src/pkg/json/indent.go

// Copyright 2010 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package json

import (
	"bytes"
	"os"
)

// Compact appends to dst the JSON-encoded src with
// insignificant space characters elided.
func Compact(dst *bytes.Buffer, src []byte) os.Error {
	origLen := dst.Len()
	var scan scanner
	scan.reset()
	start := 0
	for i, c := range src {
		v := scan.step(&scan, int(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 has no trailing newline, to make it easier
// to embed inside other formatted JSON data.
func Indent(dst *bytes.Buffer, src []byte, prefix, indent string) os.Error {
	origLen := dst.Len()
	var scan scanner
	scan.reset()
	needIndent := false
	depth := 0
	for _, c := range src {
		v := scan.step(&scan, int(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 {
		case '{', '[':
			// 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 '}', ']':
			if needIndent {
				// 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
}