message.go

/*
Copyright (c) 2014 Ashley Jeffs

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
*/

package types

//--------------------------------------------------------------------------------------------------

// Message - A struct containing any relevant fields of a benthos message and helper functions.
type Message struct {
	Parts [][]byte `json:"parts"`
}

// NewMessage - Initializes an empty message.
func NewMessage() Message {
	return Message{
		Parts: [][]byte{},
	}
}

//--------------------------------------------------------------------------------------------------

/*
Internal message blob format:

- Four bytes containing number of message parts in big endian
- For each message part:
    + Four bytes containing length of message part in big endian
    + Content of message part

                                         # Of bytes in message 2
                                         |
# Of message parts (big endian)          |           Content of message 2
|                                        |           |
v                                        v           v
| 0| 0| 0| 2| 0| 0| 0| 5| h| e| l| l| o| 0| 0| 0| 5| w| o| r| l| d|
  0  1  2  3  4  5  6  7  8  9 10 11 13 14 15 16 17 18 19 20 21 22
              ^           ^
              |           |
              |           Content of message 1
              |
              # Of bytes in message 1 (big endian)
*/

// Reserve  bytes for our length counter (4 * 8 = 32 bit)
var intLen uint32 = 4

// Bytes - Serialise the message into a single byte array.
func (m *Message) Bytes() []byte {
	lenParts := uint32(len(m.Parts))

	l := (lenParts + 1) * intLen
	for i := range m.Parts {
		l += uint32(len(m.Parts[i]))
	}
	b := make([]byte, l)

	b[0] = byte(lenParts >> 24)
	b[1] = byte(lenParts >> 16)
	b[2] = byte(lenParts >> 8)
	b[3] = byte(lenParts)

	b2 := b[intLen:]
	for i := range m.Parts {
		le := uint32(len(m.Parts[i]))

		b2[0] = byte(le >> 24)
		b2[1] = byte(le >> 16)
		b2[2] = byte(le >> 8)
		b2[3] = byte(le)

		b2 = b2[intLen:]

		copy(b2, m.Parts[i])
		b2 = b2[len(m.Parts[i]):]
	}
	return b
}

// FromBytes - Deserialise a Message from a byte array.
func FromBytes(b []byte) (Message, error) {
	var m Message

	if len(b) < 4 {
		return m, ErrBadMessageBytes
	}

	numParts := uint32(b[0])<<24 | uint32(b[1])<<16 | uint32(b[2])<<8 | uint32(b[3])
	if numParts >= uint32(len(b)) {
		return m, ErrBadMessageBytes
	}

	m.Parts = make([][]byte, numParts)

	b = b[4:]

	for i := uint32(0); i < numParts; i++ {
		if len(b) < 4 {
			return m, ErrBadMessageBytes
		}
		partSize := uint32(b[0])<<24 | uint32(b[1])<<16 | uint32(b[2])<<8 | uint32(b[3])
		b = b[4:]

		if uint32(len(b)) < partSize {
			return m, ErrBadMessageBytes
		}
		m.Parts[i] = b[:partSize]
		b = b[partSize:]
	}
	return m, nil
}

//--------------------------------------------------------------------------------------------------