siyuan-note/siyuan · warning

font file is too large

Error message

font file is too large

What it means

InstallCustomFont enforces a hard size limit of MaxCustomFontSize (64 MiB) on custom font files. This error is thrown when the staged temp file exceeds that limit, protecting memory and disk from oversized font uploads.

Solutions

1. Check the file size against util.MaxCustomFontSize before uploading/installing and reject early with a clear message
2. Ask the user to subset the font (e.g. fonttools pyftsubset) to used glyphs to reduce size below 64 MiB
3. Split or use a lighter weight/variant of the font family
4. If the limit is genuinely too small for the product, raise MaxCustomFontSize (a code change, not a workaround at call time)

Example fix

// before
font, installed, err := util.InstallCustomFont(tempPath)
// after
if info, err := os.Stat(tempPath); err == nil && info.Size() > util.MaxCustomFontSize {
    return fmt.Errorf("font exceeds %d bytes; subset or compress it", util.MaxCustomFontSize)
}
font, installed, err := util.InstallCustomFont(tempPath)

if info, err := os.Stat(tempPath); err == nil && info.Size() > util.MaxCustomFontSize {
    return fmt.Errorf("font too large: %d > %d", info.Size(), util.MaxCustomFontSize)
}

font, _, err := util.InstallCustomFont(tempPath)
if err != nil && err.Error() == "font file is too large" {
    // surface a subset-the-font message to the user
}

When it happens

Trigger: Calling InstallCustomFont(tempPath) where os.Stat reports info.Size() > 64*1024*1024 bytes — e.g. a huge font collection file (TTC), a font with embedded bitmaps, or an accidental upload of a non-font archive.

Common situations: Users trying to install very large CJK/pan-CJK fonts (often >64 MiB); uploading a .ttc collection or a renamed archive; backend accepting uploads without a client-side size check so the rejection happens only at install time.

Understand the failure class

Background: "File too large" / "file size exceeds limit" errors: why libraries cap file sizes and how to fix them — this error's family across 46 libraries.

Related errors

• font file is empty
• invalid custom font ID
• 106
• 199
• active tab [ ] is not a direct child of [ ]

AI-assisted analysis of siyuan-note/siyuan@9f775e8a12 (2026-09-19). Data as JSON: /api/errors/04aaef394f7d92f3. Report an issue: GitHub.

Appendix: source

Thrown at kernel/util/custom_font.go:109

	defer customFontsLock.Unlock()

	loadCustomFontsLocked()
	return cloneCustomFonts(customFonts)
}

func InstallCustomFont(tempPath string) (*CustomFont, bool, error) {
	customFontsLock.Lock()
	defer customFontsLock.Unlock()

	info, err := os.Stat(tempPath)
	if err != nil {
		return nil, false, err
	}
	if !info.Mode().IsRegular() || info.Size() < 1 {
		return nil, false, errors.New("font file is empty")
	}
	if MaxCustomFontSize < info.Size() {
		return nil, false, errors.New("font file is too large")
	}

	fontFile, err := os.Open(tempPath)
	if err != nil {
		return nil, false, err
	}

	extension, err := detectCustomFontExtension(fontFile)
	if err != nil {
		fontFile.Close()
		return nil, false, err
	}
	if _, err = fontFile.Seek(0, io.SeekStart); err != nil {
		fontFile.Close()
		return nil, false, err
	}

	id, err := customFontHash(fontFile)

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