Can I send a custom Error message from server to client GRPC?

[kanishka]

I am working with Node js and GRPC . i have created a simple GRPC server and client . 

What i want to do is create a custom error in the server and pass it to the client . my code looks like this .

Server.js

var error = require('error');

var PROTO_PATH = grpc.load(__dirname + '/proto/hello.proto');
var hello_proto = PROTO_PATH.hello;

function sayHello(call, callback) {

    try {
        var jsErr = new Error('MY_ERROR');
        jsErr.newStatus = 401;
        jsErr.newMessage = 'custom unAuthorized error';
        console.log(Object.getOwnPropertyNames(jsErr));
        console.log(jsErr);
        callback(jsErr);

    } catch(e) {
        callback(e);
    }
}

function sayHelloAgain(call, callback) {
    callback(null, {message: 'Hello Again ' + call.request.name});
}

function main() {

    var server = new grpc.Server();
    server.addProtoService(hello_proto.Hello.service, {sayHello: sayHello,sayHelloAgain: sayHelloAgain });
    server.bind('0.0.0.0:50051', grpc.ServerCredentials.createInsecure());
    server.start();
}

main();

Client.js

var grpc = require('grpc');

var PROTO_PATH = grpc.load(__dirname + '/proto/hello.proto');
var hello_proto = PROTO_PATH.hello;

function main() {
    var client = new hello_proto.Hello('localhost:50051',grpc.credentials.createInsecure());
    var user;
    if (process.argv.length >= 3) {
        user = process.argv[2];
    } else {
        user = 'world';
    }

    client.sayHello({name: user}, function(err, response) {

        console.log(Object.getOwnPropertyNames(err));
        console.log(err);
    });
}

main();

and my proto file 

syntax = "proto3";

package hello;

service Hello {
    rpc sayHello(sayHelloRequest) returns (sayHelloResponse) {}
    rpc sayHelloAgain(sayHelloRequest) returns (sayHelloResponse) {}
}


message sayHelloRequest {
    string name = 1;
}

message sayHelloResponse {
    string message = 1;
}

when i run the cient the result from each looks like this 

Server .

[ 'stack', 'message', 'newStatus', 'newMessage' ]
{ [Error: MY_ERROR] newStatus: 401, newMessage: 'custom unAutorized error' }

Client .

[ 'stack', 'message', 'code', 'metadata' ]
{ [Error: MY_ERROR] code: 2, metadata: Metadata { _internal_repr: {} } }

So my created custom javascript error's newStatus, newMessage properties have removed and it has converted to GRPC standard error message . 

My Questions are 

1. Is it possible to send a custom message to client ?
2. Can i create a GRPC error , not a javascript error ?
3. one way to send custom attributes to client is i think is add the custom data to Metadata . but i am also not sure how to do it . 

Please help . Thanks in advance .

[Michael Lumish]

You can send a custom status message to the client using the Error object's message property. In your example, that is "MY_ERROR". The status code should be in the "code" property, just like how you see it on the client side.

If you want to use the gRPC status structure instead of a JavaScript error, you can do so by populating the "code" property and the "message" or "details" property of the object.

If you want to send metadata, you should construct an instance of the grpc.Metadata class, then add key/value pairs to the resulting object. Then you can pass it as the third argument of the callback or set the error's "metadata" property to send it to the client with the error.

Please note that the status codes that gRPC uses are not HTTP status codes, but gRPC specific codes that are defined in grpc.status. You should only set the error's code property using those codes. If you want to send your own codes, use metadata instead.

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