可以将protobuf元帅消息发送到已分配的字节数组而无需复制吗？

Question

I am implementing client server communication by self defined packets. I am using Go net.conn. It can dial tcp/unix schemes which is very convenient. I use protocol buffer to define my messages.

I defined a Packet which contains length and buffer

type Packet struct {
    length uint32
    buffer []byte
}

The API function is like this:
func(api *API) Send(m *proto.Message) error
func(api *API) Receive(p *Packet) error

Take send function as an example, it takes in a protobuf message, marshal it into Packet. And write it to the net.conn.

Here is a simplified version of the Send function:

func(api *API) Send(m *proto.Message) error {
    bytes, err := proto.Marshal(m)
    if err != nil {
        return err
    }
    buffer := api.packet[:length]
    copy(buffer, bytes)
    _, err := api.conn.Write(buffer)
    if err != nil {
        return err
    }
    return nil
}

I was copying bytes into buffer. Because Go protocol buffer API only provides
func Marshal(pb Message) ([]byte, error)

In protocol buffer C++, it provides bool SerializeToArray(void * data, int size) const, which is serializing the message and storing it in the given byte array. But I can not find the same thing in Go protocol buffer API.

Is there any way to avoid the copy if I want to directly storing serialized result in the given byte array?

Answer 1

It is not clear what you are asking. Notice that the proto Marshal() function does exactly what you are looking for: It serializes the message into a byte slice (what you probably mean by byte array)

See if either of these help:

func(api *API) Send(m *proto.Message) error {
    p := Packet{}
    p.buffer, err := proto.Marshal(m)
    if err != nil {
        return err
    }
    _, err := api.conn.Write(p.buffer)
    if err != nil {
        return err
    }
    return nil
}

Or

func(api *API) Send(m *proto.Message) error {
    buffer := api.packet[:length]
    buffer, err := proto.Marshal(m)
    if err != nil {
        return err
    }
    _, err := api.conn.Write(buffer)
    if err != nil {
        return err
    }
    return nil
}