Package bytes

Overview

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

Index

Package files

buffer.go bytes.go reader.go

Constants

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. 

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 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

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
}

Code:

// Binary search to find a matching byte slice.
var needle []byte
var haystack [][]byte // Assume sorted
i := sort.Search(len(haystack), func(i int) bool {
    // Return haystack[i] >= needle.
    return bytes.Compare(haystack[i], needle) >= 0
})
if i < len(haystack) && bytes.Equal(haystack[i], needle) {
    // Found it!
}

func Contains 

func Contains(b, subslice []byte) bool

Contains reports whether subslice is within b.

Example

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 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

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 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

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.

Example

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

Example

Code:

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

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, which is a more general form of case-insensitivity.

Example

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.

Example

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) and assumes that f always returns the same value for a given c.

Example

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.

Example

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.

Example

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.

Example

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.

Example

Code:

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

Output:

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

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.

Example

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.

Example

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.

Example

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.

Example

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.

Example

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 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

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.

Example

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.

Example

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.

Example

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.

Example

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 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

Code:

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

Output:

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

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.

Example

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.

Example

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

Example

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

Example

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.

Example

Code:

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

Output:

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

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.

Example

Code:

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

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

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.

Example

Code:

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

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

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.

Example

Code:

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 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.

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

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).

Example

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.

Example

Code:

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

Output:

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

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 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

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.

Example

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).

Example

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.

Example

Code:

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

Output:

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

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

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. 

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

Example

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!

Example (Reader)

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 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) 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.

Example

Code:

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 (*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.

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

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()).

Example

Code:

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

Output:

5

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>".

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 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 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

Code:

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

Output:

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 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 1.1 

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

WriteTo implements the io.WriterTo interface.

Bugs

  • ☞

    The rule Title uses for word boundaries does not handle Unicode punctuation properly.

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Licensed under the Creative Commons Attribution License 3.0.
http://golang.org/pkg/bytes/