Documentation
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Overview ¶
Package codec implements the general-purpose part of an encoder for Go values. It relies on code generation rather than reflection so it is significantly faster than reflection-based encoders like gob. It also preserves sharing among struct pointers (but not other forms of sharing, like other pointer types or sub-slices). These features are sufficient for encoding the structures of the go/ast package, which is its sole purpose.
Encoding Scheme ¶
Every encoded value begins with a single byte that describes what (if anything) follows. There is enough information to skip over the value, since the decoder must be able to do that if it encounters a struct field it doesn't know.
Most of the values of that initial byte can be devoted to small unsigned integers. For example, the number 17 is represented by the single byte 17. Only a few byte values have special meaning.
The nil code indicates that the value is nil. We don't absolutely need this: we could always represent the nil value for a type as something that couldn't be mistaken for an encoded value of that type. For instance, we could use 0 for nil in the case of slices (which always begin with the nValues code), and for pointers to numbers like *int, we could use something like "nBytes 0". But it is simpler to have a reserved value for nil.
The nBytes code indicates that an unsigned integer N is encoded next, followed by N bytes of data. This is used to represent strings and byte slices, as well numbers bigger than can fit into the initial byte. For example, the string "hi" is represented as:
nBytes 2 'h' 'i'
Unsigned integers that can't fit into the initial byte are encoded as byte sequences of length 4 or 8, holding little-endian uint32 or uint64 values. We use uint32s where possible to save space. We could have saved more space by also considering 16-byte numbers, or using a variable-length encoding like varints or gob's representation, but it didn't seem worth the additional complexity.
The nValues code is for sequences of values whose size is known beforehand, like a Go slice or array. The slice []string{"hi", "bye"} is encoded as
nValues 2 nBytes 2 'h' 'i' nBytes 3 'b' 'y' 'e'
The ref code is used to refer to an earlier encoded value. It is followed by a uint denoting the index data of the value to use.
The start and end codes delimit a value whose length is unknown beforehand. It is used for structs.
Index ¶
- func GenerateFile(filename, packageName string, values ...any) error
- func Register(x any, enc encodeFunc, dec decodeFunc)
- type Decoder
- func (d *Decoder) Decode() (_ any, err error)
- func (d *Decoder) DecodeAny() any
- func (d *Decoder) DecodeBool() bool
- func (d *Decoder) DecodeBytes() []byte
- func (d *Decoder) DecodeFloat() float64
- func (d *Decoder) DecodeInt() int64
- func (d *Decoder) DecodeString() string
- func (d *Decoder) DecodeUint() uint64
- func (d *Decoder) NextStructField() int
- func (d *Decoder) StartList() int
- func (d *Decoder) StartStruct() (bool, any)
- func (d *Decoder) StoreRef(p any)
- func (d *Decoder) UnknownField(typeName string, num int)
- type Encoder
- func (e *Encoder) Bytes() []byte
- func (e *Encoder) Encode(x any) (err error)
- func (e *Encoder) EncodeAny(x any)
- func (e *Encoder) EncodeBool(b bool)
- func (e *Encoder) EncodeBytes(b []byte)
- func (e *Encoder) EncodeFloat(f float64)
- func (e *Encoder) EncodeInt(i int64)
- func (e *Encoder) EncodeNil()
- func (e *Encoder) EncodeString(s string)
- func (e *Encoder) EncodeUint(u uint64)
- func (e *Encoder) EndStruct()
- func (e *Encoder) StartList(len int)
- func (e *Encoder) StartStruct(isNil bool, p any) bool
Constants ¶
This section is empty.
Variables ¶
This section is empty.
Functions ¶
func GenerateFile ¶
GenerateFile writes encoders and decoders to filename. It generates code for the type of each given value, as well as any types they depend on. packageName is the name following the file's package declaration.
Types ¶
type Decoder ¶
type Decoder struct {
// contains filtered or unexported fields
}
A Decoder decodes a Go value encoded by an Encoder. To use a Decoder: - Pass NewDecoder the return value of Encoder.Bytes. - Call the Decode method once for each call to Encoder.Encode.
func NewDecoder ¶
NewDecoder returns a Decoder for the given bytes.
func (*Decoder) DecodeBytes ¶
DecodeBytes decodes a byte slice. It does no copying.
func (*Decoder) DecodeFloat ¶
DecodeFloat decodes a float64.
func (*Decoder) DecodeString ¶
DecodeString decodes a string.
func (*Decoder) NextStructField ¶
NextStructField should be called by a struct decoder in a loop. It returns the field number of the next encoded field, or -1 if there are no more fields.
func (*Decoder) StartList ¶
StartList should be called before decoding any sequence of variable-length values. It returns -1 if the encoded list was nil. Otherwise, it returns the length of the sequence.
func (*Decoder) StartStruct ¶
StartStruct should be called before decoding a struct pointer. If it returns false, decoding should not proceed. If it returns true and the second return value is non-nil, it is a reference to a previous value and should be used instead of proceeding with decoding.
func (*Decoder) StoreRef ¶
StoreRef should be called by a struct decoder immediately after it allocates a struct pointer.
func (*Decoder) UnknownField ¶
UnknownField should be called by a struct decoder when it sees a field number that it doesn't know.
type Encoder ¶
type Encoder struct {
// contains filtered or unexported fields
}
An Encoder encodes Go values into a sequence of bytes. To use an Encoder: - Create one with NewEncoder. - Call the Encode method one or more times. - Retrieve the resulting bytes by calling Bytes.
func (*Encoder) EncodeAny ¶
EncodeAny encodes a Go type. The type must have been registered with Register.
func (*Encoder) EncodeBytes ¶
EncodeBytes encodes a byte slice.
func (*Encoder) EncodeFloat ¶
EncodeFloat encodes a float64.
func (*Encoder) EncodeString ¶
EncodeString encodes a string.
func (*Encoder) EndStruct ¶
func (e *Encoder) EndStruct()
EndStruct should be called after encoding a struct.
Source Files