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// Copyright (C) 2022-2023 Luke Shumaker <lukeshu@lukeshu.com>
//
// SPDX-License-Identifier: GPL-2.0-or-later
package jsonstring
import (
"fmt"
"io"
"unicode/utf8"
"git.lukeshu.com/go/lowmemjson/internal/fastio"
"git.lukeshu.com/go/lowmemjson/internal/fastio/noescape"
)
// BackslashEscapeMode is describe in the main lowmemjson package
// docs.
type BackslashEscapeMode uint8
const (
BackslashEscapeNone BackslashEscapeMode = iota
BackslashEscapeShort
BackslashEscapeUnicode
)
// BackslashEscaper is describe in the main lowmemjson package docs.
type BackslashEscaper = func(rune, BackslashEscapeMode) BackslashEscapeMode
func writeStringUnicodeEscape(w io.Writer, c rune) error {
const alphabet = "0123456789abcdef"
buf := [6]byte{
'\\',
'u',
alphabet[(c>>12)&0xf],
alphabet[(c>>8)&0xf],
alphabet[(c>>4)&0xf],
alphabet[(c>>0)&0xf],
}
_, err := noescape.Write(w, buf[:])
return err
}
func writeStringShortEscape(w io.Writer, c rune) 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(fmt.Errorf("should not happen: writeStringShortEscape called with invalid rune: %q", c))
}
buf := [2]byte{'\\', b}
_, err := noescape.Write(w, buf[:])
return err
}
func WriteStringChar(w fastio.AllWriter, c rune, escape BackslashEscapeMode) error {
switch escape {
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
_, err := w.WriteRune(c)
return err
}
case BackslashEscapeShort:
switch c {
case '"', '\\', '/', '\b', '\f', '\n', '\r', '\t': // obey
return writeStringShortEscape(w, c)
default: // override, can't short-escape these
_, err := w.WriteRune(c)
return err
}
case BackslashEscapeUnicode:
switch {
case c > 0xFFFF: // override, can't escape these (TODO: unless we use UTF-16 surrogates?)
_, err := w.WriteRune(c)
return err
default: // obey
return writeStringUnicodeEscape(w, c)
}
default:
panic("escaper returned an invalid escape mode")
}
}
func EncodeStringFromString(w fastio.AllWriter, escaper BackslashEscaper, str string) error {
if err := w.WriteByte('"'); err != nil {
return err
}
for _, c := range str {
if err := WriteStringChar(w, c, escaper(c, BackslashEscapeNone)); err != nil {
return err
}
}
if err := w.WriteByte('"'); err != nil {
return err
}
return nil
}
func EncodeStringFromBytes(w fastio.AllWriter, escaper BackslashEscaper, str []byte) error {
if err := w.WriteByte('"'); err != nil {
return err
}
for i := 0; i < len(str); {
c, size := utf8.DecodeRune(str[i:])
if err := WriteStringChar(w, c, escaper(c, BackslashEscapeNone)); err != nil {
return err
}
i += size
}
if err := w.WriteByte('"'); err != nil {
return err
}
return nil
}
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