00, 0x00, // outer size
-            0x03, 'd', 0x00,        // entry: embedded document "d"
-            0xFF, 0xFF, 0xFF, 0x7F, //   embedded size 0x7FFFFFFF
-            0x0A, 'a', 0x00,        //   entry: null "a"
-            0x00,                   //   embedded end marker
-            0x08, 'h', 0x00, 0x01,  // entry: bool "h" = true
-            0x00                    // outer end marker
-        };
-        CHECK_THROWS_WITH_AS(_ = json::from_bson(input), "[json.exception.parse_error.112] parse error at byte 15: syntax error while parsing BSON document: document size 2147483647 does not match the number of bytes read (8)", json::parse_error&);
-        CHECK(json::from_bson(input, true, false).is_discarded());
-    }
-
-    SECTION("embedded array whose size disagrees with its terminator")
-    {
-        // array [42] is 12 bytes, but the length prefix claims 13
-        std::vector<std::uint8_t> const input =
-        {
-            0x00, 0x00, 0x00, 0x00, // outer size
-            0x04, 'a', 0x00,        // entry: array "a"
-            0x0D, 0x00, 0x00, 0x00, //   array size 13 (real is 12)
-            0x10, '0', 0x00, 0x2A, 0x00, 0x00, 0x00, //   entry: int32 "0" = 42
-            0x00,                   //   array end marker
-            0x00                    // outer end marker
-        };
-        CHECK_THROWS_WITH_AS(_ = json::from_bson(input), "[json.exception.parse_error.112] parse error at byte 19: syntax error while parsing BSON document: document size 13 does not match the number of bytes read (12)", json::parse_error&);
-        CHECK(json::from_bson(input, true, false).is_discarded());
-    }
-}
-
 TEST_CASE("BSON numerical data")
 {
     SECTION("number")

tests/src/unit-class_lexer.cpp

@@ -12,6 +12,10 @@
 #include <nlohmann/json.hpp>
 using nlohmann::json;
 
+#include <sstream> // stringstream
+#include <string> // string
+#include <vector> // vector
+
 namespace
 {
 // shortcut to scan a string literal
@@ -224,3 +228,75 @@ TEST_CASE("lexer class")
         CHECK((scan_string("/**//**//**/", true) == json::lexer::token_type::end_of_input));
     }
 }
+
+TEST_CASE("lexer number fast path")
+{
+    // The contiguous fast path (used for pointer/string input) must agree with
+    // the streaming byte path (used for std::istream) on token type, numeric
+    // value, and round-trip text for every well-formed number, and reject the
+    // same malformed numbers with the same message.
+    SECTION("contiguous vs streaming parity")
+    {
+        const std::vector<std::string> numbers =
+        {
+            "0", "-0", "1", "-1", "42", "-42", "10", "100", "1234567890",
+            "0.0", "-0.0", "3.14", "-3.14", "0.5", "-0.001", "123.456789",
+            "1e0", "1E0", "1e10", "1e-10", "1e+10", "1.5e3", "-2.5E-4",
+            "9223372036854775807",             // INT64_MAX -> unsigned
+            "9223372036854775808",             // INT64_MAX + 1 -> unsigned
+            "18446744073709551615",            // UINT64_MAX -> unsigned
+            "18446744073709551616",            // UINT64_MAX + 1 -> float
+            "-9223372036854775808",            // INT64_MIN -> integer
+            "-9223372036854775809",            // INT64_MIN - 1 -> float
+            "123456789012345678901234567890",  // huge -> float
+            "0.30000000000000004", "2.2250738585072014e-308", "1e308",
+            // high-precision / wide-exponent values that exercise the
+            // std::from_chars (Eisel-Lemire) path beyond the Clinger subset
+            "1.7976931348623157e308", "1.2345678901234567e-250",
+            "9007199254740993", "5e-324", "1e-320"
+        };
+
+        for (const auto& n : numbers)
+        {
+            const std::string doc = "[" + n + "]";
+
+            // contiguous fast path
+            const json a = json::parse(doc);
+            // streaming byte path
+            std::stringstream ss(doc);
+            const json b = json::parse(ss);
+
+            CAPTURE(n);
+            CHECK(a == b);
+            CHECK(a.dump() == b.dump());
+            CHECK(a[0].type() == b[0].type());
+        }
+    }
+
+    SECTION("token type classification")
+    {
+        CHECK((scan_string("0") == json::lexer::token_type::value_unsigned));
+        CHECK((scan_string("-1") == json::lexer::token_type::value_integer));
+        CHECK((scan_string("1.5") == json::lexer::token_type::value_float));
+        CHECK((scan_string("1e5") == json::lexer::token_type::value_float));
+        CHECK((scan_string("18446744073709551615") == json::lexer::token_type::value_unsigned));
+        CHECK((scan_string("18446744073709551616") == json::lexer::token_type::value_float));
+        CHECK((scan_string("-9223372036854775808") == json::lexer::token_type::value_integer));
+        CHECK((scan_string("-9223372036854775809") == json::lexer::token_type::value_float));
+    }
+
+    SECTION("malformed numbers are rejected identically")
+    {
+        for (const char* bad :
+                {"-", "1.", "1e", "1e+", "1.2e", "01", "-01", "1..2", "1.2.3"
+                })
+        {
+            CAPTURE(bad);
+            // the contiguous fast path must decline and let the byte path report
+            const std::string doc = std::string("[") + bad + "]";
+            CHECK_FALSE(json::accept(doc));
+            std::stringstream ss(doc);
+            CHECK_FALSE(json::accept(ss));
+        }
+    }
+}

tests/src/unit-convenience.cpp

@@ -100,6 +100,7 @@ void check_escaped(const char* original, const char* escaped, const bool ensure_
     std::stringstream ss;
     json::serializer s(nlohmann::detail::output_adapter<char>(ss), ' ');
     s.dump_escaped(original, ensure_ascii);
+    s.flush(); // dump_escaped writes into the serializer's internal buffer
     CHECK(ss.str() == escaped);
 }
 } // namespace

tests/src/unit-serialization.cpp

@@ -382,3 +382,91 @@ TEST_CASE("dump for basic_json with long double number_float_t")
         check_same(100.0L,  100.0);
     }
 }
+
+TEST_CASE("serialization of strings (bulk fast path)")
+{
+    // These cases exercise the SWAR bulk-copy fast path in dump_escaped and the
+    // internal write buffer: long runs, escapes interrupting runs, 0x7F/DEL,
+    // multibyte UTF-8 under both ensure_ascii settings, and payloads larger than
+    // the write buffer.
+
+    SECTION("long unescaped ASCII exceeds the write buffer")
+    {
+        const std::string big(3000, 'a');
+        const json j = big;
+        CHECK(j.dump() == '"' + big + '"');
+        CHECK(j.dump(-1, ' ', true) == '"' + big + '"');
+        // round-trips
+        CHECK(json::parse(j.dump()) == j);
+    }
+
+    SECTION("runs interrupted by escapes")
+    {
+        const json j = std::string(500, 'x') + "\n\"\\" + std::string(500, 'y');
+        const std::string out = j.dump();
+        CHECK(out == '"' + std::string(500, 'x') + "\\n\\\"\\\\" + std::string(500, 'y') + '"');
+        CHECK(json::parse(out) == j);
+    }
+
+    SECTION("DEL (0x7F) depends on ensure_ascii")
+    {
+        const json j = std::string("a\x7f" "b");
+        CHECK(j.dump(-1, ' ', false) == "\"a\x7f" "b\"");   // copied verbatim
+        CHECK(j.dump(-1, ' ', true) == "\"a\\u007fb\"");    // escaped
+    }
+
+    SECTION("multibyte UTF-8 under both ensure_ascii settings")
+    {
+        const json j = std::string("A\xc3\xa9\xe4\xbd\xa0\xf0\x9f\x98\x80Z"); // A é 你 😀 Z
+        // not escaping non-ASCII: bytes are copied through the bulk validator
+        CHECK(j.dump(-1, ' ', false) == "\"A\xc3\xa9\xe4\xbd\xa0\xf0\x9f\x98\x80Z\"");
+        // ensure_ascii: escaped (with a surrogate pair for the emoji)
+        CHECK(j.dump(-1, ' ', true) == "\"A\\u00e9\\u4f60\\ud83d\\ude00Z\"");
+        CHECK(json::parse(j.dump(-1, ' ', true)) == j);
+    }
+
+    SECTION("many small structural writes exceed the write buffer")
+    {
+        json arr = json::array();
+        for (int i = 0; i < 2000; ++i)
+        {
+            arr.push_back(i);
+        }
+        const std::string out = arr.dump();
+        CHECK(out.front() == '[');
+        CHECK(out.back() == ']');
+        CHECK(json::parse(out) == arr);
+
+        json obj = json::object();
+        for (int i = 0; i < 500; ++i)
+        {
+            obj["key" + std::to_string(i)] = i;
+        }
+        CHECK(json::parse(obj.dump()) == obj);
+        CHECK(json::parse(obj.dump(2)) == obj);
+
+        // an array of many empty strings emits a long run of single-character
+        // writes ('"', '"', ',') at shallow nesting depth, so the write buffer
+        // fills and flushes mid-run without the deep recursion that would
+        // overflow the stack on some debug builds
+        json many_empty = json::array();
+        for (int i = 0; i < 500; ++i)
+        {
+            many_empty.push_back("");
+        }
+        const std::string out2 = many_empty.dump();
+        CHECK(out2.size() > 1024); // spans multiple write-buffer flushes
+        CHECK(out2.front() == '[');
+        CHECK(out2.back() == ']');
+        CHECK(json::parse(out2) == many_empty);
+    }
+
+    SECTION("invalid UTF-8 handling is unaffected by the fast path")
+    {
+        const json j = std::string("valid\xff" "more");
+        CHECK_THROWS_WITH_AS(j.dump(), "[json.exception.type_error.316] invalid UTF-8 byte at index 5: 0xFF", json::type_error&);
+        CHECK(j.dump(-1, ' ', false, json::error_handler_t::replace) == "\"valid\xef\xbf\xbd" "more\"");
+        CHECK(j.dump(-1, ' ', true, json::error_handler_t::replace) == "\"valid\\ufffdmore\"");
+        CHECK(j.dump(-1, ' ', false, json::error_handler_t::ignore) == "\"validmore\"");
+    }
+}

tests/src/unit-ubjson.cpp

@@ -1862,31 +1862,6 @@ TEST_CASE("UBJSON")
                 json _;
                 CHECK_THROWS_WITH_AS(_ = json::from_ubjson(v), "[json.exception.parse_error.113] parse error at byte 2: syntax error while parsing UBJSON string: expected length type specification (U, i, I, l, L); last byte: 0x31", json::parse_error&);
             }
-
-            SECTION("negative length")
-            {
-                json _;
-
-                std::vector<uint8_t> const vi = {'S', 'i', 0xFF};
-                CHECK_THROWS_WITH_AS(_ = json::from_ubjson(vi), "[json.exception.parse_error.113] parse error at byte 3: syntax error while parsing UBJSON string: string length must not be negative", json::parse_error&);
-                CHECK(json::from_ubjson(vi, true, false).is_discarded());
-
-                std::vector<uint8_t> const vI = {'S', 'I', 0xFF, 0xFF};
-                CHECK_THROWS_WITH_AS(_ = json::from_ubjson(vI), "[json.exception.parse_error.113] parse error at byte 4: syntax error while parsing UBJSON string: string length must not be negative", json::parse_error&);
-                CHECK(json::from_ubjson(vI, true, false).is_discarded());
-
-                std::vector<uint8_t> const vl = {'S', 'l', 0xFF, 0xFF, 0xFF, 0xFF};
-                CHECK_THROWS_WITH_AS(_ = json::from_ubjson(vl), "[json.exception.parse_error.113] parse error at byte 6: syntax error while parsing UBJSON string: string length must not be negative", json::parse_error&);
-                CHECK(json::from_ubjson(vl, true, false).is_discarded());
-
-                std::vector<uint8_t> const vL = {'S', 'L', 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
-                CHECK_THROWS_WITH_AS(_ = json::from_ubjson(vL), "[json.exception.parse_error.113] parse error at byte 10: syntax error while parsing UBJSON string: string length must not be negative", json::parse_error&);
-                CHECK(json::from_ubjson(vL, true, false).is_discarded());
-
-                // a length of zero remains valid and yields an empty string
-                std::vector<uint8_t> const v0 = {'S', 'i', 0};
-                CHECK(json::from_ubjson(v0) == json(""));
-            }
         }
 
         SECTION("array")