gRPC & Kafka — Series 2

Preview — 3 of 10 questions

Why does removing a field require the reserved declaration?

javascript

message Order {
  string id = 1;
  // string coupon = 2;   removed in v2
  int32 amount = 3;
  reserved 2;
  reserved "coupon";
}

ABecause the compiler refuses to generate code for a message with a gap in its numbering

BBecause reserved fields are still transmitted, preserving the message's byte layout

CBecause reserved retains the field for one release so old clients keep receiving it

DBecause field numbers, not names, identify data on the wire — reusing number 2 for a different type later would make old producers' bytes decode as the new field, silently corrupting data; reserving the number and name makes that mistake a compile error

How does a deadline differ from an ordinary client-side timeout?

javascript

const metadata = new Metadata();
this.ordersService.findOne({ id }, metadata, { deadline: Date.now() + 2000 });

AIt is enforced only by the client, exactly like a timeout, but with nicer syntax

BIt is transmitted to the server, which can observe it, abort work when it passes, and propagate the remaining budget to its own downstream calls — so the whole call tree stops instead of continuing work nobody is waiting for

CIt applies per message in a stream rather than to the call as a whole

DIt causes the server to queue the request until it can be served within the deadline

What distinguishes this from throwing NotFoundException?

javascript

throw new RpcException({ code: status.NOT_FOUND, message: 'Order not found' });

ANothing; Nest converts HTTP exceptions to gRPC statuses automatically

BRpcException is only valid in event handlers, not in gRPC methods

CgRPC has its own status code space (NOT_FOUND, INVALID_ARGUMENT, PERMISSION_DENIED, …) that is not HTTP's; RpcException carries a code from that space, whereas an HTTP exception thrown from a gRPC handler reaches the client as a generic UNKNOWN with its details flattened into a message string

DRpcException is caught by exception filters while NotFoundException is not

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