TypeScript client#

pw_rpc: Efficient, low-code-size RPC system for embedded devices

Pigweed TypeScript client provides two ways to call RPCs. The Device API is easier to work with if you are using the RPC via HDLC over WebSerial.

If the device abstraction is not a good fit, Pigweed provides pw_rpc module, which makes it possible to call Pigweed RPCs from TypeScript. The module includes client library to facilitate handling RPCs.

Creating an RPC Client#

The RPC client is instantiated from a list of channels and a set of protos.

import { ProtoCollection } from 'pigweedjs/protos/collection';

const channels = [new Channel(1, savePacket), new Channel(5)];
const client = Client.fromProtoSet(channels, new ProtoCollection());

function savePacket(packetBytes: Uint8Array): void {
  const packet = RpcPacket.deserializeBinary(packetBytes);
  ...
}

To generate a ProtoSet/ProtoCollection from your own .proto files, use pw_proto_compiler in your package.json like this:

...
"scripts": {
  "build-protos": "pw_proto_compiler -p protos/rpc1.proto -p protos/rpc2.proto --out dist/protos",

This will generate a collection.js file which can be used similar to above example.

Finding an RPC Method#

Once the client is instantiated with the correct proto library, the target RPC method is found by searching based on the full name: {packageName}.{serviceName}.{methodName}

const channel = client.channel()!;
unaryStub = channel.methodStub('pw.rpc.test1.TheTestService.SomeUnary')!
    as UnaryMethodStub;

The four possible RPC stubs are UnaryMethodStub, ServerStreamingMethodStub, ClientStreamingMethodStub, and BidirectionalStreamingMethodStub. Note that channel.methodStub() returns a general stub. Since each stub type has different invoke parameters, the general stub should be typecast before using.

Invoke an RPC with callbacks#

invoke(request?: Message,
    onNext: Callback = () => {},
    onCompleted: Callback = () => {},
    onError: Callback = () => {},
    maxResponses: number = DEFAULT_MAX_STREAM_RESPONSES): Call

All RPC methods can be invoked with a set of callbacks that are triggered when either a response is received, the RPC is completed, or an error occurs. The example below demonstrates registering these callbacks on a Bidirectional RPC. Other RPC types can be invoked in a similar fashion. The request parameter may differ slightly between RPC types.

Server streaming and bidirectional streaming methods can receive many responses from the server. The client limits the maximum number of responses it stores for a single RPC call to avoid unbounded memory usage in long-running streams. Once the limit is reached, the oldest responses will be replaced as new ones arrives. By default, the limit is set to DEFAULT_MAX_STREAM_RESPONSES (=16384), but this can be configured on a per-call basis.

bidiRpc = client.channel()?.methodStub(
    'pw.rpc.test1.TheTestService.SomeBidi')!
    as BidirectionalStreamingMethodStub;

// Configure callback functions
const onNext = (response: Message) => {
  console.log(response);
}
const onComplete = (status: Status) => {
  console.log('completed!');
}
const onError = (error: Error) => {
  console.log();
}

bidiRpc.invoke(request, onNext, onComplete, onError);

Open an RPC: ignore initial errors#

Open allows you to start and register an RPC without crashing on errors. This is useful for starting an RPC before the server is ready. For instance, starting a logging RPC while the device is booting.

open(request?: Message,
    onNext: Callback = () => {},
    onCompleted: Callback = () => {},
    onError: Callback = () => {}): Call

Blocking RPCs: promise API#

Each MethodStub type provides an call() function that allows sending requests and awaiting responses through the promise API. The timeout field is optional. If no timeout is specified, the RPC will wait indefinitely.

Unary RPC#

unaryRpc = client.channel()?.methodStub(
    'pw.rpc.test1.TheTestService.SomeUnary')!
    as UnaryMethodStub;
const request = new unaryRpc.requestType();
request.setFooProperty(4);
const timeout = 2000 // 2 seconds
const [status, response] = await unaryRpc.call(request, timeout);

Server Streaming RPC#

serverStreamRpc = client.channel()?.methodStub(
    'pw.rpc.test1.TheTestService.SomeServerStreaming')!
    as ServerStreamingMethodStub;

const call = serverStreamRpc.invoke();
const timeout = 2000
for await (const response of call.getResponses(2, timeout)) {
 console.log(response);
}
const responses = call.getResponses() // All responses until stream end.
while (!responses.done) {
  console.log(await responses.value());
}

Client Streaming RPC#

clientStreamRpc = client.channel()!.methodStub(
  'pw.rpc.test1.TheTestService.SomeClientStreaming')!
  as ClientStreamingMethodStub;
clientStreamRpc.invoke();
const request = new clientStreamRpc.method.requestType();
request.setFooProperty('foo_test');
clientStreamRpc.send(request);

// Send three more requests, end the stream, and wait for a response.
const timeout = 2000 // 2 seconds
request.finishAndWait([request, request, request], timeout)
    .then((status, response) => {
      console.log(`Client stream finished successfully: ${response}`);
    })
    .catch((reason) => {
      console.log(`Client stream error: ${reason}`);
    });

Bidirectional Stream RPC#

bidiStreamingRpc = client.channel()!.methodStub(
  'pw.rpc.test1.TheTestService.SomeBidiStreaming')!
  as BidirectionalStreamingMethodStub;
bidiStreamingRpc.invoke();
const request = new bidiStreamingRpc.method.requestType();
request.setFooProperty('foo_test');

// Send requests
bidiStreamingRpc.send(request);

// Receive responses
const timeout = 2000 // 2 seconds
for await (const response of call.getResponses(1, timeout)) {
 console.log(response);
}

// Send three more requests, end the stream, and wait for a response.
request.finishAndWait([request, request, request], timeout)
    .then(() => {
      console.log('Bidirectional stream finished successfully');
    })
    .catch((reason) => {
      console.log(`Bidirectional stream error: ${reason}`);
    });
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