mirror of
https://github.com/42wim/matterbridge.git
synced 2024-11-22 10:42:02 -08:00
83 lines
2.6 KiB
Go
83 lines
2.6 KiB
Go
// Copyright 2015 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 unicode
|
|
|
|
import (
|
|
"golang.org/x/text/transform"
|
|
)
|
|
|
|
// BOMOverride returns a new decoder transformer that is identical to fallback,
|
|
// except that the presence of a Byte Order Mark at the start of the input
|
|
// causes it to switch to the corresponding Unicode decoding. It will only
|
|
// consider BOMs for UTF-8, UTF-16BE, and UTF-16LE.
|
|
//
|
|
// This differs from using ExpectBOM by allowing a BOM to switch to UTF-8, not
|
|
// just UTF-16 variants, and allowing falling back to any encoding scheme.
|
|
//
|
|
// This technique is recommended by the W3C for use in HTML 5: "For
|
|
// compatibility with deployed content, the byte order mark (also known as BOM)
|
|
// is considered more authoritative than anything else."
|
|
// http://www.w3.org/TR/encoding/#specification-hooks
|
|
//
|
|
// Using BOMOverride is mostly intended for use cases where the first characters
|
|
// of a fallback encoding are known to not be a BOM, for example, for valid HTML
|
|
// and most encodings.
|
|
func BOMOverride(fallback transform.Transformer) transform.Transformer {
|
|
// TODO: possibly allow a variadic argument of unicode encodings to allow
|
|
// specifying details of which fallbacks are supported as well as
|
|
// specifying the details of the implementations. This would also allow for
|
|
// support for UTF-32, which should not be supported by default.
|
|
return &bomOverride{fallback: fallback}
|
|
}
|
|
|
|
type bomOverride struct {
|
|
fallback transform.Transformer
|
|
current transform.Transformer
|
|
}
|
|
|
|
func (d *bomOverride) Reset() {
|
|
d.current = nil
|
|
d.fallback.Reset()
|
|
}
|
|
|
|
var (
|
|
// TODO: we could use decode functions here, instead of allocating a new
|
|
// decoder on every NewDecoder as IgnoreBOM decoders can be stateless.
|
|
utf16le = UTF16(LittleEndian, IgnoreBOM)
|
|
utf16be = UTF16(BigEndian, IgnoreBOM)
|
|
)
|
|
|
|
const utf8BOM = "\ufeff"
|
|
|
|
func (d *bomOverride) Transform(dst, src []byte, atEOF bool) (nDst, nSrc int, err error) {
|
|
if d.current != nil {
|
|
return d.current.Transform(dst, src, atEOF)
|
|
}
|
|
if len(src) < 3 && !atEOF {
|
|
return 0, 0, transform.ErrShortSrc
|
|
}
|
|
d.current = d.fallback
|
|
bomSize := 0
|
|
if len(src) >= 2 {
|
|
if src[0] == 0xFF && src[1] == 0xFE {
|
|
d.current = utf16le.NewDecoder()
|
|
bomSize = 2
|
|
} else if src[0] == 0xFE && src[1] == 0xFF {
|
|
d.current = utf16be.NewDecoder()
|
|
bomSize = 2
|
|
} else if len(src) >= 3 &&
|
|
src[0] == utf8BOM[0] &&
|
|
src[1] == utf8BOM[1] &&
|
|
src[2] == utf8BOM[2] {
|
|
d.current = transform.Nop
|
|
bomSize = 3
|
|
}
|
|
}
|
|
if bomSize < len(src) {
|
|
nDst, nSrc, err = d.current.Transform(dst, src[bomSize:], atEOF)
|
|
}
|
|
return nDst, nSrc + bomSize, err
|
|
}
|