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// Copyright 2015 The TCell Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use file except in compliance with the License.
// You may obtain a copy of the license at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package tcell
import (
"strings"
"sync"
"golang.org/x/text/encoding"
gencoding "github.com/gdamore/encoding"
)
var encodings map[string]encoding.Encoding
var encodingLk sync.Mutex
var encodingFallback EncodingFallback = EncodingFallbackFail
// RegisterEncoding may be called by the application to register an encoding.
// The presence of additional encodings will facilitate application usage with
// terminal environments where the I/O subsystem does not support Unicode.
//
// Windows systems use Unicode natively, and do not need any of the encoding
// subsystem when using Windows Console screens.
//
// Please see the Go documentation for golang.org/x/text/encoding -- most of
// the common ones exist already as stock variables. For example, ISO8859-15
// can be registered using the following code:
//
// import "golang.org/x/text/encoding/charmap"
//
// ...
// RegisterEncoding("ISO8859-15", charmap.ISO8859_15)
//
// Aliases can be registered as well, for example "8859-15" could be an alias
// for "ISO8859-15".
//
// For POSIX systems, the tcell package will check the environment variables
// LC_ALL, LC_CTYPE, and LANG (in that order) to determine the character set.
// These are expected to have the following pattern:
//
// $language[.$codeset[@$variant]
//
// We extract only the $codeset part, which will usually be something like
// UTF-8 or ISO8859-15 or KOI8-R. Note that if the locale is either "POSIX"
// or "C", then we assume US-ASCII (the POSIX 'portable character set'
// and assume all other characters are somehow invalid.)
//
// Modern POSIX systems and terminal emulators may use UTF-8, and for those
// systems, this API is also unnecessary. For example, Darwin (MacOS X) and
// modern Linux running modern xterm generally will out of the box without
// any of this. Use of UTF-8 is recommended when possible, as it saves
// quite a lot processing overhead.
//
// Note that some encodings are quite large (for example GB18030 which is a
// superset of Unicode) and so the application size can be expected ot
// increase quite a bit as each encoding is added. The East Asian encodings
// have been seen to add 100-200K per encoding to the application size.
//
func RegisterEncoding(charset string, enc encoding.Encoding) {
encodingLk.Lock()
charset = strings.ToLower(charset)
encodings[charset] = enc
encodingLk.Unlock()
}
// EncodingFallback describes how the system behavees when the locale
// requires a character set that we do not support. The system always
// supports UTF-8 and US-ASCII. On Windows consoles, UTF-16LE is also
// supported automatically. Other character sets must be added using the
// RegisterEncoding API. (A large group of nearly all of them can be
// added using the RegisterAll function in the encoding sub package.)
type EncodingFallback int
const (
// EncodingFallbackFail behavior causes GetEncoding to fail
// when it cannot find an encoding.
EncodingFallbackFail = iota
// EncodingFallbackASCII behaviore causes GetEncoding to fall back
// to a 7-bit ASCII encoding, if no other encoding can be found.
EncodingFallbackASCII
// EncodingFallbackUTF8 behavior causes GetEncoding to assume
// UTF8 can pass unmodified upon failure. Note that this behavior
// is not recommended, unless you are sure your terminal can cope
// with real UTF8 sequences.
EncodingFallbackUTF8
)
// SetEncodingFallback changes the behavior of GetEncoding when a suitable
// encoding is not found. The default is EncodingFallbackFail, which
// causes GetEncoding to simply return nil.
func SetEncodingFallback(fb EncodingFallback) {
encodingLk.Lock()
encodingFallback = fb
encodingLk.Unlock()
}
// GetEncoding is used by Screen implementors who want to locate an encoding
// for the given character set name. Note that this will return nil for
// either the Unicode (UTF-8) or ASCII encodings, since we don't use
// encodings for them but instead have our own native methods.
func GetEncoding(charset string) encoding.Encoding {
charset = strings.ToLower(charset)
encodingLk.Lock()
defer encodingLk.Unlock()
if enc, ok := encodings[charset]; ok {
return enc
}
switch encodingFallback {
case EncodingFallbackASCII:
return gencoding.ASCII
case EncodingFallbackUTF8:
return encoding.Nop
}
return nil
}
func init() {
// We always support UTF-8 and ASCII.
encodings = make(map[string]encoding.Encoding)
encodings["utf-8"] = gencoding.UTF8
encodings["utf8"] = gencoding.UTF8
encodings["us-ascii"] = gencoding.ASCII
encodings["ascii"] = gencoding.ASCII
encodings["iso646"] = gencoding.ASCII
}
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