TUN-3201: Create base cloudflared UI structure

vendor/github.com/gdamore/tcell/encoding.go

@@ -0,0 +1,139 @@
+// 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
+}