Source file src/bytes/bytes.go

Documentation: bytes

     1  // Copyright 2009 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package bytes implements functions for the manipulation of byte slices.
     6  // It is analogous to the facilities of the strings package.
     7  package bytes
     8  
     9  import (
    10  	"internal/bytealg"
    11  	"unicode"
    12  	"unicode/utf8"
    13  )
    14  
    15  // Equal reports whether a and b
    16  // are the same length and contain the same bytes.
    17  // A nil argument is equivalent to an empty slice.
    18  func Equal(a, b []byte) bool {
    19  	// Neither cmd/compile nor gccgo allocates for these string conversions.
    20  	return string(a) == string(b)
    21  }
    22  
    23  // Compare returns an integer comparing two byte slices lexicographically.
    24  // The result will be 0 if a == b, -1 if a < b, and +1 if a > b.
    25  // A nil argument is equivalent to an empty slice.
    26  func Compare(a, b []byte) int {
    27  	return bytealg.Compare(a, b)
    28  }
    29  
    30  // explode splits s into a slice of UTF-8 sequences, one per Unicode code point (still slices of bytes),
    31  // up to a maximum of n byte slices. Invalid UTF-8 sequences are chopped into individual bytes.
    32  func explode(s []byte, n int) [][]byte {
    33  	if n <= 0 || n > len(s) {
    34  		n = len(s)
    35  	}
    36  	a := make([][]byte, n)
    37  	var size int
    38  	na := 0
    39  	for len(s) > 0 {
    40  		if na+1 >= n {
    41  			a[na] = s
    42  			na++
    43  			break
    44  		}
    45  		_, size = utf8.DecodeRune(s)
    46  		a[na] = s[0:size:size]
    47  		s = s[size:]
    48  		na++
    49  	}
    50  	return a[0:na]
    51  }
    52  
    53  // Count counts the number of non-overlapping instances of sep in s.
    54  // If sep is an empty slice, Count returns 1 + the number of UTF-8-encoded code points in s.
    55  func Count(s, sep []byte) int {
    56  	// special case
    57  	if len(sep) == 0 {
    58  		return utf8.RuneCount(s) + 1
    59  	}
    60  	if len(sep) == 1 {
    61  		return bytealg.Count(s, sep[0])
    62  	}
    63  	n := 0
    64  	for {
    65  		i := Index(s, sep)
    66  		if i == -1 {
    67  			return n
    68  		}
    69  		n++
    70  		s = s[i+len(sep):]
    71  	}
    72  }
    73  
    74  // Contains reports whether subslice is within b.
    75  func Contains(b, subslice []byte) bool {
    76  	return Index(b, subslice) != -1
    77  }
    78  
    79  // ContainsAny reports whether any of the UTF-8-encoded code points in chars are within b.
    80  func ContainsAny(b []byte, chars string) bool {
    81  	return IndexAny(b, chars) >= 0
    82  }
    83  
    84  // ContainsRune reports whether the rune is contained in the UTF-8-encoded byte slice b.
    85  func ContainsRune(b []byte, r rune) bool {
    86  	return IndexRune(b, r) >= 0
    87  }
    88  
    89  // IndexByte returns the index of the first instance of c in b, or -1 if c is not present in b.
    90  func IndexByte(b []byte, c byte) int {
    91  	return bytealg.IndexByte(b, c)
    92  }
    93  
    94  func indexBytePortable(s []byte, c byte) int {
    95  	for i, b := range s {
    96  		if b == c {
    97  			return i
    98  		}
    99  	}
   100  	return -1
   101  }
   102  
   103  // LastIndex returns the index of the last instance of sep in s, or -1 if sep is not present in s.
   104  func LastIndex(s, sep []byte) int {
   105  	n := len(sep)
   106  	switch {
   107  	case n == 0:
   108  		return len(s)
   109  	case n == 1:
   110  		return LastIndexByte(s, sep[0])
   111  	case n == len(s):
   112  		if Equal(s, sep) {
   113  			return 0
   114  		}
   115  		return -1
   116  	case n > len(s):
   117  		return -1
   118  	}
   119  	// Rabin-Karp search from the end of the string
   120  	hashss, pow := bytealg.HashStrRevBytes(sep)
   121  	last := len(s) - n
   122  	var h uint32
   123  	for i := len(s) - 1; i >= last; i-- {
   124  		h = h*bytealg.PrimeRK + uint32(s[i])
   125  	}
   126  	if h == hashss && Equal(s[last:], sep) {
   127  		return last
   128  	}
   129  	for i := last - 1; i >= 0; i-- {
   130  		h *= bytealg.PrimeRK
   131  		h += uint32(s[i])
   132  		h -= pow * uint32(s[i+n])
   133  		if h == hashss && Equal(s[i:i+n], sep) {
   134  			return i
   135  		}
   136  	}
   137  	return -1
   138  }
   139  
   140  // LastIndexByte returns the index of the last instance of c in s, or -1 if c is not present in s.
   141  func LastIndexByte(s []byte, c byte) int {
   142  	for i := len(s) - 1; i >= 0; i-- {
   143  		if s[i] == c {
   144  			return i
   145  		}
   146  	}
   147  	return -1
   148  }
   149  
   150  // IndexRune interprets s as a sequence of UTF-8-encoded code points.
   151  // It returns the byte index of the first occurrence in s of the given rune.
   152  // It returns -1 if rune is not present in s.
   153  // If r is utf8.RuneError, it returns the first instance of any
   154  // invalid UTF-8 byte sequence.
   155  func IndexRune(s []byte, r rune) int {
   156  	switch {
   157  	case 0 <= r && r < utf8.RuneSelf:
   158  		return IndexByte(s, byte(r))
   159  	case r == utf8.RuneError:
   160  		for i := 0; i < len(s); {
   161  			r1, n := utf8.DecodeRune(s[i:])
   162  			if r1 == utf8.RuneError {
   163  				return i
   164  			}
   165  			i += n
   166  		}
   167  		return -1
   168  	case !utf8.ValidRune(r):
   169  		return -1
   170  	default:
   171  		var b [utf8.UTFMax]byte
   172  		n := utf8.EncodeRune(b[:], r)
   173  		return Index(s, b[:n])
   174  	}
   175  }
   176  
   177  // IndexAny interprets s as a sequence of UTF-8-encoded Unicode code points.
   178  // It returns the byte index of the first occurrence in s of any of the Unicode
   179  // code points in chars. It returns -1 if chars is empty or if there is no code
   180  // point in common.
   181  func IndexAny(s []byte, chars string) int {
   182  	if chars == "" {
   183  		// Avoid scanning all of s.
   184  		return -1
   185  	}
   186  	if len(s) == 1 {
   187  		r := rune(s[0])
   188  		if r >= utf8.RuneSelf {
   189  			// search utf8.RuneError.
   190  			for _, r = range chars {
   191  				if r == utf8.RuneError {
   192  					return 0
   193  				}
   194  			}
   195  			return -1
   196  		}
   197  		if bytealg.IndexByteString(chars, s[0]) >= 0 {
   198  			return 0
   199  		}
   200  		return -1
   201  	}
   202  	if len(chars) == 1 {
   203  		r := rune(chars[0])
   204  		if r >= utf8.RuneSelf {
   205  			r = utf8.RuneError
   206  		}
   207  		return IndexRune(s, r)
   208  	}
   209  	if len(s) > 8 {
   210  		if as, isASCII := makeASCIISet(chars); isASCII {
   211  			for i, c := range s {
   212  				if as.contains(c) {
   213  					return i
   214  				}
   215  			}
   216  			return -1
   217  		}
   218  	}
   219  	var width int
   220  	for i := 0; i < len(s); i += width {
   221  		r := rune(s[i])
   222  		if r < utf8.RuneSelf {
   223  			if bytealg.IndexByteString(chars, s[i]) >= 0 {
   224  				return i
   225  			}
   226  			width = 1
   227  			continue
   228  		}
   229  		r, width = utf8.DecodeRune(s[i:])
   230  		if r != utf8.RuneError {
   231  			// r is 2 to 4 bytes
   232  			if len(chars) == width {
   233  				if chars == string(r) {
   234  					return i
   235  				}
   236  				continue
   237  			}
   238  			// Use bytealg.IndexString for performance if available.
   239  			if bytealg.MaxLen >= width {
   240  				if bytealg.IndexString(chars, string(r)) >= 0 {
   241  					return i
   242  				}
   243  				continue
   244  			}
   245  		}
   246  		for _, ch := range chars {
   247  			if r == ch {
   248  				return i
   249  			}
   250  		}
   251  	}
   252  	return -1
   253  }
   254  
   255  // LastIndexAny interprets s as a sequence of UTF-8-encoded Unicode code
   256  // points. It returns the byte index of the last occurrence in s of any of
   257  // the Unicode code points in chars. It returns -1 if chars is empty or if
   258  // there is no code point in common.
   259  func LastIndexAny(s []byte, chars string) int {
   260  	if chars == "" {
   261  		// Avoid scanning all of s.
   262  		return -1
   263  	}
   264  	if len(s) > 8 {
   265  		if as, isASCII := makeASCIISet(chars); isASCII {
   266  			for i := len(s) - 1; i >= 0; i-- {
   267  				if as.contains(s[i]) {
   268  					return i
   269  				}
   270  			}
   271  			return -1
   272  		}
   273  	}
   274  	if len(s) == 1 {
   275  		r := rune(s[0])
   276  		if r >= utf8.RuneSelf {
   277  			for _, r = range chars {
   278  				if r == utf8.RuneError {
   279  					return 0
   280  				}
   281  			}
   282  			return -1
   283  		}
   284  		if bytealg.IndexByteString(chars, s[0]) >= 0 {
   285  			return 0
   286  		}
   287  		return -1
   288  	}
   289  	if len(chars) == 1 {
   290  		cr := rune(chars[0])
   291  		if cr >= utf8.RuneSelf {
   292  			cr = utf8.RuneError
   293  		}
   294  		for i := len(s); i > 0; {
   295  			r, size := utf8.DecodeLastRune(s[:i])
   296  			i -= size
   297  			if r == cr {
   298  				return i
   299  			}
   300  		}
   301  		return -1
   302  	}
   303  	for i := len(s); i > 0; {
   304  		r := rune(s[i-1])
   305  		if r < utf8.RuneSelf {
   306  			if bytealg.IndexByteString(chars, s[i-1]) >= 0 {
   307  				return i - 1
   308  			}
   309  			i--
   310  			continue
   311  		}
   312  		r, size := utf8.DecodeLastRune(s[:i])
   313  		i -= size
   314  		if r != utf8.RuneError {
   315  			// r is 2 to 4 bytes
   316  			if len(chars) == size {
   317  				if chars == string(r) {
   318  					return i
   319  				}
   320  				continue
   321  			}
   322  			// Use bytealg.IndexString for performance if available.
   323  			if bytealg.MaxLen >= size {
   324  				if bytealg.IndexString(chars, string(r)) >= 0 {
   325  					return i
   326  				}
   327  				continue
   328  			}
   329  		}
   330  		for _, ch := range chars {
   331  			if r == ch {
   332  				return i
   333  			}
   334  		}
   335  	}
   336  	return -1
   337  }
   338  
   339  // Generic split: splits after each instance of sep,
   340  // including sepSave bytes of sep in the subslices.
   341  func genSplit(s, sep []byte, sepSave, n int) [][]byte {
   342  	if n == 0 {
   343  		return nil
   344  	}
   345  	if len(sep) == 0 {
   346  		return explode(s, n)
   347  	}
   348  	if n < 0 {
   349  		n = Count(s, sep) + 1
   350  	}
   351  	if n > len(s)+1 {
   352  		n = len(s) + 1
   353  	}
   354  
   355  	a := make([][]byte, n)
   356  	n--
   357  	i := 0
   358  	for i < n {
   359  		m := Index(s, sep)
   360  		if m < 0 {
   361  			break
   362  		}
   363  		a[i] = s[: m+sepSave : m+sepSave]
   364  		s = s[m+len(sep):]
   365  		i++
   366  	}
   367  	a[i] = s
   368  	return a[:i+1]
   369  }
   370  
   371  // SplitN slices s into subslices separated by sep and returns a slice of
   372  // the subslices between those separators.
   373  // If sep is empty, SplitN splits after each UTF-8 sequence.
   374  // The count determines the number of subslices to return:
   375  //
   376  //	n > 0: at most n subslices; the last subslice will be the unsplit remainder.
   377  //	n == 0: the result is nil (zero subslices)
   378  //	n < 0: all subslices
   379  //
   380  // To split around the first instance of a separator, see Cut.
   381  func SplitN(s, sep []byte, n int) [][]byte { return genSplit(s, sep, 0, n) }
   382  
   383  // SplitAfterN slices s into subslices after each instance of sep and
   384  // returns a slice of those subslices.
   385  // If sep is empty, SplitAfterN splits after each UTF-8 sequence.
   386  // The count determines the number of subslices to return:
   387  //
   388  //	n > 0: at most n subslices; the last subslice will be the unsplit remainder.
   389  //	n == 0: the result is nil (zero subslices)
   390  //	n < 0: all subslices
   391  func SplitAfterN(s, sep []byte, n int) [][]byte {
   392  	return genSplit(s, sep, len(sep), n)
   393  }
   394  
   395  // Split slices s into all subslices separated by sep and returns a slice of
   396  // the subslices between those separators.
   397  // If sep is empty, Split splits after each UTF-8 sequence.
   398  // It is equivalent to SplitN with a count of -1.
   399  //
   400  // To split around the first instance of a separator, see Cut.
   401  func Split(s, sep []byte) [][]byte { return genSplit(s, sep, 0, -1) }
   402  
   403  // SplitAfter slices s into all subslices after each instance of sep and
   404  // returns a slice of those subslices.
   405  // If sep is empty, SplitAfter splits after each UTF-8 sequence.
   406  // It is equivalent to SplitAfterN with a count of -1.
   407  func SplitAfter(s, sep []byte) [][]byte {
   408  	return genSplit(s, sep, len(sep), -1)
   409  }
   410  
   411  var asciiSpace = [256]uint8{'\t': 1, '\n': 1, '\v': 1, '\f': 1, '\r': 1, ' ': 1}
   412  
   413  // Fields interprets s as a sequence of UTF-8-encoded code points.
   414  // It splits the slice s around each instance of one or more consecutive white space
   415  // characters, as defined by unicode.IsSpace, returning a slice of subslices of s or an
   416  // empty slice if s contains only white space.
   417  func Fields(s []byte) [][]byte {
   418  	// First count the fields.
   419  	// This is an exact count if s is ASCII, otherwise it is an approximation.
   420  	n := 0
   421  	wasSpace := 1
   422  	// setBits is used to track which bits are set in the bytes of s.
   423  	setBits := uint8(0)
   424  	for i := 0; i < len(s); i++ {
   425  		r := s[i]
   426  		setBits |= r
   427  		isSpace := int(asciiSpace[r])
   428  		n += wasSpace & ^isSpace
   429  		wasSpace = isSpace
   430  	}
   431  
   432  	if setBits >= utf8.RuneSelf {
   433  		// Some runes in the input slice are not ASCII.
   434  		return FieldsFunc(s, unicode.IsSpace)
   435  	}
   436  
   437  	// ASCII fast path
   438  	a := make([][]byte, n)
   439  	na := 0
   440  	fieldStart := 0
   441  	i := 0
   442  	// Skip spaces in the front of the input.
   443  	for i < len(s) && asciiSpace[s[i]] != 0 {
   444  		i++
   445  	}
   446  	fieldStart = i
   447  	for i < len(s) {
   448  		if asciiSpace[s[i]] == 0 {
   449  			i++
   450  			continue
   451  		}
   452  		a[na] = s[fieldStart:i:i]
   453  		na++
   454  		i++
   455  		// Skip spaces in between fields.
   456  		for i < len(s) && asciiSpace[s[i]] != 0 {
   457  			i++
   458  		}
   459  		fieldStart = i
   460  	}
   461  	if fieldStart < len(s) { // Last field might end at EOF.
   462  		a[na] = s[fieldStart:len(s):len(s)]
   463  	}
   464  	return a
   465  }
   466  
   467  // FieldsFunc interprets s as a sequence of UTF-8-encoded code points.
   468  // It splits the slice s at each run of code points c satisfying f(c) and
   469  // returns a slice of subslices of s. If all code points in s satisfy f(c), or
   470  // len(s) == 0, an empty slice is returned.
   471  //
   472  // FieldsFunc makes no guarantees about the order in which it calls f(c)
   473  // and assumes that f always returns the same value for a given c.
   474  func FieldsFunc(s []byte, f func(rune) bool) [][]byte {
   475  	// A span is used to record a slice of s of the form s[start:end].
   476  	// The start index is inclusive and the end index is exclusive.
   477  	type span struct {
   478  		start int
   479  		end   int
   480  	}
   481  	spans := make([]span, 0, 32)
   482  
   483  	// Find the field start and end indices.
   484  	// Doing this in a separate pass (rather than slicing the string s
   485  	// and collecting the result substrings right away) is significantly
   486  	// more efficient, possibly due to cache effects.
   487  	start := -1 // valid span start if >= 0
   488  	for i := 0; i < len(s); {
   489  		size := 1
   490  		r := rune(s[i])
   491  		if r >= utf8.RuneSelf {
   492  			r, size = utf8.DecodeRune(s[i:])
   493  		}
   494  		if f(r) {
   495  			if start >= 0 {
   496  				spans = append(spans, span{start, i})
   497  				start = -1
   498  			}
   499  		} else {
   500  			if start < 0 {
   501  				start = i
   502  			}
   503  		}
   504  		i += size
   505  	}
   506  
   507  	// Last field might end at EOF.
   508  	if start >= 0 {
   509  		spans = append(spans, span{start, len(s)})
   510  	}
   511  
   512  	// Create subslices from recorded field indices.
   513  	a := make([][]byte, len(spans))
   514  	for i, span := range spans {
   515  		a[i] = s[span.start:span.end:span.end]
   516  	}
   517  
   518  	return a
   519  }
   520  
   521  // Join concatenates the elements of s to create a new byte slice. The separator
   522  // sep is placed between elements in the resulting slice.
   523  func Join(s [][]byte, sep []byte) []byte {
   524  	if len(s) == 0 {
   525  		return []byte{}
   526  	}
   527  	if len(s) == 1 {
   528  		// Just return a copy.
   529  		return append([]byte(nil), s[0]...)
   530  	}
   531  	n := len(sep) * (len(s) - 1)
   532  	for _, v := range s {
   533  		n += len(v)
   534  	}
   535  
   536  	b := make([]byte, n)
   537  	bp := copy(b, s[0])
   538  	for _, v := range s[1:] {
   539  		bp += copy(b[bp:], sep)
   540  		bp += copy(b[bp:], v)
   541  	}
   542  	return b
   543  }
   544  
   545  // HasPrefix tests whether the byte slice s begins with prefix.
   546  func HasPrefix(s, prefix []byte) bool {
   547  	return len(s) >= len(prefix) && Equal(s[0:len(prefix)], prefix)
   548  }
   549  
   550  // HasSuffix tests whether the byte slice s ends with suffix.
   551  func HasSuffix(s, suffix []byte) bool {
   552  	return len(s) >= len(suffix) && Equal(s[len(s)-len(suffix):], suffix)
   553  }
   554  
   555  // Map returns a copy of the byte slice s with all its characters modified
   556  // according to the mapping function. If mapping returns a negative value, the character is
   557  // dropped from the byte slice with no replacement. The characters in s and the
   558  // output are interpreted as UTF-8-encoded code points.
   559  func Map(mapping func(r rune) rune, s []byte) []byte {
   560  	// In the worst case, the slice can grow when mapped, making
   561  	// things unpleasant. But it's so rare we barge in assuming it's
   562  	// fine. It could also shrink but that falls out naturally.
   563  	maxbytes := len(s) // length of b
   564  	nbytes := 0        // number of bytes encoded in b
   565  	b := make([]byte, maxbytes)
   566  	for i := 0; i < len(s); {
   567  		wid := 1
   568  		r := rune(s[i])
   569  		if r >= utf8.RuneSelf {
   570  			r, wid = utf8.DecodeRune(s[i:])
   571  		}
   572  		r = mapping(r)
   573  		if r >= 0 {
   574  			rl := utf8.RuneLen(r)
   575  			if rl < 0 {
   576  				rl = len(string(utf8.RuneError))
   577  			}
   578  			if nbytes+rl > maxbytes {
   579  				// Grow the buffer.
   580  				maxbytes = maxbytes*2 + utf8.UTFMax
   581  				nb := make([]byte, maxbytes)
   582  				copy(nb, b[0:nbytes])
   583  				b = nb
   584  			}
   585  			nbytes += utf8.EncodeRune(b[nbytes:maxbytes], r)
   586  		}
   587  		i += wid
   588  	}
   589  	return b[0:nbytes]
   590  }
   591  
   592  // Repeat returns a new byte slice consisting of count copies of b.
   593  //
   594  // It panics if count is negative or if
   595  // the result of (len(b) * count) overflows.
   596  func Repeat(b []byte, count int) []byte {
   597  	if count == 0 {
   598  		return []byte{}
   599  	}
   600  	// Since we cannot return an error on overflow,
   601  	// we should panic if the repeat will generate
   602  	// an overflow.
   603  	// See Issue golang.org/issue/16237.
   604  	if count < 0 {
   605  		panic("bytes: negative Repeat count")
   606  	} else if len(b)*count/count != len(b) {
   607  		panic("bytes: Repeat count causes overflow")
   608  	}
   609  
   610  	nb := make([]byte, len(b)*count)
   611  	bp := copy(nb, b)
   612  	for bp < len(nb) {
   613  		copy(nb[bp:], nb[:bp])
   614  		bp *= 2
   615  	}
   616  	return nb
   617  }
   618  
   619  // ToUpper returns a copy of the byte slice s with all Unicode letters mapped to
   620  // their upper case.
   621  func ToUpper(s []byte) []byte {
   622  	isASCII, hasLower := true, false
   623  	for i := 0; i < len(s); i++ {
   624  		c := s[i]
   625  		if c >= utf8.RuneSelf {
   626  			isASCII = false
   627  			break
   628  		}
   629  		hasLower = hasLower || ('a' <= c && c <= 'z')
   630  	}
   631  
   632  	if isASCII { // optimize for ASCII-only byte slices.
   633  		if !hasLower {
   634  			// Just return a copy.
   635  			return append([]byte(""), s...)
   636  		}
   637  		b := make([]byte, len(s))
   638  		for i := 0; i < len(s); i++ {
   639  			c := s[i]
   640  			if 'a' <= c && c <= 'z' {
   641  				c -= 'a' - 'A'
   642  			}
   643  			b[i] = c
   644  		}
   645  		return b
   646  	}
   647  	return Map(unicode.ToUpper, s)
   648  }
   649  
   650  // ToLower returns a copy of the byte slice s with all Unicode letters mapped to
   651  // their lower case.
   652  func ToLower(s []byte) []byte {
   653  	isASCII, hasUpper := true, false
   654  	for i := 0; i < len(s); i++ {
   655  		c := s[i]
   656  		if c >= utf8.RuneSelf {
   657  			isASCII = false
   658  			break
   659  		}
   660  		hasUpper = hasUpper || ('A' <= c && c <= 'Z')
   661  	}
   662  
   663  	if isASCII { // optimize for ASCII-only byte slices.
   664  		if !hasUpper {
   665  			return append([]byte(""), s...)
   666  		}
   667  		b := make([]byte, len(s))
   668  		for i := 0; i < len(s); i++ {
   669  			c := s[i]
   670  			if 'A' <= c && c <= 'Z' {
   671  				c += 'a' - 'A'
   672  			}
   673  			b[i] = c
   674  		}
   675  		return b
   676  	}
   677  	return Map(unicode.ToLower, s)
   678  }
   679  
   680  // ToTitle treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their title case.
   681  func ToTitle(s []byte) []byte { return Map(unicode.ToTitle, s) }
   682  
   683  // ToUpperSpecial treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their
   684  // upper case, giving priority to the special casing rules.
   685  func ToUpperSpecial(c unicode.SpecialCase, s []byte) []byte {
   686  	return Map(c.ToUpper, s)
   687  }
   688  
   689  // ToLowerSpecial treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their
   690  // lower case, giving priority to the special casing rules.
   691  func ToLowerSpecial(c unicode.SpecialCase, s []byte) []byte {
   692  	return Map(c.ToLower, s)
   693  }
   694  
   695  // ToTitleSpecial treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their
   696  // title case, giving priority to the special casing rules.
   697  func ToTitleSpecial(c unicode.SpecialCase, s []byte) []byte {
   698  	return Map(c.ToTitle, s)
   699  }
   700  
   701  // ToValidUTF8 treats s as UTF-8-encoded bytes and returns a copy with each run of bytes
   702  // representing invalid UTF-8 replaced with the bytes in replacement, which may be empty.
   703  func ToValidUTF8(s, replacement []byte) []byte {
   704  	b := make([]byte, 0, len(s)+len(replacement))
   705  	invalid := false // previous byte was from an invalid UTF-8 sequence
   706  	for i := 0; i < len(s); {
   707  		c := s[i]
   708  		if c < utf8.RuneSelf {
   709  			i++
   710  			invalid = false
   711  			b = append(b, c)
   712  			continue
   713  		}
   714  		_, wid := utf8.DecodeRune(s[i:])
   715  		if wid == 1 {
   716  			i++
   717  			if !invalid {
   718  				invalid = true
   719  				b = append(b, replacement...)
   720  			}
   721  			continue
   722  		}
   723  		invalid = false
   724  		b = append(b, s[i:i+wid]...)
   725  		i += wid
   726  	}
   727  	return b
   728  }
   729  
   730  // isSeparator reports whether the rune could mark a word boundary.
   731  // TODO: update when package unicode captures more of the properties.
   732  func isSeparator(r rune) bool {
   733  	// ASCII alphanumerics and underscore are not separators
   734  	if r <= 0x7F {
   735  		switch {
   736  		case '0' <= r && r <= '9':
   737  			return false
   738  		case 'a' <= r && r <= 'z':
   739  			return false
   740  		case 'A' <= r && r <= 'Z':
   741  			return false
   742  		case r == '_':
   743  			return false
   744  		}
   745  		return true
   746  	}
   747  	// Letters and digits are not separators
   748  	if unicode.IsLetter(r) || unicode.IsDigit(r) {
   749  		return false
   750  	}
   751  	// Otherwise, all we can do for now is treat spaces as separators.
   752  	return unicode.IsSpace(r)
   753  }
   754  
   755  // Title treats s as UTF-8-encoded bytes and returns a copy with all Unicode letters that begin
   756  // words mapped to their title case.
   757  //
   758  // Deprecated: The rule Title uses for word boundaries does not handle Unicode
   759  // punctuation properly. Use golang.org/x/text/cases instead.
   760  func Title(s []byte) []byte {
   761  	// Use a closure here to remember state.
   762  	// Hackish but effective. Depends on Map scanning in order and calling
   763  	// the closure once per rune.
   764  	prev := ' '
   765  	return Map(
   766  		func(r rune) rune {
   767  			if isSeparator(prev) {
   768  				prev = r
   769  				return unicode.ToTitle(r)
   770  			}
   771  			prev = r
   772  			return r
   773  		},
   774  		s)
   775  }
   776  
   777  // TrimLeftFunc treats s as UTF-8-encoded bytes and returns a subslice of s by slicing off
   778  // all leading UTF-8-encoded code points c that satisfy f(c).
   779  func TrimLeftFunc(s []byte, f func(r rune) bool) []byte {
   780  	i := indexFunc(s, f, false)
   781  	if i == -1 {
   782  		return nil
   783  	}
   784  	return s[i:]
   785  }
   786  
   787  // TrimRightFunc returns a subslice of s by slicing off all trailing
   788  // UTF-8-encoded code points c that satisfy f(c).
   789  func TrimRightFunc(s []byte, f func(r rune) bool) []byte {
   790  	i := lastIndexFunc(s, f, false)
   791  	if i >= 0 && s[i] >= utf8.RuneSelf {
   792  		_, wid := utf8.DecodeRune(s[i:])
   793  		i += wid
   794  	} else {
   795  		i++
   796  	}
   797  	return s[0:i]
   798  }
   799  
   800  // TrimFunc returns a subslice of s by slicing off all leading and trailing
   801  // UTF-8-encoded code points c that satisfy f(c).
   802  func TrimFunc(s []byte, f func(r rune) bool) []byte {
   803  	return TrimRightFunc(TrimLeftFunc(s, f), f)
   804  }
   805  
   806  // TrimPrefix returns s without the provided leading prefix string.
   807  // If s doesn't start with prefix, s is returned unchanged.
   808  func TrimPrefix(s, prefix []byte) []byte {
   809  	if HasPrefix(s, prefix) {
   810  		return s[len(prefix):]
   811  	}
   812  	return s
   813  }
   814  
   815  // TrimSuffix returns s without the provided trailing suffix string.
   816  // If s doesn't end with suffix, s is returned unchanged.
   817  func TrimSuffix(s, suffix []byte) []byte {
   818  	if HasSuffix(s, suffix) {
   819  		return s[:len(s)-len(suffix)]
   820  	}
   821  	return s
   822  }
   823  
   824  // IndexFunc interprets s as a sequence of UTF-8-encoded code points.
   825  // It returns the byte index in s of the first Unicode
   826  // code point satisfying f(c), or -1 if none do.
   827  func IndexFunc(s []byte, f func(r rune) bool) int {
   828  	return indexFunc(s, f, true)
   829  }
   830  
   831  // LastIndexFunc interprets s as a sequence of UTF-8-encoded code points.
   832  // It returns the byte index in s of the last Unicode
   833  // code point satisfying f(c), or -1 if none do.
   834  func LastIndexFunc(s []byte, f func(r rune) bool) int {
   835  	return lastIndexFunc(s, f, true)
   836  }
   837  
   838  // indexFunc is the same as IndexFunc except that if
   839  // truth==false, the sense of the predicate function is
   840  // inverted.
   841  func indexFunc(s []byte, f func(r rune) bool, truth bool) int {
   842  	start := 0
   843  	for start < len(s) {
   844  		wid := 1
   845  		r := rune(s[start])
   846  		if r >= utf8.RuneSelf {
   847  			r, wid = utf8.DecodeRune(s[start:])
   848  		}
   849  		if f(r) == truth {
   850  			return start
   851  		}
   852  		start += wid
   853  	}
   854  	return -1
   855  }
   856  
   857  // lastIndexFunc is the same as LastIndexFunc except that if
   858  // truth==false, the sense of the predicate function is
   859  // inverted.
   860  func lastIndexFunc(s []byte, f func(r rune) bool, truth bool) int {
   861  	for i := len(s); i > 0; {
   862  		r, size := rune(s[i-1]), 1
   863  		if r >= utf8.RuneSelf {
   864  			r, size = utf8.DecodeLastRune(s[0:i])
   865  		}
   866  		i -= size
   867  		if f(r) == truth {
   868  			return i
   869  		}
   870  	}
   871  	return -1
   872  }
   873  
   874  // asciiSet is a 32-byte value, where each bit represents the presence of a
   875  // given ASCII character in the set. The 128-bits of the lower 16 bytes,
   876  // starting with the least-significant bit of the lowest word to the
   877  // most-significant bit of the highest word, map to the full range of all
   878  // 128 ASCII characters. The 128-bits of the upper 16 bytes will be zeroed,
   879  // ensuring that any non-ASCII character will be reported as not in the set.
   880  // This allocates a total of 32 bytes even though the upper half
   881  // is unused to avoid bounds checks in asciiSet.contains.
   882  type asciiSet [8]uint32
   883  
   884  // makeASCIISet creates a set of ASCII characters and reports whether all
   885  // characters in chars are ASCII.
   886  func makeASCIISet(chars string) (as asciiSet, ok bool) {
   887  	for i := 0; i < len(chars); i++ {
   888  		c := chars[i]
   889  		if c >= utf8.RuneSelf {
   890  			return as, false
   891  		}
   892  		as[c/32] |= 1 << (c % 32)
   893  	}
   894  	return as, true
   895  }
   896  
   897  // contains reports whether c is inside the set.
   898  func (as *asciiSet) contains(c byte) bool {
   899  	return (as[c/32] & (1 << (c % 32))) != 0
   900  }
   901  
   902  // containsRune is a simplified version of strings.ContainsRune
   903  // to avoid importing the strings package.
   904  // We avoid bytes.ContainsRune to avoid allocating a temporary copy of s.
   905  func containsRune(s string, r rune) bool {
   906  	for _, c := range s {
   907  		if c == r {
   908  			return true
   909  		}
   910  	}
   911  	return false
   912  }
   913  
   914  // Trim returns a subslice of s by slicing off all leading and
   915  // trailing UTF-8-encoded code points contained in cutset.
   916  func Trim(s []byte, cutset string) []byte {
   917  	if len(s) == 0 {
   918  		// This is what we've historically done.
   919  		return nil
   920  	}
   921  	if cutset == "" {
   922  		return s
   923  	}
   924  	if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
   925  		return trimLeftByte(trimRightByte(s, cutset[0]), cutset[0])
   926  	}
   927  	if as, ok := makeASCIISet(cutset); ok {
   928  		return trimLeftASCII(trimRightASCII(s, &as), &as)
   929  	}
   930  	return trimLeftUnicode(trimRightUnicode(s, cutset), cutset)
   931  }
   932  
   933  // TrimLeft returns a subslice of s by slicing off all leading
   934  // UTF-8-encoded code points contained in cutset.
   935  func TrimLeft(s []byte, cutset string) []byte {
   936  	if len(s) == 0 {
   937  		// This is what we've historically done.
   938  		return nil
   939  	}
   940  	if cutset == "" {
   941  		return s
   942  	}
   943  	if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
   944  		return trimLeftByte(s, cutset[0])
   945  	}
   946  	if as, ok := makeASCIISet(cutset); ok {
   947  		return trimLeftASCII(s, &as)
   948  	}
   949  	return trimLeftUnicode(s, cutset)
   950  }
   951  
   952  func trimLeftByte(s []byte, c byte) []byte {
   953  	for len(s) > 0 && s[0] == c {
   954  		s = s[1:]
   955  	}
   956  	if len(s) == 0 {
   957  		// This is what we've historically done.
   958  		return nil
   959  	}
   960  	return s
   961  }
   962  
   963  func trimLeftASCII(s []byte, as *asciiSet) []byte {
   964  	for len(s) > 0 {
   965  		if !as.contains(s[0]) {
   966  			break
   967  		}
   968  		s = s[1:]
   969  	}
   970  	if len(s) == 0 {
   971  		// This is what we've historically done.
   972  		return nil
   973  	}
   974  	return s
   975  }
   976  
   977  func trimLeftUnicode(s []byte, cutset string) []byte {
   978  	for len(s) > 0 {
   979  		r, n := rune(s[0]), 1
   980  		if r >= utf8.RuneSelf {
   981  			r, n = utf8.DecodeRune(s)
   982  		}
   983  		if !containsRune(cutset, r) {
   984  			break
   985  		}
   986  		s = s[n:]
   987  	}
   988  	if len(s) == 0 {
   989  		// This is what we've historically done.
   990  		return nil
   991  	}
   992  	return s
   993  }
   994  
   995  // TrimRight returns a subslice of s by slicing off all trailing
   996  // UTF-8-encoded code points that are contained in cutset.
   997  func TrimRight(s []byte, cutset string) []byte {
   998  	if len(s) == 0 || cutset == "" {
   999  		return s
  1000  	}
  1001  	if len(cutset) == 1 && cutset[0] < utf8.RuneSelf {
  1002  		return trimRightByte(s, cutset[0])
  1003  	}
  1004  	if as, ok := makeASCIISet(cutset); ok {
  1005  		return trimRightASCII(s, &as)
  1006  	}
  1007  	return trimRightUnicode(s, cutset)
  1008  }
  1009  
  1010  func trimRightByte(s []byte, c byte) []byte {
  1011  	for len(s) > 0 && s[len(s)-1] == c {
  1012  		s = s[:len(s)-1]
  1013  	}
  1014  	return s
  1015  }
  1016  
  1017  func trimRightASCII(s []byte, as *asciiSet) []byte {
  1018  	for len(s) > 0 {
  1019  		if !as.contains(s[len(s)-1]) {
  1020  			break
  1021  		}
  1022  		s = s[:len(s)-1]
  1023  	}
  1024  	return s
  1025  }
  1026  
  1027  func trimRightUnicode(s []byte, cutset string) []byte {
  1028  	for len(s) > 0 {
  1029  		r, n := rune(s[len(s)-1]), 1
  1030  		if r >= utf8.RuneSelf {
  1031  			r, n = utf8.DecodeLastRune(s)
  1032  		}
  1033  		if !containsRune(cutset, r) {
  1034  			break
  1035  		}
  1036  		s = s[:len(s)-n]
  1037  	}
  1038  	return s
  1039  }
  1040  
  1041  // TrimSpace returns a subslice of s by slicing off all leading and
  1042  // trailing white space, as defined by Unicode.
  1043  func TrimSpace(s []byte) []byte {
  1044  	// Fast path for ASCII: look for the first ASCII non-space byte
  1045  	start := 0
  1046  	for ; start < len(s); start++ {
  1047  		c := s[start]
  1048  		if c >= utf8.RuneSelf {
  1049  			// If we run into a non-ASCII byte, fall back to the
  1050  			// slower unicode-aware method on the remaining bytes
  1051  			return TrimFunc(s[start:], unicode.IsSpace)
  1052  		}
  1053  		if asciiSpace[c] == 0 {
  1054  			break
  1055  		}
  1056  	}
  1057  
  1058  	// Now look for the first ASCII non-space byte from the end
  1059  	stop := len(s)
  1060  	for ; stop > start; stop-- {
  1061  		c := s[stop-1]
  1062  		if c >= utf8.RuneSelf {
  1063  			return TrimFunc(s[start:stop], unicode.IsSpace)
  1064  		}
  1065  		if asciiSpace[c] == 0 {
  1066  			break
  1067  		}
  1068  	}
  1069  
  1070  	// At this point s[start:stop] starts and ends with an ASCII
  1071  	// non-space bytes, so we're done. Non-ASCII cases have already
  1072  	// been handled above.
  1073  	if start == stop {
  1074  		// Special case to preserve previous TrimLeftFunc behavior,
  1075  		// returning nil instead of empty slice if all spaces.
  1076  		return nil
  1077  	}
  1078  	return s[start:stop]
  1079  }
  1080  
  1081  // Runes interprets s as a sequence of UTF-8-encoded code points.
  1082  // It returns a slice of runes (Unicode code points) equivalent to s.
  1083  func Runes(s []byte) []rune {
  1084  	t := make([]rune, utf8.RuneCount(s))
  1085  	i := 0
  1086  	for len(s) > 0 {
  1087  		r, l := utf8.DecodeRune(s)
  1088  		t[i] = r
  1089  		i++
  1090  		s = s[l:]
  1091  	}
  1092  	return t
  1093  }
  1094  
  1095  // Replace returns a copy of the slice s with the first n
  1096  // non-overlapping instances of old replaced by new.
  1097  // If old is empty, it matches at the beginning of the slice
  1098  // and after each UTF-8 sequence, yielding up to k+1 replacements
  1099  // for a k-rune slice.
  1100  // If n < 0, there is no limit on the number of replacements.
  1101  func Replace(s, old, new []byte, n int) []byte {
  1102  	m := 0
  1103  	if n != 0 {
  1104  		// Compute number of replacements.
  1105  		m = Count(s, old)
  1106  	}
  1107  	if m == 0 {
  1108  		// Just return a copy.
  1109  		return append([]byte(nil), s...)
  1110  	}
  1111  	if n < 0 || m < n {
  1112  		n = m
  1113  	}
  1114  
  1115  	// Apply replacements to buffer.
  1116  	t := make([]byte, len(s)+n*(len(new)-len(old)))
  1117  	w := 0
  1118  	start := 0
  1119  	for i := 0; i < n; i++ {
  1120  		j := start
  1121  		if len(old) == 0 {
  1122  			if i > 0 {
  1123  				_, wid := utf8.DecodeRune(s[start:])
  1124  				j += wid
  1125  			}
  1126  		} else {
  1127  			j += Index(s[start:], old)
  1128  		}
  1129  		w += copy(t[w:], s[start:j])
  1130  		w += copy(t[w:], new)
  1131  		start = j + len(old)
  1132  	}
  1133  	w += copy(t[w:], s[start:])
  1134  	return t[0:w]
  1135  }
  1136  
  1137  // ReplaceAll returns a copy of the slice s with all
  1138  // non-overlapping instances of old replaced by new.
  1139  // If old is empty, it matches at the beginning of the slice
  1140  // and after each UTF-8 sequence, yielding up to k+1 replacements
  1141  // for a k-rune slice.
  1142  func ReplaceAll(s, old, new []byte) []byte {
  1143  	return Replace(s, old, new, -1)
  1144  }
  1145  
  1146  // EqualFold reports whether s and t, interpreted as UTF-8 strings,
  1147  // are equal under simple Unicode case-folding, which is a more general
  1148  // form of case-insensitivity.
  1149  func EqualFold(s, t []byte) bool {
  1150  	for len(s) != 0 && len(t) != 0 {
  1151  		// Extract first rune from each.
  1152  		var sr, tr rune
  1153  		if s[0] < utf8.RuneSelf {
  1154  			sr, s = rune(s[0]), s[1:]
  1155  		} else {
  1156  			r, size := utf8.DecodeRune(s)
  1157  			sr, s = r, s[size:]
  1158  		}
  1159  		if t[0] < utf8.RuneSelf {
  1160  			tr, t = rune(t[0]), t[1:]
  1161  		} else {
  1162  			r, size := utf8.DecodeRune(t)
  1163  			tr, t = r, t[size:]
  1164  		}
  1165  
  1166  		// If they match, keep going; if not, return false.
  1167  
  1168  		// Easy case.
  1169  		if tr == sr {
  1170  			continue
  1171  		}
  1172  
  1173  		// Make sr < tr to simplify what follows.
  1174  		if tr < sr {
  1175  			tr, sr = sr, tr
  1176  		}
  1177  		// Fast check for ASCII.
  1178  		if tr < utf8.RuneSelf {
  1179  			// ASCII only, sr/tr must be upper/lower case
  1180  			if 'A' <= sr && sr <= 'Z' && tr == sr+'a'-'A' {
  1181  				continue
  1182  			}
  1183  			return false
  1184  		}
  1185  
  1186  		// General case. SimpleFold(x) returns the next equivalent rune > x
  1187  		// or wraps around to smaller values.
  1188  		r := unicode.SimpleFold(sr)
  1189  		for r != sr && r < tr {
  1190  			r = unicode.SimpleFold(r)
  1191  		}
  1192  		if r == tr {
  1193  			continue
  1194  		}
  1195  		return false
  1196  	}
  1197  
  1198  	// One string is empty. Are both?
  1199  	return len(s) == len(t)
  1200  }
  1201  
  1202  // Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.
  1203  func Index(s, sep []byte) int {
  1204  	n := len(sep)
  1205  	switch {
  1206  	case n == 0:
  1207  		return 0
  1208  	case n == 1:
  1209  		return IndexByte(s, sep[0])
  1210  	case n == len(s):
  1211  		if Equal(sep, s) {
  1212  			return 0
  1213  		}
  1214  		return -1
  1215  	case n > len(s):
  1216  		return -1
  1217  	case n <= bytealg.MaxLen:
  1218  		// Use brute force when s and sep both are small
  1219  		if len(s) <= bytealg.MaxBruteForce {
  1220  			return bytealg.Index(s, sep)
  1221  		}
  1222  		c0 := sep[0]
  1223  		c1 := sep[1]
  1224  		i := 0
  1225  		t := len(s) - n + 1
  1226  		fails := 0
  1227  		for i < t {
  1228  			if s[i] != c0 {
  1229  				// IndexByte is faster than bytealg.Index, so use it as long as
  1230  				// we're not getting lots of false positives.
  1231  				o := IndexByte(s[i+1:t], c0)
  1232  				if o < 0 {
  1233  					return -1
  1234  				}
  1235  				i += o + 1
  1236  			}
  1237  			if s[i+1] == c1 && Equal(s[i:i+n], sep) {
  1238  				return i
  1239  			}
  1240  			fails++
  1241  			i++
  1242  			// Switch to bytealg.Index when IndexByte produces too many false positives.
  1243  			if fails > bytealg.Cutover(i) {
  1244  				r := bytealg.Index(s[i:], sep)
  1245  				if r >= 0 {
  1246  					return r + i
  1247  				}
  1248  				return -1
  1249  			}
  1250  		}
  1251  		return -1
  1252  	}
  1253  	c0 := sep[0]
  1254  	c1 := sep[1]
  1255  	i := 0
  1256  	fails := 0
  1257  	t := len(s) - n + 1
  1258  	for i < t {
  1259  		if s[i] != c0 {
  1260  			o := IndexByte(s[i+1:t], c0)
  1261  			if o < 0 {
  1262  				break
  1263  			}
  1264  			i += o + 1
  1265  		}
  1266  		if s[i+1] == c1 && Equal(s[i:i+n], sep) {
  1267  			return i
  1268  		}
  1269  		i++
  1270  		fails++
  1271  		if fails >= 4+i>>4 && i < t {
  1272  			// Give up on IndexByte, it isn't skipping ahead
  1273  			// far enough to be better than Rabin-Karp.
  1274  			// Experiments (using IndexPeriodic) suggest
  1275  			// the cutover is about 16 byte skips.
  1276  			// TODO: if large prefixes of sep are matching
  1277  			// we should cutover at even larger average skips,
  1278  			// because Equal becomes that much more expensive.
  1279  			// This code does not take that effect into account.
  1280  			j := bytealg.IndexRabinKarpBytes(s[i:], sep)
  1281  			if j < 0 {
  1282  				return -1
  1283  			}
  1284  			return i + j
  1285  		}
  1286  	}
  1287  	return -1
  1288  }
  1289  
  1290  // Cut slices s around the first instance of sep,
  1291  // returning the text before and after sep.
  1292  // The found result reports whether sep appears in s.
  1293  // If sep does not appear in s, cut returns s, nil, false.
  1294  //
  1295  // Cut returns slices of the original slice s, not copies.
  1296  func Cut(s, sep []byte) (before, after []byte, found bool) {
  1297  	if i := Index(s, sep); i >= 0 {
  1298  		return s[:i], s[i+len(sep):], true
  1299  	}
  1300  	return s, nil, false
  1301  }
  1302  

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