func scanNumber()

in metric/parse.go [436:547]

• 80 lines of code
• 40 McCabe index (conditional complexity)

func scanNumber(buf []byte, i int) (int, error) {
	start := i
	var isInt bool

	// Is negative number?
	if i < len(buf) && buf[i] == '-' {
		i++
		// There must be more characters now, as just '-' is illegal.
		if i == len(buf) {
			return i, ErrInvalidNumber
		}
	}

	// how many decimal points we've see
	decimal := false

	// indicates the number is float in scientific notation
	scientific := false

	for {
		if i >= len(buf) {
			break
		}

		if buf[i] == ',' || buf[i] == ' ' {
			break
		}

		if buf[i] == 'i' && i > start && !isInt {
			isInt = true
			i++
			continue
		}

		if buf[i] == '.' {
			// Can't have more than 1 decimal (e.g. 1.1.1 should fail)
			if decimal {
				return i, ErrInvalidNumber
			}
			decimal = true
		}

		// `e` is valid for floats but not as the first char
		if i > start && (buf[i] == 'e' || buf[i] == 'E') {
			scientific = true
			i++
			continue
		}

		// + and - are only valid at this point if they follow an e (scientific notation)
		if (buf[i] == '+' || buf[i] == '-') && (buf[i-1] == 'e' || buf[i-1] == 'E') {
			i++
			continue
		}

		// NaN is an unsupported value
		if i+2 < len(buf) && (buf[i] == 'N' || buf[i] == 'n') {
			return i, ErrInvalidNumber
		}

		if !isNumeric(buf[i]) {
			return i, ErrInvalidNumber
		}
		i++
	}

	if isInt && (decimal || scientific) {
		return i, ErrInvalidNumber
	}

	numericDigits := i - start
	if isInt {
		numericDigits--
	}
	if decimal {
		numericDigits--
	}
	if buf[start] == '-' {
		numericDigits--
	}

	if numericDigits == 0 {
		return i, ErrInvalidNumber
	}

	// It's more common that numbers will be within min/max range for their type but we need to prevent
	// out or range numbers from being parsed successfully.  This uses some simple heuristics to decide
	// if we should parse the number to the actual type.  It does not do it all the time because it incurs
	// extra allocations and we end up converting the type again when writing points to disk.
	if isInt {
		// Make sure the last char is an 'i' for integers (e.g. 9i10 is not valid)
		if buf[i-1] != 'i' {
			return i, ErrInvalidNumber
		}
		// Parse the int to check bounds the number of digits could be larger than the max range
		// We subtract 1 from the index to remove the `i` from our tests
		if len(buf[start:i-1]) >= maxInt64Digits || len(buf[start:i-1]) >= minInt64Digits {
			if _, err := parseIntBytes(buf[start:i-1], 10, 64); err != nil {
				return i, makeError(fmt.Sprintf("unable to parse integer %s: %s", buf[start:i-1], err), buf, i)
			}
		}
	} else {
		// Parse the float to check bounds if it's scientific or the number of digits could be larger than the max range
		if scientific || len(buf[start:i]) >= maxFloat64Digits || len(buf[start:i]) >= minFloat64Digits {
			if _, err := parseFloatBytes(buf[start:i], 10); err != nil {
				return i, makeError("invalid float", buf, i)
			}
		}
	}

	return i, nil
}