gRPC protocol updates

docs/sources/next/using-k6/protocols/grpc.md

@@ -17,5 +17,322 @@ The binary format makes data transfer faster and more compact.
 In the benchmarks we've seen, gRPC has proved much faster than REST, gRPC's more traditional, JSON-based counterpart.
 The messages and services used for gRPC are described in `.proto` files, containing definitions for [Protocol Buffers](https://en.wikipedia.org/wiki/Protocol_Buffers) (protobuf).
 
-k6 also supports unary gRPC requests to the [k6/net/grpc](https://grafana.com/docs/k6/<K6_VERSION>/javascript-api/k6-net-grpc) built-in module.
-For further information, read [our tutorial about performance testing gRPC services](https://k6.io/blog/performance-testing-grpc-services/).
+## Load testing gRPC services with k6
+
+Support of the unary gRPC requests was added to k6 in v0.29.0, streaming support was initially introduced in k6 v0.45.0 as an experimental module and with k6 v0.49.0 became a part [core's module `k6/net/grpc`](https://grafana.com/docs/k6/<K6_VERSION>/javascript-api/k6-net-grpc/).
+
+### gRPC definitions
+
+Before interacting with a gRPC service, k6 needs to learn the definitions of the messages and services.
+
+One way to do that is to explicitly use `Client.load()` method and load definitions to client from local file system. The method accepts a list of import paths and a list of `.proto` files. The k6 will load all the definitions from the files and their dependencies.
+
+{{< code >}}
+
+```javascript
+import { Client } from 'k6/net/grpc';
+
+const client = new Client();
+client.load(['definitions'], 'hello.proto');
+```
+
+{{< /code >}}
+
+Alternatively, the definitions could be dynamically loaded by using gRPC reflection protocol. To enable reflection, pass `reflect: true` option to `Client.connect()` method. k6 will load all the definitions from the server and their dependencies.
+
+This is only possible if the server has been instrumented with reflection support, which is not always the case.
+
+{{< code >}}
+
+```javascript
+import { Client } from 'k6/net/grpc';
+
+const client = new Client();
+client.connect('127.0.0.1:10000', { reflect: true });
+```
+
+{{< /code >}}
+
+### Unary gRPC requests
+
+Unary calls work the same way as regular HTTP requests. A single request sent to a server and the server replies with a single response.
+
+{{< code >}}
+
+```javascript
+import { Client, StatusOK } from 'k6/net/grpc';
+import { check, sleep } from 'k6';
+
+const client = new Client();
+client.load(['definitions'], 'hello.proto');
+
+export default () => {
+  client.connect('127.0.0.1:10000', {});
+
+  const data = { greeting: 'Bert' };
+  const response = client.invoke('hello.HelloService/SayHello', data);
+
+  check(response, {
+    'status is OK': (r) => r && r.status === StatusOK,
+  });
+
+  console.log(JSON.stringify(response.message));
+
+  client.close();
+  sleep(1);
+};
+```
+
+{{< /code >}}
+
+### Server gRPC streaming
+
+In server streaming mode, the client sends a single request to the server, which in turn replies with multiple responses.
+
+The example below demonstrates client streaming.
+
+{{< code >}}
+
+```javascript
+import { Client, Stream } from 'k6/net/grpc';
+import { sleep } from 'k6';
+
+const COORD_FACTOR = 1e7;
+
+const client = new Client();
+
+export default () => {
+  if (__ITER == 0) {
+    client.connect('127.0.0.1:10000', { plaintext: true, reflect: true });
+  }
+
+  const stream = new Stream(client, 'main.FeatureExplorer/ListFeatures', null);
+
+  stream.on('data', function (feature) {
+    console.log(
+      `Found feature called "${feature.name}" at ${feature.location.latitude / COORD_FACTOR}, ${
+        feature.location.longitude / COORD_FACTOR
+      }`
+    );
+  });
+
+  stream.on('end', function () {
+    // The server has finished sending
+    client.close();
+    console.log('All done');
+  });
+
+  // send a message to the server
+  stream.write({
+    lo: {
+      latitude: 400000000,
+      longitude: -750000000,
+    },
+    hi: {
+      latitude: 420000000,
+      longitude: -730000000,
+    },
+  });
+
+  sleep(0.5);
+};
+```
+
+{{< /code >}}
+
+It connects to a gRPC server, creates a stream, and sends a message to the server with latitude and longitude coordinates. When the server sends data back, it logs the feature name and its location. When the server finishes sending data, it closes the client connection and logs a completion message.
+
+### Client gRPC streaming
+
+The client streaming mode is the opposite of the server streaming mode. The client sends multiple requests to the server, which in turn replies with a single response.
+
+The example below demonstrates client streaming.
+
+{{< code >}}
+
+```javascript
+import { Client, Stream } from 'k6/net/grpc';
+import { sleep } from 'k6';
+
+const COORD_FACTOR = 1e7;
+const client = new Client();
+
+// a sample points collection
+const points = [
+  {
+    location: { latitude: 407838351, longitude: -746143763 },
+    name: 'Patriots Path, Mendham, NJ 07945, USA',
+  },
+  {
+    location: { latitude: 408122808, longitude: -743999179 },
+    name: '101 New Jersey 10, Whippany, NJ 07981, USA',
+  },
+  {
+    location: { latitude: 413628156, longitude: -749015468 },
+    name: 'U.S. 6, Shohola, PA 18458, USA',
+  },
+  {
+    location: { latitude: 419999544, longitude: -740371136 },
+    name: '5 Conners Road, Kingston, NY 12401, USA',
+  },
+  {
+    location: { latitude: 414008389, longitude: -743951297 },
+    name: 'Mid Hudson Psychiatric Center, New Hampton, NY 10958, USA',
+  },
+];
+
+export default () => {
+  if (__ITER == 0) {
+    client.connect('127.0.0.1:10000', { plaintext: true, reflect: true });
+  }
+
+  const stream = new Stream(client, 'main.RouteGuide/RecordRoute');
+
+  stream.on('data', (stats) => {
+    console.log(`Finished trip with ${stats.pointCount} points`);
+    console.log(`Passed ${stats.featureCount} features`);
+    console.log(`Travelled ${stats.distance} meters`);
+    console.log(`It took ${stats.elapsedTime} seconds`);
+  });
+
+  stream.on('end', () => {
+    client.close();
+    console.log('All done');
+  });
+
+  // send 3 random points
+  for (let i = 0; i < 3; i++) {
+    const point = points[Math.floor(Math.random() * points.length)];
+    pointSender(stream, point);
+  }
+
+  // close the client stream
+  stream.end();
+};
+
+const pointSender = (stream, point) => {
+  console.log(
+    `Visiting point ${point.name} ${point.location.latitude / COORD_FACTOR}, ${
+      point.location.longitude / COORD_FACTOR
+    }`
+  );
+
+  // send the location to the server
+  stream.write(point.location);
+
+  sleep(0.5);
+};
+```
+
+{{< /code >}}
+
+It establishes a connection to a gRPC server, creates a stream, and sends three random points. The server responds with statistics about the trip, which are logged to the console. The code also handles the end of the stream, closing the client and logging a completion message.
+
+### Bidirectional gRPC streaming
+
+In bi-directional streaming mode, both the client and the server may send multiple messages.
+
+From the API perspective, it combines the client and server streaming modes, so the code is similar to the examples above.
+
+### Streaming error handling
+
+To catch errors that occur during streaming, you can use the `error` event handler.
+
+The handler receives [an error object](https://grafana.com/docs/k6/<K6_VERSION>/javascript-api/k6-net-grpc/stream/stream-error/).
+
+{{< code >}}
+
+```javascript
+import { Client, Stream } from 'k6/net/grpc';
+
+const client = new Client();
+const stream = new Stream(client, 'main.RouteGuide/RecordRoute');
+
+stream.on('error', function (e) {
+  // An error has occurred and the stream has been closed.
+  console.log('Error: ' + JSON.stringify(e));
+});
+```
+
+{{< /code >}}
+
+### Handling special cases in message Marshaling/Unmarshaling
+
+It is worth mentioning that for encoding and decoding of the messages, k6 uses [protojson](https://pkg.go.dev/google.golang.org/protobuf/encoding/protojson) package.
+
+Certain gRPC well-known types or wrappers have specific marshaling/unmarshaling rules.
+
+For instance, if you import `"google/protobuf/wrappers.proto"` and your proto-definitions look like this:
+
+```proto
+syntax = "proto3";
+
+package testing;
+
+import "google/protobuf/wrappers.proto";
+
+service Service {
+   rpc SayHey(google.protobuf.StringValue) returns (google.protobuf.StringValue);
+   rpc DoubleInteger(google.protobuf.Int64Value) returns (google.protobuf.Int64Value);
+}
+
+```
+
+When passing a message, you should use a string or an integer, not an object. As a result, you will receive a type that has already been marshaled.
+
+{{< code >}}
+
+```javascript
+import { Client } from 'k6/net/grpc';
+const client = new Client();
+
+// an example of passing a string
+const respString = client.invoke('testing.Service/SayHey', 'John');
+if (respString.message !== 'hey John') {
+  throw new Error("expected to get 'hey John', but got a " + respString.message);
+}
+
+// an example of passing an integer
+const respInt = client.invoke('testing.Service/DoubleInteger', '3');
+if (respInt.message !== '6') {
+  throw new Error("expected to get '6', but got a " + respInt.message);
+}
+```
+
+{{< /code >}}
+
+Another special case could be usage of `oneof`. Let's say you have a proto-definition like this:
+
+```proto
+syntax = "proto3";
+
+package testing;
+
+service Service {
+   rpc Test(Foo)  returns (Foo) {}
+}
+
+message Foo {
+   oneof Bar {
+     string code = 1;
+     uint32 id = 2;
+   }
+}
+```
+
+In this case, you should pass an object either with `code` or `id` fields.
+
+{{< code >}}
+
+```javascript
+import { Client } from 'k6/net/grpc';
+const client = new Client();
+
+// calling RPC with filled code field
+const respWithCode = client.invoke('testing.Service/Test', { code: 'abc-123' });
+
+// calling RPC with filled id field
+const respWithID = client.invoke('testing.Service/Test', { id: 123 });
+```
+
+{{< /code >}}