How to implement a simple RPC client using PHP

RPC (Remote Procedure Call) is a computer communication protocol that allows a program to call a subprogram in another space or machine. This protocol allows us to call functions in remote services just like calling local functions, provided that we must implement the client and server of the RPC protocol.

This article will introduce how to use PHP to implement a simple RPC. We will use the JSON-RPC protocol, which is a lightweight and simple protocol.

1. Preparation

Before we start writing code, we need to understand the following:

• What is the JSON-RPC protocol and it has What are the characteristics?
• PHP socket programming, especially the use of socket sockets.
• JSON parsing and serialization for PHP.

2. PHP implements a simple RPC client

We can use PHP to implement a simple RPC client, which is responsible for sending requests and receiving responses. Its workflow is as follows:

• Create a socket socket.
• Use the socket_create() function to create a socket.
• Use the socket_connect() function to connect to the server.
• Send the request information to the server.
• Use the socket_read() function to read the results returned by the server.

The following is an implementation example:

class RpcClient
{
    private $url;
    private $port;
    private $timeout;
    private $socket;

    public function __construct($url, $port, $timeout = 30)
    {
        $this->url = $url;
        $this->port = $port;
        $this->timeout = $timeout;
        $this->connect();
    }

    private function connect()
    {
        $this->socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
        if ($this->socket === false) {
            throw new Exception("unable to create socket: " . socket_strerror(socket_last_error()));
        }
        $result = socket_connect($this->socket, $this->url, $this->port);
        if ($result === false) {
            throw new Exception("unable to connect socket: " . socket_strerror(socket_last_error()));
        }
    }

    public function call($function_name, $parameters = [])
    {
        $request_body = json_encode([
            "jsonrpc" => "2.0",
            "method" => $function_name,
            "params" => $parameters,
            "id" => 1
        ]);

        $result = $this->send($request_body);
        $response = json_decode($result, true);
        if ($response['id'] != 1) {
            throw new Exception("incorrect response ID (expected: 1, actual: " . $response['id'] . ")");
        }

        if (isset($response['error'])) {
            throw new Exception("server returned error: " . print_r($response, true));
        }

        return $response['result'];
    }

    private function send($request_body)
    {
        $result = socket_write($this->socket, $request_body . "\n", strlen($request_body) + 1);
        if ($result === false) {
            throw new Exception("unable to send request: " . socket_strerror(socket_last_error()));
        }

        $response = "";
        do {
            $buffer = socket_read($this->socket, 1024);
            $response .= $buffer;
            if (strlen($buffer) < 1024) {
                break;
            }
        } while(true);

        return $response;
    }
}

In the above code, the connect() method creates a socket and uses socket_connect() to connect to the RPC server. The call() method will send a request information in JSON format, and the send() method will send the request information to the server and return the response result of the server.

When creating an RpcClient object, you need to pass in the address and port that the server listens on and the timeout period for waiting for a connection.

3. PHP implements a simple RPC server

Implementing the RPC protocol on the server requires the following steps:

• Create a listening socket socket.
• Use the socket_bind() function to bind the socket to a specific IP address and port number.
• Use the socket_listen() function to listen to the socket socket.
• Use the socket_accept() function to accept a client connection request and return a new socket.
• Parse the client's request information and execute the corresponding function.
• Send response information to the client.

The following is an example of a simple RPC server:

class RpcServer
{
    private $url;
    private $port;
    private $timeout;
    private $socket;

    public function __construct($url, $port, $timeout = 30)
    {
        $this->url = $url;
        $this->port = $port;
        $this->timeout = $timeout;
        $this->listen();
    }

    private function listen()
    {
        $this->socket = socket_create(AF_INET, SOCK_STREAM, SOL_TCP);
        if ($this->socket === false) {
            throw new Exception("unable to create socket: " . socket_strerror(socket_last_error()));
        }

        $result = socket_bind($this->socket, $this->url, $this->port);
        if ($result === false) {
            throw new Exception("unable to bind socket to $this->url:$this->port: " . socket_strerror(socket_last_error()));
        }

        $result = socket_listen($this->socket, 5);
        if ($result === false) {
            throw new Exception("unable to listen on socket: " . socket_strerror(socket_last_error()));
        }

        while (true) {
            $client = socket_accept($this->socket);
            $request_string = socket_read($client, 1024);
            $response_string = $this->handle_request($request_string);
            socket_write($client, $response_string, strlen($response_string));
            socket_close($client);
        }
    }

    private function handle_request($request_string)
    {
        $request = json_decode($request_string, true);
        $method = $request['method'];
        $params = $request['params'];

        if (!function_exists($method)) {
            return json_encode([
                "jsonrpc" => "2.0",
                "id" => $request['id'],
                "error" => [
                    "code" => -32601,
                    "message" => "Method not found"
                ]
            ]);
        }

        $result = call_user_func_array($method, $params);

        return json_encode([
            "jsonrpc" => "2.0",
            "id" => $request['id'],
            "result" => $result
        ]);
    }
}

In the above code, the listen() method creates a socket and binds it using socket_bind() to the specified IP address and port. Then socket_listen() is called to listen on the socket, accept the client connection request and use the socket_accept() function to return a new socket for communication.

Next, the server will parse the client's request information and determine whether the method requested by the client exists. If it does not exist, it will return an error code. If the method exists, the server will execute the corresponding function and send the result to the client.

When creating an RpcServer object, you need to pass in the address and port that the server listens on and the timeout period for waiting for a connection.

4. Summary

In this article, we learned how to implement a simple RPC application using PHP and communicate using the JSON-RPC protocol. Through the study of this article, we understand the basic principles of the RPC protocol, understand the basic usage of socket programming, and master the JSON parsing and serialization methods of PHP. We can further study the RPC protocol and related application scenarios in depth.

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