json.gno

  1package safe
  2
  3import (
  4	"strconv"
  5	"strings"
  6)
  7
  8// JSONString returns s as a quoted JSON string. Beyond the mandatory
  9// escapes it also escapes U+2028/U+2029 (RA L-12) and '<', '>', '&', so the
 10// output is safe to inline in HTML as well.
 11func JSONString(s string) string {
 12	const hexDigits = "0123456789abcdef"
 13	var b strings.Builder
 14	b.WriteByte('"')
 15	for _, r := range s {
 16		switch r {
 17		case '"':
 18			b.WriteString(`\"`)
 19		case '\\':
 20			b.WriteString(`\\`)
 21		case '\n':
 22			b.WriteString(`\n`)
 23		case '\r':
 24			b.WriteString(`\r`)
 25		case '\t':
 26			b.WriteString(`\t`)
 27		case '<', '>', '&', 0x2028, 0x2029:
 28			b.WriteString(`\u`)
 29			b.WriteString(PadHex(int64(r), 4))
 30		default:
 31			if r < 0x20 || r == 0x7f {
 32				b.WriteString(`\u00`)
 33				b.WriteByte(hexDigits[(r>>4)&0xf])
 34				b.WriteByte(hexDigits[r&0xf])
 35				continue
 36			}
 37			b.WriteRune(r)
 38		}
 39	}
 40	b.WriteByte('"')
 41	return b.String()
 42}
 43
 44// PadHex renders n in lowercase hex, zero-padded to width.
 45func PadHex(n int64, width int) string {
 46	s := strconv.FormatInt(n, 16)
 47	if len(s) >= width {
 48		return s
 49	}
 50	return strings.Repeat("0", width-len(s)) + s
 51}
 52
 53// JSONWriter is the single JSON producer of every read API (design
 54// §2.5: reads return primitives or JSON, never positional text). It tracks
 55// commas itself, so callers only describe structure:
 56//
 57//	w := &safe.JSONWriter{}
 58//	w.BeginObject(); w.Key("id"); w.Str("1"); w.EndObject()
 59type JSONWriter struct {
 60	b        strings.Builder
 61	hasItems []bool // one entry per open container
 62	afterKey bool
 63}
 64
 65func (w *JSONWriter) BeginObject() { w.open('{') }
 66func (w *JSONWriter) EndObject()   { w.close('}') }
 67func (w *JSONWriter) BeginArray()  { w.open('[') }
 68func (w *JSONWriter) EndArray()    { w.close(']') }
 69
 70// Key starts an object member; the next value call writes its value.
 71func (w *JSONWriter) Key(k string) {
 72	w.separate()
 73	w.b.WriteString(JSONString(k))
 74	w.b.WriteByte(':')
 75	w.afterKey = true
 76}
 77
 78func (w *JSONWriter) Str(v string) { w.value(JSONString(v)) }
 79func (w *JSONWriter) Int(v int64)  { w.value(strconv.FormatInt(v, 10)) }
 80func (w *JSONWriter) Bool(v bool)  { w.value(strconv.FormatBool(v)) }
 81
 82// Raw writes v verbatim. Only for JSON produced by another JSONWriter.
 83func (w *JSONWriter) Raw(v string) { w.value(v) }
 84
 85// StrField and IntField are Key+value shorthands.
 86func (w *JSONWriter) StrField(k, v string) { w.Key(k); w.Str(v) }
 87func (w *JSONWriter) IntField(k string, v int64) { w.Key(k); w.Int(v) }
 88func (w *JSONWriter) BoolField(k string, v bool) { w.Key(k); w.Bool(v) }
 89
 90func (w *JSONWriter) String() string { return w.b.String() }
 91
 92func (w *JSONWriter) open(c byte) {
 93	w.separate()
 94	w.b.WriteByte(c)
 95	w.hasItems = append(w.hasItems, false)
 96}
 97
 98func (w *JSONWriter) close(c byte) {
 99	if len(w.hasItems) == 0 {
100		panic("JSONWriter: close without open")
101	}
102	w.hasItems = w.hasItems[:len(w.hasItems)-1]
103	w.b.WriteByte(c)
104}
105
106func (w *JSONWriter) value(v string) {
107	w.separate()
108	w.b.WriteString(v)
109}
110
111// separate writes the comma before an item, except right after a key.
112func (w *JSONWriter) separate() {
113	if w.afterKey {
114		w.afterKey = false
115		return
116	}
117	if n := len(w.hasItems); n > 0 {
118		if w.hasItems[n-1] {
119			w.b.WriteByte(',')
120		}
121		w.hasItems[n-1] = true
122	}
123}