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// 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.
//go:generate go run gen.go
// Package ianaindex maps names to Encodings as specified by the IANA registry.
// This includes both the MIME and IANA names.
// See for
// more details.
package ianaindex
import (
// TODO: remove the "Status... incomplete" in the package doc comment.
// TODO: allow users to specify their own aliases?
// TODO: allow users to specify their own indexes?
// TODO: allow canonicalizing names
// NOTE: only use these top-level variables if we can get the linker to drop
// the indexes when they are not used. Make them a function or perhaps only
// support MIME otherwise.
var (
// MIME is an index to map MIME names.
MIME *Index = mime
// IANA is an index that supports all names and aliases using IANA names as
// the canonical identifier.
IANA *Index = iana
// MIB is an index that associates the MIB display name with an Encoding.
MIB *Index = mib
mime = &Index{mimeName, ianaToMIB, ianaAliases, encodings[:]}
iana = &Index{ianaName, ianaToMIB, ianaAliases, encodings[:]}
mib = &Index{mibName, ianaToMIB, ianaAliases, encodings[:]}
// Index maps names registered by IANA to Encodings.
// Currently different Indexes only differ in the names they return for
// encodings. In the future they may also differ in supported aliases.
type Index struct {
names func(i int) string
toMIB []identifier.MIB // Sorted slice of supported MIBs
alias map[string]int
enc []encoding.Encoding
var (
errInvalidName = errors.New("ianaindex: invalid encoding name")
errUnknown = errors.New("ianaindex: unknown Encoding")
errUnsupported = errors.New("ianaindex: unsupported Encoding")
// Encoding returns an Encoding for IANA-registered names. Matching is
// case-insensitive.
func (x *Index) Encoding(name string) (encoding.Encoding, error) {
name = strings.TrimSpace(name)
// First try without lowercasing (possibly creating an allocation).
i, ok := x.alias[name]
if !ok {
i, ok = x.alias[strings.ToLower(name)]
if !ok {
return nil, errInvalidName
return x.enc[i], nil
// Name reports the canonical name of the given Encoding. It will return an
// error if the e is not associated with a known encoding scheme.
func (x *Index) Name(e encoding.Encoding) (string, error) {
id, ok := e.(identifier.Interface)
if !ok {
return "", errUnknown
mib, _ := id.ID()
if mib == 0 {
return "", errUnknown
v := findMIB(x.toMIB, mib)
if v == -1 {
return "", errUnsupported
return x.names(v), nil
// TODO: the coverage of this index is rather spotty. Allowing users to set
// encodings would allow:
// - users to increase coverage
// - allow a partially loaded set of encodings in case the user doesn't need to
// them all.
// - write an OS-specific wrapper for supported encodings and set them.
// The exact definition of Set depends a bit on if and how we want to let users
// write their own Encoding implementations. Also, it is not possible yet to
// only partially load the encodings without doing some refactoring. Until this
// is solved, we might as well not support Set.
// // Set sets the e to be used for the encoding scheme identified by name. Only
// // canonical names may be used. An empty name assigns e to its internally
// // associated encoding scheme.
// func (x *Index) Set(name string, e encoding.Encoding) error {
// panic("TODO: implement")
// }
func findMIB(x []identifier.MIB, mib identifier.MIB) int {
i := sort.Search(len(x), func(i int) bool { return x[i] >= mib })
if i < len(x) && x[i] == mib {
return i
return -1
const maxMIMENameLen = '0' - 1 // officially 40, but we leave some buffer.
func mimeName(x int) string {
n := ianaNames[x]
// See gen.go for a description of the encoding.
if n[0] <= maxMIMENameLen {
return n[1:n[0]]
return n
func ianaName(x int) string {
n := ianaNames[x]
// See gen.go for a description of the encoding.
if n[0] <= maxMIMENameLen {
return n[n[0]:]
return n
func mibName(x int) string {
return mibNames[x]
var encodings = [numIANA]encoding.Encoding{
enc106: unicode.UTF8,
enc1015: unicode.UTF16(unicode.BigEndian, unicode.UseBOM),
enc1013: unicode.UTF16(unicode.BigEndian, unicode.IgnoreBOM),
enc1014: unicode.UTF16(unicode.LittleEndian, unicode.IgnoreBOM),
enc2028: charmap.CodePage037,
enc2011: charmap.CodePage437,
enc2009: charmap.CodePage850,
enc2010: charmap.CodePage852,
enc2046: charmap.CodePage855,
enc2089: charmap.CodePage858,
enc2048: charmap.CodePage860,
enc2013: charmap.CodePage862,
enc2050: charmap.CodePage863,
enc2052: charmap.CodePage865,
enc2086: charmap.CodePage866,
enc2102: charmap.CodePage1047,
enc2091: charmap.CodePage1140,
enc4: charmap.ISO8859_1,
enc5: charmap.ISO8859_2,
enc6: charmap.ISO8859_3,
enc7: charmap.ISO8859_4,
enc8: charmap.ISO8859_5,
enc9: charmap.ISO8859_6,
enc81: charmap.ISO8859_6E,
enc82: charmap.ISO8859_6I,
enc10: charmap.ISO8859_7,
enc11: charmap.ISO8859_8,
enc84: charmap.ISO8859_8E,
enc85: charmap.ISO8859_8I,
enc12: charmap.ISO8859_9,
enc13: charmap.ISO8859_10,
enc109: charmap.ISO8859_13,
enc110: charmap.ISO8859_14,
enc111: charmap.ISO8859_15,
enc112: charmap.ISO8859_16,
enc2084: charmap.KOI8R,
enc2088: charmap.KOI8U,
enc2027: charmap.Macintosh,
enc2109: charmap.Windows874,
enc2250: charmap.Windows1250,
enc2251: charmap.Windows1251,
enc2252: charmap.Windows1252,
enc2253: charmap.Windows1253,
enc2254: charmap.Windows1254,
enc2255: charmap.Windows1255,
enc2256: charmap.Windows1256,
enc2257: charmap.Windows1257,
enc2258: charmap.Windows1258,
enc18: japanese.EUCJP,
enc39: japanese.ISO2022JP,
enc17: japanese.ShiftJIS,
enc38: korean.EUCKR,
enc114: simplifiedchinese.GB18030,
enc113: simplifiedchinese.GBK,
enc2085: simplifiedchinese.HZGB2312,
enc2026: traditionalchinese.Big5,