decode_string.go

Documentation: google.golang.org/protobuf/internal/encoding/json

     1  // Copyright 2018 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package json
     6  
     7  import (
     8  	"strconv"
     9  	"unicode"
    10  	"unicode/utf16"
    11  	"unicode/utf8"
    12  
    13  	"google.golang.org/protobuf/internal/strs"
    14  )
    15  
    16  func (d *Decoder) parseString(in []byte) (string, int, error) {
    17  	in0 := in
    18  	if len(in) == 0 {
    19  		return "", 0, ErrUnexpectedEOF
    20  	}
    21  	if in[0] != '"' {
    22  		return "", 0, d.newSyntaxError(d.currPos(), "invalid character %q at start of string", in[0])
    23  	}
    24  	in = in[1:]
    25  	i := indexNeedEscapeInBytes(in)
    26  	in, out := in[i:], in[:i:i] // set cap to prevent mutations
    27  	for len(in) > 0 {
    28  		switch r, n := utf8.DecodeRune(in); {
    29  		case r == utf8.RuneError && n == 1:
    30  			return "", 0, d.newSyntaxError(d.currPos(), "invalid UTF-8 in string")
    31  		case r < ' ':
    32  			return "", 0, d.newSyntaxError(d.currPos(), "invalid character %q in string", r)
    33  		case r == '"':
    34  			in = in[1:]
    35  			n := len(in0) - len(in)
    36  			return string(out), n, nil
    37  		case r == '\\':
    38  			if len(in) < 2 {
    39  				return "", 0, ErrUnexpectedEOF
    40  			}
    41  			switch r := in[1]; r {
    42  			case '"', '\\', '/':
    43  				in, out = in[2:], append(out, r)
    44  			case 'b':
    45  				in, out = in[2:], append(out, '\b')
    46  			case 'f':
    47  				in, out = in[2:], append(out, '\f')
    48  			case 'n':
    49  				in, out = in[2:], append(out, '\n')
    50  			case 'r':
    51  				in, out = in[2:], append(out, '\r')
    52  			case 't':
    53  				in, out = in[2:], append(out, '\t')
    54  			case 'u':
    55  				if len(in) < 6 {
    56  					return "", 0, ErrUnexpectedEOF
    57  				}
    58  				v, err := strconv.ParseUint(string(in[2:6]), 16, 16)
    59  				if err != nil {
    60  					return "", 0, d.newSyntaxError(d.currPos(), "invalid escape code %q in string", in[:6])
    61  				}
    62  				in = in[6:]
    63  
    64  				r := rune(v)
    65  				if utf16.IsSurrogate(r) {
    66  					if len(in) < 6 {
    67  						return "", 0, ErrUnexpectedEOF
    68  					}
    69  					v, err := strconv.ParseUint(string(in[2:6]), 16, 16)
    70  					r = utf16.DecodeRune(r, rune(v))
    71  					if in[0] != '\\' || in[1] != 'u' ||
    72  						r == unicode.ReplacementChar || err != nil {
    73  						return "", 0, d.newSyntaxError(d.currPos(), "invalid escape code %q in string", in[:6])
    74  					}
    75  					in = in[6:]
    76  				}
    77  				out = append(out, string(r)...)
    78  			default:
    79  				return "", 0, d.newSyntaxError(d.currPos(), "invalid escape code %q in string", in[:2])
    80  			}
    81  		default:
    82  			i := indexNeedEscapeInBytes(in[n:])
    83  			in, out = in[n+i:], append(out, in[:n+i]...)
    84  		}
    85  	}
    86  	return "", 0, ErrUnexpectedEOF
    87  }
    88  
    89  // indexNeedEscapeInBytes returns the index of the character that needs
    90  // escaping. If no characters need escaping, this returns the input length.
    91  func indexNeedEscapeInBytes(b []byte) int { return indexNeedEscapeInString(strs.UnsafeString(b)) }
    92
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