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Websocket ⋅ Introduction

amphp/websocket-client provides an asynchronous WebSocket client for PHP based on Amp. WebSockets are full-duplex communication channels, which are mostly used for realtime communication where the HTTP request / response cycle has too much overhead. They’re also used if the server should be able to push data to the client without an explicit request.

There are various use cases for a WebSocket client in PHP, such as consuming realtime APIs, writing tests for a WebSocket server, or controlling web browsers via their remote debugging APIs, which are based on WebSockets.

Installation

The server can be installed as a Composer dependency.

composer require amphp/websocket-client

Connecting

You can create new WebSocket connections using Amp\Websocket\connect(). It accepts a string as first argument, which must use the ws or wss (WebSocket over TLS) scheme. Options can be specified by passing a Handshake object instead of a string as first argument, which can also be used to pass additional headers with the initial handshake. Further optional arguments are ConnectContext, and a CancellationToken.

<?php

require 'vendor/autoload.php';

use Amp\Websocket\Client;

Amp\Loop::run(function () {
    /** @var Client\Connection $connection */
    $connection = yield Client\connect('ws://localhost:1337/ws');

    // do something
});

Sending Data

WebSocket messages can be sent using the send() and sendBinary() methods. Text messages sent with send() must be valid UTF-8. Binary messages send with sendBinary() can be arbitrary data.

Both methods return a Promise that is resolved as soon as the message has been fully written to the send buffer. This doesn’t mean that the message has been received by the other party or that the message even left the local system’s send buffer, yet.

Receiving Data

WebSocket messages can be received using the receive() method. The Promise returned from receive() resolves once the client has started to receive a message. This allows streaming WebSocket messages, which might be pretty large. In practice, most messages are rather small, and it’s fine buffering them completely. The Promise returned from receive() resolves to a Message, which allows easy buffered and streamed consumption.

Amp\Websocket\Message differs from the now deprecated Amp\ByteStream\Message. Amp\ByteStream\Message directly implemented Promise, which is not possible for promise resolution values and has been confusing for most users. A consumer has to call Amp\Websocket\Message::buffer() which returns a Promise resolving to the entire message contents like in Amp\ByteStream\Payload.

Demo

The following example connects to a WebSocket demo server that just echos all messages it receives.

<?php

require 'vendor/autoload.php';

use Amp\Delayed;
use Amp\Websocket;
use Amp\Websocket\Client;

Amp\Loop::run(function () {
    /** @var Client\Connection $connection */
    $connection = yield Client\connect('ws://demos.kaazing.com/echo');
    yield $connection->send('Hello!');

    $i = 0;

    /** @var Websocket\Message $message */
    while ($message = yield $connection->receive()) {
        $payload = yield $message->buffer();

        printf("Received: %s\n", $payload);

        if ($payload === 'Goodbye!') {
            $connection->close();
            break;
        }

        yield new Delayed(1000);

        if ($i < 3) {
            yield $connection->send('Ping: ' . ++$i);
        } else {
            yield $connection->send('Goodbye!');
        }
    }
});