Package bytes

import "bytes"
Overview
Index
Examples
Documentation

Overview

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

Index

Constants
Variables
func Compare(a, b []byte) int
func Contains(b, subslice []byte) bool
func ContainsAny(b []byte, chars string) bool
func ContainsRune(b []byte, r rune) bool
func Count(s, sep []byte) int
func Equal(a, b []byte) bool
func EqualFold(s, t []byte) bool
func Fields(s []byte) [][]byte
func FieldsFunc(s []byte, f func(rune) bool) [][]byte
func HasPrefix(s, prefix []byte) bool
func HasSuffix(s, suffix []byte) bool
func Index(s, sep []byte) int
func IndexAny(s []byte, chars string) int
func IndexByte(s []byte, c byte) int
func IndexFunc(s []byte, f func(r rune) bool) int
func IndexRune(s []byte, r rune) int
func Join(s [][]byte, sep []byte) []byte
func LastIndex(s, sep []byte) int
func LastIndexAny(s []byte, chars string) int
func LastIndexByte(s []byte, c byte) int
func LastIndexFunc(s []byte, f func(r rune) bool) int
func Map(mapping func(r rune) rune, s []byte) []byte
func Repeat(b []byte, count int) []byte
func Replace(s, old, new []byte, n int) []byte
func Runes(s []byte) []rune
func Split(s, sep []byte) [][]byte
func SplitAfter(s, sep []byte) [][]byte
func SplitAfterN(s, sep []byte, n int) [][]byte
func SplitN(s, sep []byte, n int) [][]byte
func Title(s []byte) []byte
func ToLower(s []byte) []byte
func ToLowerSpecial(c unicode.SpecialCase, s []byte) []byte
func ToTitle(s []byte) []byte
func ToTitleSpecial(c unicode.SpecialCase, s []byte) []byte
func ToUpper(s []byte) []byte
func ToUpperSpecial(c unicode.SpecialCase, s []byte) []byte
func Trim(s []byte, cutset string) []byte
func TrimFunc(s []byte, f func(r rune) bool) []byte
func TrimLeft(s []byte, cutset string) []byte
func TrimLeftFunc(s []byte, f func(r rune) bool) []byte
func TrimPrefix(s, prefix []byte) []byte
func TrimRight(s []byte, cutset string) []byte
func TrimRightFunc(s []byte, f func(r rune) bool) []byte
func TrimSpace(s []byte) []byte
func TrimSuffix(s, suffix []byte) []byte
type Buffer
func NewBuffer(buf []byte) *Buffer
func NewBufferString(s string) *Buffer
func (b *Buffer) Bytes() []byte
func (b *Buffer) Cap() int
func (b *Buffer) Grow(n int)
func (b *Buffer) Len() int
func (b *Buffer) Next(n int) []byte
func (b *Buffer) Read(p []byte) (n int, err error)
func (b *Buffer) ReadByte() (byte, error)
func (b *Buffer) ReadBytes(delim byte) (line []byte, err error)
func (b *Buffer) ReadFrom(r io.Reader) (n int64, err error)
func (b *Buffer) ReadRune() (r rune, size int, err error)
func (b *Buffer) ReadString(delim byte) (line string, err error)
func (b *Buffer) Reset()
func (b *Buffer) String() string
func (b *Buffer) Truncate(n int)
func (b *Buffer) UnreadByte() error
func (b *Buffer) UnreadRune() error
func (b *Buffer) Write(p []byte) (n int, err error)
func (b *Buffer) WriteByte(c byte) error
func (b *Buffer) WriteRune(r rune) (n int, err error)
func (b *Buffer) WriteString(s string) (n int, err error)
func (b *Buffer) WriteTo(w io.Writer) (n int64, err error)
type Reader
func NewReader(b []byte) *Reader
func (r *Reader) Len() int
func (r *Reader) Read(b []byte) (n int, err error)
func (r *Reader) ReadAt(b []byte, off int64) (n int, err error)
func (r *Reader) ReadByte() (byte, error)
func (r *Reader) ReadRune() (ch rune, size int, err error)
func (r *Reader) Reset(b []byte)
func (r *Reader) Seek(offset int64, whence int) (int64, error)
func (r *Reader) Size() int64
func (r *Reader) UnreadByte() error
func (r *Reader) UnreadRune() error
func (r *Reader) WriteTo(w io.Writer) (n int64, err error)

Examples

Buffer
Buffer (Reader)
Buffer.Grow
Compare
Compare (Search)
Contains
ContainsAny
ContainsRune
Count
Equal
EqualFold
Fields
FieldsFunc
HasPrefix
HasSuffix
Index
IndexAny
IndexByte
IndexFunc
IndexRune
Join
LastIndex
LastIndexAny
LastIndexByte
LastIndexFunc
Map
Reader.Len
Repeat
Replace
Runes
Split
SplitAfter
SplitAfterN
SplitN
Title
ToLower
ToTitle
ToUpper
Trim
TrimFunc
TrimLeft
TrimLeftFunc
TrimPrefix
TrimRight
TrimRightFunc
TrimSpace
TrimSuffix

Documentation

Constants

const MinRead = 512

MinRead is the minimum slice size passed to a 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, ReadFrom will not grow the underlying buffer.

Variables

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

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

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.

Code:

// 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
}

func Contains

func Contains(b, subslice []byte) bool

Contains reports whether subslice is within b.

Code:

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

func ContainsAny

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

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

Code:

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

func ContainsRune

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

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

Code:

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

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.

Code:

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

Output:

3
5

func Equal

func Equal(a, b []byte) bool

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

Code:

fmt.Println(bytes.Equal([]byte("Go"), []byte("Go")))
fmt.Println(bytes.Equal([]byte("Go"), []byte("go")))

Output:

true
false

func EqualFold

func EqualFold(s, t []byte) bool

EqualFold reports whether s and t, interpreted as UTF-8 strings, are equal under Unicode case-folding.

Code:

fmt.Println(bytes.EqualFold([]byte("Go"), []byte("go")))

Output:

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.

Code:

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

Output:

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). If f does not return consistent results for a given c, FieldsFunc may crash.

Code:

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"]

func HasPrefix

func HasPrefix(s, prefix []byte) bool

HasPrefix tests whether the byte slice s begins with prefix.

Code:

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

func HasSuffix

func HasSuffix(s, suffix []byte) bool

HasSuffix tests whether the byte slice s ends with suffix.

Code:

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

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.

Code:

fmt.Println(bytes.Index([]byte("chicken"), []byte("ken")))
fmt.Println(bytes.Index([]byte("chicken"), []byte("dmr")))

Output:

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.

Code:

fmt.Println(bytes.IndexAny([]byte("chicken"), "aeiouy"))
fmt.Println(bytes.IndexAny([]byte("crwth"), "aeiouy"))

Output:

2
-1

func IndexByte

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

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

Code:

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

Output:

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.

Code:

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

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.

Code:

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

Output:

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.

Code:

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

Output:

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.

Code:

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

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.

Code:

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

func LastIndexByte

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.

Code:

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

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.

Code:

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

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.

Code:

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", bytes.Map(rot13, []byte("'Twas brillig and the slithy gopher...")))

Output:

'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.

Code:

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

Output:

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.

Code:

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 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.

Code:

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'

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.

Code:

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" " "]
[""]

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.

Code:

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

Output:

["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

Code:

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

Output:

["a," "b,c"]

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

Code:

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)

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.

BUG(rsc): The rule Title uses for word boundaries does not handle Unicode punctuation properly.

Code:

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

Output:

Her Royal Highness

func ToLower

func ToLower(s []byte) []byte

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

Code:

fmt.Printf("%s", bytes.ToLower([]byte("Gopher")))

Output:

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.

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.

Code:

fmt.Printf("%s\n", bytes.ToTitle([]byte("loud noises")))
fmt.Printf("%s\n", bytes.ToTitle([]byte("хлеб")))

Output:

LOUD NOISES
ХЛЕБ

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.

func ToUpper

func ToUpper(s []byte) []byte

ToUpper treats s as UTF-8-encoded bytes and returns a copy with all the Unicode letters within it mapped to their upper case.

Code:

fmt.Printf("%s", bytes.ToUpper([]byte("Gopher")))

Output:

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.

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.

Code:

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

Output:

["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).

Code:

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!

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.

Code:

fmt.Print(string(bytes.TrimLeft([]byte("+ 005400"), "+0 ")))

Output:

5400

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).

Code:

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

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.

Code:

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!

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.

Code:

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

Output:

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).

Code:

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!

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.

Code:

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

Output:

a lone gopher

func TrimSuffix

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.

Code:

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!

type Buffer

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

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

Code:

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

Output:

Hello world!

Code:

// 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

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 size 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.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 Read, Write, Reset, or 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.

func Buffer.Cap

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.

func Buffer.Grow

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.

Code:

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 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()).

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 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.

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.

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.

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 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>".

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 ReadRune. If the most recent read or write operation on the buffer was not a successful ReadRune, UnreadRune returns an error. (In this regard it is stricter than 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 implement io.ByteWriter. 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

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

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.

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.

Code:

fmt.Println(bytes.NewReader([]byte("")).Len())
fmt.Println(bytes.NewReader([]byte("Hi!")).Len())
fmt.Println(bytes.NewReader([]byte("Hello Gopher!")).Len())

Output:

0
3
13

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

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

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 ReadAt. The returned value is always the same and is not affected by calls to any other method.

func Reader.UnreadByte

func (r *Reader) UnreadByte() error

UnreadByte complements ReadByte in implementing the io.ByteScanner interface.

func Reader.UnreadRune

func (r *Reader) UnreadRune() error

UnreadRune complements ReadRune in implementing the io.RuneScanner interface.

func Reader.WriteTo

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

WriteTo implements the io.WriterTo interface.