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// Copyright 2009 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 utf8 implements functions and constants to support text encoded in
// UTF-8. It includes functions to translate between runes and UTF-8 byte sequences.
package utf8
// The conditions RuneError==unicode.ReplacementChar and
// MaxRune==unicode.MaxRune are verified in the tests.
// Defining them locally avoids this package depending on package unicode.
// Numbers fundamental to the encoding.
const (
RuneError = '\uFFFD' // the "error" Rune or "Unicode replacement character"
RuneSelf = 0x80 // characters below Runeself are represented as themselves in a single byte.
MaxRune = '\U0010FFFF' // Maximum valid Unicode code point.
UTFMax = 4 // maximum number of bytes of a UTF-8 encoded Unicode character.
)
// Code points in the surrogate range are not valid for UTF-8.
const (
surrogateMin = 0xD800
surrogateMax = 0xDFFF
)
const (
t1 = 0x00 // 0000 0000
tx = 0x80 // 1000 0000
t2 = 0xC0 // 1100 0000
t3 = 0xE0 // 1110 0000
t4 = 0xF0 // 1111 0000
t5 = 0xF8 // 1111 1000
maskx = 0x3F // 0011 1111
mask2 = 0x1F // 0001 1111
mask3 = 0x0F // 0000 1111
mask4 = 0x07 // 0000 0111
rune1Max = 1<<7 - 1
rune2Max = 1<<11 - 1
rune3Max = 1<<16 - 1
)
func decodeRuneInternal(p []byte) (r rune, size int, short bool) {
n := len(p)
if n < 1 {
return RuneError, 0, true
}
c0 := p[0]
// 1-byte, 7-bit sequence?
if c0 < tx {
return rune(c0), 1, false
}
// unexpected continuation byte?
if c0 < t2 {
return RuneError, 1, false
}
// need first continuation byte
if n < 2 {
return RuneError, 1, true
}
c1 := p[1]
if c1 < tx || t2 <= c1 {
return RuneError, 1, false
}
// 2-byte, 11-bit sequence?
if c0 < t3 {
r = rune(c0&mask2)<<6 | rune(c1&maskx)
if r <= rune1Max {
return RuneError, 1, false
}
return r, 2, false
}
// need second continuation byte
if n < 3 {
return RuneError, 1, true
}
c2 := p[2]
if c2 < tx || t2 <= c2 {
return RuneError, 1, false
}
// 3-byte, 16-bit sequence?
if c0 < t4 {
r = rune(c0&mask3)<<12 | rune(c1&maskx)<<6 | rune(c2&maskx)
if r <= rune2Max {
return RuneError, 1, false
}
if surrogateMin <= r && r <= surrogateMax {
return RuneError, 1, false
}
return r, 3, false
}
// need third continuation byte
if n < 4 {
return RuneError, 1, true
}
c3 := p[3]
if c3 < tx || t2 <= c3 {
return RuneError, 1, false
}
// 4-byte, 21-bit sequence?
if c0 < t5 {
r = rune(c0&mask4)<<18 | rune(c1&maskx)<<12 | rune(c2&maskx)<<6 | rune(c3&maskx)
if r <= rune3Max || MaxRune < r {
return RuneError, 1, false
}
return r, 4, false
}
// error
return RuneError, 1, false
}
func decodeRuneInStringInternal(s string) (r rune, size int, short bool) {
n := len(s)
if n < 1 {
return RuneError, 0, true
}
c0 := s[0]
// 1-byte, 7-bit sequence?
if c0 < tx {
return rune(c0), 1, false
}
// unexpected continuation byte?
if c0 < t2 {
return RuneError, 1, false
}
// need first continuation byte
if n < 2 {
return RuneError, 1, true
}
c1 := s[1]
if c1 < tx || t2 <= c1 {
return RuneError, 1, false
}
// 2-byte, 11-bit sequence?
if c0 < t3 {
r = rune(c0&mask2)<<6 | rune(c1&maskx)
if r <= rune1Max {
return RuneError, 1, false
}
return r, 2, false
}
// need second continuation byte
if n < 3 {
return RuneError, 1, true
}
c2 := s[2]
if c2 < tx || t2 <= c2 {
return RuneError, 1, false
}
// 3-byte, 16-bit sequence?
if c0 < t4 {
r = rune(c0&mask3)<<12 | rune(c1&maskx)<<6 | rune(c2&maskx)
if r <= rune2Max {
return RuneError, 1, false
}
if surrogateMin <= r && r <= surrogateMax {
return RuneError, 1, false
}
return r, 3, false
}
// need third continuation byte
if n < 4 {
return RuneError, 1, true
}
c3 := s[3]
if c3 < tx || t2 <= c3 {
return RuneError, 1, false
}
// 4-byte, 21-bit sequence?
if c0 < t5 {
r = rune(c0&mask4)<<18 | rune(c1&maskx)<<12 | rune(c2&maskx)<<6 | rune(c3&maskx)
if r <= rune3Max || MaxRune < r {
return RuneError, 1, false
}
return r, 4, false
}
// error
return RuneError, 1, false
}
// FullRune reports whether the bytes in p begin with a full UTF-8 encoding of a rune.
// An invalid encoding is considered a full Rune since it will convert as a width-1 error rune.
func FullRune(p []byte) bool {
_, _, short := decodeRuneInternal(p)
return !short
}
// FullRuneInString is like FullRune but its input is a string.
func FullRuneInString(s string) bool {
_, _, short := decodeRuneInStringInternal(s)
return !short
}
// DecodeRune unpacks the first UTF-8 encoding in p and returns the rune and
// its width in bytes. If p is empty it returns (RuneError, 0). Otherwise, if
// the encoding is invalid, it returns (RuneError, 1). Both are impossible
// results for correct UTF-8.
//
// An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
// out of range, or is not the shortest possible UTF-8 encoding for the
// value. No other validation is performed.
func DecodeRune(p []byte) (r rune, size int) {
r, size, _ = decodeRuneInternal(p)
return
}
// DecodeRuneInString is like DecodeRune but its input is a string. If s is
// empty it returns (RuneError, 0). Otherwise, if the encoding is invalid, it
// returns (RuneError, 1). Both are impossible results for correct UTF-8.
//
// An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
// out of range, or is not the shortest possible UTF-8 encoding for the
// value. No other validation is performed.
func DecodeRuneInString(s string) (r rune, size int) {
r, size, _ = decodeRuneInStringInternal(s)
return
}
// DecodeLastRune unpacks the last UTF-8 encoding in p and returns the rune and
// its width in bytes. If p is empty it returns (RuneError, 0). Otherwise, if
// the encoding is invalid, it returns (RuneError, 1). Both are impossible
// results for correct UTF-8.
//
// An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
// out of range, or is not the shortest possible UTF-8 encoding for the
// value. No other validation is performed.
func DecodeLastRune(p []byte) (r rune, size int) {
end := len(p)
if end == 0 {
return RuneError, 0
}
start := end - 1
r = rune(p[start])
if r < RuneSelf {
return r, 1
}
// guard against O(n^2) behavior when traversing
// backwards through strings with long sequences of
// invalid UTF-8.
lim := end - UTFMax
if lim < 0 {
lim = 0
}
for start--; start >= lim; start-- {
if RuneStart(p[start]) {
break
}
}
if start < 0 {
start = 0
}
r, size = DecodeRune(p[start:end])
if start+size != end {
return RuneError, 1
}
return r, size
}
// DecodeLastRuneInString is like DecodeLastRune but its input is a string. If
// s is empty it returns (RuneError, 0). Otherwise, if the encoding is invalid,
// it returns (RuneError, 1). Both are impossible results for correct UTF-8.
//
// An encoding is invalid if it is incorrect UTF-8, encodes a rune that is
// out of range, or is not the shortest possible UTF-8 encoding for the
// value. No other validation is performed.
func DecodeLastRuneInString(s string) (r rune, size int) {
end := len(s)
if end == 0 {
return RuneError, 0
}
start := end - 1
r = rune(s[start])
if r < RuneSelf {
return r, 1
}
// guard against O(n^2) behavior when traversing
// backwards through strings with long sequences of
// invalid UTF-8.
lim := end - UTFMax
if lim < 0 {
lim = 0
}
for start--; start >= lim; start-- {
if RuneStart(s[start]) {
break
}
}
if start < 0 {
start = 0
}
r, size = DecodeRuneInString(s[start:end])
if start+size != end {
return RuneError, 1
}
return r, size
}
// RuneLen returns the number of bytes required to encode the rune.
// It returns -1 if the rune is not a valid value to encode in UTF-8.
func RuneLen(r rune) int {
switch {
case r < 0:
return -1
case r <= rune1Max:
return 1
case r <= rune2Max:
return 2
case surrogateMin <= r && r <= surrogateMax:
return -1
case r <= rune3Max:
return 3
case r <= MaxRune:
return 4
}
return -1
}
// EncodeRune writes into p (which must be large enough) the UTF-8 encoding of the rune.
// It returns the number of bytes written.
func EncodeRune(p []byte, r rune) int {
// Negative values are erroneous. Making it unsigned addresses the problem.
switch i := uint32(r); {
case i <= rune1Max:
p[0] = byte(r)
return 1
case i <= rune2Max:
p[0] = t2 | byte(r>>6)
p[1] = tx | byte(r)&maskx
return 2
case i > MaxRune, surrogateMin <= i && i <= surrogateMax:
r = RuneError
fallthrough
case i <= rune3Max:
p[0] = t3 | byte(r>>12)
p[1] = tx | byte(r>>6)&maskx
p[2] = tx | byte(r)&maskx
return 3
default:
p[0] = t4 | byte(r>>18)
p[1] = tx | byte(r>>12)&maskx
p[2] = tx | byte(r>>6)&maskx
p[3] = tx | byte(r)&maskx
return 4
}
}
// RuneCount returns the number of runes in p. Erroneous and short
// encodings are treated as single runes of width 1 byte.
func RuneCount(p []byte) int {
i := 0
var n int
for n = 0; i < len(p); n++ {
if p[i] < RuneSelf {
i++
} else {
_, size := DecodeRune(p[i:])
i += size
}
}
return n
}
// RuneCountInString is like RuneCount but its input is a string.
func RuneCountInString(s string) (n int) {
for range s {
n++
}
return
}
// RuneStart reports whether the byte could be the first byte of
// an encoded rune. Second and subsequent bytes always have the top
// two bits set to 10.
func RuneStart(b byte) bool { return b&0xC0 != 0x80 }
// Valid reports whether p consists entirely of valid UTF-8-encoded runes.
func Valid(p []byte) bool {
i := 0
for i < len(p) {
if p[i] < RuneSelf {
i++
} else {
_, size := DecodeRune(p[i:])
if size == 1 {
// All valid runes of size 1 (those
// below RuneSelf) were handled above.
// This must be a RuneError.
return false
}
i += size
}
}
return true
}
// ValidString reports whether s consists entirely of valid UTF-8-encoded runes.
func ValidString(s string) bool {
for i, r := range s {
if r == RuneError {
// The RuneError value can be an error
// sentinel value (if it's size 1) or the same
// value encoded properly. Decode it to see if
// it's the 1 byte sentinel value.
_, size := DecodeRuneInString(s[i:])
if size == 1 {
return false
}
}
}
return true
}
// ValidRune reports whether r can be legally encoded as UTF-8.
// Code points that are out of range or a surrogate half are illegal.
func ValidRune(r rune) bool {
switch {
case r < 0:
return false
case surrogateMin <= r && r <= surrogateMax:
return false
case r > MaxRune:
return false
}
return true
}