Package bytes

MinRead is the minimum slice size passed to a Buffer.Read call by Buffer.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.

const MinRead = 512

Variables

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

var ErrTooLarge = errors.New("bytes.Buffer: too large")

func Clone 1.20

func Clone(b []byte) []byte

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

▸ Example

▾ Example

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)
}

abc
abc
dbc

func Compare

func Compare(a, b []byte) int

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.

▸ Example

▾ Example

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
	}
}

▸ Example (Search)

▾ Example (Search)

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!
	}
}

func Contains

func Contains(b, subslice []byte) bool

Contains reports whether subslice is within b.

▸ Example

▾ Example

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("")))
}

true
false
true
true

func ContainsAny 1.7

func ContainsAny(b []byte, chars string) bool

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

▸ Example

▾ Example

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(""), ""))
}

true
true
false
false

func ContainsFunc 1.21

func ContainsFunc(b []byte, f func(rune) bool) bool

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

▸ Example

▾ Example

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))
}

false
true

func ContainsRune 1.7

func ContainsRune(b []byte, r rune) bool

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

▸ Example

▾ Example

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(""), '@'))
}

true
false
true
true
false

func Count

func Count(s, sep []byte) int

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.

▸ Example

▾ Example

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
}

3
5

func Cut 1.18

func Cut(s, sep []byte) (before, after []byte, found bool)

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.

▸ Example

▾ Example

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")
}

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

func CutPrefix 1.20

func CutPrefix(s, prefix []byte) (after []byte, found bool)

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.

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

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

func CutSuffix 1.20

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.

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

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

func Equal

func Equal(a, b []byte) bool

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

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

true
false

func EqualFold

func EqualFold(s, t []byte) bool

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.

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

true

func Fields

func Fields(s []byte) [][]byte

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.

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

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

func FieldsFunc

func FieldsFunc(s []byte, f func(rune) bool) [][]byte

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.

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.

▸ Example

▾ Example

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))
}

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

func FieldsFuncSeq 1.24

func FieldsFuncSeq(s []byte, f func(rune) bool) iter.Seq[[]byte]

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.

func FieldsSeq 1.24

func FieldsSeq(s []byte) iter.Seq[[]byte]

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.

func HasPrefix

func HasPrefix(s, prefix []byte) bool

HasPrefix reports whether the byte slice s begins with prefix.

▸ Example

▾ Example

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("")))
}

true
false
true

func HasSuffix

func HasSuffix(s, suffix []byte) bool

HasSuffix reports whether the byte slice s ends with suffix.

▸ Example

▾ Example

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("")))
}

true
false
false
true

func Index

func Index(s, sep []byte) int

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

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

4
-1

func IndexAny

func IndexAny(s []byte, chars string) int

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.

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

2
-1

func IndexByte

func IndexByte(b []byte, c byte) int

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

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

4
-1

func IndexFunc

func IndexFunc(s []byte, f func(r rune) bool) int

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.

▸ Example

▾ Example

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))
}

7
-1

func IndexRune

func IndexRune(s []byte, r rune) int

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.

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

4
-1

func Join

func Join(s [][]byte, sep []byte) []byte

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

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

foo, bar, baz

func LastIndex

func LastIndex(s, sep []byte) int

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

▸ Example

▾ Example

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")))
}

0
3
-1

func LastIndexAny

func LastIndexAny(s []byte, chars string) int

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.

▸ Example

▾ Example

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,!."))
}

5
3
-1

func LastIndexByte 1.5

func LastIndexByte(s []byte, c byte) int

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

▸ Example

▾ Example

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')))
}

3
8
-1

func LastIndexFunc

func LastIndexFunc(s []byte, f func(r rune) bool) int

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.

▸ Example

▾ Example

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))
}

8
9
-1

func Lines 1.24

func Lines(s []byte) iter.Seq[[]byte]

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.

func Map

func Map(mapping func(r rune) rune, s []byte) []byte

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.

▸ Example

▾ Example

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...")))
}

'Gjnf oevyyvt naq gur fyvgul tbcure...

func Repeat

func Repeat(b []byte, count int) []byte

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.

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

banana

func Replace

func Replace(s, old, new []byte, n int) []byte

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.

▸ Example

▾ Example

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))
}

oinky oinky oink
moo moo moo

func ReplaceAll 1.12

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.

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

moo moo moo

func Runes

func Runes(s []byte) []rune

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

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

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'

func Split

func Split(s, sep []byte) [][]byte

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.

▸ Example

▾ Example

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")))
}

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

func SplitAfter

func SplitAfter(s, sep []byte) [][]byte

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.

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

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

func SplitAfterN

func SplitAfterN(s, sep []byte, n int) [][]byte

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:

n > 0: at most n subslices; the last subslice will be the unsplit remainder;
n == 0: the result is nil (zero subslices);
n < 0: all subslices.

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

["a," "b,c"]

func SplitAfterSeq 1.24

func SplitAfterSeq(s, sep []byte) iter.Seq[[]byte]

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.

func SplitN

func SplitN(s, sep []byte, n int) [][]byte

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:

n > 0: at most n subslices; the last subslice will be the unsplit remainder;
n == 0: the result is nil (zero subslices);
n < 0: all subslices.

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

▸ Example

▾ Example

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)
}

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

func SplitSeq 1.24

func SplitSeq(s, sep []byte) iter.Seq[[]byte]

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.

func Title

func Title(s []byte) []byte

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.

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

Her Royal Highness

func ToLower

func ToLower(s []byte) []byte

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

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

gopher

func ToLowerSpecial

func ToLowerSpecial(c unicode.SpecialCase, s []byte) []byte

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.

▸ Example

▾ Example

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))
}

Original : AHOJ VÝVOJÁRİ GOLANG
ToLower : ahoj vývojári golang

func ToTitle

func ToTitle(s []byte) []byte

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

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

LOUD NOISES
БРАТ

func ToTitleSpecial

func ToTitleSpecial(c unicode.SpecialCase, s []byte) []byte

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.

▸ Example

▾ Example

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))
}

Original : ahoj vývojári golang
ToTitle : AHOJ VÝVOJÁRİ GOLANG

func ToUpper

func ToUpper(s []byte) []byte

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

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

GOPHER

func ToUpperSpecial

func ToUpperSpecial(c unicode.SpecialCase, s []byte) []byte

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.

▸ Example

▾ Example

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))
}

Original : ahoj vývojári golang
ToUpper : AHOJ VÝVOJÁRİ GOLANG

func ToValidUTF8 1.13

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.

▸ Example

▾ Example

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")))
}

abc
abc
abc

func Trim

func Trim(s []byte, cutset string) []byte

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

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

["Achtung! Achtung"]

func TrimFunc

func TrimFunc(s []byte, f func(r rune) bool) []byte

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

▸ Example

▾ Example

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)))
}

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

func TrimLeft

func TrimLeft(s []byte, cutset string) []byte

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

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

gopher8257

func TrimLeftFunc

func TrimLeftFunc(s []byte, f func(r rune) bool) []byte

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).

▸ Example

▾ Example

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)))
}

-gopher
go-gopher!
go-gopher!567

func TrimPrefix 1.1

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.

▸ Example

▾ Example

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)
}

Hello, world!

func TrimRight

func TrimRight(s []byte, cutset string) []byte

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

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

453gopher

func TrimRightFunc

func TrimRightFunc(s []byte, f func(r rune) bool) []byte

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

▸ Example

▾ Example

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)))
}

go-
go-gopher
1234go-gopher!

func TrimSpace

func TrimSpace(s []byte) []byte

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

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

a lone gopher

func TrimSuffix 1.1

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.

▸ Example

▾ Example

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)
}

Hello, world!

type Buffer

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.

type Buffer struct {
    // contains filtered or unexported fields
}

▸ Example

▾ Example

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)
}

Hello world!

▸ Example (Reader)

▾ Example (Reader)

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)
}

Gophers rule!

func NewBuffer

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.

func NewBufferString

func NewBufferString(s string) *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 (*Buffer) Available 1.21

func (b *Buffer) Available() int

Available returns how many bytes are unused in the buffer.

func (*Buffer) AvailableBuffer 1.21

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.

▸ Example

▾ Example

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())
}

0 1 2 3

func (*Buffer) Bytes

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.

▸ Example

▾ Example

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())
}

hello world

func (*Buffer) Cap 1.5

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.

▸ Example

▾ Example

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())
}

10
10

func (*Buffer) Grow 1.1

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.

▸ Example

▾ Example

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()])
}

"64 bytes or fewer"

func (*Buffer) Len

func (b *Buffer) Len() int

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

▸ Example

▾ Example

package main

import (
	"bytes"
	"fmt"
)

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

func (*Buffer) Next

func (b *Buffer) Next(n int) []byte

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.

▸ Example

▾ Example

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))
}

ab
cd
e

func (*Buffer) Read

func (b *Buffer) Read(p []byte) (n int, err error)

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.

▸ Example

▾ Example

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))
}

1
bcde
a

func (*Buffer) ReadByte

func (b *Buffer) ReadByte() (byte, error)

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

▸ Example

▾ Example

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())
}

97
bcde

func (*Buffer) ReadBytes

func (b *Buffer) ReadBytes(delim byte) (line []byte, err error)

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.

func (*Buffer) ReadFrom

func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error)

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.

func (*Buffer) ReadRune

func (b *Buffer) ReadRune() (r rune, size int, err error)

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.

func (*Buffer) ReadString

func (b *Buffer) ReadString(delim byte) (line string, err error)

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.

func (*Buffer) Reset

func (b *Buffer) Reset()

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).

func (*Buffer) String

func (b *Buffer) String() string

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

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

func (*Buffer) Truncate

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 (*Buffer) UnreadByte

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 (*Buffer) UnreadRune

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.)

func (*Buffer) Write

func (b *Buffer) Write(p []byte) (n int, err error)

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.

func (*Buffer) WriteByte

func (b *Buffer) WriteByte(c byte) error

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 with ErrTooLarge.

func (*Buffer) WriteRune

func (b *Buffer) WriteRune(r rune) (n int, err error)

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.

func (*Buffer) WriteString

func (b *Buffer) WriteString(s string) (n int, err error)

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.

func (*Buffer) WriteTo

func (b *Buffer) WriteTo(w io.Writer) (n int64, err error)

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.

type Reader

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.

type Reader struct {
    // contains filtered or unexported fields
}

func NewReader

func NewReader(b []byte) *Reader

NewReader returns a new Reader reading from b.

func (*Reader) Len

func (r *Reader) Len() int

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

▸ Example

▾ Example

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())
}

3
16

func (*Reader) Read

func (r *Reader) Read(b []byte) (n int, err error)

Read implements the io.Reader interface.

func (*Reader) ReadAt

func (r *Reader) ReadAt(b []byte, off int64) (n int, err error)

ReadAt implements the io.ReaderAt interface.

func (*Reader) ReadByte

func (r *Reader) ReadByte() (byte, error)

ReadByte implements the io.ByteReader interface.

func (*Reader) ReadRune

func (r *Reader) ReadRune() (ch rune, size int, err error)

ReadRune implements the io.RuneReader interface.

func (*Reader) Reset 1.7

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

Reset resets the Reader to be reading from b.

func (*Reader) Seek

func (r *Reader) Seek(offset int64, whence int) (int64, error)

Seek implements the io.Seeker interface.

func (*Reader) Size 1.5

func (r *Reader) Size() int64

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.

func (*Reader) UnreadByte

func (r *Reader) UnreadByte() error

UnreadByte complements Reader.ReadByte in implementing the io.ByteScanner interface.

func (*Reader) UnreadRune

func (r *Reader) UnreadRune() error

UnreadRune complements Reader.ReadRune in implementing the io.RuneScanner interface.

func (*Reader) WriteTo 1.1

func (r *Reader) WriteTo(w io.Writer) (n int64, err error)

WriteTo implements the io.WriterTo interface.