pkgsite: golang.org/x/pkgsite/internal/godoc/codec Index | Files

package codec

import "golang.org/x/pkgsite/internal/godoc/codec"

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

Package Files

codec.go doc.go generate.go

func GenerateFile Uses

func GenerateFile(filename, packageName string, values ...interface{}) error

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.

func Register Uses

func Register(x interface{}, enc encodeFunc, dec decodeFunc)

Register records the type of x for use by Encoders and Decoders.

type Decoder Uses

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 Uses

func NewDecoder(data []byte) *Decoder

NewDecoder returns a Decoder for the given bytes.

func (*Decoder) Decode Uses

func (d *Decoder) Decode() (_ interface{}, err error)

Decode decodes a value encoded with Encoder.Encode.

func (*Decoder) DecodeAny Uses

func (d *Decoder) DecodeAny() interface{}

DecodeAny decodes a value encoded by EncodeAny.

func (*Decoder) DecodeBool Uses

func (d *Decoder) DecodeBool() bool

DecodeBool decodes a bool.

func (*Decoder) DecodeBytes Uses

func (d *Decoder) DecodeBytes() []byte

DecodeBytes decodes a byte slice. It does no copying.

func (*Decoder) DecodeFloat Uses

func (d *Decoder) DecodeFloat() float64

DecodeFloat decodes a float64.

func (*Decoder) DecodeInt Uses

func (d *Decoder) DecodeInt() int64

DecodeInt decodes a signed integer.

func (*Decoder) DecodeString Uses

func (d *Decoder) DecodeString() string

DecodeString decodes a string.

func (*Decoder) DecodeUint Uses

func (d *Decoder) DecodeUint() uint64

DecodeUint decodes a uint64.

func (*Decoder) NextStructField Uses

func (d *Decoder) NextStructField() int

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 Uses

func (d *Decoder) StartList() int

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 Uses

func (d *Decoder) StartStruct() (bool, interface{})

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 Uses

func (d *Decoder) StoreRef(p interface{})

StoreRef should be called by a struct decoder immediately after it allocates a struct pointer.

func (*Decoder) UnknownField Uses

func (d *Decoder) UnknownField(typeName string, num int)

UnknownField should be called by a struct decoder when it sees a field number that it doesn't know.

type Encoder Uses

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 NewEncoder Uses

func NewEncoder() *Encoder

NewEncoder returns an Encoder.

func (*Encoder) Bytes Uses

func (e *Encoder) Bytes() []byte

Bytes returns the encoded byte slice.

func (*Encoder) Encode Uses

func (e *Encoder) Encode(x interface{}) (err error)

Encode encodes x.

func (*Encoder) EncodeAny Uses

func (e *Encoder) EncodeAny(x interface{})

EncodeAny encodes a Go type. The type must have been registered with Register.

func (*Encoder) EncodeBool Uses

func (e *Encoder) EncodeBool(b bool)

EncodeBool encodes a bool.

func (*Encoder) EncodeBytes Uses

func (e *Encoder) EncodeBytes(b []byte)

EncodeBytes encodes a byte slice.

func (*Encoder) EncodeFloat Uses

func (e *Encoder) EncodeFloat(f float64)

EncodeFloat encodes a float64.

func (*Encoder) EncodeInt Uses

func (e *Encoder) EncodeInt(i int64)

EncodeInt encodes a signed integer.

func (*Encoder) EncodeNil Uses

func (e *Encoder) EncodeNil()

func (*Encoder) EncodeString Uses

func (e *Encoder) EncodeString(s string)

EncodeString encodes a string.

func (*Encoder) EncodeUint Uses

func (e *Encoder) EncodeUint(u uint64)

EncodeUint encodes a uint64.

func (*Encoder) EndStruct Uses

func (e *Encoder) EndStruct()

EndStruct should be called after encoding a struct.

func (*Encoder) StartList Uses

func (e *Encoder) StartList(len int)

StartList should be called before encoding any sequence of variable-length values.

func (*Encoder) StartStruct Uses

func (e *Encoder) StartStruct(isNil bool, p interface{}) bool

StartStruct should be called before encoding a struct pointer. The isNil argument says whether the pointer is nil. The p argument is the struct pointer. If StartStruct returns false, encoding should not proceed.

Package codec imports 12 packages (graph) and is imported by 2 packages. Updated 2021-01-20. Refresh now. Tools for package owners.