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// Copyright 2015 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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//go:generate go run gen.go
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// Package htmlindex maps character set encoding names to Encodings as
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// recommended by the W3C for use in HTML 5. See http://www.w3.org/TR/encoding.
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package htmlindex
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// TODO: perhaps have a "bare" version of the index (used by this package) that
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// is not pre-loaded with all encodings. Global variables in encodings prevent
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// the linker from being able to purge unneeded tables. This means that
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// referencing all encodings, as this package does for the default index, links
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// in all encodings unconditionally.
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//
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// This issue can be solved by either solving the linking issue (see
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// https://github.com/golang/go/issues/6330) or refactoring the encoding tables
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// (e.g. moving the tables to internal packages that do not use global
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// variables).
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// TODO: allow canonicalizing names
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import (
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	"errors"
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	"strings"
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	"sync"
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	"golang.org/x/text/encoding"
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	"golang.org/x/text/encoding/internal/identifier"
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	"golang.org/x/text/language"
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)
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var (
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	errInvalidName = errors.New("htmlindex: invalid encoding name")
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	errUnknown     = errors.New("htmlindex: unknown Encoding")
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	errUnsupported = errors.New("htmlindex: this encoding is not supported")
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)
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var (
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	matcherOnce sync.Once
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	matcher     language.Matcher
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)
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// LanguageDefault returns the canonical name of the default encoding for a
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// given language.
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func LanguageDefault(tag language.Tag) string {
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	matcherOnce.Do(func() {
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		tags := []language.Tag{}
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		for _, t := range strings.Split(locales, " ") {
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			tags = append(tags, language.MustParse(t))
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		}
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		matcher = language.NewMatcher(tags, language.PreferSameScript(true))
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	})
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	_, i, _ := matcher.Match(tag)
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	return canonical[localeMap[i]] // Default is Windows-1252.
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}
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// Get returns an Encoding for one of the names listed in
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// http://www.w3.org/TR/encoding using the Default Index. Matching is case-
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// insensitive.
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func Get(name string) (encoding.Encoding, error) {
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	x, ok := nameMap[strings.ToLower(strings.TrimSpace(name))]
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	if !ok {
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		return nil, errInvalidName
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	}
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	return encodings[x], nil
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}
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// Name reports the canonical name of the given Encoding. It will return
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// an error if e is not associated with a supported encoding scheme.
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func Name(e encoding.Encoding) (string, error) {
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	id, ok := e.(identifier.Interface)
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	if !ok {
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		return "", errUnknown
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	}
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	mib, _ := id.ID()
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	if mib == 0 {
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		return "", errUnknown
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	}
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	v, ok := mibMap[mib]
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	if !ok {
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		return "", errUnsupported
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	}
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	return canonical[v], nil
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}
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