message.go

package netlink

/*
  Copyright (c) 2011, Abneptis LLC. All rights reserved.
  Original Author: James D. Nurmi <james@abneptis.com>

  See LICENSE for details
*/

import (
	"errors"
	"fmt"
)
import "bytes"

import "io"

// A netlink message contains a Netlink header,
// and a body of bytes.
type Message struct {
	Header *Header
	Body   []byte
}

// NetlinkMarshaler's are used to format netlink data.
type NetlinkMarshaler interface {
	MarshalNetlink() ([]byte, error)
}

// Creates a new message from a marshalable object
func NewMessage(t MessageType, f MessageFlags, u NetlinkMarshaler) (msg *Message, err error) {
	msg = &Message{Header: NewHeader(t, f, 0)}
	msg.Body, err = u.MarshalNetlink()
	if err == nil {
		msg.Header.SetMessageLength(uint32(msg.Header.Len()) + uint32(len(msg.Body)))
	}
	return
}

// Reads a message from an io.Reader, with attributes alinged to 4 bytes.
// NB: Netlink uses a very strict protocol, and it is encouraged
// that r be a bufio.Reader
func ReadMessage(r io.Reader) (msg *Message, err error) {
	var n int
	msg = &Message{Header: &Header{}}
	ib := make([]byte, msg.Header.Len())
	n, err = r.Read(ib)
	if err == nil && n != msg.Header.Len() {
		err = errors.New("Incomplete netlink header")
	}
	if err == nil {
		err = msg.Header.UnmarshalNetlink(ib)
		if err == nil {
			msg.Body = make([]byte, msg.Header.MessageLength()-uint32(msg.Header.Len()))
			n, err = r.Read(msg.Body)
			if err == nil && n != int(msg.Header.MessageLength())-int(msg.Header.Len()) {
				err = errors.New(fmt.Sprintf("Incomplete netlink message body (Got: %d; Expected: %d)", n, int(msg.Header.MessageLength())-int(msg.Header.Len())))
			} else {
			}
		}
	}
	return
}

// Marshals a message with aligned attributes..
func (self Message) MarshalNetlink() (out []byte, err error) {
	hdrout, err := self.Header.MarshalNetlink()
	if err == nil {
		out = bytes.Join([][]byte{hdrout, self.Body}, []byte{})
	}
	return
}