How to instantiate Service?

[pronebird]

Hi,

I am following the example at https://github.com/dcodeIO/protobuf.js/wiki/Services and creating my RPC.

Everything seems fine but I cannot create a new instance of Service. it says:

Service is not a constructor

  var Service = root.lookup('MailService');
  var RequestType = root.lookup('RequestType');
  var ResponseType = root.lookup('ResponseType');

  function rpcHandler(method, req, callback) {
    var request = RequestType.decode(data);
    var response = new ResponseType();

    if(method === '.MailService.addMailbox') {
      // add mailbox
    } else if(method === '.MailService.removeMailbox') {
     // remove mailbox
    }

    callback(response.toBuffer());
  }

  var srv = new Service(rpcHandler); // CRASH

[dcodeIO]

The wiki refers to protobuf.js 5.

Using protobuf.js 6, services are instances of the service class here. You can look them up, but there is not a lot of functionality within. You can, however, get the resolved request and response types of the respective methods.

var service = root.lookup("MyService");
var method = service.methods["myMethod"].resolve();

var reqType = method.resolvedRequestType;
var resType = method.resolvedResponseType;
...

There has been a bit of discussion previously to support use cases like grpc out of the box, but as I am not using services myself, I'd require some suggestions.

[dcodeIO]

This commit adds the following API:

var MyService = root.lookup("MyService");

// First, implement the RPC channel:
function rpc(method, requestData, callback) {
  // send requestData (binary) over the network
  ...
  // then call the callback with error, if any, and the received responseData (binary)
  callback(null, responseData);
}

// Create a runtime service:
var myService = MyService.create(/* your rpc implementation */ rpc, /* requestDelimited? */ true, /* responseDelimited? */ true);

// Call its methods (uses your RPC channel)
myService.MyMethod({ awesomeField: "awesomeText" }, function(err, responseMessage) {
   ...
});

[dcodeIO]

Feel free to reopen if there are still any issues or if you have a suggestion on how this should be implemented.

[pronebird]

@dcodeIO thanks Daniel! Works like a charm!

One quick question, maybe I found a bug...:

So in RPC I do this:

function rpc(method, requestData, callback) {
  var RequestType = root.lookup('RequestType');

  // CRASH in ReaderPrototype.skip on throw indexOutOfRange(this);
  var request = RequestType.decode(requestData); 

Trying to debug:

$ requestData.toString()
"\u0000"

I know it's silly that my messages are empty at the moment, but I guess it shouldn't crash anyway and it's good for QA:

message RequestType {}
message ResponseType {}

service MailService {
  rpc addMailbox(RequestType) returns (ResponseType);
  rpc removeMailbox(RequestType) returns (ResponseType);
}

[dcodeIO]

So, your messages are length delimited, right? Did you specify that to Service.create?

var myService = MyService.create(/* your rpc implementation */ rpc, /* requestDelimited? */ true, /* responseDelimited? */ true);

Otherwise the length-bytes will be interpreted as message contents and throwing there is actually what it should do.

[pronebird]

Well I am not sure whether message without any fields is delimited or not. But if I create RPC with MailService.create(rpc, false, false) then it works fine. It feels like if there are no any fields in message then it shouldn't attempt to read it..

[dcodeIO]

Above you mentioned that, in one of your messages, there was a single zero byte:

$ requestData.toString()
"\u0000"

That's why I assumed that it is a length-delimited empty message which of course throws if interpreted as a non-delimited message.

[pronebird]

Yeah strange, that's how I call the method:

service.addMailbox(RequestType.create(), function (err, res) {
    console.log(err);
});

Not sure where 0-byte comes from. RequestType as is without any fields.

Update: if I specify that request is length delimited then rpc receives a buffer with one 0-byte, otherwise 0-length buffer is received.

[dcodeIO]

Strange. in fact. The code encoding to a buffer is here: https://github.com/dcodeIO/protobuf.js/blob/master/src/service.js#L159

If shouldn't generate the zero byte, except if there is something true-ish specified for requestDelimited.

[pronebird]

This is the source code if it helps ( bare bones)

#!/usr/bin/env node

var ProtoBuf = require("protobufjs");

ProtoBuf.load('mailservice.proto', function (err, root) {
  var MailService = root.lookup('MailService');
  var RequestType = root.lookup('RequestType');
  var ResponseType = root.lookup('ResponseType');

  function rpc(method, requestData, callback) {
    var request = RequestType.decode(requestData);

    if(method.fullName === '.MailService.addMailbox') {
      // add mailbox
      var response = ResponseType.create();
      callback(null, response);
    } else if(method.fullName === '.MailService.removeMailbox') {
      // remove mailbox
      var response = ResponseType.create();
      callback(null, response);
    } else {
      throw new Error('Not implemented.');
    }
  }

  var service = MailService.create(rpc, true, false);
  service.addMailbox(RequestType.create(), function (err, res) {
    console.log(err);
  });
});

mailservice.proto:

syntax="proto3";

message Mailbox {
  required string name = 1;
  repeated Mail messages = 2;
}

message Mail {
  string subject = 1;
  string body = 2;
}

message RequestType {}
message ResponseType {}

service MailService {
  rpc addMailbox(RequestType) returns (ResponseType);
  rpc removeMailbox(RequestType) returns (ResponseType);
}

[pronebird]

Hey, quick question:

so with Protobuf.js I can create RPC server in Node.js and that's pretty clear, however, how do I define an RPC client? Do I have to funnel data to remote RPC and pass back results somehow? I use ZeroMQ as transport to pass data between processes. As I understand there is no Rpc channel/controller for that so I have to implement all of that myself?

i.e:

message RpcCall {
  string method = 1;
  bytes message = 2;
}

[dcodeIO]

There is an example in the README.

There is also a streaming rpc example here.

It basically works the same way on a client or a server. You just have to implement rpcImpl accordingly.