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Source file src/encoding/json/indent.go

Documentation: encoding/json

     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  }
   142  

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