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Fixes Issue #328 #329

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Merged
merged 4 commits into from
May 1, 2023
Merged

Fixes Issue #328 #329

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d2531f8
Fixes Issue #328
RupertAvery Apr 29, 2023
7c097e1
Use built-in UTF8 encoding field
drewnoakes May 1, 2023
efafc95
Fix byte length computation and add comment
drewnoakes May 1, 2023
02750ea
Merge remote-tracking branch 'origin/master' into fix-328
drewnoakes May 1, 2023
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12 changes: 10 additions & 2 deletions MetadataExtractor/Formats/Png/PngMetadataReader.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -90,6 +90,7 @@ public static DirectoryList ReadMetadata(Stream stream)
/// For more guidance: http://www.w3.org/TR/PNG-Decoders.html#D.Text-chunk-processing
/// </summary>
private static readonly Encoding _latin1Encoding = Encoding.GetEncoding("ISO-8859-1");
private static readonly Encoding _utf8Encoding = Encoding.GetEncoding("UTF-8");

/// <exception cref="PngProcessingException"/>
/// <exception cref="IOException"/>
Expand Down Expand Up @@ -248,7 +249,7 @@ private static IEnumerable<Directory> ProcessChunk(PngChunk chunk)
else if (chunkType == PngChunkType.iTXt)
{
var reader = new SequentialByteArrayReader(bytes);
var keyword = reader.GetNullTerminatedStringValue(maxLengthBytes: 79).ToString(_latin1Encoding);
var keyword = reader.GetNullTerminatedStringValue(maxLengthBytes: 79).ToString(_utf8Encoding);
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There's actually now an issue slightly below here. The bytesLeft value was based on the length of the string in bytes, which for latin1 is the same as the length of the string in characters. With UTF-8 that's not the case. I'll patch this up and push to your PR.

var compressionFlag = reader.GetSByte();
var compressionMethod = reader.GetSByte();

Expand Down Expand Up @@ -432,7 +433,14 @@ IEnumerable<Directory> ProcessTextChunk(string keyword, byte[] textBytes)

static PngDirectory ReadTextDirectory(string keyword, byte[] textBytes, PngChunkType pngChunkType)
{
var textPairs = new[] { new KeyValuePair(keyword, new StringValue(textBytes, _latin1Encoding)) };
var encoding = _latin1Encoding;

if (pngChunkType == PngChunkType.iTXt)
{
encoding = _utf8Encoding;
}

var textPairs = new[] { new KeyValuePair(keyword, new StringValue(textBytes, encoding)) };
var directory = new PngDirectory(pngChunkType);
directory.Set(PngDirectory.TagTextualData, textPairs);
return directory;
Expand Down