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relay_codec.go
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/
relay_codec.go
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// Copyright 2021 PairMesh, Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package codec
import (
"bytes"
"encoding/binary"
"errors"
"github.com/pairmesh/pairmesh/constant"
"github.com/pairmesh/pairmesh/message"
)
type (
RelayCodec struct {
buf *bytes.Buffer
size int
typ message.PacketType
nonce uint32
}
RawPacket struct {
Type message.PacketType
Nonce uint32
Payload []byte
}
)
func NewCodec() *RelayCodec {
return &RelayCodec{
buf: bytes.NewBuffer(nil),
size: -1,
}
}
// Encode encodes the protobuf message in relay command form into bytes.
func (c *RelayCodec) Encode(nonce uint32, typ message.PacketType, data []byte) ([]byte, error) {
payloadSize := uint32(len(data))
// Command packet format:
// | nonce(4bytes) | type(2bytes) | payload size (4bytes) | payload |
buffer := make([]byte, constant.PacketHeaderSize+payloadSize)
// nonce
from := 0
to := constant.HeaderNonceSize
binary.BigEndian.PutUint32(buffer[:to], nonce)
// type
from = constant.HeaderNonceSize
to = from + constant.HeaderPacketTypeSize
typeNumber := uint16(typ) ^ uint16(nonce&(1<<16-1))
binary.BigEndian.PutUint16(buffer[from:to], typeNumber)
// payload size
from = constant.HeaderNonceSize + constant.HeaderPacketTypeSize
to = constant.PacketHeaderSize
binary.BigEndian.PutUint32(buffer[from:to], payloadSize)
// payload
from = constant.PacketHeaderSize
copy(buffer[from:], data)
return buffer, nil
}
// Decode decodes the protobuf message into MERP command.
func (c *RelayCodec) Decode(input []byte) ([]RawPacket, error) {
c.buf.Write(input)
// Check the buffer size to ensure at-least have one message.
if c.buf.Len() < constant.PacketHeaderSize {
return nil, nil
}
readHeader := func() {
header := c.buf.Next(constant.PacketHeaderSize)
// nonce
from := 0
to := constant.HeaderNonceSize
nonce := binary.BigEndian.Uint32(header[:to])
// type
from = constant.HeaderNonceSize
to = from + constant.HeaderPacketTypeSize
typeNumber := binary.BigEndian.Uint16(header[from:to])
typ := message.PacketType(typeNumber ^ uint16(nonce&(1<<16-1)))
// frame size
from = constant.HeaderNonceSize + constant.HeaderPacketTypeSize
to = constant.PacketHeaderSize
c.size = int(binary.BigEndian.Uint32(header[from:to]))
c.typ = typ
c.nonce = nonce
}
// Negative size means there is no reading message.
if c.size < 0 {
readHeader()
}
var output []RawPacket
// Read all messages.
for c.size > 0 && c.size <= c.buf.Len() {
if c.size > constant.MaxMessageSize {
return nil, errors.New("message size exceed")
}
// RawPacket content
buffer := c.buf.Next(c.size)
payload := make([]byte, len(buffer))
copy(payload, buffer)
output = append(output, RawPacket{
Type: c.typ,
Nonce: c.nonce,
Payload: payload,
})
// Read the next command header.
if c.buf.Len() >= constant.PacketHeaderSize {
readHeader()
} else {
c.size = -1
}
}
return output, nil
}