fix: improve CSV encoding detection for non-UTF-8 files - #293
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li5435945-ship-it wants to merge 2 commits into
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fix: improve CSV encoding detection for non-UTF-8 files#293li5435945-ship-it wants to merge 2 commits into
li5435945-ship-it wants to merge 2 commits into
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June 2, 2026 14:25
Fix UnicodeDecodeError when chardet misdetects Shift-JIS/CP932 files as UTF-8 due to ASCII-heavy headers. Changes: - Increase chardet sample size from 4KB to 64KB for better accuracy - Add encoding validation: verify detected encoding can decode the sample - Add fallback mechanism: try common encodings (cp932, shift_jis, gb18030, latin-1) - Add _retry_csv_with_fallback_encodings() for runtime retry on UnicodeDecodeError Fixes danny-avila#291
Add comprehensive tests for detect_file_encoding() to verify: - UTF-8 and UTF-8 BOM detection - UTF-16 LE detection - Shift-JIS detection with ASCII headers (issue danny-avila#291 scenario) - GB18030 detection with ASCII headers - Latin-1 fallback detection - CSVLoader integration test with Shift-JIS file These tests ensure the encoding detection fix works correctly for non-UTF-8 CSV files with ASCII-heavy headers.
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Problem
CSVLoader fails with
UnicodeDecodeErrorfor non-UTF-8 CSV files (e.g., Shift-JIS / CP932 from Japanese Excel) when the file has a mostly-ASCII header. Thechardetdetection only inspects the first 4096 bytes, which contains too few non-ASCII characters to detect Shift-JIS reliably.Fixes #291
Root Cause
detect_file_encoding()reads only 4096 bytes. For CSV files with English column headers and Japanese data rows, chardet returns "utf-8" because the sample is mostly ASCII.Solution
Three-layer approach:
Changes
app/utils/document_loader.py: 81 insertions, 4 deletionsTesting
Tested with a Shift-JIS CSV file (English headers, Japanese data) that was previously misdetected as UTF-8.