server msgpack practise

[ZPL]

Hi list:

I'm now building a tcp server, use  https://github.com/ugorji/go to serilize/deserialize all messages between clients and server, I have some question on converting the decoded "interface" to correct types.

here's the example:

// client will send following 2 kinds of message to server

type HeartbeatMsg struct {

    Msgid int

    Seq   int

}

type LoginMsg struct {

    Msgid       int

    Username    string

    Password    string

}

// handle hearbeat msg

func handlHeartbeat(msg *HeartbeatMsg , conn net.Conn) {

    

}

// handle login msg

func handleLogin(msg *LoginMsg,conn net.Conn) {

    

}

func handleMsg(conn net.Conn) {

    var MsgpackHandle codec.MsgpackHandle

    // create a decoder for conn

    d := codec.NewDecoder(conn, &golib.MsgpackHandle)

    for {

        // use interface because we don't know what exactely client send to us

        var imsg interface{}

        err := d.Decode(&msg)

        // what can I do here to convert imsg to HeartbeatMsg or LoginMsg?
     }

}

Currently, I know there is Msgid of int at the begining of client message, I can access imsg with reflect to get that value, then make a deep copy of imsg to destination.

But there are cases that client messages don't share a COMMON HEADER, there should be a clean way to archive this.

[Giulio Iotti]

On Tuesday, December 8, 2015 at 4:33:47 PM UTC+1, ZPL wrote:

Currently, I know there is Msgid of int at the begining of client message, I can access imsg with reflect to get that value, then make a deep copy of imsg to destination.

But there are cases that client messages don't share a COMMON HEADER, there should be a clean way to archive this.

The clean way is not to use reflection and make a real interface: https://play.golang.org/p/crVgeYVU6v

-- 

Giulio Iotti

 

[刘志平]

thanks Giulio, but it's different. 

In my case,  imsg is "pure" interface, not a reference to user defined struct, so I can't use type assert on imsg.

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刘志平

[MODCLOUD LU]

sorry I used wrong email address to reply.

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--刘志平

[Konstantin Shaposhnikov]

switch m := msg.(type) {
case HeartbeatMsg:
    // m is a HeartbeatMsg
case LoginMsg:
    // m is a LoginMsg
default:
    // m is some other type that we didn't name.
}

[MODCLOUD LU]

Sorry I didn't make it clear, This question is related to msgpack seriliazation, here:

https://github.com/ugorji/go/tree/master/codec#readme

Take the example again:

var MsgpackHandle codec.MsgpackHandle

d := codec.NewDecoder(conn, MsgpackHandle)

var msg interface{}

d.Decode(&msg)

logger.Info("type name:%s", reflect.ValueOf(msg).Kind())

It will print "slice" NOT "struct". so I can't do type assertion.

--刘志平

[Giulio Iotti]

On Wednesday, December 9, 2015 at 4:02:38 PM UTC+2, ZPL wrote:

It will print "slice" NOT "struct". so I can't do type assertion.

Then you have a slice of interface{} that you can use the type switch on:

ms := msg.([]interface{})

for _, m := range ms {

    // type switch as shown above...

} 

-- 

Giulio Iotti

[Konstantin Shaposhnikov]

Correct me if I am wrong but I beleive that msgpack doesn't encode the type of the struct that you send. You will have to do send it together with the message. But instead of re-implementing RPC protocol yourself maybe you can use an existing one, such as grpc?

[ZP L]

yes, this might solve my problem, I'll try later!

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--刘志平

[ZP L]

yes. msgpack doesn't encode the type of struct, and for some reason, my server is not using RPC, but RPC seems to be a right choice.