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// Copyright 2018 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package json
import (
"bytes"
"strconv"
)
// parseNumber reads the given []byte for a valid JSON number. If it is valid,
// it returns the number of bytes. Parsing logic follows the definition in
// https://tools.ietf.org/html/rfc7159#section-6, and is based off
// encoding/json.isValidNumber function.
func parseNumber(input []byte) (int, bool) {
var n int
s := input
if len(s) == 0 {
return 0, false
}
// Optional -
if s[0] == '-' {
s = s[1:]
n++
if len(s) == 0 {
return 0, false
}
}
// Digits
switch {
case s[0] == '0':
s = s[1:]
n++
case '1' <= s[0] && s[0] <= '9':
s = s[1:]
n++
for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
s = s[1:]
n++
}
default:
return 0, false
}
// . followed by 1 or more digits.
if len(s) >= 2 && s[0] == '.' && '0' <= s[1] && s[1] <= '9' {
s = s[2:]
n += 2
for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
s = s[1:]
n++
}
}
// e or E followed by an optional - or + and
// 1 or more digits.
if len(s) >= 2 && (s[0] == 'e' || s[0] == 'E') {
s = s[1:]
n++
if s[0] == '+' || s[0] == '-' {
s = s[1:]
n++
if len(s) == 0 {
return 0, false
}
}
for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
s = s[1:]
n++
}
}
// Check that next byte is a delimiter or it is at the end.
if n < len(input) && isNotDelim(input[n]) {
return 0, false
}
return n, true
}
// numberParts is the result of parsing out a valid JSON number. It contains
// the parts of a number. The parts are used for integer conversion.
type numberParts struct {
neg bool
intp []byte
frac []byte
exp []byte
}
// parseNumber constructs numberParts from given []byte. The logic here is
// similar to consumeNumber above with the difference of having to construct
// numberParts. The slice fields in numberParts are subslices of the input.
func parseNumberParts(input []byte) (numberParts, bool) {
var neg bool
var intp []byte
var frac []byte
var exp []byte
s := input
if len(s) == 0 {
return numberParts{}, false
}
// Optional -
if s[0] == '-' {
neg = true
s = s[1:]
if len(s) == 0 {
return numberParts{}, false
}
}
// Digits
switch {
case s[0] == '0':
// Skip first 0 and no need to store.
s = s[1:]
case '1' <= s[0] && s[0] <= '9':
intp = s
n := 1
s = s[1:]
for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
s = s[1:]
n++
}
intp = intp[:n]
default:
return numberParts{}, false
}
// . followed by 1 or more digits.
if len(s) >= 2 && s[0] == '.' && '0' <= s[1] && s[1] <= '9' {
frac = s[1:]
n := 1
s = s[2:]
for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
s = s[1:]
n++
}
frac = frac[:n]
}
// e or E followed by an optional - or + and
// 1 or more digits.
if len(s) >= 2 && (s[0] == 'e' || s[0] == 'E') {
s = s[1:]
exp = s
n := 0
if s[0] == '+' || s[0] == '-' {
s = s[1:]
n++
if len(s) == 0 {
return numberParts{}, false
}
}
for len(s) > 0 && '0' <= s[0] && s[0] <= '9' {
s = s[1:]
n++
}
exp = exp[:n]
}
return numberParts{
neg: neg,
intp: intp,
frac: bytes.TrimRight(frac, "0"), // Remove unnecessary 0s to the right.
exp: exp,
}, true
}
// normalizeToIntString returns an integer string in normal form without the
// E-notation for given numberParts. It will return false if it is not an
// integer or if the exponent exceeds than max/min int value.
func normalizeToIntString(n numberParts) (string, bool) {
intpSize := len(n.intp)
fracSize := len(n.frac)
if intpSize == 0 && fracSize == 0 {
return "0", true
}
var exp int
if len(n.exp) > 0 {
i, err := strconv.ParseInt(string(n.exp), 10, 32)
if err != nil {
return "", false
}
exp = int(i)
}
var num []byte
if exp >= 0 {
// For positive E, shift fraction digits into integer part and also pad
// with zeroes as needed.
// If there are more digits in fraction than the E value, then the
// number is not an integer.
if fracSize > exp {
return "", false
}
// Make sure resulting digits are within max value limit to avoid
// unnecessarily constructing a large byte slice that may simply fail
// later on.
const maxDigits = 20 // Max uint64 value has 20 decimal digits.
if intpSize+exp > maxDigits {
return "", false
}
// Set cap to make a copy of integer part when appended.
num = n.intp[:len(n.intp):len(n.intp)]
num = append(num, n.frac...)
for i := 0; i < exp-fracSize; i++ {
num = append(num, '0')
}
} else {
// For negative E, shift digits in integer part out.
// If there are fractions, then the number is not an integer.
if fracSize > 0 {
return "", false
}
// index is where the decimal point will be after adjusting for negative
// exponent.
index := intpSize + exp
if index < 0 {
return "", false
}
num = n.intp
// If any of the digits being shifted to the right of the decimal point
// is non-zero, then the number is not an integer.
for i := index; i < intpSize; i++ {
if num[i] != '0' {
return "", false
}
}
num = num[:index]
}
if n.neg {
return "-" + string(num), true
}
return string(num), true
}
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