Using Server-Sent Events in PHP

SSE writes event-stream frames over a long-lived HTTP response for one-way server updates.

What It Does and When to Use It

Emit an SSE event with the required blank-line separator. Direct PHP code exposes the underlying operation clearly; a framework can supply lifecycle hooks, dependency wiring and retries.

Requirements, Inputs and Expected Behavior

Confirm the runtime, extension, environment variables, and permissions before running the examples in production. Disable output buffering where appropriate, handle disconnects and keep heartbeat intervals modest.

Example 1: Basic Operation

Emit an SSE event with the required blank-line separator.

<?php
header('Content-Type: text/event-stream');
 header('Cache-Control: no-cache');
 echo "event: ready
";
 echo 'data: ', json_encode(['status' => 'ok'], JSON_THROW_ON_ERROR), "

";
 flush();

Example 2: Behavior and Validation

Attach event IDs so a browser can resume from Last-Event-ID.

<?php
header('Content-Type: text/event-stream');
 for ($id = 1; $id <= 3; $id++) {
     echo "id: $id
";
     echo 'data: ', json_encode(['progress' => $id * 25]), "

";
     flush();
 }

Practical Example: Application Use

Send a heartbeat and observe client disconnection; configure proxy buffering separately.

<?php
header('Content-Type: text/event-stream');
 @ini_set('output_buffering', 'off');
 while (ob_get_level() > 0) ob_end_flush();
 echo ": keepalive

";
 flush();
 if (connection_aborted()) exit;

Important Behavior and Edge Cases

The second example highlights: Attach event IDs so a browser can resume from Last-Event-ID. The practical example adds: Send a heartbeat and observe client disconnection; configure proxy buffering separately.

Comparison with Related Approaches

Common Beginner Mistakes

Key Takeaways

• SSE writes event-stream frames over a long-lived HTTP response for one-way server updates.
• Send a heartbeat and observe client disconnection; configure proxy buffering separately.
• Choose based on deployment requirements and verify actual behavior rather than assuming defaults.