inancgumus/learngo · error

file size < len(buf)

Error message

file size < len(buf)

What it means

read() guards against files too small to contain the signature buffer: after Stat(), if the file size is less than or equal to len(buf), there cannot be enough bytes to match a header (e.g. the 8-byte PNG signature), so the error is returned to the detector, which then classifies the file as invalid/unknown. Fires on empty or truncated files.

Source

Thrown at advfuncs/08-png-detector-with-panic/main.go:107

func read(filename string, buf []byte) error {
	file, err := os.Open(filename)
	if err != nil {
		return err
	}
	defer file.Close()

	fi, err := file.Stat()
	if err != nil {
		return err
	}

	if fi.Size() <= int64(len(buf)) {
		return fmt.Errorf("file size < len(buf)")
	}

	_, err = io.ReadFull(file, buf)
	return err
}

View on GitHub (pinned to 3c475a78e5)

Solutions

1. Treat the error as "not a valid image" and skip the file.
2. Check fi.Size() before reading and handle short files explicitly with a clearer message.
3. Provide a larger/correct file to the detector.

When it happens

Trigger: Thrown at advfuncs/08-png-detector-with-panic/main.go:107 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of inancgumus/learngo@3c475a78e5 (2026-09-02). Data as JSON: /api/errors/a4d658842b5d5d8d. Report an issue: GitHub.