bytes package - bytes - Go Packages (original) (raw)

Package bytes implements functions for the manipulation of byte slices. It is analogous to the facilities of the strings package.

MinRead is the minimum slice size passed to a Buffer.Read call byBuffer.ReadFrom. As long as the Buffer has at least MinRead bytes beyond what is required to hold the contents of r, Buffer.ReadFrom will not grow the underlying buffer.

ErrTooLarge is passed to panic if memory cannot be allocated to store data in a buffer.

Clone returns a copy of b[:len(b)]. The result may have additional unused capacity. Clone(nil) returns nil.

package main

import ( "bytes" "fmt" )

func main() { b := []byte("abc") clone := bytes.Clone(b) fmt.Printf("%s\n", clone) clone[0] = 'd' fmt.Printf("%s\n", b) fmt.Printf("%s\n", clone) }

Output:

abc abc dbc

Compare returns an integer comparing two byte slices lexicographically. The result will be 0 if a == b, -1 if a < b, and +1 if a > b. A nil argument is equivalent to an empty slice.

package main

import ( "bytes" )

func main() { // Interpret Compare's result by comparing it to zero. var a, b []byte if bytes.Compare(a, b) < 0 { // a less b } if bytes.Compare(a, b) <= 0 { // a less or equal b } if bytes.Compare(a, b) > 0 { // a greater b } if bytes.Compare(a, b) >= 0 { // a greater or equal b }

// Prefer Equal to Compare for equality comparisons.
if bytes.Equal(a, b) {
    // a equal b
}
if !bytes.Equal(a, b) {
    // a not equal b
}

}

package main

import ( "bytes" "slices" )

func main() { // Binary search to find a matching byte slice. var needle []byte var haystack [][]byte // Assume sorted _, found := slices.BinarySearchFunc(haystack, needle, bytes.Compare) if found { // Found it! } }

Contains reports whether subslice is within b.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.Contains([]byte("seafood"), []byte("foo"))) fmt.Println(bytes.Contains([]byte("seafood"), []byte("bar"))) fmt.Println(bytes.Contains([]byte("seafood"), []byte(""))) fmt.Println(bytes.Contains([]byte(""), []byte(""))) }

Output:

true false true true

ContainsAny reports whether any of the UTF-8-encoded code points in chars are within b.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.ContainsAny([]byte("I like seafood."), "fÄo!")) fmt.Println(bytes.ContainsAny([]byte("I like seafood."), "去是伟大的.")) fmt.Println(bytes.ContainsAny([]byte("I like seafood."), "")) fmt.Println(bytes.ContainsAny([]byte(""), "")) }

Output:

true true false false

ContainsFunc reports whether any of the UTF-8-encoded code points r within b satisfy f(r).

package main

import ( "bytes" "fmt" )

func main() { f := func(r rune) bool { return r >= 'a' && r <= 'z' } fmt.Println(bytes.ContainsFunc([]byte("HELLO"), f)) fmt.Println(bytes.ContainsFunc([]byte("World"), f)) }

Output:

false true

ContainsRune reports whether the rune is contained in the UTF-8-encoded byte slice b.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.ContainsRune([]byte("I like seafood."), 'f')) fmt.Println(bytes.ContainsRune([]byte("I like seafood."), 'ö')) fmt.Println(bytes.ContainsRune([]byte("去是伟大的!"), '大')) fmt.Println(bytes.ContainsRune([]byte("去是伟大的!"), '!')) fmt.Println(bytes.ContainsRune([]byte(""), '@')) }

Output:

true false true true false

Count counts the number of non-overlapping instances of sep in s. If sep is an empty slice, Count returns 1 + the number of UTF-8-encoded code points in s.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.Count([]byte("cheese"), []byte("e"))) fmt.Println(bytes.Count([]byte("five"), []byte(""))) // before & after each rune }

Output:

3 5

Cut slices s around the first instance of sep, returning the text before and after sep. The found result reports whether sep appears in s. If sep does not appear in s, cut returns s, nil, false.

Cut returns slices of the original slice s, not copies.

package main

import ( "bytes" "fmt" )

func main() { show := func(s, sep string) { before, after, found := bytes.Cut([]byte(s), []byte(sep)) fmt.Printf("Cut(%q, %q) = %q, %q, %v\n", s, sep, before, after, found) } show("Gopher", "Go") show("Gopher", "ph") show("Gopher", "er") show("Gopher", "Badger") }

Output:

Cut("Gopher", "Go") = "", "pher", true Cut("Gopher", "ph") = "Go", "er", true Cut("Gopher", "er") = "Goph", "", true Cut("Gopher", "Badger") = "Gopher", "", false

CutPrefix returns s without the provided leading prefix byte slice and reports whether it found the prefix. If s doesn't start with prefix, CutPrefix returns s, false. If prefix is the empty byte slice, CutPrefix returns s, true.

CutPrefix returns slices of the original slice s, not copies.

package main

import ( "bytes" "fmt" )

func main() { show := func(s, prefix string) { after, found := bytes.CutPrefix([]byte(s), []byte(prefix)) fmt.Printf("CutPrefix(%q, %q) = %q, %v\n", s, prefix, after, found) } show("Gopher", "Go") show("Gopher", "ph") }

Output:

CutPrefix("Gopher", "Go") = "pher", true CutPrefix("Gopher", "ph") = "Gopher", false

func CutSuffix(s, suffix []byte) (before []byte, found bool)

CutSuffix returns s without the provided ending suffix byte slice and reports whether it found the suffix. If s doesn't end with suffix, CutSuffix returns s, false. If suffix is the empty byte slice, CutSuffix returns s, true.

CutSuffix returns slices of the original slice s, not copies.

package main

import ( "bytes" "fmt" )

func main() { show := func(s, suffix string) { before, found := bytes.CutSuffix([]byte(s), []byte(suffix)) fmt.Printf("CutSuffix(%q, %q) = %q, %v\n", s, suffix, before, found) } show("Gopher", "Go") show("Gopher", "er") }

Output:

CutSuffix("Gopher", "Go") = "Gopher", false CutSuffix("Gopher", "er") = "Goph", true

Equal reports whether a and b are the same length and contain the same bytes. A nil argument is equivalent to an empty slice.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.Equal([]byte("Go"), []byte("Go"))) fmt.Println(bytes.Equal([]byte("Go"), []byte("C++"))) }

Output:

true false

EqualFold reports whether s and t, interpreted as UTF-8 strings, are equal under simple Unicode case-folding, which is a more general form of case-insensitivity.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.EqualFold([]byte("Go"), []byte("go"))) }

Output:

true

Fields interprets s as a sequence of UTF-8-encoded code points. It splits the slice s around each instance of one or more consecutive white space characters, as defined by unicode.IsSpace, returning a slice of subslices of s or an empty slice if s contains only white space. Every element of the returned slice is non-empty. Unlike Split, leading and trailing runs of white space characters are discarded.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("Fields are: %q", bytes.Fields([]byte(" foo bar baz "))) }

Output:

Fields are: ["foo" "bar" "baz"]

FieldsFunc interprets s as a sequence of UTF-8-encoded code points. It splits the slice s at each run of code points c satisfying f(c) and returns a slice of subslices of s. If all code points in s satisfy f(c), or len(s) == 0, an empty slice is returned. Every element of the returned slice is non-empty. Unlike [SplitFunc], leading and trailing runs of code points satisfying f(c) are discarded.

FieldsFunc makes no guarantees about the order in which it calls f(c) and assumes that f always returns the same value for a given c.

package main

import ( "bytes" "fmt" "unicode" )

func main() { f := func(c rune) bool { return !unicode.IsLetter(c) && !unicode.IsNumber(c) } fmt.Printf("Fields are: %q", bytes.FieldsFunc([]byte(" foo1;bar2,baz3..."), f)) }

Output:

Fields are: ["foo1" "bar2" "baz3"]

FieldsFuncSeq returns an iterator over subslices of s split around runs of Unicode code points satisfying f(c). The iterator yields the same subslices that would be returned by FieldsFunc(s), but without constructing a new slice containing the subslices.

package main

import ( "bytes" "fmt" "unicode" )

func main() { text := []byte("The quick brown fox") fmt.Println("Split on whitespace(similar to FieldsSeq):") for word := range bytes.FieldsFuncSeq(text, unicode.IsSpace) { fmt.Printf("%q\n", word) }

mixedText := []byte("abc123def456ghi")
fmt.Println("\nSplit on digits:")
for word := range bytes.FieldsFuncSeq(mixedText, unicode.IsDigit) {
    fmt.Printf("%q\n", word)
}

}

Output:

Split on whitespace(similar to FieldsSeq): "The" "quick" "brown" "fox"

Split on digits: "abc" "def" "ghi"

FieldsSeq returns an iterator over subslices of s split around runs of whitespace characters, as defined by unicode.IsSpace. The iterator yields the same subslices that would be returned by Fields(s), but without constructing a new slice containing the subslices.

package main

import ( "bytes" "fmt" )

func main() { text := []byte("The quick brown fox") fmt.Println("Split byte slice into fields:") for word := range bytes.FieldsSeq(text) { fmt.Printf("%q\n", word) }

textWithSpaces := []byte("  lots   of   spaces  ")
fmt.Println("\nSplit byte slice with multiple spaces:")
for word := range bytes.FieldsSeq(textWithSpaces) {
    fmt.Printf("%q\n", word)
}

}

Output:

Split byte slice into fields: "The" "quick" "brown" "fox"

Split byte slice with multiple spaces: "lots" "of" "spaces"

HasPrefix reports whether the byte slice s begins with prefix.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.HasPrefix([]byte("Gopher"), []byte("Go"))) fmt.Println(bytes.HasPrefix([]byte("Gopher"), []byte("C"))) fmt.Println(bytes.HasPrefix([]byte("Gopher"), []byte(""))) }

Output:

true false true

HasSuffix reports whether the byte slice s ends with suffix.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.HasSuffix([]byte("Amigo"), []byte("go"))) fmt.Println(bytes.HasSuffix([]byte("Amigo"), []byte("O"))) fmt.Println(bytes.HasSuffix([]byte("Amigo"), []byte("Ami"))) fmt.Println(bytes.HasSuffix([]byte("Amigo"), []byte(""))) }

Output:

true false false true

Index returns the index of the first instance of sep in s, or -1 if sep is not present in s.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.Index([]byte("chicken"), []byte("ken"))) fmt.Println(bytes.Index([]byte("chicken"), []byte("dmr"))) }

Output:

4 -1

IndexAny interprets s as a sequence of UTF-8-encoded Unicode code points. It returns the byte index of the first occurrence in s of any of the Unicode code points in chars. It returns -1 if chars is empty or if there is no code point in common.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.IndexAny([]byte("chicken"), "aeiouy")) fmt.Println(bytes.IndexAny([]byte("crwth"), "aeiouy")) }

Output:

2 -1

IndexByte returns the index of the first instance of c in b, or -1 if c is not present in b.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.IndexByte([]byte("chicken"), byte('k'))) fmt.Println(bytes.IndexByte([]byte("chicken"), byte('g'))) }

Output:

4 -1

IndexFunc interprets s as a sequence of UTF-8-encoded code points. It returns the byte index in s of the first Unicode code point satisfying f(c), or -1 if none do.

package main

import ( "bytes" "fmt" "unicode" )

func main() { f := func(c rune) bool { return unicode.Is(unicode.Han, c) } fmt.Println(bytes.IndexFunc([]byte("Hello, 世界"), f)) fmt.Println(bytes.IndexFunc([]byte("Hello, world"), f)) }

Output:

7 -1

IndexRune interprets s as a sequence of UTF-8-encoded code points. It returns the byte index of the first occurrence in s of the given rune. It returns -1 if rune is not present in s. If r is utf8.RuneError, it returns the first instance of any invalid UTF-8 byte sequence.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.IndexRune([]byte("chicken"), 'k')) fmt.Println(bytes.IndexRune([]byte("chicken"), 'd')) }

Output:

4 -1

Join concatenates the elements of s to create a new byte slice. The separator sep is placed between elements in the resulting slice.

package main

import ( "bytes" "fmt" )

func main() { s := [][]byte{[]byte("foo"), []byte("bar"), []byte("baz")} fmt.Printf("%s", bytes.Join(s, []byte(", "))) }

Output:

foo, bar, baz

LastIndex returns the index of the last instance of sep in s, or -1 if sep is not present in s.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.Index([]byte("go gopher"), []byte("go"))) fmt.Println(bytes.LastIndex([]byte("go gopher"), []byte("go"))) fmt.Println(bytes.LastIndex([]byte("go gopher"), []byte("rodent"))) }

Output:

0 3 -1

LastIndexAny interprets s as a sequence of UTF-8-encoded Unicode code points. It returns the byte index of the last occurrence in s of any of the Unicode code points in chars. It returns -1 if chars is empty or if there is no code point in common.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.LastIndexAny([]byte("go gopher"), "MüQp")) fmt.Println(bytes.LastIndexAny([]byte("go 地鼠"), "地大")) fmt.Println(bytes.LastIndexAny([]byte("go gopher"), "z,!.")) }

Output:

5 3 -1

LastIndexByte returns the index of the last instance of c in s, or -1 if c is not present in s.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.LastIndexByte([]byte("go gopher"), byte('g'))) fmt.Println(bytes.LastIndexByte([]byte("go gopher"), byte('r'))) fmt.Println(bytes.LastIndexByte([]byte("go gopher"), byte('z'))) }

Output:

3 8 -1

LastIndexFunc interprets s as a sequence of UTF-8-encoded code points. It returns the byte index in s of the last Unicode code point satisfying f(c), or -1 if none do.

package main

import ( "bytes" "fmt" "unicode" )

func main() { fmt.Println(bytes.LastIndexFunc([]byte("go gopher!"), unicode.IsLetter)) fmt.Println(bytes.LastIndexFunc([]byte("go gopher!"), unicode.IsPunct)) fmt.Println(bytes.LastIndexFunc([]byte("go gopher!"), unicode.IsNumber)) }

Output:

8 9 -1

Lines returns an iterator over the newline-terminated lines in the byte slice s. The lines yielded by the iterator include their terminating newlines. If s is empty, the iterator yields no lines at all. If s does not end in a newline, the final yielded line will not end in a newline. It returns a single-use iterator.

package main

import ( "bytes" "fmt" )

func main() { text := []byte("Hello\nWorld\nGo Programming\n") for line := range bytes.Lines(text) { fmt.Printf("%q\n", line) }

}

Output:

"Hello\n" "World\n" "Go Programming\n"

Map returns a copy of the byte slice s with all its characters modified according to the mapping function. If mapping returns a negative value, the character is dropped from the byte slice with no replacement. The characters in s and the output are interpreted as UTF-8-encoded code points.

package main

import ( "bytes" "fmt" )

func main() { rot13 := func(r rune) rune { switch { case r >= 'A' && r <= 'Z': return 'A' + (r-'A'+13)%26 case r >= 'a' && r <= 'z': return 'a' + (r-'a'+13)%26 } return r } fmt.Printf("%s\n", bytes.Map(rot13, []byte("'Twas brillig and the slithy gopher..."))) }

Output:

'Gjnf oevyyvt naq gur fyvgul tbcure...

Repeat returns a new byte slice consisting of count copies of b.

It panics if count is negative or if the result of (len(b) * count) overflows.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("ba%s", bytes.Repeat([]byte("na"), 2)) }

Output:

banana

Replace returns a copy of the slice s with the first n non-overlapping instances of old replaced by new. If old is empty, it matches at the beginning of the slice and after each UTF-8 sequence, yielding up to k+1 replacements for a k-rune slice. If n < 0, there is no limit on the number of replacements.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("%s\n", bytes.Replace([]byte("oink oink oink"), []byte("k"), []byte("ky"), 2)) fmt.Printf("%s\n", bytes.Replace([]byte("oink oink oink"), []byte("oink"), []byte("moo"), -1)) }

Output:

oinky oinky oink moo moo moo

func ReplaceAll(s, old, new []byte) []byte

ReplaceAll returns a copy of the slice s with all non-overlapping instances of old replaced by new. If old is empty, it matches at the beginning of the slice and after each UTF-8 sequence, yielding up to k+1 replacements for a k-rune slice.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("%s\n", bytes.ReplaceAll([]byte("oink oink oink"), []byte("oink"), []byte("moo"))) }

Output:

moo moo moo

Runes interprets s as a sequence of UTF-8-encoded code points. It returns a slice of runes (Unicode code points) equivalent to s.

package main

import ( "bytes" "fmt" )

func main() { rs := bytes.Runes([]byte("go gopher")) for _, r := range rs { fmt.Printf("%#U\n", r) } }

Output:

U+0067 'g' U+006F 'o' U+0020 ' ' U+0067 'g' U+006F 'o' U+0070 'p' U+0068 'h' U+0065 'e' U+0072 'r'

Split slices s into all subslices separated by sep and returns a slice of the subslices between those separators. If sep is empty, Split splits after each UTF-8 sequence. It is equivalent to SplitN with a count of -1.

To split around the first instance of a separator, see Cut.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("%q\n", bytes.Split([]byte("a,b,c"), []byte(","))) fmt.Printf("%q\n", bytes.Split([]byte("a man a plan a canal panama"), []byte("a "))) fmt.Printf("%q\n", bytes.Split([]byte(" xyz "), []byte(""))) fmt.Printf("%q\n", bytes.Split([]byte(""), []byte("Bernardo O'Higgins"))) }

Output:

["a" "b" "c"] ["" "man " "plan " "canal panama"] [" " "x" "y" "z" " "] [""]

SplitAfter slices s into all subslices after each instance of sep and returns a slice of those subslices. If sep is empty, SplitAfter splits after each UTF-8 sequence. It is equivalent to SplitAfterN with a count of -1.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("%q\n", bytes.SplitAfter([]byte("a,b,c"), []byte(","))) }

Output:

["a," "b," "c"]

SplitAfterN slices s into subslices after each instance of sep and returns a slice of those subslices. If sep is empty, SplitAfterN splits after each UTF-8 sequence. The count determines the number of subslices to return:

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("%q\n", bytes.SplitAfterN([]byte("a,b,c"), []byte(","), 2)) }

Output:

["a," "b,c"]

SplitAfterSeq returns an iterator over subslices of s split after each instance of sep. The iterator yields the same subslices that would be returned by SplitAfter(s, sep), but without constructing a new slice containing the subslices. It returns a single-use iterator.

package main

import ( "bytes" "fmt" )

func main() { s := []byte("a,b,c,d") for part := range bytes.SplitAfterSeq(s, []byte(",")) { fmt.Printf("%q\n", part) }

}

Output:

"a," "b," "c," "d"

SplitN slices s into subslices separated by sep and returns a slice of the subslices between those separators. If sep is empty, SplitN splits after each UTF-8 sequence. The count determines the number of subslices to return:

To split around the first instance of a separator, see Cut.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("%q\n", bytes.SplitN([]byte("a,b,c"), []byte(","), 2)) z := bytes.SplitN([]byte("a,b,c"), []byte(","), 0) fmt.Printf("%q (nil = %v)\n", z, z == nil) }

Output:

["a" "b,c"] [] (nil = true)

SplitSeq returns an iterator over all subslices of s separated by sep. The iterator yields the same subslices that would be returned by Split(s, sep), but without constructing a new slice containing the subslices. It returns a single-use iterator.

package main

import ( "bytes" "fmt" )

func main() { s := []byte("a,b,c,d") for part := range bytes.SplitSeq(s, []byte(",")) { fmt.Printf("%q\n", part) }

}

Output:

"a" "b" "c" "d"

Title treats s as UTF-8-encoded bytes and returns a copy with all Unicode letters that begin words mapped to their title case.

Deprecated: The rule Title uses for word boundaries does not handle Unicode punctuation properly. Use golang.org/x/text/cases instead.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("%s", bytes.Title([]byte("her royal highness"))) }

Output:

Her Royal Highness

ToLower returns a copy of the byte slice s with all Unicode letters mapped to their lower case.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("%s", bytes.ToLower([]byte("Gopher"))) }

Output:

gopher

ToLowerSpecial treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their lower case, giving priority to the special casing rules.

package main

import ( "bytes" "fmt" "unicode" )

func main() { str := []byte("AHOJ VÝVOJÁRİ GOLANG") totitle := bytes.ToLowerSpecial(unicode.AzeriCase, str) fmt.Println("Original : " + string(str)) fmt.Println("ToLower : " + string(totitle)) }

Output:

Original : AHOJ VÝVOJÁRİ GOLANG ToLower : ahoj vývojári golang

ToTitle treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their title case.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("%s\n", bytes.ToTitle([]byte("loud noises"))) fmt.Printf("%s\n", bytes.ToTitle([]byte("брат"))) }

Output:

LOUD NOISES БРАТ

ToTitleSpecial treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their title case, giving priority to the special casing rules.

package main

import ( "bytes" "fmt" "unicode" )

func main() { str := []byte("ahoj vývojári golang") totitle := bytes.ToTitleSpecial(unicode.AzeriCase, str) fmt.Println("Original : " + string(str)) fmt.Println("ToTitle : " + string(totitle)) }

Output:

Original : ahoj vývojári golang ToTitle : AHOJ VÝVOJÁRİ GOLANG

ToUpper returns a copy of the byte slice s with all Unicode letters mapped to their upper case.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("%s", bytes.ToUpper([]byte("Gopher"))) }

Output:

GOPHER

ToUpperSpecial treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters mapped to their upper case, giving priority to the special casing rules.

package main

import ( "bytes" "fmt" "unicode" )

func main() { str := []byte("ahoj vývojári golang") totitle := bytes.ToUpperSpecial(unicode.AzeriCase, str) fmt.Println("Original : " + string(str)) fmt.Println("ToUpper : " + string(totitle)) }

Output:

Original : ahoj vývojári golang ToUpper : AHOJ VÝVOJÁRİ GOLANG

func ToValidUTF8(s, replacement []byte) []byte

ToValidUTF8 treats s as UTF-8-encoded bytes and returns a copy with each run of bytes representing invalid UTF-8 replaced with the bytes in replacement, which may be empty.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("%s\n", bytes.ToValidUTF8([]byte("abc"), []byte("\uFFFD"))) fmt.Printf("%s\n", bytes.ToValidUTF8([]byte("a\xffb\xC0\xAFc\xff"), []byte(""))) fmt.Printf("%s\n", bytes.ToValidUTF8([]byte("\xed\xa0\x80"), []byte("abc"))) }

Output:

abc abc abc

Trim returns a subslice of s by slicing off all leading and trailing UTF-8-encoded code points contained in cutset.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("[%q]", bytes.Trim([]byte(" !!! Achtung! Achtung! !!! "), "! ")) }

Output:

["Achtung! Achtung"]

TrimFunc returns a subslice of s by slicing off all leading and trailing UTF-8-encoded code points c that satisfy f(c).

package main

import ( "bytes" "fmt" "unicode" )

func main() { fmt.Println(string(bytes.TrimFunc([]byte("go-gopher!"), unicode.IsLetter))) fmt.Println(string(bytes.TrimFunc([]byte(""go-gopher!""), unicode.IsLetter))) fmt.Println(string(bytes.TrimFunc([]byte("go-gopher!"), unicode.IsPunct))) fmt.Println(string(bytes.TrimFunc([]byte("1234go-gopher!567"), unicode.IsNumber))) }

Output:

-gopher! "go-gopher!" go-gopher go-gopher!

TrimLeft returns a subslice of s by slicing off all leading UTF-8-encoded code points contained in cutset.

package main

import ( "bytes" "fmt" )

func main() { fmt.Print(string(bytes.TrimLeft([]byte("453gopher8257"), "0123456789"))) }

Output:

gopher8257

TrimLeftFunc treats s as UTF-8-encoded bytes and returns a subslice of s by slicing off all leading UTF-8-encoded code points c that satisfy f(c).

package main

import ( "bytes" "fmt" "unicode" )

func main() { fmt.Println(string(bytes.TrimLeftFunc([]byte("go-gopher"), unicode.IsLetter))) fmt.Println(string(bytes.TrimLeftFunc([]byte("go-gopher!"), unicode.IsPunct))) fmt.Println(string(bytes.TrimLeftFunc([]byte("1234go-gopher!567"), unicode.IsNumber))) }

Output:

-gopher go-gopher! go-gopher!567

func TrimPrefix(s, prefix []byte) []byte

TrimPrefix returns s without the provided leading prefix string. If s doesn't start with prefix, s is returned unchanged.

package main

import ( "bytes" "fmt" )

func main() { var b = []byte("Goodbye,, world!") b = bytes.TrimPrefix(b, []byte("Goodbye,")) b = bytes.TrimPrefix(b, []byte("See ya,")) fmt.Printf("Hello%s", b) }

Output:

Hello, world!

TrimRight returns a subslice of s by slicing off all trailing UTF-8-encoded code points that are contained in cutset.

package main

import ( "bytes" "fmt" )

func main() { fmt.Print(string(bytes.TrimRight([]byte("453gopher8257"), "0123456789"))) }

Output:

453gopher

TrimRightFunc returns a subslice of s by slicing off all trailing UTF-8-encoded code points c that satisfy f(c).

package main

import ( "bytes" "fmt" "unicode" )

func main() { fmt.Println(string(bytes.TrimRightFunc([]byte("go-gopher"), unicode.IsLetter))) fmt.Println(string(bytes.TrimRightFunc([]byte("go-gopher!"), unicode.IsPunct))) fmt.Println(string(bytes.TrimRightFunc([]byte("1234go-gopher!567"), unicode.IsNumber))) }

Output:

go- go-gopher 1234go-gopher!

TrimSpace returns a subslice of s by slicing off all leading and trailing white space, as defined by Unicode.

package main

import ( "bytes" "fmt" )

func main() { fmt.Printf("%s", bytes.TrimSpace([]byte(" \t\n a lone gopher \n\t\r\n"))) }

Output:

a lone gopher

func TrimSuffix(s, suffix []byte) []byte

TrimSuffix returns s without the provided trailing suffix string. If s doesn't end with suffix, s is returned unchanged.

package main

import ( "bytes" "os" )

func main() { var b = []byte("Hello, goodbye, etc!") b = bytes.TrimSuffix(b, []byte("goodbye, etc!")) b = bytes.TrimSuffix(b, []byte("gopher")) b = append(b, bytes.TrimSuffix([]byte("world!"), []byte("x!"))...) os.Stdout.Write(b) }

Output:

Hello, world!

A Buffer is a variable-sized buffer of bytes with Buffer.Read and Buffer.Write methods. The zero value for Buffer is an empty buffer ready to use.

package main

import ( "bytes" "fmt" "os" )

func main() { var b bytes.Buffer // A Buffer needs no initialization. b.Write([]byte("Hello ")) fmt.Fprintf(&b, "world!") b.WriteTo(os.Stdout) }

Output:

Hello world!

package main

import ( "bytes" "encoding/base64" "io" "os" )

func main() { // A Buffer can turn a string or a []byte into an io.Reader. buf := bytes.NewBufferString("R29waGVycyBydWxlIQ==") dec := base64.NewDecoder(base64.StdEncoding, buf) io.Copy(os.Stdout, dec) }

Output:

Gophers rule!

func NewBuffer(buf []byte) *Buffer

NewBuffer creates and initializes a new Buffer using buf as its initial contents. The new Buffer takes ownership of buf, and the caller should not use buf after this call. NewBuffer is intended to prepare a Buffer to read existing data. It can also be used to set the initial size of the internal buffer for writing. To do that, buf should have the desired capacity but a length of zero.

In most cases, new(Buffer) (or just declaring a Buffer variable) is sufficient to initialize a Buffer.

NewBufferString creates and initializes a new Buffer using string s as its initial contents. It is intended to prepare a buffer to read an existing string.

In most cases, new(Buffer) (or just declaring a Buffer variable) is sufficient to initialize a Buffer.

func (b *Buffer) Available() int

Available returns how many bytes are unused in the buffer.

func (b *Buffer) AvailableBuffer() []byte

AvailableBuffer returns an empty buffer with b.Available() capacity. This buffer is intended to be appended to and passed to an immediately succeeding Buffer.Write call. The buffer is only valid until the next write operation on b.

package main

import ( "bytes" "os" "strconv" )

func main() { var buf bytes.Buffer for i := 0; i < 4; i++ { b := buf.AvailableBuffer() b = strconv.AppendInt(b, int64(i), 10) b = append(b, ' ') buf.Write(b) } os.Stdout.Write(buf.Bytes()) }

Output:

0 1 2 3

func (b *Buffer) Bytes() []byte

Bytes returns a slice of length b.Len() holding the unread portion of the buffer. The slice is valid for use only until the next buffer modification (that is, only until the next call to a method like Buffer.Read, Buffer.Write, Buffer.Reset, or Buffer.Truncate). The slice aliases the buffer content at least until the next buffer modification, so immediate changes to the slice will affect the result of future reads.

package main

import ( "bytes" "os" )

func main() { buf := bytes.Buffer{} buf.Write([]byte{'h', 'e', 'l', 'l', 'o', ' ', 'w', 'o', 'r', 'l', 'd'}) os.Stdout.Write(buf.Bytes()) }

Output:

hello world

func (b *Buffer) Cap() int

Cap returns the capacity of the buffer's underlying byte slice, that is, the total space allocated for the buffer's data.

package main

import ( "bytes" "fmt" )

func main() { buf1 := bytes.NewBuffer(make([]byte, 10)) buf2 := bytes.NewBuffer(make([]byte, 0, 10)) fmt.Println(buf1.Cap()) fmt.Println(buf2.Cap()) }

Output:

10 10

func (b *Buffer) Grow(n int)

Grow grows the buffer's capacity, if necessary, to guarantee space for another n bytes. After Grow(n), at least n bytes can be written to the buffer without another allocation. If n is negative, Grow will panic. If the buffer can't grow it will panic with ErrTooLarge.

package main

import ( "bytes" "fmt" )

func main() { var b bytes.Buffer b.Grow(64) bb := b.Bytes() b.Write([]byte("64 bytes or fewer")) fmt.Printf("%q", bb[:b.Len()]) }

Output:

"64 bytes or fewer"

func (b *Buffer) Len() int

Len returns the number of bytes of the unread portion of the buffer; b.Len() == len(b.Bytes()).

package main

import ( "bytes" "fmt" )

func main() { var b bytes.Buffer b.Grow(64) b.Write([]byte("abcde")) fmt.Printf("%d", b.Len()) }

Output:

5

Next returns a slice containing the next n bytes from the buffer, advancing the buffer as if the bytes had been returned by Buffer.Read. If there are fewer than n bytes in the buffer, Next returns the entire buffer. The slice is only valid until the next call to a read or write method.

package main

import ( "bytes" "fmt" )

func main() { var b bytes.Buffer b.Grow(64) b.Write([]byte("abcde")) fmt.Printf("%s\n", b.Next(2)) fmt.Printf("%s\n", b.Next(2)) fmt.Printf("%s", b.Next(2)) }

Output:

ab cd e

Read reads the next len(p) bytes from the buffer or until the buffer is drained. The return value n is the number of bytes read. If the buffer has no data to return, err is io.EOF (unless len(p) is zero); otherwise it is nil.

package main

import ( "bytes" "fmt" )

func main() { var b bytes.Buffer b.Grow(64) b.Write([]byte("abcde")) rdbuf := make([]byte, 1) n, err := b.Read(rdbuf) if err != nil { panic(err) } fmt.Println(n) fmt.Println(b.String()) fmt.Println(string(rdbuf)) }

Output:

1 bcde a

ReadByte reads and returns the next byte from the buffer. If no byte is available, it returns error io.EOF.

package main

import ( "bytes" "fmt" )

func main() { var b bytes.Buffer b.Grow(64) b.Write([]byte("abcde")) c, err := b.ReadByte() if err != nil { panic(err) } fmt.Println(c) fmt.Println(b.String()) }

Output:

97 bcde

ReadBytes reads until the first occurrence of delim in the input, returning a slice containing the data up to and including the delimiter. If ReadBytes encounters an error before finding a delimiter, it returns the data read before the error and the error itself (often io.EOF). ReadBytes returns err != nil if and only if the returned data does not end in delim.

ReadFrom reads data from r until EOF and appends it to the buffer, growing the buffer as needed. The return value n is the number of bytes read. Any error except io.EOF encountered during the read is also returned. If the buffer becomes too large, ReadFrom will panic with ErrTooLarge.

ReadRune reads and returns the next UTF-8-encoded Unicode code point from the buffer. If no bytes are available, the error returned is io.EOF. If the bytes are an erroneous UTF-8 encoding, it consumes one byte and returns U+FFFD, 1.

ReadString reads until the first occurrence of delim in the input, returning a string containing the data up to and including the delimiter. If ReadString encounters an error before finding a delimiter, it returns the data read before the error and the error itself (often io.EOF). ReadString returns err != nil if and only if the returned data does not end in delim.

Reset resets the buffer to be empty, but it retains the underlying storage for use by future writes. Reset is the same as Buffer.Truncate(0).

String returns the contents of the unread portion of the buffer as a string. If the Buffer is a nil pointer, it returns "".

To build strings more efficiently, see the strings.Builder type.

func (b *Buffer) Truncate(n int)

Truncate discards all but the first n unread bytes from the buffer but continues to use the same allocated storage. It panics if n is negative or greater than the length of the buffer.

func (b *Buffer) UnreadByte() error

UnreadByte unreads the last byte returned by the most recent successful read operation that read at least one byte. If a write has happened since the last read, if the last read returned an error, or if the read read zero bytes, UnreadByte returns an error.

func (b *Buffer) UnreadRune() error

UnreadRune unreads the last rune returned by Buffer.ReadRune. If the most recent read or write operation on the buffer was not a successful Buffer.ReadRune, UnreadRune returns an error. (In this regard it is stricter than Buffer.UnreadByte, which will unread the last byte from any read operation.)

Write appends the contents of p to the buffer, growing the buffer as needed. The return value n is the length of p; err is always nil. If the buffer becomes too large, Write will panic with ErrTooLarge.

WriteByte appends the byte c to the buffer, growing the buffer as needed. The returned error is always nil, but is included to match bufio.Writer's WriteByte. If the buffer becomes too large, WriteByte will panic withErrTooLarge.

WriteRune appends the UTF-8 encoding of Unicode code point r to the buffer, returning its length and an error, which is always nil but is included to match bufio.Writer's WriteRune. The buffer is grown as needed; if it becomes too large, WriteRune will panic with ErrTooLarge.

WriteString appends the contents of s to the buffer, growing the buffer as needed. The return value n is the length of s; err is always nil. If the buffer becomes too large, WriteString will panic with ErrTooLarge.

WriteTo writes data to w until the buffer is drained or an error occurs. The return value n is the number of bytes written; it always fits into an int, but it is int64 to match the io.WriterTo interface. Any error encountered during the write is also returned.

A Reader implements the io.Reader, io.ReaderAt, io.WriterTo, io.Seeker,io.ByteScanner, and io.RuneScanner interfaces by reading from a byte slice. Unlike a Buffer, a Reader is read-only and supports seeking. The zero value for Reader operates like a Reader of an empty slice.

func NewReader(b []byte) *Reader

NewReader returns a new Reader reading from b.

func (r *Reader) Len() int

Len returns the number of bytes of the unread portion of the slice.

package main

import ( "bytes" "fmt" )

func main() { fmt.Println(bytes.NewReader([]byte("Hi!")).Len()) fmt.Println(bytes.NewReader([]byte("こんにちは!")).Len()) }

Output:

3 16

func (r *Reader) Reset(b []byte)

Reset resets the Reader to be reading from b.

Size returns the original length of the underlying byte slice. Size is the number of bytes available for reading via Reader.ReadAt. The result is unaffected by any method calls except Reader.Reset.