libgo/go/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 (
   8         "bytes"
   9         "os"
  10 )
  11
  12 // Compact appends to dst the JSON-encoded src with
  13 // insignificant space characters elided.
  14 func Compact(dst *bytes.Buffer, src []byte) os.Error {
  15         origLen := dst.Len()
  16         var scan scanner
  17         scan.reset()
  18         start := 0
  19         for i, c := range src {
  20                 v := scan.step(&scan, int(c))
  21                 if v >= scanSkipSpace {
  22                         if v == scanError {
  23                                 break
  24                         }
  25                         if start < i {
  26                                 dst.Write(src[start:i])
  27                         }
  28                         start = i + 1
  29                 }
  30         }
  31         if scan.eof() == scanError {
  32                 dst.Truncate(origLen)
  33                 return scan.err
  34         }
  35         if start < len(src) {
  36                 dst.Write(src[start:])
  37         }
  38         return nil
  39 }
  40
  41 func newline(dst *bytes.Buffer, prefix, indent string, depth int) {
  42         dst.WriteByte('\n')
  43         dst.WriteString(prefix)
  44         for i := 0; i < depth; i++ {
  45                 dst.WriteString(indent)
  46         }
  47 }
  48
  49 // Indent appends to dst an indented form of the JSON-encoded src.
  50 // Each element in a JSON object or array begins on a new,
  51 // indented line beginning with prefix followed by one or more
  52 // copies of indent according to the indentation nesting.
  53 // The data appended to dst has no trailing newline, to make it easier
  54 // to embed inside other formatted JSON data.
  55 func Indent(dst *bytes.Buffer, src []byte, prefix, indent string) os.Error {
  56         origLen := dst.Len()
  57         var scan scanner
  58         scan.reset()
  59         needIndent := false
  60         depth := 0
  61         for _, c := range src {
  62                 v := scan.step(&scan, int(c))
  63                 if v == scanSkipSpace {
  64                         continue
  65                 }
  66                 if v == scanError {
  67                         break
  68                 }
  69                 if needIndent && v != scanEndObject && v != scanEndArray {
  70                         needIndent = false
  71                         depth++
  72                         newline(dst, prefix, indent, depth)
  73                 }
  74
  75                 // Emit semantically uninteresting bytes
  76                 // (in particular, punctuation in strings) unmodified.
  77                 if v == scanContinue {
  78                         dst.WriteByte(c)
  79                         continue
  80                 }
  81
  82                 // Add spacing around real punctuation.
  83                 switch c {
  84                 case '{', '[':
  85                         // delay indent so that empty object and array are formatted as {} and [].
  86                         needIndent = true
  87                         dst.WriteByte(c)
  88
  89                 case ',':
  90                         dst.WriteByte(c)
  91                         newline(dst, prefix, indent, depth)
  92
  93                 case ':':
  94                         dst.WriteByte(c)
  95                         dst.WriteByte(' ')
  96
  97                 case '}', ']':
  98                         if needIndent {
  99                                 // suppress indent in empty object/array
 100                                 needIndent = false
 101                         } else {
 102                                 depth--
 103                                 newline(dst, prefix, indent, depth)
 104                         }
 105                         dst.WriteByte(c)
 106
 107                 default:
 108                         dst.WriteByte(c)
 109                 }
 110         }
 111         if scan.eof() == scanError {
 112                 dst.Truncate(origLen)
 113                 return scan.err
 114         }
 115         return nil
 116 }