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  )
    10  
    11  // Compact appends to dst the JSON-encoded src with
    12  // insignificant space characters elided.
    13  func Compact(dst *bytes.Buffer, src []byte) error {
    14  	return compact(dst, src, false)
    15  }
    16  
    17  func compact(dst *bytes.Buffer, src []byte, escape bool) error {
    18  	origLen := dst.Len()
    19  	scan := newScanner()
    20  	defer freeScanner(scan)
    21  	start := 0
    22  	for i, c := range src {
    23  		if escape && (c == '<' || c == '>' || c == '&') {
    24  			if start < i {
    25  				dst.Write(src[start:i])
    26  			}
    27  			dst.WriteString(`\u00`)
    28  			dst.WriteByte(hex[c>>4])
    29  			dst.WriteByte(hex[c&0xF])
    30  			start = i + 1
    31  		}
    32  		// Convert U+2028 and U+2029 (E2 80 A8 and E2 80 A9).
    33  		if escape && c == 0xE2 && i+2 < len(src) && src[i+1] == 0x80 && src[i+2]&^1 == 0xA8 {
    34  			if start < i {
    35  				dst.Write(src[start:i])
    36  			}
    37  			dst.WriteString(`\u202`)
    38  			dst.WriteByte(hex[src[i+2]&0xF])
    39  			start = i + 3
    40  		}
    41  		v := scan.step(scan, c)
    42  		if v >= scanSkipSpace {
    43  			if v == scanError {
    44  				break
    45  			}
    46  			if start < i {
    47  				dst.Write(src[start:i])
    48  			}
    49  			start = i + 1
    50  		}
    51  	}
    52  	if scan.eof() == scanError {
    53  		dst.Truncate(origLen)
    54  		return scan.err
    55  	}
    56  	if start < len(src) {
    57  		dst.Write(src[start:])
    58  	}
    59  	return nil
    60  }
    61  
    62  func newline(dst *bytes.Buffer, prefix, indent string, depth int) {
    63  	dst.WriteByte('\n')
    64  	dst.WriteString(prefix)
    65  	for i := 0; i < depth; i++ {
    66  		dst.WriteString(indent)
    67  	}
    68  }
    69  
    70  // Indent appends to dst an indented form of the JSON-encoded src.
    71  // Each element in a JSON object or array begins on a new,
    72  // indented line beginning with prefix followed by one or more
    73  // copies of indent according to the indentation nesting.
    74  // The data appended to dst does not begin with the prefix nor
    75  // any indentation, to make it easier to embed inside other formatted JSON data.
    76  // Although leading space characters (space, tab, carriage return, newline)
    77  // at the beginning of src are dropped, trailing space characters
    78  // at the end of src are preserved and copied to dst.
    79  // For example, if src has no trailing spaces, neither will dst;
    80  // if src ends in a trailing newline, so will dst.
    81  func Indent(dst *bytes.Buffer, src []byte, prefix, indent string) error {
    82  	origLen := dst.Len()
    83  	scan := newScanner()
    84  	defer freeScanner(scan)
    85  	needIndent := false
    86  	depth := 0
    87  	for _, c := range src {
    88  		scan.bytes++
    89  		v := scan.step(scan, c)
    90  		if v == scanSkipSpace {
    91  			continue
    92  		}
    93  		if v == scanError {
    94  			break
    95  		}
    96  		if needIndent && v != scanEndObject && v != scanEndArray {
    97  			needIndent = false
    98  			depth++
    99  			newline(dst, prefix, indent, depth)
   100  		}
   101  
   102  		// Emit semantically uninteresting bytes
   103  		// (in particular, punctuation in strings) unmodified.
   104  		if v == scanContinue {
   105  			dst.WriteByte(c)
   106  			continue
   107  		}
   108  
   109  		// Add spacing around real punctuation.
   110  		switch c {
   111  		case '{', '[':
   112  			// delay indent so that empty object and array are formatted as {} and [].
   113  			needIndent = true
   114  			dst.WriteByte(c)
   115  
   116  		case ',':
   117  			dst.WriteByte(c)
   118  			newline(dst, prefix, indent, depth)
   119  
   120  		case ':':
   121  			dst.WriteByte(c)
   122  			dst.WriteByte(' ')
   123  
   124  		case '}', ']':
   125  			if needIndent {
   126  				// suppress indent in empty object/array
   127  				needIndent = false
   128  			} else {
   129  				depth--
   130  				newline(dst, prefix, indent, depth)
   131  			}
   132  			dst.WriteByte(c)
   133  
   134  		default:
   135  			dst.WriteByte(c)
   136  		}
   137  	}
   138  	if scan.eof() == scanError {
   139  		dst.Truncate(origLen)
   140  		return scan.err
   141  	}
   142  	return nil
   143  }
   144
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