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.

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.

Appendix: 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
}

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