wmjordan/PDFPatcher · warning · ExifLibException

Malformed Exif data

Error message

Malformed Exif data

What it means

JpgHelper.CreateTagIndex throws ExifLibException('Malformed Exif data') when the 2 bytes immediately after the 'Exif' signature are not zero. Per the Exif spec these two padding bytes must be 0x0000; a non-zero value indicates the Exif header is corrupt or the segment was truncated/misaligned.

Solutions

1. Catch ExifLibException and degrade gracefully to 'no Exif' for corrupt segments.
2. Validate the Exif segment structure before deep parsing; abort early on the first integrity check failure.
3. Re-encode or repair the JPEG with a reliable image tool to regenerate a clean Exif block.
4. Skip the corrupt file in batch processing and log it for later repair.

Example fix

// before
if (ReadUShort() != 0)
  throw new ExifLibException("Malformed Exif data");

// after
if (ReadUShort() != 0) {
  Tracker.TraceMessage(Tracker.Category.Warning, "Exif 数据损坏，跳过。");
  _ifd0Catalogue = new Dictionary<ushort, long>();
  return;
}

// Structural integrity cannot be pre-validated cheaply; rely on catch.

try { CreateTagIndex(); }
catch (ExifLibException) { _ifd0Catalogue = new Dictionary<ushort, long>(); }

When it happens

Trigger: A JPEG whose APP1 Exif segment has been corrupted, truncated, or misaligned such that the 2-byte padding after 'Exif' is non-zero. This points to structural damage in the Exif block rather than missing metadata.

Common situations: A JPEG damaged in transit/storage; an Exif block written by buggy encoding software; manual editing of the JPEG that shifted bytes; a truncated download.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

Related errors

• Error in TIFF data
• Could not find Exif data block
• Exif data not found
• File is not a valid JPEG
• 合并图片失败：粘贴操作出错

AI-assisted analysis of wmjordan/PDFPatcher@4782bbd9ad (2026-08-13). Data as JSON: /api/errors/4866a0a59033a221. Report an issue: GitHub.

Appendix: source

Thrown at App/Processor/Imaging/JpgHelper.cs:412

				if (markerStart != 0xFF || markerNumber != 0xE1)
					throw new ExifLibException("Could not find Exif data block");
			}

			/// <summary>
			/// Reads through the Exif data and builds an index of all Exif tags in the document
			/// </summary>
			/// <returns></returns>
			private void CreateTagIndex() {
				// The next 4 bytes are the size of the Exif data.
				ReadUShort();

				// Next is the Exif data itself. It starts with the ASCII "Exif" followed by 2 zero bytes.
				if (ReadString(4) != "Exif")
					throw new ExifLibException("Exif data not found");

				// 2 zero bytes
				if (ReadUShort() != 0)
					throw new ExifLibException("Malformed Exif data");

				// We're now into the TIFF format
				_tiffHeaderStart = _stream.Position;

				// What byte align will be used for the TIFF part of the document? II for Intel, MM for Motorola
				_isLittleEndian = ReadString(2) == "II";

				// Next 2 bytes are always the same.
				if (ReadUShort() != 0x002A)
					throw new ExifLibException("Error in TIFF data");

				// Get the offset to the IFD (image file directory)
				var ifdOffset = ReadUint();

				// Note that this offset is from the first byte of the TIFF header. Jump to the IFD.
				_stream.Position = ifdOffset + _tiffHeaderStart;

				// Catalogue this first IFD (there will be another IFD)

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