summaryrefslogtreecommitdiff
path: root/misc.go
blob: dce9dac3610de786800c7f31583b6f30333312f2 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
// Copyright (C) 2022  Luke Shumaker <lukeshu@lukeshu.com>
//
// SPDX-License-Identifier: GPL-2.0-or-later

package lowmemjson

import (
	"encoding/json"
	"io"
	"reflect"
	"unicode/utf8"
)

const Tab = "\t"

const hex = "0123456789abcdef"

func hex2int[T interface{ byte | rune }](c T) (byte, bool) {
	switch {
	case '0' <= c && c <= '9':
		return byte(c) - '0', true
	case 'a' <= c && c <= 'f':
		return byte(c) - 'a' + 10, true
	case 'A' <= c && c <= 'F':
		return byte(c) - 'A' + 10, true
	default:
		return 0, false
	}
}

var (
	numberType    = reflect.TypeOf(json.Number(""))
	byteType      = reflect.TypeOf(byte(0))
	byteSliceType = reflect.TypeOf(([]byte)(nil))
)

// generic I/O /////////////////////////////////////////////////////////////////

func writeByte(w io.Writer, c byte) error {
	if br, ok := w.(interface{ WriteByte(byte) error }); ok {
		return br.WriteByte(c)
	}
	var buf [1]byte
	buf[0] = c
	if _, err := w.Write(buf[:]); err != nil {
		return err
	}
	return nil
}

func writeRune(w io.Writer, c rune) (int, error) {
	if rw, ok := w.(interface{ WriteRune(rune) (int, error) }); ok {
		return rw.WriteRune(c)
	}
	var buf [utf8.UTFMax]byte
	n := utf8.EncodeRune(buf[:], c)
	return w.Write(buf[:n])
}

// JSON string encoding ////////////////////////////////////////////////////////

type BackslashEscapeMode uint8

const (
	BackslashEscapeNone = BackslashEscapeMode(iota)
	BackslashEscapeShort
	BackslashEscapeUnicode
)

func EscapeJSSafe(c rune, _ BackslashEscapeMode) BackslashEscapeMode {
	// JSON is notionally a JS subset, but that's not actually
	// true.
	//
	// http://timelessrepo.com/json-isnt-a-javascript-subset
	switch c {
	case '\u2028', '\u2029':
		return BackslashEscapeUnicode
	default:
		return BackslashEscapeNone
	}
}

func EscapeHTMLSafe(c rune, wasEscaped BackslashEscapeMode) BackslashEscapeMode {
	switch c {
	case '&', '<', '>':
		return BackslashEscapeUnicode
	default:
		return EscapeJSSafe(c, wasEscaped)
	}
}

func EscapeDefault(c rune, wasEscaped BackslashEscapeMode) BackslashEscapeMode {
	switch c {
	case '\b', '\f', utf8.RuneError:
		return BackslashEscapeUnicode
	default:
		return EscapeHTMLSafe(c, wasEscaped)
	}
}

func EscapePreserve(_ rune, wasEscaped BackslashEscapeMode) BackslashEscapeMode {
	return wasEscaped
}

func writeStringUnicodeEscape(w io.Writer, c rune) (int, error) {
	buf := [6]byte{
		'\\',
		'u',
		hex[(c>>12)&0xf],
		hex[(c>>8)&0xf],
		hex[(c>>4)&0xf],
		hex[(c>>0)&0xf],
	}
	return w.Write(buf[:])
}
func writeStringShortEscape(w io.Writer, c rune) (int, error) {
	var b byte
	switch c {
	case '"', '\\', '/':
		b = byte(c)
	case '\b':
		b = 'b'
	case '\f':
		b = 'f'
	case '\n':
		b = 'n'
	case '\r':
		b = 'r'
	case '\t':
		b = 't'
	default:
		panic("should not happen")
	}
	buf := [2]byte{'\\', b}
	return w.Write(buf[:])
}
func writeStringChar(w io.Writer, c rune, wasEscaped BackslashEscapeMode, escaper func(rune, BackslashEscapeMode) BackslashEscapeMode) (int, error) {
	if escaper == nil {
		escaper = EscapeDefault
	}
	switch escaper(c, wasEscaped) {
	case BackslashEscapeNone:
		switch {
		case c < 0x0020: // override, gotta escape these
			switch c {
			case '\b', '\f', '\n', '\r', '\t': // short-escape if possible
				return writeStringShortEscape(w, c)
			default:
				return writeStringUnicodeEscape(w, c)
			}
		case c == '"' || c == '\\': // override, gotta escape these
			return writeStringShortEscape(w, c)
		default: // obey
			return writeRune(w, c)
		}
	case BackslashEscapeShort:
		switch c {
		case '"', '\\', '/', '\b', '\f', '\n', '\r', '\t': // obey
			return writeStringShortEscape(w, c)
		default: // override, can't short-escape these
			return writeRune(w, c)
		}
	case BackslashEscapeUnicode:
		switch {
		case c > 0xFFFF: // override, can't escape these (TODO: unless we use UTF-16 surrogates?)
			return writeRune(w, c)
		default: // obey
			return writeStringUnicodeEscape(w, c)
		}
	default:
		panic("escaper returned an invalid escape mode")
	}
}