05 Errors and status codes

gRPC has a standard set of status codes (like HTTP status codes, but for RPC). Instead of throwing exceptions, the server passes an error object with a code and message to the callback. The client receives it as an err in the callback (unary) or an error event (streaming).

Update sayHello to validate input

// server.js — updated sayHello
function sayHello(call, callback) {
  if (!call.request.name) {
    return callback({
      code: grpc.status.INVALID_ARGUMENT,
      message: "name required",
    });
  }
  callback(null, { message: `Hello, ${call.request.name}` });
}

Handle the error in the client

// client.js — handle the error case
client.SayHello({ name: "" }, (err, response) => {
  if (err) {
    console.error(`error ${err.code}: ${err.details}`);
    return;
  }
  console.log(response.message);
});

Common gRPC status codes

Code	Value	Meaning
OK	0	Success
CANCELLED	1	Operation cancelled by caller
INVALID_ARGUMENT	3	Bad input from the client
NOT_FOUND	5	Resource does not exist
ALREADY_EXISTS	6	Resource already exists
PERMISSION_DENIED	7	Not authorized
INTERNAL	13	Server-side error
UNAVAILABLE	14	Server is down or overloaded
DEADLINE_EXCEEDED	4	Call ran past its deadline

Use grpc.status.<NAME> in Node — they are integers under the hood.

Checkpoint

Update server.js with the validation. Then call with an empty name:

node client.js   # with name: ""
# error 3: name required

3 is INVALID_ARGUMENT. Call with a valid name and you still get Hello, Ada.

Next: 06 Deadlines and run