import "bytes"
Package bytes implements functions for the manipulation of byte slices. It is analogous to the facilities of the strings package.
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.
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(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 }
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(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(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(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(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(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.
Code:
fmt.Println(bytes.Equal([]byte("Go"), []byte("Go")))
fmt.Println(bytes.Equal([]byte("Go"), []byte("C++")))
Output:
true false
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(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(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(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(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(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(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(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.
Code:
fmt.Println(bytes.IndexByte([]byte("chicken"), byte('k')))
fmt.Println(bytes.IndexByte([]byte("chicken"), byte('g')))
Output:
4 -1
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(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(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(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(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(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(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(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(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(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 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.
Code:
fmt.Printf("%s\n", bytes.ReplaceAll([]byte("oink oink oink"), []byte("oink"), []byte("moo")))
Output:
moo moo moo
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(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(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(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(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(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(s []byte) []byte
ToLower returns a copy of the byte slice s with all Unicode letters mapped to their lower case.
Code:
fmt.Printf("%s", bytes.ToLower([]byte("Gopher")))
Output:
gopher
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.
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(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(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.
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(s []byte) []byte
ToUpper returns a copy of the byte slice s with all Unicode letters mapped to their upper case.
Code:
fmt.Printf("%s", bytes.ToUpper([]byte("Gopher")))
Output:
GOPHER
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.
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(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(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(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(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("453gopher8257"), "0123456789")))
Output:
gopher8257
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(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(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(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(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(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 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(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(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 (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 (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 (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 (b *Buffer) Len() int
Len returns the number of bytes of the unread portion of the buffer; b.Len() == len(b.Bytes()).
Code:
var b bytes.Buffer
b.Grow(64)
b.Write([]byte("abcde"))
fmt.Printf("%d", b.Len())
Output:
5
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 (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 (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 (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 (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 (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 (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 (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 (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 (b *Buffer) Truncate(n int)
Truncate discards all but the first n unread bytes from the buffer but continues to use the same allocated storage. It panics if n is negative or greater than the length of the buffer.
func (b *Buffer) UnreadByte() error
UnreadByte unreads the last byte returned by the most recent successful read operation that read at least one byte. If a write has happened since the last read, if the last read returned an error, or if the read read zero bytes, UnreadByte returns an error.
func (b *Buffer) UnreadRune() error
UnreadRune unreads the last rune returned by 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 (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 (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 (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 (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 (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 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. The zero value for Reader operates like a Reader of an empty slice.
func NewReader(b []byte) *Reader
NewReader returns a new Reader reading from b.
func (r *Reader) Len() int
Len returns the number of bytes of the unread portion of the slice.
Code:
fmt.Println(bytes.NewReader([]byte("Hi!")).Len())
fmt.Println(bytes.NewReader([]byte("こんにちは!")).Len())
Output:
3 16
func (r *Reader) Read(b []byte) (n int, err error)
Read implements the io.Reader interface.
func (r *Reader) ReadAt(b []byte, off int64) (n int, err error)
ReadAt implements the io.ReaderAt interface.
func (r *Reader) ReadByte() (byte, error)
ReadByte implements the io.ByteReader interface.
func (r *Reader) ReadRune() (ch rune, size int, err error)
ReadRune implements the io.RuneReader interface.
func (r *Reader) Reset(b []byte)
Reset resets the Reader to be reading from b.
func (r *Reader) Seek(offset int64, whence int) (int64, error)
Seek implements the io.Seeker interface.
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 (r *Reader) UnreadByte() error
UnreadByte complements ReadByte in implementing the io.ByteScanner interface.
func (r *Reader) UnreadRune() error
UnreadRune complements ReadRune in implementing the io.RuneScanner interface.
func (r *Reader) WriteTo(w io.Writer) (n int64, err error)