nice-grpc-server-middleware-terminator

Server middleware for nice-grpc that makes it possible to prevent long-running calls from blocking server graceful shutdown.

When server.shutdown() is called, the server stops accepting new calls, but the returned promise only resolves once all inflight requests finish. If you have a long-running call like an infinite stream, the shutdown will block until the client cancels the call. With this middleware, service implementation methods can alter this behavior, so that on shutdown the call would be aborted and clients would receive gRPC error UNAVAILABLE: Server shutting down.

Installation

npm install nice-grpc-server-middleware-terminator

Usage

Consider the following service definition with a streaming method:

service ExampleService {
  rpc ExampleMethod(ExampleRequest)
    returns (stream ExampleResponse) {};
}

In this example implementation we emit a response every second until aborted:

import {ServiceImplementation, CallContext} from 'nice-grpc';
import {TerminatorContext} from 'nice-grpc-server-middleware-terminator';
import {delay} from 'abort-controller-x';
import {
  ExampleServiceDefinition,
  ExampleRequest,
  ExampleResponse,
  DeepPartial,
} from './compiled_proto/example';

const exampleServiceImpl: ServiceImplementation<
  typeof ExampleServiceDefinition,
  TerminatorContext
> = {
  async *exampleMethod(
    request: ExampleRequest,
    context: CallContext & TerminatorContext,
  ): AsyncIterable> {
    // When `terminatorMiddleware.terminate()` is called, `context.signal` will
    // be aborted. Note that the method is still responsible for aborting all
    // the work once `context.signal` is aborted.
    context.abortOnTerminate();

    while (true) {
      await delay(context.signal, 1000);

      yield {
        /* ... */
      };
    }
  },
};

Attach the middleware to the server and terminate it before shutdown:

import {createServer} from 'nice-grpc';
import {TerminatorMiddleware} from 'nice-grpc-server-middleware-terminator';
import {ExampleServiceDefinition} from './compiled_proto/example';

const terminatorMiddleware = TerminatorMiddleware();

const server = createServer().use(terminatorMiddleware);
server.add(ExampleServiceDefinition, exampleServiceImpl);
await server.listen('0.0.0.0:8080');

// ... terminate middleware before shutdown:

terminatorMiddleware.terminate();
await server.shutdown();