libgo/go/encoding/json/indent.go

   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
   5 package json
   6
   7 import "bytes"
   8
   9 // Compact appends to dst the JSON-encoded src with
  10 // insignificant space characters elided.
  11 func Compact(dst *bytes.Buffer, src []byte) error {
  12         return compact(dst, src, false)
  13 }
  14
  15 func compact(dst *bytes.Buffer, src []byte, escape bool) error {
  16         origLen := dst.Len()
  17         var scan scanner
  18         scan.reset()
  19         start := 0
  20         for i, c := range src {
  21                 if escape && (c == '<' || c == '>' || c == '&') {
  22                         if start < i {
  23                                 dst.Write(src[start:i])
  24                         }
  25                         dst.WriteString(`\u00`)
  26                         dst.WriteByte(hex[c>>4])
  27                         dst.WriteByte(hex[c&0xF])
  28                         start = i + 1
  29                 }
  30                 // Convert U+2028 and U+2029 (E2 80 A8 and E2 80 A9).
  31                 if c == 0xE2 && i+2 < len(src) && src[i+1] == 0x80 && src[i+2]&^1 == 0xA8 {
  32                         if start < i {
  33                                 dst.Write(src[start:i])
  34                         }
  35                         dst.WriteString(`\u202`)
  36                         dst.WriteByte(hex[src[i+2]&0xF])
  37                         start = i + 3
  38                 }
  39                 v := scan.step(&scan, c)
  40                 if v >= scanSkipSpace {
  41                         if v == scanError {
  42                                 break
  43                         }
  44                         if start < i {
  45                                 dst.Write(src[start:i])
  46                         }
  47                         start = i + 1
  48                 }
  49         }
  50         if scan.eof() == scanError {
  51                 dst.Truncate(origLen)
  52                 return scan.err
  53         }
  54         if start < len(src) {
  55                 dst.Write(src[start:])
  56         }
  57         return nil
  58 }
  59
  60 func newline(dst *bytes.Buffer, prefix, indent string, depth int) {
  61         dst.WriteByte('\n')
  62         dst.WriteString(prefix)
  63         for i := 0; i < depth; i++ {
  64                 dst.WriteString(indent)
  65         }
  66 }
  67
  68 // Indent appends to dst an indented form of the JSON-encoded src.
  69 // Each element in a JSON object or array begins on a new,
  70 // indented line beginning with prefix followed by one or more
  71 // copies of indent according to the indentation nesting.
  72 // The data appended to dst does not begin with the prefix nor
  73 // any indentation, to make it easier to embed inside other formatted JSON data.
  74 // Although leading space characters (space, tab, carriage return, newline)
  75 // at the beginning of src are dropped, trailing space characters
  76 // at the end of src are preserved and copied to dst.
  77 // For example, if src has no trailing spaces, neither will dst;
  78 // if src ends in a trailing newline, so will dst.
  79 func Indent(dst *bytes.Buffer, src []byte, prefix, indent string) error {
  80         origLen := dst.Len()
  81         var scan scanner
  82         scan.reset()
  83         needIndent := false
  84         depth := 0
  85         for _, c := range src {
  86                 scan.bytes++
  87                 v := scan.step(&scan, c)
  88                 if v == scanSkipSpace {
  89                         continue
  90                 }
  91                 if v == scanError {
  92                         break
  93                 }
  94                 if needIndent && v != scanEndObject && v != scanEndArray {
  95                         needIndent = false
  96                         depth++
  97                         newline(dst, prefix, indent, depth)
  98                 }
  99
 100                 // Emit semantically uninteresting bytes
 101                 // (in particular, punctuation in strings) unmodified.
 102                 if v == scanContinue {
 103                         dst.WriteByte(c)
 104                         continue
 105                 }
 106
 107                 // Add spacing around real punctuation.
 108                 switch c {
 109                 case '{', '[':
 110                         // delay indent so that empty object and array are formatted as {} and [].
 111                         needIndent = true
 112                         dst.WriteByte(c)
 113
 114                 case ',':
 115                         dst.WriteByte(c)
 116                         newline(dst, prefix, indent, depth)
 117
 118                 case ':':
 119                         dst.WriteByte(c)
 120                         dst.WriteByte(' ')
 121
 122                 case '}', ']':
 123                         if needIndent {
 124                                 // suppress indent in empty object/array
 125                                 needIndent = false
 126                         } else {
 127                                 depth--
 128                                 newline(dst, prefix, indent, depth)
 129                         }
 130                         dst.WriteByte(c)
 131
 132                 default:
 133                         dst.WriteByte(c)
 134                 }
 135         }
 136         if scan.eof() == scanError {
 137                 dst.Truncate(origLen)
 138                 return scan.err
 139         }
 140         return nil
 141 }