encoding/base64

Package base64 implements base64 encoding as specified by RFC 4648. It provides functions for encoding and decoding data using base64 encoding schemes.

Overview

The base64 package provides:

Standard base64 encoding - Using + and / for characters 62 and 63
URL-safe base64 encoding - Using - and _ for characters 62 and 63
Raw (unpadded) variants - Without padding characters
Streaming encoding/decoding - For processing large amounts of data

Constants

Padding

const StdPadding rune = '=' // Standard padding character
const NoPadding rune = -1   // No padding

Variables

Standard Encodings

var StdEncoding = NewEncoding("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/")

StdEncoding is the standard base64 encoding, as defined in RFC 4648.

var URLEncoding = NewEncoding("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_")

URLEncoding is the alternate base64 encoding defined in RFC 4648. It is typically used in URLs and file names.

var RawStdEncoding = StdEncoding.WithPadding(NoPadding)

RawStdEncoding is the standard raw, unpadded base64 encoding, as defined in RFC 4648 section 3.2.

var RawURLEncoding = URLEncoding.WithPadding(NoPadding)

RawURLEncoding is the unpadded alternate base64 encoding defined in RFC 4648. It is typically used in URLs and file names.

Types

Encoding

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

An Encoding is a radix 64 encoding/decoding scheme, defined by a 64-character alphabet. The most common encoding is the “base64” encoding defined in RFC 4648.

NewEncoding

func NewEncoding(encoder string) *Encoding

NewEncoding returns a new padded Encoding defined by the given alphabet, which must be a 64-byte string that contains unique byte values.

encoder

string

required

A 64-character string defining the encoding alphabet

*Encoding

A new Encoding instance using the default padding character (’=‘)

Methods

Encode

func (enc *Encoding) Encode(dst, src []byte)

Encode encodes src using the encoding enc, writing EncodedLen(len(src)) bytes to dst.

dst

[]byte

required

Destination buffer to write encoded data to. Must have length at least EncodedLen(len(src)).

src

[]byte

required

Source data to encode

Example:

data := []byte("Hello, world!")
dst := make([]byte, base64.StdEncoding.EncodedLen(len(data)))
base64.StdEncoding.Encode(dst, data)
fmt.Println(string(dst))
// Output: SGVsbG8sIHdvcmxkIQ==

EncodeToString

func (enc *Encoding) EncodeToString(src []byte) string

EncodeToString returns the base64 encoding of src.

src

[]byte

required

The data to encode

string

The base64-encoded string

Example:

msg := "Hello, 世界"
encoded := base64.StdEncoding.EncodeToString([]byte(msg))
fmt.Println(encoded)
// Output: SGVsbG8sIOS4lueVjA==

AppendEncode

func (enc *Encoding) AppendEncode(dst, src []byte) []byte

AppendEncode appends the base64 encoded src to dst and returns the extended buffer.

dst

[]byte

required

Destination buffer to append to

src

[]byte

required

Source data to encode and append

[]byte

The extended buffer containing dst followed by the encoded src

Decode

func (enc *Encoding) Decode(dst, src []byte) (n int, err error)

Decode decodes src using the encoding enc. It writes at most DecodedLen(len(src)) bytes to dst and returns the number of bytes written.

dst

[]byte

required

Destination buffer to write decoded data to

src

[]byte

required

Base64-encoded source data

int

The number of bytes written to dst

err

error

Returns CorruptInputError if the input is not valid base64

Example:

str := "SGVsbG8sIHdvcmxkIQ=="
dst := make([]byte, base64.StdEncoding.DecodedLen(len(str)))
n, err := base64.StdEncoding.Decode(dst, []byte(str))
if err != nil {
    fmt.Println("decode error:", err)
    return
}
dst = dst[:n]
fmt.Printf("%q\n", dst)
// Output: "Hello, world!"

DecodeString

func (enc *Encoding) DecodeString(s string) ([]byte, error)

DecodeString returns the bytes represented by the base64 string s.

string

required

The base64-encoded string to decode

[]byte

The decoded data

error

Returns CorruptInputError if the input is not valid base64

Example:

str := "c29tZSBkYXRhIHdpdGggACBhbmQg77u/"
data, err := base64.StdEncoding.DecodeString(str)
if err != nil {
    fmt.Println("error:", err)
    return
}
fmt.Printf("%q\n", data)
// Output: "some data with \x00 and \ufeff"

AppendDecode

func (enc *Encoding) AppendDecode(dst, src []byte) ([]byte, error)

AppendDecode appends the base64 decoded src to dst and returns the extended buffer.

dst

[]byte

required

Destination buffer to append to

src

[]byte

required

Base64-encoded source data to decode and append

[]byte

The extended buffer containing dst followed by the decoded src

error

Returns CorruptInputError if the input is not valid base64

EncodedLen

func (enc *Encoding) EncodedLen(n int) int

EncodedLen returns the length in bytes of the base64 encoding of an input buffer of length n.

int

required

The length of the input data

int

The length of the encoded output

DecodedLen

func (enc *Encoding) DecodedLen(n int) int

DecodedLen returns the maximum length in bytes of the decoded data corresponding to n bytes of base64-encoded data.

int

required

The length of the encoded data

int

The maximum length of the decoded output

WithPadding

func (enc Encoding) WithPadding(padding rune) *Encoding

WithPadding creates a new encoding identical to enc except with a specified padding character, or NoPadding to disable padding.

padding

rune

required

The padding character to use, or NoPadding (-1) to disable padding

*Encoding

A new Encoding instance with the specified padding

Strict

func (enc Encoding) Strict() *Encoding

Strict creates a new encoding identical to enc except with strict decoding enabled. In this mode, the decoder requires that trailing padding bits are zero.

*Encoding

A new Encoding instance with strict decoding enabled

Streaming Encoder

NewEncoder

func NewEncoder(enc *Encoding, w io.Writer) io.WriteCloser

NewEncoder returns a new base64 stream encoder. Data written to the returned writer will be encoded using enc and then written to w. Base64 encodings operate in 4-byte blocks; when finished writing, the caller must Close the returned encoder to flush any partially written blocks.

enc

*Encoding

required

The encoding to use

io.Writer

required

The writer to write encoded data to

io.WriteCloser

A WriteCloser that encodes data written to it

Example:

input := []byte("foo\x00bar")
encoder := base64.NewEncoder(base64.StdEncoding, os.Stdout)
encoder.Write(input)
// Must close the encoder when finished to flush any partial blocks
encoder.Close()
// Output: Zm9vAGJhcg==

Streaming Decoder

NewDecoder

func NewDecoder(enc *Encoding, r io.Reader) io.Reader

NewDecoder constructs a new base64 stream decoder.

enc

*Encoding

required

The encoding to use

io.Reader

required

The reader to read encoded data from

io.Reader

A Reader that decodes data read from it

Error Types

CorruptInputError

type CorruptInputError int64

CorruptInputError indicates that the input data is corrupted. The int64 value indicates the byte offset where the corruption was detected.

func (e CorruptInputError) Error() string

Encoding Examples

Standard Base64

// Encoding
data := []byte("any + old & data")
str := base64.StdEncoding.EncodeToString(data)
fmt.Println(str)
// Output: YW55ICsgb2xkICYgZGF0YQ==

// Decoding
str := "SGVsbG8sIOS4lueVjA=="
decoded, err := base64.StdEncoding.DecodeString(str)
if err != nil {
    fmt.Println("decode error:", err)
    return
}
fmt.Println(string(decoded))
// Output: Hello, 世界

URL-Safe Base64

// Use URLEncoding for URLs and filenames
data := []byte("test?data=value&param=123")
encoded := base64.URLEncoding.EncodeToString(data)
fmt.Println(encoded)

decoded, _ := base64.URLEncoding.DecodeString(encoded)
fmt.Println(string(decoded))

Raw (Unpadded) Base64

// Use RawStdEncoding for base64 without padding
data := []byte("hello")
encoded := base64.RawStdEncoding.EncodeToString(data)
fmt.Println(encoded)
// Output: aGVsbG8 (no padding)

// Use RawURLEncoding for URL-safe base64 without padding
encoded = base64.RawURLEncoding.EncodeToString(data)
fmt.Println(encoded)

Custom Encoding

// Create a custom encoding with different alphabet
customEnc := base64.NewEncoding("ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_")
encoded := customEnc.EncodeToString([]byte("test"))

// Create encoding without padding
noPadEnc := customEnc.WithPadding(base64.NoPadding)
encoded = noPadEnc.EncodeToString([]byte("test"))

Language Constructs

I/O & System

Data Structures

Networking

Encoding

Cryptography

Concurrency

Testing & Debugging

Reflection & Parsing

encoding/base64

encoding/base64

Overview

Constants

Padding

Variables

Standard Encodings

Types

Encoding

NewEncoding

Methods

Streaming Encoder

NewEncoder

Streaming Decoder

NewDecoder

Error Types

CorruptInputError

Encoding Examples

Standard Base64

URL-Safe Base64

Raw (Unpadded) Base64

Custom Encoding

Build docs developers (and LLMs) love

Language Constructs

I/O & System

Data Structures

Networking

Encoding

Cryptography

Concurrency

Testing & Debugging

Reflection & Parsing

​encoding/base64

​Overview

​Constants

​Padding

​Variables

​Standard Encodings

​Types

​Encoding

​NewEncoding

​Methods

​Streaming Encoder

​NewEncoder

​Streaming Decoder

​NewDecoder

​Error Types

​CorruptInputError

​Encoding Examples

​Standard Base64

​URL-Safe Base64

​Raw (Unpadded) Base64

​Custom Encoding

Build docs developers (and LLMs) love

encoding/base64

Overview

Constants

Padding

Variables

Standard Encodings

Types

Encoding

NewEncoding

Methods

Streaming Encoder

NewEncoder

Streaming Decoder

NewDecoder

Error Types

CorruptInputError

Encoding Examples

Standard Base64

URL-Safe Base64

Raw (Unpadded) Base64

Custom Encoding