Source: indent.go in package encoding/json


package json

import (
	"bytes"
)

Compact appends to dst the JSON-encoded src with insignificant space characters elided.

func Compact(dst *bytes.Buffer, src []byte) error {
	return compact(dst, src, false)
}

func compact(dst *bytes.Buffer, src []byte, escape bool) error {
	origLen := dst.Len()
	scan := newScanner()
	defer freeScanner(scan)
	start := 0
	for i, c := range src {
		if escape && (c == '<' || c == '>' || c == '&') {
			if start < i {
				dst.Write(src[start:i])
			}
			dst.WriteString(`\u00`)
			dst.WriteByte(hex[c>>4])
			dst.WriteByte(hex[c&0xF])
			start = i + 1

Convert U+2028 and U+2029 (E2 80 A8 and E2 80 A9).

		if escape && c == 0xE2 && i+2 < len(src) && src[i+1] == 0x80 && src[i+2]&^1 == 0xA8 {
			if start < i {
				dst.Write(src[start:i])
			}
			dst.WriteString(`\u202`)
			dst.WriteByte(hex[src[i+2]&0xF])
			start = i + 3
		}
		v := scan.step(scan, c)
		if v >= scanSkipSpace {
			if v == scanError {
				break
			}
			if start < i {
				dst.Write(src[start:i])
			}
			start = i + 1
		}
	}
	if scan.eof() == scanError {
		dst.Truncate(origLen)
		return scan.err
	}
	if start < len(src) {
		dst.Write(src[start:])
	}
	return nil
}

func newline(dst *bytes.Buffer, prefix, indent string, depth int) {
	dst.WriteByte('\n')
	dst.WriteString(prefix)
	for i := 0; i < depth; i++ {
		dst.WriteString(indent)
	}
}

Indent appends to dst an indented form of the JSON-encoded src. Each element in a JSON object or array begins on a new, indented line beginning with prefix followed by one or more copies of indent according to the indentation nesting. The data appended to dst does not begin with the prefix nor any indentation, to make it easier to embed inside other formatted JSON data. Although leading space characters (space, tab, carriage return, newline) at the beginning of src are dropped, trailing space characters at the end of src are preserved and copied to dst. For example, if src has no trailing spaces, neither will dst; if src ends in a trailing newline, so will dst.

func Indent(dst *bytes.Buffer, src []byte, prefix, indent string) error {
	origLen := dst.Len()
	scan := newScanner()
	defer freeScanner(scan)
	needIndent := false
	depth := 0
	for _, c := range src {
		scan.bytes++
		v := scan.step(scan, c)
		if v == scanSkipSpace {
			continue
		}
		if v == scanError {
			break
		}
		if needIndent && v != scanEndObject && v != scanEndArray {
			needIndent = false
			depth++
			newline(dst, prefix, indent, depth)
		}

Emit semantically uninteresting bytes (in particular, punctuation in strings) unmodified.

		if v == scanContinue {
			dst.WriteByte(c)
			continue
		}

Add spacing around real punctuation.

		switch c {

delay indent so that empty object and array are formatted as {} and [].

			needIndent = true
			dst.WriteByte(c)

		case ',':
			dst.WriteByte(c)
			newline(dst, prefix, indent, depth)

		case ':':
			dst.WriteByte(c)
			dst.WriteByte(' ')

		case '}', ']':

suppress indent in empty object/array

				needIndent = false
			} else {
				depth--
				newline(dst, prefix, indent, depth)
			}
			dst.WriteByte(c)

		default:
			dst.WriteByte(c)
		}
	}
	if scan.eof() == scanError {
		dst.Truncate(origLen)
		return scan.err
	}
	return nil