1.stdEncoding：标准的base64编码

type Encoding struct {
    encode    [64]byte
    decodeMap [256]byte
    padChar   rune
    strict    bool
}

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

const encodeStd = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
const encodeURL = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_"
// NewEncoding returns a new padded Encoding defined by the given alphabet,
// which must be a 64-byte string that does not contain the padding character
// or CR / LF ('\r', '\n').
// The resulting Encoding uses the default padding character ('='),
// which may be changed or disabled via WithPadding.
func NewEncoding(encoder string) *Encoding {
    if len(encoder) != 64 {
        panic("encoding alphabet is not 64-bytes long")
    }
    for i := 0; i < len(encoder); i++ {
        if encoder[i] == '\n' || encoder[i] == '\r' {
            panic("encoding alphabet contains newline character")
        }
    }

    e := new(Encoding)
    e.padChar = StdPadding
    copy(e.encode[:], encoder)

    for i := 0; i < len(e.decodeMap); i++ {
        e.decodeMap[i] = 0xFF
    }
    for i := 0; i < len(encoder); i++ {
        e.decodeMap[encoder[i]] = byte(i)
    }
    return e
}

// StdEncoding is the standard base64 encoding, as defined in
// RFC 4648.
var StdEncoding = NewEncoding(encodeStd)

// URLEncoding is the alternate base64 encoding defined in RFC 4648.
// It is typically used in URLs and file names.
var URLEncoding = NewEncoding(encodeURL)


// EncodeToString returns the base64 encoding of src.
func (enc *Encoding) EncodeToString(src []byte) string {
    buf := make([]byte, enc.EncodedLen(len(src)))
    enc.Encode(buf, src)
    return string(buf)
}

示例

    d := "This is a golang test."
    encodedContent := base64.StdEncoding.EncodeToString([]byte(d))
    fmt.Println(encodedContent)
    sourceContent,_ := base64.StdEncoding.DecodeString(encodedContent)
    fmt.Println(string(sourceContent))

Output:

VGhpcyBpcyBhIGdvbGFuZyB0ZXN0Lg==
This is a golang test.