1// Copyright 2010 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
5package json
6
7import "bytes"
8
9// HTMLEscape appends to dst the JSON-encoded src with <, >, &, U+2028 and U+2029
10// characters inside string literals changed to \u003c, \u003e, \u0026, \u2028, \u2029
11// so that the JSON will be safe to embed inside HTML <script> tags.
12// For historical reasons, web browsers don't honor standard HTML
13// escaping within <script> tags, so an alternative JSON encoding must be used.
14func HTMLEscape(dst *bytes.Buffer, src []byte) {
15 dst.Grow(len(src))
16 dst.Write(appendHTMLEscape(dst.AvailableBuffer(), src))
17}
18
19func appendHTMLEscape(dst, src []byte) []byte {
20 // The characters can only appear in string literals,
21 // so just scan the string one byte at a time.
22 start := 0
23 for i, c := range src {
24 if c == '<' || c == '>' || c == '&' {
25 dst = append(dst, src[start:i]...)
26 dst = append(dst, '\\', 'u', '0', '0', hex[c>>4], hex[c&0xF])
27 start = i + 1
28 }
29 // Convert U+2028 and U+2029 (E2 80 A8 and E2 80 A9).
30 if c == 0xE2 && i+2 < len(src) && src[i+1] == 0x80 && src[i+2]&^1 == 0xA8 {
31 dst = append(dst, src[start:i]...)
32 dst = append(dst, '\\', 'u', '2', '0', '2', hex[src[i+2]&0xF])
33 start = i + len("\u2029")
34 }
35 }
36 return append(dst, src[start:]...)
37}
38
39// Compact appends to dst the JSON-encoded src with
40// insignificant space characters elided.
41func Compact(dst *bytes.Buffer, src []byte) error {
42 dst.Grow(len(src))
43 b := dst.AvailableBuffer()
44 b, err := appendCompact(b, src, false)
45 dst.Write(b)
46 return err
47}
48
49func appendCompact(dst, src []byte, escape bool) ([]byte, error) {
50 origLen := len(dst)
51 scan := newScanner()
52 defer freeScanner(scan)
53 start := 0
54 for i, c := range src {
55 if escape && (c == '<' || c == '>' || c == '&') {
56 if start < i {
57 dst = append(dst, src[start:i]...)
58 }
59 dst = append(dst, '\\', 'u', '0', '0', hex[c>>4], hex[c&0xF])
60 start = i + 1
61 }
62 // Convert U+2028 and U+2029 (E2 80 A8 and E2 80 A9).
63 if escape && c == 0xE2 && i+2 < len(src) && src[i+1] == 0x80 && src[i+2]&^1 == 0xA8 {
64 if start < i {
65 dst = append(dst, src[start:i]...)
66 }
67 dst = append(dst, '\\', 'u', '2', '0', '2', hex[src[i+2]&0xF])
68 start = i + 3
69 }
70 v := scan.step(scan, c)
71 if v >= scanSkipSpace {
72 if v == scanError {
73 break
74 }
75 if start < i {
76 dst = append(dst, src[start:i]...)
77 }
78 start = i + 1
79 }
80 }
81 if scan.eof() == scanError {
82 return dst[:origLen], scan.err
83 }
84 if start < len(src) {
85 dst = append(dst, src[start:]...)
86 }
87 return dst, nil
88}
89
90func appendNewline(dst []byte, prefix, indent string, depth int) []byte {
91 dst = append(dst, '\n')
92 dst = append(dst, prefix...)
93 for i := 0; i < depth; i++ {
94 dst = append(dst, indent...)
95 }
96 return dst
97}
98
99// indentGrowthFactor specifies the growth factor of indenting JSON input.
100// Empirically, the growth factor was measured to be between 1.4x to 1.8x
101// for some set of compacted JSON with the indent being a single tab.
102// Specify a growth factor slightly larger than what is observed
103// to reduce probability of allocation in appendIndent.
104// A factor no higher than 2 ensures that wasted space never exceeds 50%.
105const indentGrowthFactor = 2
106
107// Indent appends to dst an indented form of the JSON-encoded src.
108// Each element in a JSON object or array begins on a new,
109// indented line beginning with prefix followed by one or more
110// copies of indent according to the indentation nesting.
111// The data appended to dst does not begin with the prefix nor
112// any indentation, to make it easier to embed inside other formatted JSON data.
113// Although leading space characters (space, tab, carriage return, newline)
114// at the beginning of src are dropped, trailing space characters
115// at the end of src are preserved and copied to dst.
116// For example, if src has no trailing spaces, neither will dst;
117// if src ends in a trailing newline, so will dst.
118func Indent(dst *bytes.Buffer, src []byte, prefix, indent string) error {
119 dst.Grow(indentGrowthFactor * len(src))
120 b := dst.AvailableBuffer()
121 b, err := appendIndent(b, src, prefix, indent)
122 dst.Write(b)
123 return err
124}
125
126func appendIndent(dst, src []byte, prefix, indent string) ([]byte, error) {
127 origLen := len(dst)
128 scan := newScanner()
129 defer freeScanner(scan)
130 needIndent := false
131 depth := 0
132 for _, c := range src {
133 scan.bytes++
134 v := scan.step(scan, c)
135 if v == scanSkipSpace {
136 continue
137 }
138 if v == scanError {
139 break
140 }
141 if needIndent && v != scanEndObject && v != scanEndArray {
142 needIndent = false
143 depth++
144 dst = appendNewline(dst, prefix, indent, depth)
145 }
146
147 // Emit semantically uninteresting bytes
148 // (in particular, punctuation in strings) unmodified.
149 if v == scanContinue {
150 dst = append(dst, c)
151 continue
152 }
153
154 // Add spacing around real punctuation.
155 switch c {
156 case '{', '[':
157 // delay indent so that empty object and array are formatted as {} and [].
158 needIndent = true
159 dst = append(dst, c)
160 case ',':
161 dst = append(dst, c)
162 dst = appendNewline(dst, prefix, indent, depth)
163 case ':':
164 dst = append(dst, c, ' ')
165 case '}', ']':
166 if needIndent {
167 // suppress indent in empty object/array
168 needIndent = false
169 } else {
170 depth--
171 dst = appendNewline(dst, prefix, indent, depth)
172 }
173 dst = append(dst, c)
174 default:
175 dst = append(dst, c)
176 }
177 }
178 if scan.eof() == scanError {
179 return dst[:origLen], scan.err
180 }
181 return dst, nil
182}