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// Copyright (C) 2022 Luke Shumaker <lukeshu@lukeshu.com>
//
// SPDX-License-Identifier: GPL-2.0-or-later
package lowmemjson
import (
"encoding/json"
"io"
"reflect"
"unicode/utf8"
)
const Tab = "\t"
const hex = "0123456789abcdef"
func hex2int[T interface{ byte | rune }](c T) (byte, bool) {
switch {
case '0' <= c && c <= '9':
return byte(c) - '0', true
case 'a' <= c && c <= 'f':
return byte(c) - 'a' + 10, true
case 'A' <= c && c <= 'F':
return byte(c) - 'A' + 10, true
default:
return 0, false
}
}
var (
numberType = reflect.TypeOf(json.Number(""))
byteType = reflect.TypeOf(byte(0))
byteSliceType = reflect.TypeOf(([]byte)(nil))
)
// generic I/O /////////////////////////////////////////////////////////////////
func writeByte(w io.Writer, c byte) error {
if br, ok := w.(interface{ WriteByte(byte) error }); ok {
return br.WriteByte(c)
}
var buf [1]byte
buf[0] = c
if _, err := w.Write(buf[:]); err != nil {
return err
}
return nil
}
func writeRune(w io.Writer, c rune) (int, error) {
if rw, ok := w.(interface{ WriteRune(rune) (int, error) }); ok {
return rw.WriteRune(c)
}
var buf [utf8.UTFMax]byte
n := utf8.EncodeRune(buf[:], c)
return w.Write(buf[:n])
}
// JSON string encoding ////////////////////////////////////////////////////////
type BackslashEscapeMode uint8
const (
BackslashEscapeNone = BackslashEscapeMode(iota)
BackslashEscapeShort
BackslashEscapeUnicode
)
func EscapeJSSafe(c rune, _ BackslashEscapeMode) BackslashEscapeMode {
// JSON is notionally a JS subset, but that's not actually
// true.
//
// http://timelessrepo.com/json-isnt-a-javascript-subset
switch c {
case '\u2028', '\u2029':
return BackslashEscapeUnicode
default:
return BackslashEscapeNone
}
}
func EscapeHTMLSafe(c rune, wasEscaped BackslashEscapeMode) BackslashEscapeMode {
switch c {
case '&', '<', '>':
return BackslashEscapeUnicode
default:
return EscapeJSSafe(c, wasEscaped)
}
}
func EscapeDefault(c rune, wasEscaped BackslashEscapeMode) BackslashEscapeMode {
switch c {
case '\b', '\f', utf8.RuneError:
return BackslashEscapeUnicode
default:
return EscapeHTMLSafe(c, wasEscaped)
}
}
func EscapePreserve(_ rune, wasEscaped BackslashEscapeMode) BackslashEscapeMode {
return wasEscaped
}
func writeStringUnicodeEscape(w io.Writer, c rune) (int, error) {
buf := [6]byte{
'\\',
'u',
hex[(c>>12)&0xf],
hex[(c>>8)&0xf],
hex[(c>>4)&0xf],
hex[(c>>0)&0xf],
}
return w.Write(buf[:])
}
func writeStringShortEscape(w io.Writer, c rune) (int, error) {
var b byte
switch c {
case '"', '\\', '/':
b = byte(c)
case '\b':
b = 'b'
case '\f':
b = 'f'
case '\n':
b = 'n'
case '\r':
b = 'r'
case '\t':
b = 't'
default:
panic("should not happen")
}
buf := [2]byte{'\\', b}
return w.Write(buf[:])
}
func writeStringChar(w io.Writer, c rune, wasEscaped BackslashEscapeMode, escaper func(rune, BackslashEscapeMode) BackslashEscapeMode) (int, error) {
if escaper == nil {
escaper = EscapeDefault
}
switch escaper(c, wasEscaped) {
case BackslashEscapeNone:
switch {
case c < 0x0020: // override, gotta escape these
switch c {
case '\b', '\f', '\n', '\r', '\t': // short-escape if possible
return writeStringShortEscape(w, c)
default:
return writeStringUnicodeEscape(w, c)
}
case c == '"' || c == '\\': // override, gotta escape these
return writeStringShortEscape(w, c)
default: // obey
return writeRune(w, c)
}
case BackslashEscapeShort:
switch c {
case '"', '\\', '/', '\b', '\f', '\n', '\r', '\t': // obey
return writeStringShortEscape(w, c)
default: // override, can't short-escape these
return writeRune(w, c)
}
case BackslashEscapeUnicode:
switch {
case c > 0xFFFF: // override, can't escape these (TODO: unless we use UTF-16 surrogates?)
return writeRune(w, c)
default: // obey
return writeStringUnicodeEscape(w, c)
}
default:
panic("escaper returned an invalid escape mode")
}
}
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