Instant real-time updates. Lightweight EventSource client receiving live messages via HTML5 Server-Sent Events (SSE). Fast stream processing built on top of ReactPHP's event-driven architecture.

v1.2.0 2024-01-25 13:06 UTC

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Last update: 2024-03-25 13:35:46 UTC


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Instant real-time updates. Lightweight EventSource client receiving live messages via HTML5 Server-Sent Events (SSE). Fast stream processing built on top of ReactPHP's event-driven architecture.

Table of contents

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Quickstart example

Once installed, you can use the following code to stream messages from any Server-Sent Events (SSE) server endpoint:

data: {"name":"Alice","message":"Hello everybody!"}

data: {"name":"Bob","message":"Hey Alice!"}

data: {"name":"Carol","message":"Nice to see you Alice!"}

data: {"name":"Alice","message":"What a lovely chat!"}

data: {"name":"Bob","message":"All powered by ReactPHP, such an awesome piece of technology :)"}
$es = new Clue\React\EventSource\EventSource('');

$es->on('message', function (Clue\React\EventSource\MessageEvent $message) {
    $json = json_decode($message->data);
    echo $json->name . ': ' . $json->message . PHP_EOL;

See the examples.



The EventSource class is responsible for communication with the remote Server-Sent Events (SSE) endpoint.

The EventSource object works very similar to the one found in common web browsers. Unless otherwise noted, it follows the same semantics as defined under

Its constructor simply requires the URL to the remote Server-Sent Events (SSE) endpoint:

$es = new Clue\React\EventSource\EventSource('');

If you need custom connector settings (DNS resolution, TLS parameters, timeouts, proxy servers etc.), you can explicitly pass a custom instance of the ConnectorInterface to the Browser instance and pass it as an additional argument to the EventSource like this:

$connector = new React\Socket\Connector([
    'dns' => '',
    'tcp' => [
        'bindto' => ''
    'tls' => [
        'verify_peer' => false,
        'verify_peer_name' => false
$browser = new React\Http\Browser($connector);

$es = new Clue\React\EventSource\EventSource('', $browser);

This class takes an optional LoopInterface|null $loop parameter that can be used to pass the event loop instance to use for this object. You can use a null value here in order to use the default loop. This value SHOULD NOT be given unless you're sure you want to explicitly use a given event loop instance.

message event

The message event will be emitted whenever an EventSource message is received.

$es->on('message', function (Clue\React\EventSource\MessageEvent $message) {
    // $json = json_decode($message->data);

The EventSource stream may emit any number of messages over its lifetime. Each message event will receive a MessageEvent object.

The MessageEvent::$data property can be used to access the message payload data. It is commonly used for transporting structured data such as JSON:

data: {"name":"Alice","age":30}

data: {"name":"Bob","age":50}
$es->on('message', function (Clue\React\EventSource\MessageEvent $message) {
    $json = json_decode($message->data);
    echo "{$json->name} is {$json->age} years old" . PHP_EOL;

The EventSource stream may specify an event type for each incoming message. This event field can be used to emit appropriate event types like this:

data: Alice
event: join

data: Hello!
event: chat

data: Bob
event: leave
$es->on('join', function (Clue\React\EventSource\MessageEvent $message) {
    echo $message->data . ' joined' . PHP_EOL;

$es->on('chat', function (Clue\React\EventSource\MessageEvent $message) {
    echo 'Message: ' . $message->data . PHP_EOL;

$es->on('leave', function (Clue\React\EventSource\MessageEvent $message) {
    echo $message->data . ' left' . PHP_EOL;

See also MessageEvent::$type property for more details.

open event

The open event will be emitted when the EventSource connection is successfully established.

$es->on('open', function () {
    echo 'Connection opened' . PHP_EOL;

Once the EventSource connection is open, it may emit any number of message events.

If the connection can not be opened successfully, it will emit an error event instead.

error event

The error event will be emitted when the EventSource connection fails. The event receives a single Exception argument for the error instance.

$redis->on('error', function (Exception $e) {
    echo 'Error: ' . $e->getMessage() . PHP_EOL;

The EventSource connection will be retried automatically when it is temporarily disconnected. If the server sends a non-successful HTTP status code or an invalid Content-Type response header, the connection will fail permanently.

$es->on('error', function (Exception $e) use ($es) {
    if ($es->readyState === Clue\React\EventSource\EventSource::CLOSED) {
        echo 'Permanent error: ' . $e->getMessage() . PHP_EOL;
    } else {
        echo 'Temporary error: ' . $e->getMessage() . PHP_EOL;

See also the EventSource::$readyState property.


The int $readyState property can be used to check the current EventSource connection state.

The state is read-only and can be in one of three states over its lifetime:

  • EventSource::CONNECTING
  • EventSource::OPEN
  • EventSource::CLOSED


The readonly string $url property can be used to get the EventSource URL as given to the constructor.


The close(): void method can be used to forcefully close the EventSource connection.

This will close any active connections or connection attempts and go into the EventSource::CLOSED state.


The MessageEvent class represents an incoming EventSource message.


The new MessageEvent(string $data, string $lastEventId = '', string $type = 'message') constructor can be used to create a new MessageEvent instance.

This is mostly used internally to represent each incoming message event (see also message event). Likewise, you can also use this class in test cases to test how your application reacts to incoming messages.

The constructor validates and initializes all properties of this class. It throws an InvalidArgumentException if any parameters are invalid.


The readonly string $data property can be used to access the message payload data.

data: hello
assert($message->data === 'hello');

The data field may also span multiple lines. This is commonly used for transporting structured data such as JSON:

data: {
data:     "message": "hello"
data: }
$json = json_decode($message->data);
assert($json->message === 'hello');

If the message does not contain a data field or the data field is empty, the message will be discarded without emitting an event.


The readonly string $lastEventId property can be used to access the last event ID.

data: hello
id: 1
assert($message->data === 'hello');
assert($message->lastEventId === '1');

Internally, the id field will automatically be used as the Last-Event-ID HTTP request header in case the connection is interrupted.

If the message does not contain an id field, the $lastEventId property will be the value of the last ID received. If no previous message contained an ID, it will default to an empty string.


The readonly string $type property can be used to access the message event type.

data: Alice
event: join
assert($message->data === 'Alice');
assert($message->type === 'join');

Internally, the event field will be used to emit the appropriate event type. See also message event.

If the message does not contain a event field or the event field is empty, the $type property will default to message.


The recommended way to install this library is through Composer. New to Composer?

This project follows SemVer. This will install the latest supported version:

composer require clue/reactphp-eventsource:^1.2

See also the CHANGELOG for details about version upgrades.

This project aims to run on any platform and thus does not require any PHP extensions and supports running on legacy PHP 5.4 through current PHP 8+. It's highly recommended to use the latest supported PHP version for this project.


To run the test suite, you first need to clone this repo and then install all dependencies through Composer:

composer install

To run the test suite, go to the project root and run:


The test suite is set up to always ensure 100% code coverage across all supported environments. If you have the Xdebug extension installed, you can also generate a code coverage report locally like this:

XDEBUG_MODE=coverage vendor/bin/phpunit --coverage-text


This project is released under the permissive MIT license.

Did you know that I offer custom development services and issuing invoices for sponsorships of releases and for contributions? Contact me (@clue) for details.


  • If you want to learn more about processing streams of data, refer to the documentation of the underlying react/stream component.

  • If you're looking to run the server side of your Server-Sent Events (SSE) application, you may want to use the powerful server implementation provided by Framework X.