forked from ipld/go-ipld-prime
/
json_decode_string.go
269 lines (251 loc) · 7.62 KB
/
json_decode_string.go
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package jsontoken
import (
"fmt"
"strconv"
"unicode"
"unicode/utf16"
"unicode/utf8"
"github.com/ipld/go-ipld-prime/codec/codectools/scratch"
)
// License note: the string and numeric parsers here borrow
// heavily from the golang stdlib json parser scanner.
// That code is originally Copyright 2010 The Go Authors,
// and is governed by a BSD-style license.
// DecodeString will attempt to decode data in the format of a JSON string from the reader.
// If the first byte read is not `"`, it is not a string at all, and an error is returned.
// Any other parse errors of json strings also result in error.
func DecodeString(r *scratch.Reader) (string, error) {
// Check that this actually begins like a string.
majorByte, err := r.Readn1()
if err != nil {
return "", err
}
if majorByte != '"' {
return "", fmt.Errorf("not a string: strings must begin with '\"', not %q", majorByte)
}
// Decode the string body.
s, err := DecodeStringBody(r)
if err != nil {
return "", err
}
// Swallow the trailing `"` again (which DecodeStringBody has insured we have).
r.Readn1()
return s, nil
}
// DecodeStringBody will attempt to decode data in the format of a JSON string from the reader,
// except it assumes that the leading `"` has already been consumed,
// and will similarly leave the trailing `"` unread (although it will check for its presence).
//
// Implementation note: you'll find that this method is used in the Decoder's implementation,
// while DecodeString is actually not. This is because when doing a whole document parse,
// the leading `"` is always already consumed because it's how we discovered it's time to parse a string.
func DecodeStringBody(r *scratch.Reader) (string, error) {
// First `"` is presumed already eaten.
// Start tracking the byte slice; real string starts here.
r.Track()
// Scan until scanner tells us end of string.
for step := strscan_normal; step != nil; {
majorByte, err := r.Readn1()
if err != nil {
return "", err
}
step, err = step(majorByte)
if err != nil {
return "", err
}
}
// Unread one. The scan loop consumed the trailing quote already,
// which we don't want to pass onto the parser.
r.Unreadn1()
// Parse!
s, ok := parseString(r.StopTrack())
if !ok {
panic("string parse failed") // this is a sanity check; our scan phase should've already excluded any data that would cause this.
}
return string(s), nil
}
// strscanStep steps are applied over the data to find how long the string is.
// A nil step func is returned to indicate the string is done.
// Actually parsing the string is done by 'parseString()'.
type strscanStep func(c byte) (strscanStep, error)
// The default string scanning step state. Starts here.
func strscan_normal(c byte) (strscanStep, error) {
if c == '"' { // done!
return nil, nil
}
if c == '\\' {
return strscan_esc, nil
}
if c < 0x20 { // Unprintable bytes are invalid in a json string.
return nil, fmt.Errorf("invalid unprintable byte in string literal: 0x%x", c)
}
return strscan_normal, nil
}
// "esc" is the state after reading `"\` during a quoted string.
func strscan_esc(c byte) (strscanStep, error) {
switch c {
case 'b', 'f', 'n', 'r', 't', '\\', '/', '"':
return strscan_normal, nil
case 'u':
return strscan_escU, nil
}
return nil, fmt.Errorf("invalid byte in string escape sequence: 0x%x", c)
}
// "escU" is the state after reading `"\u` during a quoted string.
func strscan_escU(c byte) (strscanStep, error) {
if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
return strscan_escU1, nil
}
return nil, fmt.Errorf("invalid byte in \\u hexadecimal character escape: 0x%x", c)
}
// "escU1" is the state after reading `"\u1` during a quoted string.
func strscan_escU1(c byte) (strscanStep, error) {
if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
return strscan_escU12, nil
}
return nil, fmt.Errorf("invalid byte in \\u hexadecimal character escape: 0x%x", c)
}
// "escU12" is the state after reading `"\u12` during a quoted string.
func strscan_escU12(c byte) (strscanStep, error) {
if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
return strscan_escU123, nil
}
return nil, fmt.Errorf("invalid byte in \\u hexadecimal character escape: 0x%x", c)
}
// "escU123" is the state after reading `"\u123` during a quoted string.
func strscan_escU123(c byte) (strscanStep, error) {
if '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F' {
return strscan_normal, nil
}
return nil, fmt.Errorf("invalid byte in \\u hexadecimal character escape: 0x%x", c)
}
// Convert a json serial byte sequence that is a complete string body (i.e., quotes from the outside excluded)
// into a natural byte sequence (escapes, etc, are processed).
//
// The given slice should already be the right length.
// A blithe false for 'ok' is returned if the data is in any way malformed.
//
// FUTURE: this is native JSON string parsing, and not as strict as DAG-JSON should be.
//
// - this does not implement UTF8-C8 unescpaing; we may want to do so.
// - this transforms invalid surrogates coming from escape sequences into uFFFD; we probably shouldn't.
// - this transforms any non-UTF-8 bytes into uFFFD rather than erroring; we might want to think twice about that.
// - this parses `\u` escape sequences at all, while also allowing UTF8 chars of the same content; we might want to reject variations.
//
// It might be desirable to implement these stricter rules as configurable.
func parseString(s []byte) (t []byte, ok bool) {
// Check for unusual characters. If there are none,
// then no unquoting is needed, so return a slice of the
// original bytes.
r := 0
for r < len(s) {
c := s[r]
if c == '\\' || c == '"' || c < ' ' {
break
}
if c < utf8.RuneSelf {
r++
continue
}
rr, size := utf8.DecodeRune(s[r:])
if rr == utf8.RuneError && size == 1 {
break
}
r += size
}
if r == len(s) {
return s, true
}
b := make([]byte, len(s)+2*utf8.UTFMax)
w := copy(b, s[0:r])
for r < len(s) {
// Out of room? Can only happen if s is full of
// malformed UTF-8 and we're replacing each
// byte with RuneError.
if w >= len(b)-2*utf8.UTFMax {
nb := make([]byte, (len(b)+utf8.UTFMax)*2)
copy(nb, b[0:w])
b = nb
}
switch c := s[r]; {
case c == '\\':
r++
if r >= len(s) {
return
}
switch s[r] {
default:
return
case '"', '\\', '/', '\'':
b[w] = s[r]
r++
w++
case 'b':
b[w] = '\b'
r++
w++
case 'f':
b[w] = '\f'
r++
w++
case 'n':
b[w] = '\n'
r++
w++
case 'r':
b[w] = '\r'
r++
w++
case 't':
b[w] = '\t'
r++
w++
case 'u':
r--
rr := getu4(s[r:])
if rr < 0 {
return
}
r += 6
if utf16.IsSurrogate(rr) {
rr1 := getu4(s[r:])
if dec := utf16.DecodeRune(rr, rr1); dec != unicode.ReplacementChar {
// A valid pair; consume.
r += 6
w += utf8.EncodeRune(b[w:], dec)
break
}
// Invalid surrogate; fall back to replacement rune.
rr = unicode.ReplacementChar
}
w += utf8.EncodeRune(b[w:], rr)
}
// Quote, control characters are invalid.
case c == '"', c < ' ':
return
// ASCII
case c < utf8.RuneSelf:
b[w] = c
r++
w++
// Coerce to well-formed UTF-8.
default:
rr, size := utf8.DecodeRune(s[r:])
r += size
w += utf8.EncodeRune(b[w:], rr)
}
}
return b[0:w], true
}
// getu4 decodes \uXXXX from the beginning of s, returning the hex value,
// or it returns -1.
func getu4(s []byte) rune {
if len(s) < 6 || s[0] != '\\' || s[1] != 'u' {
return -1
}
r, err := strconv.ParseUint(string(s[2:6]), 16, 64)
if err != nil {
return -1
}
return rune(r)
}