func extractFingerprint()

in EVChecker/main.go [182:233]
52 lines of code
20 McCabe index (conditional complexity)

func extractFingerprint(r io.RuneReader) (string, error) {
	_, err := consumeWhiteSpace(r)
	if err != nil {
		return "", errors.Wrap(err, "failed to consume the whitespace prefixing a fingerprint")
	}
	str := strings.Builder{}
	for i := 0; i < 32; i++ {
		zero, err := consumeWhiteSpace(r)
		if err != nil {
			return "", errors.Wrap(err, "failed to consume whitespace while extracting fingerprint")
		}
		if zero != '0' {
			return "", errors.New(fmt.Sprintf(`Expected the character "0" while decoding hex, got "%s"`, string(zero)))
		}
		x, _, err := r.ReadRune() // read the x in 0xAA
		if err != nil {
			return "", errors.Wrap(err, `failed to read the "x" in a hex literal`)
		}
		if x != 'x' {
			return "", errors.New(fmt.Sprintf(`Expected the character "x" while decoding hex, got "%s"`, string(x)))
		}
		b, _, err := r.ReadRune() // get the upper byte of 0xAA
		if err != nil {
			return "", errors.Wrap(err, `failed to read the upper byte in a hex literal`)
		}
		str.WriteRune(b)
		b, _, err = r.ReadRune() // get the lower byte of 0xAA
		if err != nil {
			return "", errors.Wrap(err, `failed to read the lower byte in a hex literal`)
		}
		str.WriteRune(b)
		comma, _, err := r.ReadRune() // read the , in the array literal
		if err != nil {
			return "", errors.Wrap(err, `failed to read the hex literal array delimiter`)
		}
		if comma != ',' && comma != ' ' {
			return "", errors.New(fmt.Sprintf(`Expected the character "," or " " while decoding the internals of a hex array, got "%s"`, string(x)))
		}
	}
	brace, err := consumeWhiteSpace(r)
	if err != nil {
		return "", errors.Wrap(err, "failed to consume the closing brace while extracting a fingerprint")
	}
	if brace != '}' {
		return "", errors.New(fmt.Sprintf(`Expected the character "}" while decoding a hex array, got "%s"`, string(brace)))
	}
	comma, err := consumeWhiteSpace(r)
	if comma != ',' {
		return "", errors.New(fmt.Sprintf(`Expected the character "," while decoding the end of a hex array, got "%s"`, string(comma)))
	}
	return str.String(), nil
}