What causes "avif: invalid exif magic number" in siyuan-note/siyuan?

Verify the Exif item's data extent points at the TIFF header start, not into the payload

avif: invalid exif magic number

Error message

avif: invalid exif magic number

What it means

After the byte-order marker, an EXIF TIFF header must contain the magic number 42 at offset 2. The parser read a different value, so the payload is not a valid EXIF/TIFF structure despite having plausible 'II'/'MM' markers. This confirms the payload is corrupt or not actually EXIF data.

Source

Thrown at kernel/heif/internal/h265heic/exif.go:286

	return float64(num) / float64(den)
}

func parseExifData(data []byte, exif *Exif) error {
	if len(data) < 8 {
		return errors.New("avif: exif data too short")
	}

	r := &exifReader{data: data}
	switch {
	case data[0] == 'I' && data[1] == 'I':
		r.littleEndian = true
	case data[0] == 'M' && data[1] == 'M':
	default:
		return errors.New("avif: invalid exif byte order marker")
	}

	if r.uint16(2) != 42 {
		return errors.New("avif: invalid exif magic number")
	}

	ifdOffset := r.uint32(4)
	if ifdOffset < 8 || int(ifdOffset) >= len(data) {
		return errors.New("avif: invalid exif ifd offset")
	}

	exifIFDOffset, gpsIFDOffset := parseIFD(r, int(ifdOffset), exif)
	if exifIFDOffset > 0 {
		parseExifSubIFD(r, exifIFDOffset, exif)
	}
	if gpsIFDOffset > 0 {
		parseGPSSubIFD(r, gpsIFDOffset, exif)
	}

	return nil
}

View on GitHub (pinned to 8641553a1f)

Solutions

Verify the Exif item's data extent points at the TIFF header start, not into the payload
Dump the first 8 bytes and compare against the expected II\x2a\x00 or MM\x00\x2a header
Treat EXIF as unavailable and continue rendering the image without orientation/GPS metadata
Regenerate the file with a standards-compliant writer if it is your own tooling

Defensive patterns

Strategy: validation

Validate before calling

func looksLikeExifTIFF(data []byte) bool {
	if len(data) < 4 {
		return false
	}
	if data[0] == 'I' && data[1] == 'I' {
		return binary.LittleEndian.Uint16(data[2:4]) == 42
	}
	if data[0] == 'M' && data[1] == 'M' {
		return binary.BigEndian.Uint16(data[2:4]) == 42
	}
	return false
}

Type guard

func isWellFormedTIFFHeader(b []byte) bool { return looksLikeExifTIFF(b) }

Try / catch

if err != nil && strings.Contains(err.Error(), "invalid exif magic number") {
	log.Warnf("EXIF payload is not a TIFF structure: %v", err)
	return nil
}

Prevention

Validate the full 8-byte TIFF header (marker + magic 42) before IFD parsing
Check item extents so slicing never starts mid-blob
Treat metadata parse errors as non-fatal and continue with defaults
Regenerate files with standards-compliant EXIF writers in your own pipelines

When it happens

Trigger: DecodeExif on a payload whose bytes 2-3 (per declared endianness) do not equal 42 — e.g. sliced into the middle of a larger blob, or a fabricated/fuzzed TIFF header.

Common situations: Off-by-N slicing of the Exif item; files produced by buggy metadata writers; binary blobs mislabeled as Exif items in the HEIF meta box.

Understand the failure class

Background: Schema validation failed / invalid input schema: payload rejected because its shape doesn't match the expected schema — this error's family across 28 libraries.

Related errors

AI-assisted analysis of siyuan-note/siyuan@8641553a1f (2026-09-11). Data as JSON: /api/errors/d1738c017949d41a. Report an issue: GitHub.