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Node.js Backend Development Bootcamp · Lección

RPC unarios, de servidor, de cliente y bidireccionales por streaming

Implemente los cuatro tipos de llamadas gRPC y elija el patrón adecuado para cada interacción.

RPC unarios, de servidor, de cliente y bidireccionales por streaming es una lección gratuita de Node.js Backend Development Bootcamp en CoddyKit. Esta es la lección 2 de 4. Puedes leer la lección completa abajo gratuitamente — luego la practicas en el navegador con un editor de código integrado y un tutor de IA 24/7. Forma parte de la ruta de aprendizaje de Node.js Backend Development Bootcamp, y tu progreso se sincroniza en la web y la app de CoddyKit. El curso de Node.js Backend Development Bootcamp incluye 4 lecciones en total.

Partes de esta lección aún no han sido traducidas y se muestran en inglés.

Four Ways to Call an RPC

gRPC defines four kinds of method in your .proto file, and each one maps to a different streaming shape:

  • Unary — one request, one response (like a normal function call).
  • Server streaming — one request, a stream of responses.
  • Client streaming — a stream of requests, one response.
  • Bidirectional streaming — both sides stream independently.

The stream keyword in the service definition is what decides the shape. In this lesson you'll implement all four in Node.js with @grpc/grpc-js and learn when to reach for each.

syntax = "proto3";
package chat;

service ChatService {
  // unary
  rpc GetUser (UserRequest) returns (User);
  // server streaming
  rpc ListMessages (RoomRequest) returns (stream Message);
  // client streaming
  rpc UploadLogs (stream LogLine) returns (UploadSummary);
  // bidirectional streaming
  rpc Chat (stream Message) returns (stream Message);
}

Loading the Proto in Node.js

Before you implement any handler, you load the .proto definition at runtime with @grpc/proto-loader and turn it into a gRPC service object with @grpc/grpc-js.

The loaded packageDefinition mirrors your proto packages and services. You attach handlers to the service with server.addService() — the names you provide must match the rpc names exactly.

const grpc = require('@grpc/grpc-js');
const protoLoader = require('@grpc/proto-loader');

const pkgDef = protoLoader.loadSync('chat.proto', {
  keepCase: true,
  longs: String,
  enums: String,
  defaults: true,
  oneofs: true,
});

const proto = grpc.loadPackageDefinition(pkgDef).chat;
const server = new grpc.Server();

// handlers get attached here
server.addService(proto.ChatService.service, { /* ... */ });

Unary RPC — One In, One Out

A unary handler receives (call, callback). The request payload is on call.request, and you reply by invoking the Node-style callback(error, response).

  • Pass null as the first argument for success.
  • Pass a { code, details } error object to signal failure.

Unary is the right choice for classic request/response work: fetching a record, validating input, performing a single mutation.

function getUser(call, callback) {
  const { id } = call.request;
  if (!id) {
    return callback({
      code: grpc.status.INVALID_ARGUMENT,
      details: 'id is required',
    });
  }
  const user = { id, name: 'Ada Lovelace' };
  callback(null, user);
}

server.addService(proto.ChatService.service, { GetUser: getUser });

Server Streaming — One In, Many Out

A server-streaming handler receives only (call) — there is no callback. You push each response with call.write(message), then signal completion with call.end().

This pattern shines when the server produces a sequence the client can consume incrementally: paginated results, log tails, progress events, or large result sets you don't want to buffer in memory.

function listMessages(call) {
  const { roomId } = call.request;
  const messages = loadMessagesForRoom(roomId); // array

  for (const msg of messages) {
    call.write({ id: msg.id, text: msg.text });
  }
  call.end(); // closes the stream to the client
}

server.addService(proto.ChatService.service, {
  ListMessages: listMessages,
});

Backpressure in Server Streaming

call.write() returns a boolean. When it returns false, the internal buffer is full and you should wait for the 'drain' event before writing more. Ignoring this on large streams can balloon memory usage.

The robust pattern wraps writes in a promise that resolves on drain, so an async loop naturally pauses when the consumer is slow.

function writeAsync(call, msg) {
  return new Promise((resolve) => {
    if (call.write(msg)) resolve();
    else call.once('drain', resolve);
  });
}

async function streamBigResult(call) {
  for (let i = 0; i < 100000; i++) {
    await writeAsync(call, { id: i, text: 'row ' + i });
  }
  call.end();
}

Client Streaming — Many In, One Out

A client-streaming handler receives (call, callback). You listen for incoming items with call.on('data', ...), do final work on call.on('end', ...), and send the single response via the callback.

Use it when the client feeds many items but you only need one aggregate result: bulk uploads, batched metrics ingestion, or computing a summary/average over a stream.

function uploadLogs(call, callback) {
  let count = 0;
  let bytes = 0;

  call.on('data', (logLine) => {
    count += 1;
    bytes += Buffer.byteLength(logLine.text || '');
  });

  call.on('end', () => {
    callback(null, { received: count, totalBytes: bytes });
  });

  call.on('error', (err) => console.error('client stream error', err));
}

Bidirectional Streaming — Many In, Many Out

A bidirectional handler receives only (call) and treats it as a duplex stream: read incoming items with call.on('data', ...) and emit responses with call.write(...) at any time. Both directions are fully independent.

This is ideal for chat, multiplayer state sync, or live request/response negotiation where either side may speak first or out of lockstep.

function chat(call) {
  call.on('data', (msg) => {
    // echo every message back to the sender, augmented
    call.write({ id: msg.id, text: 'echo: ' + msg.text });
  });

  call.on('end', () => call.end());
  call.on('error', (err) => console.error('chat error', err));
}

server.addService(proto.ChatService.service, { Chat: chat });

Calling From a gRPC Client

The client API mirrors the server shapes. Unary returns via a callback; server streaming returns a readable stream you iterate with 'data'; client streaming gives you a writable stream you write() to and then end(); bidirectional gives you both at once.

The single rule: the stream keyword on each side of the proto determines whether you get a callback or a stream object.

const client = new proto.ChatService(
  'localhost:50051',
  grpc.credentials.createInsecure(),
);

// unary
client.GetUser({ id: '1' }, (err, user) => console.log(user));

// server streaming
const stream = client.ListMessages({ roomId: 'general' });
stream.on('data', (m) => console.log(m.text));
stream.on('end', () => console.log('done'));

Mental Model: Pick by Cardinality

Choosing the right RPC type is almost always a question of cardinality on each side:

  • One request, one response → unary.
  • One request, results arrive over time → server streaming.
  • Many inputs collapsed into one result → client streaming.
  • Continuous, independent two-way flow → bidirectional.

Don't reach for streaming just because data is large — pagination over unary calls is often simpler. Reach for streaming when the data is open-ended in time or genuinely incremental.

A Runnable Cardinality Picker

Here's a tiny, framework-free helper that encodes the decision rule above. It takes whether each side streams and returns the gRPC method type — useful as a sanity check when designing a service.

This is plain JavaScript with no gRPC dependency, so an online judge can run it directly.

function rpcType(clientStreams, serverStreams) {
  if (!clientStreams && !serverStreams) return 'unary';
  if (!clientStreams && serverStreams) return 'server-streaming';
  if (clientStreams && !serverStreams) return 'client-streaming';
  return 'bidirectional';
}

console.log(rpcType(false, false)); // unary
console.log(rpcType(false, true));  // server-streaming
console.log(rpcType(true, false));  // client-streaming
console.log(rpcType(true, true));   // bidirectional

Errors, Deadlines, and Cleanup

Across all four types, a few production habits matter:

  • Always attach call.on('error', ...) on streaming handlers — an unhandled stream error can crash the process.
  • Respect deadlines: check call.cancelled in long loops and stop writing if the client gave up.
  • For client/bidi streams, do final work in 'end', not after the first 'data'.
  • Send domain errors with grpc.status codes (e.g. NOT_FOUND, INVALID_ARGUMENT) rather than throwing raw exceptions.
function listMessages(call) {
  let i = 0;
  const timer = setInterval(() => {
    if (call.cancelled) { clearInterval(timer); return; }
    if (i >= 10) { clearInterval(timer); return call.end(); }
    call.write({ id: i, text: 'tick ' + i++ });
  }, 100);

  call.on('error', () => clearInterval(timer));
}

Quick Check

Test your understanding of choosing the right RPC type.

Recap

You now know all four gRPC call shapes and how to implement them in Node.js with @grpc/grpc-js:

  • Unary — (call, callback); read call.request, reply once.
  • Server streaming — (call); call.write() repeatedly, then call.end(), minding backpressure via 'drain'.
  • Client streaming — (call, callback); aggregate on 'data', respond once on 'end'.
  • Bidirectional — (call); read and write independently for live, two-way flows.

Choose by cardinality and whether the data is open-ended in time, always handle stream errors, and respect client deadlines with call.cancelled.

Preguntas frecuentes

¿La lección «RPC unarios, de servidor, de cliente y bidireccionales por streaming» es gratis?

Sí — el texto completo de «RPC unarios, de servidor, de cliente y bidireccionales por streaming» es gratis para leer aquí en la web. Para practicarla de forma interactiva (editor de código integrado y tutor de IA 24/7) y desbloquear el resto del curso de Node.js Backend Development Bootcamp, actualiza a CoddyKit PRO. El curso de Node.js Backend Development Bootcamp incluye 4 lecciones en total.

¿Qué aprenderé en «RPC unarios, de servidor, de cliente y bidireccionales por streaming»?

Implemente los cuatro tipos de llamadas gRPC y elija el patrón adecuado para cada interacción. Practicas Node.js Backend Development Bootcamp con código real que ejecutas directamente en el navegador, y un tutor de IA 24/7 responde tus preguntas mientras trabajas en la lección.

¿Necesito experiencia previa para empezar Node.js Backend Development Bootcamp?

No se requiere experiencia previa. Node.js Backend Development Bootcamp en CoddyKit está estructurado para principiantes hasta estudiantes avanzados, así que puedes empezar aquí o desde el inicio y avanzar a tu ritmo. Esta es la lección 2 de 4.

¿Cuánto tiempo toma la lección «RPC unarios, de servidor, de cliente y bidireccionales por streaming»?

La mayoría de las lecciones de CoddyKit toman alrededor de 5–10 minutos. Cada una es compacta e interactiva, así que avanzas constantemente y retomas exactamente por donde dejaste en la web y la app.

¿Puedo escribir y ejecutar código en esta lección de Node.js Backend Development Bootcamp?

Sí. Cada lección de Node.js Backend Development Bootcamp incluye un editor de código integrado, así que escribes y ejecutas código real directamente en tu navegador y obtienes retroalimentación instantánea de IA — sin configuración local necesaria.

Todas las lecciones de este curso

  1. Definición de servicios y mensajes con Protobuf IDL
  2. RPC unarios, de servidor, de cliente y bidireccionales por streaming
  3. Interceptores, plazos y metadatos
  4. Evolución de Proto y compatibilidad hacia atrás
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