# Codec

High Performance, Feature-Rich Idiomatic Go codec/encoding library for
binc, msgpack, cbor, json.

Supported Serialization formats are:

  - msgpack: https://github.com/msgpack/msgpack
  - binc:    http://github.com/ugorji/binc
  - cbor:    http://cbor.io http://tools.ietf.org/html/rfc7049
  - json:    http://json.org http://tools.ietf.org/html/rfc7159
  - simple: 

To install:

    go get github.com/ugorji/go/codec

This package will carefully use 'unsafe' for performance reasons in specific places.
You can build without unsafe use by passing the safe or appengine tag
i.e. 'go install -tags=safe ...'. Note that unsafe is only supported for the last 3
go sdk versions e.g. current go release is go 1.9, so we support unsafe use only from
go 1.7+ . This is because supporting unsafe requires knowledge of implementation details.

Online documentation: http://godoc.org/github.com/ugorji/go/codec  
Detailed Usage/How-to Primer: http://ugorji.net/blog/go-codec-primer

The idiomatic Go support is as seen in other encoding packages in
the standard library (ie json, xml, gob, etc).

Rich Feature Set includes:

  - Simple but extremely powerful and feature-rich API
  - Support for go1.4 and above, while selectively using newer APIs for later releases
  - Excellent code coverage ( > 90% )
  - Very High Performance.
    Our extensive benchmarks show us outperforming Gob, Json, Bson, etc by 2-4X.
  - Careful selected use of 'unsafe' for targeted performance gains.
    100% mode exists where 'unsafe' is not used at all.
  - Lock-free (sans mutex) concurrency for scaling to 100's of cores
  - Coerce types where appropriate
    e.g. decode an int in the stream into a float, decode numbers from formatted strings, etc
  - Corner Cases: 
    Overflows, nil maps/slices, nil values in streams are handled correctly
  - Standard field renaming via tags
  - Support for omitting empty fields during an encoding
  - Encoding from any value and decoding into pointer to any value
    (struct, slice, map, primitives, pointers, interface{}, etc)
  - Extensions to support efficient encoding/decoding of any named types
  - Support encoding.(Binary|Text)(M|Unm)arshaler interfaces
  - Support IsZero() bool to determine if a value is a zero value.
    Analogous to time.Time.IsZero() bool.
  - Decoding without a schema (into a interface{}).
    Includes Options to configure what specific map or slice type to use
    when decoding an encoded list or map into a nil interface{}
  - Mapping a non-interface type to an interface, so we can decode appropriately
    into any interface type with a correctly configured non-interface value.
  - Encode a struct as an array, and decode struct from an array in the data stream
  - Option to encode struct keys as numbers (instead of strings)
    (to support structured streams with fields encoded as numeric codes)
  - Comprehensive support for anonymous fields
  - Fast (no-reflection) encoding/decoding of common maps and slices
  - Code-generation for faster performance.
  - Support binary (e.g. messagepack, cbor) and text (e.g. json) formats
  - Support indefinite-length formats to enable true streaming 
    (for formats which support it e.g. json, cbor)
  - Support canonical encoding, where a value is ALWAYS encoded as same sequence of bytes.
    This mostly applies to maps, where iteration order is non-deterministic.
  - NIL in data stream decoded as zero value
  - Never silently skip data when decoding.
    User decides whether to return an error or silently skip data when keys or indexes
    in the data stream do not map to fields in the struct.
  - Encode/Decode from/to chan types (for iterative streaming support)
  - Drop-in replacement for encoding/json. `json:` key in struct tag supported.
  - Provides a RPC Server and Client Codec for net/rpc communication protocol.
  - Handle unique idiosyncrasies of codecs e.g. 
    - For messagepack, configure how ambiguities in handling raw bytes are resolved 
    - For messagepack, provide rpc server/client codec to support
      msgpack-rpc protocol defined at:
      https://github.com/msgpack-rpc/msgpack-rpc/blob/master/spec.md

## Extension Support

Users can register a function to handle the encoding or decoding of
their custom types.

There are no restrictions on what the custom type can be. Some examples:

    type BisSet   []int
    type BitSet64 uint64
    type UUID     string
    type MyStructWithUnexportedFields struct { a int; b bool; c []int; }
    type GifImage struct { ... }

As an illustration, MyStructWithUnexportedFields would normally be
encoded as an empty map because it has no exported fields, while UUID
would be encoded as a string. However, with extension support, you can
encode any of these however you like.

## Custom Encoding and Decoding

This package maintains symmetry in the encoding and decoding halfs.
We determine how to encode or decode by walking this decision tree

  - is type a codec.Selfer?
  - is there an extension registered for the type?
  - is format binary, and is type a encoding.BinaryMarshaler and BinaryUnmarshaler?
  - is format specifically json, and is type a encoding/json.Marshaler and Unmarshaler?
  - is format text-based, and type an encoding.TextMarshaler?
  - else we use a pair of functions based on the "kind" of the type e.g. map, slice, int64, etc

This symmetry is important to reduce chances of issues happening because the
encoding and decoding sides are out of sync e.g. decoded via very specific
encoding.TextUnmarshaler but encoded via kind-specific generalized mode.

Consequently, if a type only defines one-half of the symmetry
(e.g. it implements UnmarshalJSON() but not MarshalJSON() ),
then that type doesn't satisfy the check and we will continue walking down the
decision tree.

## RPC

RPC Client and Server Codecs are implemented, so the codecs can be used
with the standard net/rpc package.

## Usage

Typical usage model:

    // create and configure Handle
    var (
      bh codec.BincHandle
      mh codec.MsgpackHandle
      ch codec.CborHandle
    )

    mh.MapType = reflect.TypeOf(map[string]interface{}(nil))

    // configure extensions
    // e.g. for msgpack, define functions and enable Time support for tag 1
    // mh.SetExt(reflect.TypeOf(time.Time{}), 1, myExt)

    // create and use decoder/encoder
    var (
      r io.Reader
      w io.Writer
      b []byte
      h = &bh // or mh to use msgpack
    )

    dec = codec.NewDecoder(r, h)
    dec = codec.NewDecoderBytes(b, h)
    err = dec.Decode(&v)

    enc = codec.NewEncoder(w, h)
    enc = codec.NewEncoderBytes(&b, h)
    err = enc.Encode(v)

    //RPC Server
    go func() {
        for {
            conn, err := listener.Accept()
            rpcCodec := codec.GoRpc.ServerCodec(conn, h)
            //OR rpcCodec := codec.MsgpackSpecRpc.ServerCodec(conn, h)
            rpc.ServeCodec(rpcCodec)
        }
    }()

    //RPC Communication (client side)
    conn, err = net.Dial("tcp", "localhost:5555")
    rpcCodec := codec.GoRpc.ClientCodec(conn, h)
    //OR rpcCodec := codec.MsgpackSpecRpc.ClientCodec(conn, h)
    client := rpc.NewClientWithCodec(rpcCodec)

## Running Tests

To run tests, use the following:

    go test

To run the full suite of tests, use the following:

    go test -tags alltests -run Suite

You can run the tag 'safe' to run tests or build in safe mode. e.g.

    go test -tags safe -run Json
    go test -tags "alltests safe" -run Suite

## Running Benchmarks

Please see http://github.com/ugorji/go-codec-bench .

## Caveats

Struct fields matching the following are ignored during encoding and decoding

  - struct tag value set to -
  - func, complex numbers, unsafe pointers
  - unexported and not embedded
  - unexported and embedded and not struct kind
  - unexported and embedded pointers (from go1.10)

Every other field in a struct will be encoded/decoded.

Embedded fields are encoded as if they exist in the top-level struct,
with some caveats. See Encode documentation.
