444 lines
10 KiB
Go
444 lines
10 KiB
Go
// 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 the encoding is invalid, it returns (RuneError, 1), an impossible result 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 the encoding is invalid, it returns (RuneError, 1), an impossible result 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 the encoding is invalid, it returns (RuneError, 1), an impossible result 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 the encoding is invalid, it returns (RuneError, 1), an impossible result 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.
|
|
if uint32(r) <= rune1Max {
|
|
p[0] = byte(r)
|
|
return 1
|
|
}
|
|
|
|
if uint32(r) <= rune2Max {
|
|
p[0] = t2 | byte(r>>6)
|
|
p[1] = tx | byte(r)&maskx
|
|
return 2
|
|
}
|
|
|
|
if uint32(r) > MaxRune {
|
|
r = RuneError
|
|
}
|
|
|
|
if surrogateMin <= r && r <= surrogateMax {
|
|
r = RuneError
|
|
}
|
|
|
|
if uint32(r) <= rune3Max {
|
|
p[0] = t3 | byte(r>>12)
|
|
p[1] = tx | byte(r>>6)&maskx
|
|
p[2] = tx | byte(r)&maskx
|
|
return 3
|
|
}
|
|
|
|
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 of 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
|
|
}
|