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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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17 changes: 14 additions & 3 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.UTF8;

/// <exception cref="PngProcessingException"/>
/// <exception cref="IOException"/>
Expand Down Expand Up @@ -248,15 +249,18 @@ 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 keywordStringValue = reader.GetNullTerminatedStringValue(maxLengthBytes: 79);
var keyword = keywordStringValue.ToString(_utf8Encoding);
var compressionFlag = reader.GetSByte();
var compressionMethod = reader.GetSByte();

// TODO we currently ignore languageTagBytes and translatedKeywordBytes
var languageTagBytes = reader.GetNullTerminatedBytes(bytes.Length);
var translatedKeywordBytes = reader.GetNullTerminatedBytes(bytes.Length);

var bytesLeft = bytes.Length - keyword.Length - 1 - 1 - 1 - languageTagBytes.Length - 1 - translatedKeywordBytes.Length - 1;
// bytes left for compressed text is:
// total bytes length - (Keyword length + null byte + comp flag byte + comp method byte + lang length + null byte + translated length + null byte)
var bytesLeft = bytes.Length - keywordStringValue.Bytes.Length - 1 - 1 - 1 - languageTagBytes.Length - 1 - translatedKeywordBytes.Length - 1;
byte[]? textBytes = null;
if (compressionFlag == 0)
{
Expand Down Expand Up @@ -432,7 +436,14 @@ 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