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add itext metadata support #491

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Merged
jamesmoore merged 2 commits into from
Mar 6, 2026
Merged

add itext metadata support #491

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85a9c36
add itext metadata support
Mar 6, 2026
a1c9750
Fix iTXt chunk parsing: dedicated parser with zlib decompression supp…
Copilot Mar 6, 2026
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3 changes: 2 additions & 1 deletion SDMeta/Metadata/PngMetadataExtractor.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -30,6 +30,7 @@ public class PngMetadataExtractor
SkipBytes(fs, 4);
break;
case "tEXt":
case "iTXt":
var keywordValuePair = await ReadTextualData(fs, chunkLength);
SkipBytes(fs, 4); // Move past the current chunk CRC
yield return keywordValuePair;
Comment on lines 33 to 36
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Copilot AI Mar 6, 2026

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iTXt chunks do not have the same payload layout as tEXt (they include compression flag/method + language tag + translated keyword + possibly zlib-compressed UTF-8 text). Routing iTXt through ReadTextualData will yield incorrect values (and can include binary bytes/garbage). Add a dedicated ReadInternationalTextualData parser for iTXt (including optional zlib decompression) and call that from this switch case instead of reusing the tEXt logic.

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Comment on lines 33 to 36
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Copilot AI Mar 6, 2026

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This change adds iTXt handling, but the test suite only covers tEXt via latin1-pngtext.png. Add at least one PNG fixture containing an iTXt chunk (ideally both compressed and uncompressed variants) and a corresponding test assertion to prevent regressions in iTXt parsing/decompression.

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Expand Down Expand Up @@ -80,7 +81,7 @@ private async static Task<string> ReadChunkType(Stream stream)
var nullIndex = dataString.IndexOf(NullTerminator);
return new (
nullIndex > -1 ? dataString.Substring(0, nullIndex) : string.Empty,
nullIndex > -1 && nullIndex + 1 < length ? dataString.Substring(nullIndex + 1).TrimEnd(NullTerminator) : string.Empty
nullIndex > -1 && nullIndex + 1 < length ? dataString.Substring(nullIndex + 1).Trim(NullTerminator) : string.Empty
);
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Copilot AI Mar 6, 2026

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ReadTextualData converts the entire chunk to a string and then trims null terminators. This breaks iTXt parsing because the bytes immediately after the keyword are binary (compression flag/method) and may legitimately be 0x00; Trim(NullTerminator) will drop those leading bytes and corrupt the payload. For iTXt, parse at the byte level (split on nulls for the keyword/language/translated keyword, then treat the remaining bytes as (optionally decompressed) UTF-8 text) rather than trimming nulls from a decoded string.

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}

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