Basics tutorial

This tutorial provides a basic PHP programmer’s introduction to working with gRPC.

By walking through this example you’ll learn how to:

• Define a service in a .proto file.
• Generate client code using the protocol buffer compiler.
• Use the PHP gRPC API to write a simple client for your service.

It assumes a passing familiarity with protocol buffers. Note that the example in this tutorial uses the proto2 version of the protocol buffers language.

Also note that currently, you can only create clients in PHP for gRPC services. Use another language to create a gRPC server.

Why use gRPC?

Our example is a simple route mapping application that lets clients get information about features on their route, create a summary of their route, and exchange route information such as traffic updates with the server and other clients.

With gRPC we can define our service once in a .proto file and generate clients and servers in any of gRPC’s supported languages, which in turn can be run in environments ranging from servers inside a large data center to your own tablet — all the complexity of communication between different languages and environments is handled for you by gRPC. We also get all the advantages of working with protocol buffers, including efficient serialization, a simple IDL, and easy interface updating.

Example code and setup

The example code for our tutorial is in grpc/grpc/examples/php/route_guide. To download the example, clone the grpc repository and its submodules by running the following command:

$ git clone --recurse-submodules -b v1.38.0 https://github.com/grpc/grpc

You need the grpc-php-plugin to help you compile .proto files. Build it from source as follows:

$ cd grpc
$ mkdir -p cmake/build
$ pushd cmake/build
$ cmake ../..
$ make protoc grpc_php_plugin
$ popd

Then change to route guide directory and compile the example’s .proto files:

$ cd examples/php/route_guide
$ ./route_guide_proto_gen.sh

Our example is a simple route mapping application that lets clients get information about features on their route, create a summary of their route, and exchange route information such as traffic updates with the server and other clients.

You also should have the relevant tools installed to generate the client interface code (and a server in another language, for testing). You can obtain the latter by following these setup instructions, for example.

Try it out!

To try the sample app, we need a gRPC server running locally. Let’s compile and run, for example, the Node.js server in this repository:

$ cd ../../node
$ npm install
$ cd dynamic_codegen/route_guide
$ nodejs ./route_guide_server.js --db_path=route_guide_db.json

Run the PHP client (in a different terminal):

$ ./run_route_guide_client.sh

The next sections guide you step-by-step through how this proto service is defined, how to generate a client library from it, and how to create a client stub that uses that library.

Defining the service

First let’s look at how the service we’re using is defined. A gRPC service and its method request and response types using protocol buffers. You can see the complete .proto file for our example in examples/protos/route_guide.proto.

To define a service, you specify a named service in your .proto file:

service RouteGuide {
   ...
}

Then you define rpc methods inside your service definition, specifying their request and response types. Protocol buffers let you define four kinds of service method, all of which are used in the RouteGuide service:

• A simple RPC where the client sends a request to the server and receives a response later, just like a normal remote procedure call.

  // Obtains the feature at a given position.
  rpc GetFeature(Point) returns (Feature) {}
  

• A response-streaming RPC where the client sends a request to the server and gets back a stream of response messages. You specify a response-streaming method by placing the stream keyword before the response type.

  // Obtains the Features available within the given Rectangle.  Results are
  // streamed rather than returned at once (e.g. in a response message with a
  // repeated field), as the rectangle may cover a large area and contain a
  // huge number of features.
  rpc ListFeatures(Rectangle) returns (stream Feature) {}
  

• A request-streaming RPC where the client sends a sequence of messages to the server. Once the client has finished writing the messages, it waits for the server to read them all and return its response. You specify a request-streaming method by placing the stream keyword before the request type.

  // Accepts a stream of Points on a route being traversed, returning a
  // RouteSummary when traversal is completed.
  rpc RecordRoute(stream Point) returns (RouteSummary) {}
  

• A bidirectional streaming RPC where both sides send a sequence of messages to the other. The two streams operate independently, so clients and servers can read and write in whatever order they like: for example, the server could wait to receive all the client messages before writing its responses, or it could alternately read a message then write a message, or some other combination of reads and writes. The order of messages in each stream is preserved. You specify this type of method by placing the stream keyword before both the request and the response.

  // Accepts a stream of RouteNotes sent while a route is being traversed,
  // while receiving other RouteNotes (e.g. from other users).
  rpc RouteChat(stream RouteNote) returns (stream RouteNote) {}
  

Our .proto file also contains protocol buffer message type definitions for all the request and response types used in our service methods - for example, here’s the Point message type:

// Points are represented as latitude-longitude pairs in the E7 representation
// (degrees multiplied by 10**7 and rounded to the nearest integer).
// Latitudes should be in the range +/- 90 degrees and longitude should be in
// the range +/- 180 degrees (inclusive).
message Point {
  int32 latitude = 1;
  int32 longitude = 2;
}

Generating client code

The PHP client stub implementation of the proto files can be generated by the gRPC PHP Protoc Plugin. To compile the plugin:

$ make grpc_php_plugin

To generate the client stub implementation .php file:

$ cd grpc
$ protoc --proto_path=examples/protos \
  --php_out=examples/php/route_guide \
  --grpc_out=examples/php/route_guide \
  --plugin=protoc-gen-grpc=bins/opt/grpc_php_plugin \
  ./examples/protos/route_guide.proto

or running the helper script under the grpc/example/php/route_guide directory if you build grpc-php-plugin by source:

$ ./route_guide_proto_gen.sh

A number of files will be generated in the examples/php/route_guide directory. You do not need to modify those files.

To load these generated files, add this section to your composer.json file under examples/php directory

  "autoload": {
    "psr-4": {
      "": "route_guide/"
    }
  }

The file contains:

• All the protocol buffer code to populate, serialize, and retrieve our request and response message types.
• A class called Routeguide\RouteGuideClient that lets clients call the methods defined in the RouteGuide service.

Creating the client

In this section, we’ll look at creating a PHP client for our RouteGuide service. You can see our complete example client code in examples/php/route_guide/route_guide_client.php.

Constructing a client object

To call service methods, we first need to create a client object, an instance of the generated RouteGuideClient class. The constructor of the class expects the server address and port we want to connect to:

$client = new Routeguide\RouteGuideClient('localhost:50051', [
    'credentials' => Grpc\ChannelCredentials::createInsecure(),
]);

Calling service methods

Now let’s look at how we call our service methods.

Simple RPC

Calling the simple RPC GetFeature is nearly as straightforward as calling a local asynchronous method.

$point = new Routeguide\Point();
$point->setLatitude(409146138);
$point->setLongitude(-746188906);
list($feature, $status) = $client->GetFeature($point)->wait();

As you can see, we create and populate a request object, i.e. an Routeguide\Point object. Then, we call the method on the stub, passing it the request object. If there is no error, then we can read the response information from the server from our response object, i.e. an Routeguide\Feature object.

print sprintf("Found %s \n  at %f, %f\n", $feature->getName(),
              $feature->getLocation()->getLatitude() / COORD_FACTOR,
              $feature->getLocation()->getLongitude() / COORD_FACTOR);

Streaming RPCs

Now let’s look at our streaming methods. Here’s where we call the server-side streaming method ListFeatures, which returns a stream of geographical Features:

$lo_point = new Routeguide\Point();
$hi_point = new Routeguide\Point();

$lo_point->setLatitude(400000000);
$lo_point->setLongitude(-750000000);
$hi_point->setLatitude(420000000);
$hi_point->setLongitude(-730000000);

$rectangle = new Routeguide\Rectangle();
$rectangle->setLo($lo_point);
$rectangle->setHi($hi_point);

$call = $client->ListFeatures($rectangle);
// an iterator over the server streaming responses
$features = $call->responses();
foreach ($features as $feature) {
  // process each feature
} // the loop will end when the server indicates there is no more responses to be sent.

The $call->responses() method call returns an iterator. When the server sends a response, a $feature object will be returned in the foreach loop, until the server indiciates that there will be no more responses to be sent.

The client-side streaming method RecordRoute is similar, except that we call $call->write($point) for each point we want to write from the client side and get back a Routeguide\RouteSummary.

$call = $client->RecordRoute();

for ($i = 0; $i < $num_points; $i++) {
  $point = new Routeguide\Point();
  $point->setLatitude($lat);
  $point->setLongitude($long);
  $call->write($point);
}

list($route_summary, $status) = $call->wait();

Finally, let’s look at our bidirectional streaming RPC routeChat(). In this case, we just pass a context to the method and get back a BidiStreamingCall stream object, which we can use to both write and read messages.

$call = $client->RouteChat();

To write messages from the client:

foreach ($notes as $n) {
  $point = new Routeguide\Point();
  $point->setLatitude($lat = $n[0]);
  $point->setLongitude($long = $n[1]);

  $route_note = new Routeguide\RouteNote();
  $route_note->setLocation($point);
  $route_note->setMessage($message = $n[2]);
  $call->write($route_note);
}
$call->writesDone();

To read messages from the server:

while ($route_note_reply = $call->read()) {
  // process $route_note_reply
}

Each side will always get the other’s messages in the order they were written, both the client and server can read and write in any order — the streams operate completely independently.