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// Copyright (C) 2022-2023 Luke Shumaker <lukeshu@lukeshu.com>
//
// SPDX-License-Identifier: GPL-2.0-or-later
package lowmemjson
import (
"unicode/utf8"
)
// BackslashEscapeMode identifies one of the three ways that a
// character may be represented in a JSON string:
//
// - literally (no backslash escaping)
//
// - as a short "well-known" `\X` backslash sequence (where `X` is a
// single-character)
//
// - as a long Unicode `\uXXXX` backslash sequence
type BackslashEscapeMode uint8
const (
BackslashEscapeNone BackslashEscapeMode = iota
BackslashEscapeShort
BackslashEscapeUnicode
)
// A BackslashEscaper controls how a ReEncoder emits a character in a
// JSON string. The `rune` argument is the character being
// considered, and the `BackslashEscapeMode` argument is how it was
// originally encoded in the input.
//
// The ReEncoder will panic if a BackslashEscaper returns an unknown
// BackslashEscapeMode.
type BackslashEscaper = func(rune, BackslashEscapeMode) BackslashEscapeMode
// EscapePreserve is a BackslashEscaper that preserves the original
// input escaping.
func EscapePreserve(_ rune, wasEscaped BackslashEscapeMode) BackslashEscapeMode {
return wasEscaped
}
// EscapeJSSafe is a BackslashEscaper that escapes strings such that
// the JSON safe to embed in JS; it otherwise preserves the original
// input escaping.
//
// JSON is notionally a JS subset, but that's not actually true; so
// more conservative backslash-escaping is necessary to safely embed
// it in JS. http://timelessrepo.com/json-isnt-a-javascript-subset
func EscapeJSSafe(c rune, wasEscaped BackslashEscapeMode) BackslashEscapeMode {
switch c {
case '\u2028', '\u2029':
return BackslashEscapeUnicode
default:
return wasEscaped
}
}
// EscapeHTMLSafe is a BackslashEscaper that escapes strings such that
// the JSON is safe to embed in HTML; it otherwise preserves the
// original input escaping.
func EscapeHTMLSafe(c rune, wasEscaped BackslashEscapeMode) BackslashEscapeMode {
switch c {
case '&', '<', '>':
return BackslashEscapeUnicode
default:
return EscapeJSSafe(c, wasEscaped)
}
}
// EscapeDefault is a BackslashEscaper that mimics the default
// behavior of encoding/json.
//
// It is like EscapeHTMLSafe, but also uses long Unicode `\uXXXX`
// sequences for `\b`, `\f`, and the `\uFFFD` Unicode replacement
// character.
//
// A ReEncoder uses EscapeDefault if a BackslashEscaper is not
// specified.
func EscapeDefault(c rune, wasEscaped BackslashEscapeMode) BackslashEscapeMode {
switch c {
case '\b', '\f', utf8.RuneError:
return BackslashEscapeUnicode
default:
return EscapeHTMLSafe(c, wasEscaped)
}
}
// EscapeDefaultNonHTMLSafe is a BackslashEscaper that mimics the
// default behavior of an encoding/json.Encoder that has had
// SetEscapeHTML(false) called on it.
//
// It is like EscapeJSSafe, but also uses long Unicode `\uXXXX`
// sequences for `\b`, `\f`, and the `\uFFFD` Unicode replacement
// character.
func EscapeDefaultNonHTMLSafe(c rune, wasEscaped BackslashEscapeMode) BackslashEscapeMode {
switch c {
case '\b', '\f', utf8.RuneError:
return BackslashEscapeUnicode
default:
return EscapeJSSafe(c, wasEscaped)
}
}
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