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Package binary

import "encoding/binary"
Overview
Index
Examples

Overview ▾

Package binary implements simple translation between numbers and byte sequences and encoding and decoding of varints.

Numbers are translated by reading and writing fixed-size values. A fixed-size value is either a fixed-size arithmetic type (bool, int8, uint8, int16, float32, complex64, ...) or an array or struct containing only fixed-size values.

The varint functions encode and decode single integer values using a variable-length encoding; smaller values require fewer bytes. For a specification, see https://developers.google.com/protocol-buffers/docs/encoding.

This package favors simplicity over efficiency. Clients that require high-performance serialization, especially for large data structures, should look at more advanced solutions such as the encoding/gob package or google.golang.org/protobuf for protocol buffers.

Constants

MaxVarintLenN is the maximum length of a varint-encoded N-bit integer. 

const (
    MaxVarintLen16 = 3
    MaxVarintLen32 = 5
    MaxVarintLen64 = 10
)

Variables

BigEndian is the big-endian implementation of ByteOrder and AppendByteOrder. 

var BigEndian bigEndian

LittleEndian is the little-endian implementation of ByteOrder and AppendByteOrder. 

var LittleEndian littleEndian

NativeEndian is the native-endian implementation of ByteOrder and AppendByteOrder. 

var NativeEndian nativeEndian

func Append 1.23 

func Append(buf []byte, order ByteOrder, data any) ([]byte, error)

Append appends the binary representation of data to buf. buf may be nil, in which case a new buffer will be allocated. See Write on which data are acceptable. It returns the (possibily extended) buffer containing data or an error.

func AppendUvarint 1.19 

func AppendUvarint(buf []byte, x uint64) []byte

AppendUvarint appends the varint-encoded form of x, as generated by PutUvarint, to buf and returns the extended buffer.

func AppendVarint 1.19 

func AppendVarint(buf []byte, x int64) []byte

AppendVarint appends the varint-encoded form of x, as generated by PutVarint, to buf and returns the extended buffer.

func Decode 1.23 

func Decode(buf []byte, order ByteOrder, data any) (int, error)

Decode decodes binary data from buf into data according to the given byte order. It returns an error if buf is too small, otherwise the number of bytes consumed from buf.

func Encode 1.23 

func Encode(buf []byte, order ByteOrder, data any) (int, error)

Encode encodes the binary representation of data into buf according to the given byte order. It returns an error if buf is too small, otherwise the number of bytes written into buf.

func PutUvarint 

func PutUvarint(buf []byte, x uint64) int

PutUvarint encodes a uint64 into buf and returns the number of bytes written. If the buffer is too small, PutUvarint will panic.

▾ Example

Code:

buf := make([]byte, binary.MaxVarintLen64)

for _, x := range []uint64{1, 2, 127, 128, 255, 256} {
    n := binary.PutUvarint(buf, x)
    fmt.Printf("%x\n", buf[:n])
}

Output:

01
02
7f
8001
ff01
8002

func PutVarint 

func PutVarint(buf []byte, x int64) int

PutVarint encodes an int64 into buf and returns the number of bytes written. If the buffer is too small, PutVarint will panic.

▾ Example

Code:

buf := make([]byte, binary.MaxVarintLen64)

for _, x := range []int64{-65, -64, -2, -1, 0, 1, 2, 63, 64} {
    n := binary.PutVarint(buf, x)
    fmt.Printf("%x\n", buf[:n])
}

Output:

8101
7f
03
01
00
02
04
7e
8001

func Read 

func Read(r io.Reader, order ByteOrder, data any) error

Read reads structured binary data from r into data. Data must be a pointer to a fixed-size value or a slice of fixed-size values. Bytes read from r are decoded using the specified byte order and written to successive fields of the data. When decoding boolean values, a zero byte is decoded as false, and any other non-zero byte is decoded as true. When reading into structs, the field data for fields with blank (_) field names is skipped; i.e., blank field names may be used for padding. When reading into a struct, all non-blank fields must be exported or Read may panic.

The error is io.EOF only if no bytes were read. If an io.EOF happens after reading some but not all the bytes, Read returns io.ErrUnexpectedEOF.

▾ Example

Code:

var pi float64
b := []byte{0x18, 0x2d, 0x44, 0x54, 0xfb, 0x21, 0x09, 0x40}
buf := bytes.NewReader(b)
err := binary.Read(buf, binary.LittleEndian, &pi)
if err != nil {
    fmt.Println("binary.Read failed:", err)
}
fmt.Print(pi)

Output:

3.141592653589793

▾ Example (Multi)

Code:

b := []byte{0x18, 0x2d, 0x44, 0x54, 0xfb, 0x21, 0x09, 0x40, 0xff, 0x01, 0x02, 0x03, 0xbe, 0xef}
r := bytes.NewReader(b)

var data struct {
    PI   float64
    Uate uint8
    Mine [3]byte
    Too  uint16
}

if err := binary.Read(r, binary.LittleEndian, &data); err != nil {
    fmt.Println("binary.Read failed:", err)
}

fmt.Println(data.PI)
fmt.Println(data.Uate)
fmt.Printf("% x\n", data.Mine)
fmt.Println(data.Too)

Output:

3.141592653589793
255
01 02 03
61374

func ReadUvarint 

func ReadUvarint(r io.ByteReader) (uint64, error)

ReadUvarint reads an encoded unsigned integer from r and returns it as a uint64. The error is io.EOF only if no bytes were read. If an io.EOF happens after reading some but not all the bytes, ReadUvarint returns io.ErrUnexpectedEOF.

func ReadVarint 

func ReadVarint(r io.ByteReader) (int64, error)

ReadVarint reads an encoded signed integer from r and returns it as an int64. The error is io.EOF only if no bytes were read. If an io.EOF happens after reading some but not all the bytes, ReadVarint returns io.ErrUnexpectedEOF.

func Size 

func Size(v any) int

Size returns how many bytes Write would generate to encode the value v, which must be a fixed-size value or a slice of fixed-size values, or a pointer to such data. If v is neither of these, Size returns -1.

func Uvarint 

func Uvarint(buf []byte) (uint64, int)

Uvarint decodes a uint64 from buf and returns that value and the number of bytes read (> 0). If an error occurred, the value is 0 and the number of bytes n is <= 0 meaning:

▾ Example

Code:

inputs := [][]byte{
    {0x01},
    {0x02},
    {0x7f},
    {0x80, 0x01},
    {0xff, 0x01},
    {0x80, 0x02},
}
for _, b := range inputs {
    x, n := binary.Uvarint(b)
    if n != len(b) {
        fmt.Println("Uvarint did not consume all of in")
    }
    fmt.Println(x)
}

Output:

1
2
127
128
255
256

func Varint 

func Varint(buf []byte) (int64, int)

Varint decodes an int64 from buf and returns that value and the number of bytes read (> 0). If an error occurred, the value is 0 and the number of bytes n is <= 0 with the following meaning:

▾ Example

Code:

inputs := [][]byte{
    {0x81, 0x01},
    {0x7f},
    {0x03},
    {0x01},
    {0x00},
    {0x02},
    {0x04},
    {0x7e},
    {0x80, 0x01},
}
for _, b := range inputs {
    x, n := binary.Varint(b)
    if n != len(b) {
        fmt.Println("Varint did not consume all of in")
    }
    fmt.Println(x)
}

Output:

-65
-64
-2
-1
0
1
2
63
64

func Write 

func Write(w io.Writer, order ByteOrder, data any) error

Write writes the binary representation of data into w. Data must be a fixed-size value or a slice of fixed-size values, or a pointer to such data. Boolean values encode as one byte: 1 for true, and 0 for false. Bytes written to w are encoded using the specified byte order and read from successive fields of the data. When writing structs, zero values are written for fields with blank (_) field names.

▾ Example

Code:

buf := new(bytes.Buffer)
var pi float64 = math.Pi
err := binary.Write(buf, binary.LittleEndian, pi)
if err != nil {
    fmt.Println("binary.Write failed:", err)
}
fmt.Printf("% x", buf.Bytes())

Output:

18 2d 44 54 fb 21 09 40

▾ Example (Multi)

Code:

buf := new(bytes.Buffer)
var data = []any{
    uint16(61374),
    int8(-54),
    uint8(254),
}
for _, v := range data {
    err := binary.Write(buf, binary.LittleEndian, v)
    if err != nil {
        fmt.Println("binary.Write failed:", err)
    }
}
fmt.Printf("%x", buf.Bytes())

Output:

beefcafe

type AppendByteOrder 1.19

AppendByteOrder specifies how to append 16-, 32-, or 64-bit unsigned integers into a byte slice.

It is implemented by LittleEndian, BigEndian, and NativeEndian. 

type AppendByteOrder interface {
    AppendUint16([]byte, uint16) []byte
    AppendUint32([]byte, uint32) []byte
    AppendUint64([]byte, uint64) []byte
    String() string
}

type ByteOrder

A ByteOrder specifies how to convert byte slices into 16-, 32-, or 64-bit unsigned integers.

It is implemented by LittleEndian, BigEndian, and NativeEndian. 

type ByteOrder interface {
    Uint16([]byte) uint16
    Uint32([]byte) uint32
    Uint64([]byte) uint64
    PutUint16([]byte, uint16)
    PutUint32([]byte, uint32)
    PutUint64([]byte, uint64)
    String() string
}

▾ Example (Get)

Code:

b := []byte{0xe8, 0x03, 0xd0, 0x07}
x1 := binary.LittleEndian.Uint16(b[0:])
x2 := binary.LittleEndian.Uint16(b[2:])
fmt.Printf("%#04x %#04x\n", x1, x2)

Output:

0x03e8 0x07d0

▾ Example (Put)

Code:

b := make([]byte, 4)
binary.LittleEndian.PutUint16(b[0:], 0x03e8)
binary.LittleEndian.PutUint16(b[2:], 0x07d0)
fmt.Printf("% x\n", b)

Output:

e8 03 d0 07