codec: simplify codec interface

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

codec/codec.go

@@ -3,17 +3,6 @@ package codec // import "go.unistack.org/micro/v3/codec"
 
 import (
 	"errors"
-	"io"
-
-	"go.unistack.org/micro/v3/metadata"
-)
-
-// Message types
-const (
-	Error MessageType = iota
-	Request
-	Response
-	Event
 )
 
 var (
@@ -32,42 +21,13 @@ var (
 	DefaultTagName = "codec"
 )
 
-// MessageType specifies message type for codec
-type MessageType int
-
-// Codec encodes/decodes various types of messages used within micro.
-// ReadHeader and ReadBody are called in pairs to read requests/responses
-// from the connection. Close is called when finished with the
-// connection. ReadBody may be called with a nil argument to force the
-// body to be read and discarded.
+// Codec encodes/decodes various types of messages.
 type Codec interface {
-	ReadHeader(r io.Reader, m *Message, mt MessageType) error
-	ReadBody(r io.Reader, v interface{}) error
-	Write(w io.Writer, m *Message, v interface{}) error
 	Marshal(v interface{}, opts ...Option) ([]byte, error)
 	Unmarshal(b []byte, v interface{}, opts ...Option) error
 	String() string
 }
 
-// Message represents detailed information about
-// the communication, likely followed by the body.
-// In the case of an error, body may be nil.
-type Message struct {
-	Header   metadata.Metadata
-	Target   string
-	Method   string
-	Endpoint string
-	Error    string
-	ID       string
-	Body     []byte
-	Type     MessageType
-}
-
-// NewMessage creates new codec message
-func NewMessage(t MessageType) *Message {
-	return &Message{Type: t, Header: metadata.New(0)}
-}
-
 // MarshalAppend calls codec.Marshal(v) and returns the data appended to buf.
 // If codec implements MarshalAppend, that is called instead.
 func MarshalAppend(buf []byte, c Codec, v interface{}, opts ...Option) ([]byte, error) {