From 07cf36cbb0de7a2774d7fa017c0f4ddf86c274d9 Mon Sep 17 00:00:00 2001
From: Yuantao Feng <yuantao.feng@outlook.com>
Date: Tue, 29 Jul 2025 17:04:55 +0800
Subject: [PATCH] Merge pull request #27587 from
 fengyuentau:4x/core/filestorage_json_support_backslash

core: support parsing back slash \ in parseKey in FileStorage (JSON) #27587

Fixes #27585

### Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

- [x] I agree to contribute to the project under Apache 2 License.
- [x] To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
- [x] The PR is proposed to the proper branch
- [x] There is a reference to the original bug report and related work
- [x] There is accuracy test, performance test and test data in opencv_extra repository, if applicable
      Patch to opencv_extra has the same branch name.
- [ ] The feature is well documented and sample code can be built with the project CMake
---
 modules/core/src/persistence_json.cpp | 17 +++++++++++++----
 modules/core/test/test_io.cpp         | 23 +++++++++++++++++++++++
 2 files changed, 36 insertions(+), 4 deletions(-)

diff --git a/modules/core/src/persistence_json.cpp b/modules/core/src/persistence_json.cpp
index 9d05650814..c63acb8c10 100644
--- a/modules/core/src/persistence_json.cpp
+++ b/modules/core/src/persistence_json.cpp
@@ -419,10 +419,19 @@ public:
             CV_PARSE_ERROR_CPP( "Key must start with \'\"\'" );
 
         char * beg = ptr + 1;
-
+        std::string key_name;
         do {
-            ++ptr;
-            CV_PERSISTENCE_CHECK_END_OF_BUFFER_BUG_CPP();
+            if (*ptr == '\\') { // skip the next character if current is back slash
+                ++ptr;
+                CV_PERSISTENCE_CHECK_END_OF_BUFFER_BUG_CPP();
+                key_name += *ptr;
+                ++ptr;
+                CV_PERSISTENCE_CHECK_END_OF_BUFFER_BUG_CPP();
+            } else {
+                ++ptr;
+                CV_PERSISTENCE_CHECK_END_OF_BUFFER_BUG_CPP();
+                if (*ptr != '\\' && *ptr != '"') key_name += *ptr;
+            }
         } while( cv_isprint(*ptr) && *ptr != '"' );
 
         if( *ptr != '"' )
@@ -430,7 +439,7 @@ public:
 
         if( ptr == beg )
             CV_PARSE_ERROR_CPP( "Key is empty" );
-        value_placeholder = fs->addNode(collection, std::string(beg, (size_t)(ptr - beg)), FileNode::NONE);
+        value_placeholder = fs->addNode(collection, key_name, FileNode::NONE);
 
         ptr++;
         ptr = skipSpaces( ptr );
diff --git a/modules/core/test/test_io.cpp b/modules/core/test/test_io.cpp
index 67b0ab5803..7e2a9d52d4 100644
--- a/modules/core/test/test_io.cpp
+++ b/modules/core/test/test_io.cpp
@@ -1569,6 +1569,29 @@ TEST(Core_InputOutput, FileStorage_json_null_object)
     fs.release();
 }
 
+TEST(Core_InputOutput, FileStorage_json_key_backslash)
+{
+    // equivalent to json text {"\"":1,"\\":59,"Ġ\"":366,"\\\\":6852}
+    std::string test = R"({"\"":1,"\\":59,"Ġ\"":366,"\\\\":6852})";
+    FileStorage fs(test, FileStorage::READ | FileStorage::MEMORY);
+
+    ASSERT_TRUE(fs[R"(")"].isNamed());  // = "\""
+    ASSERT_TRUE(fs[R"(\)"].isNamed());  // = "\\"
+    ASSERT_TRUE(fs[R"(Ġ")"].isNamed()); // = "Ġ\""
+    ASSERT_TRUE(fs[R"(\\)"].isNamed()); // = "\\\\"
+
+    ASSERT_EQ(fs[R"(")"].name(), R"(")");
+    ASSERT_EQ(fs[R"(\)"].name(), R"(\)");
+    ASSERT_EQ(fs[R"(Ġ")"].name(), R"(Ġ")");
+    ASSERT_EQ(fs[R"(\\)"].name(), R"(\\)");
+
+    ASSERT_EQ((int)fs[R"(")"], 1);
+    ASSERT_EQ((int)fs[R"(\)"], 59);
+    ASSERT_EQ((int)fs[R"(Ġ")"], 366);
+    ASSERT_EQ((int)fs[R"(\\)"], 6852);
+    fs.release();
+}
+
 TEST(Core_InputOutput, FileStorage_json_named_nodes)
 {
     std::string test =