Merge pull request #422 from reinfallt/png_iTXt_compressed

drewnoakes · web-flow · commit 6e7c1d0704a6 · 2025-05-23T01:49:08.000+10:00
Fixed PNG compressed iTXt chunk
diff --git a/MetadataExtractor/Formats/Png/PngMetadataReader.cs b/MetadataExtractor/Formats/Png/PngMetadataReader.cs
@@ -264,7 +264,9 @@ private static IEnumerable<Directory> ProcessChunk(PngChunk chunk)
                 {
                     if (compressionMethod == 0)
                     {
-                        if (!TryDeflate(bytes, bytesLeft, out textBytes, out string? errorMessage))
+                        reader.Skip(2); // Skip over the zlib header bytes (78 9C)
+                        bytesLeft -= 2;
+                        if (!TryDeflate(reader.GetBytes(bytesLeft), bytesLeft, out textBytes, out string? errorMessage))
                         {
                             var directory = new PngDirectory(PngChunkType.iTXt);
                             directory.AddError($"Exception decompressing PNG {nameof(PngChunkType.iTXt)} chunk with keyword \"{keyword}\": {errorMessage}");

Original file line number	Diff line number	Diff line change
`@@ -264,7 +264,9 @@ private static IEnumerable<Directory> ProcessChunk(PngChunk chunk)`
`264`	`264`	`{`
`265`	`265`	`if (compressionMethod == 0)`
`266`	`266`	`{`
`267`		`- if (!TryDeflate(bytes, bytesLeft, out textBytes, out string? errorMessage))`
	`267`	`+ reader.Skip(2); // Skip over the zlib header bytes (78 9C)`
	`268`	`+ bytesLeft -= 2;`
	`269`	`+ if (!TryDeflate(reader.GetBytes(bytesLeft), bytesLeft, out textBytes, out string? errorMessage))`
`268`	`270`	`{`
`269`	`271`	`var directory = new PngDirectory(PngChunkType.iTXt);`
`270`	`272`	`directory.AddError($"Exception decompressing PNG {nameof(PngChunkType.iTXt)} chunk with keyword \"{keyword}\": {errorMessage}");`