Fix ParseBom corrupting stream state on inputs shorter than 3 bytes#219
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Fix ParseBom corrupting stream state on inputs shorter than 3 bytes#219mihajlo-k wants to merge 1 commit into
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Pull request overview
Fixes a Vajson JSON parsing edge case where BOM probing on streams shorter than 3 bytes leaves the input stream in a failed state, breaking subsequent parsing.
Changes:
- Add a boundary-value test to ensure parsing succeeds for a 2-byte JSON buffer (
{}) that is shorter than the UTF-8 BOM length. - Add a regression test to ensure a UTF-8 BOM-prefixed buffer is parsed correctly.
- Update
JsonData::ParseBom()to recover the stream state when the BOM check read fails.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
score/json/internal/parser/vajson/vajson_parser_test.cpp |
Adds regression tests for short buffers and UTF-8 BOM-prefixed inputs. |
score/json/internal/parser/vajson/vajson_impl/reader/json_data.cpp |
Clears/rewinds stream on failed BOM read so parsing can continue on short inputs. |
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| // ReadString failed (e.g., stream shorter than BOM). | ||
| // Ensure stream is in a usable state for subsequent parsing. | ||
| this->stream_.get().clear(); | ||
| this->stream_.get().seekg(0, std::ios::beg); | ||
| } |
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it is very unlikely that that would happen. but we could add this to be more defensive. however, not sure if the branching with !stream.fail() is really necessary. even in the unlikely case when the stream is still in failure - seekg is just harmless no-op.
ParseBom always attempts to read 3 bytes for the UTF-8 BOM check. When the input stream has fewer than 3 bytes, stream.read() sets failbit|eofbit. The subsequent seekg() in RewindIf is a no-op when failbit is set (per C++ standard), leaving the stream in a failed state with consumed bytes not restored. All subsequent parsing fails. Fix: In ParseBom, when ReadString fails, clear the stream state and seek to position 0 to ensure the stream is usable for parsing.
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ParseBom always attempts to read 3 bytes for the UTF-8 BOM check. When the input stream has fewer than 3 bytes, stream.read() sets failbit|eofbit. The subsequent seekg() in RewindIf is a no-op when failbit is set (per C++ standard), leaving the stream in a failed state with consumed bytes not restored. All subsequent parsing fails.
Fix: In ParseBom, when ReadString fails, clear the stream state and seek to position 0 to ensure the stream is usable for parsing.