Last update: 04 Mar 2024

HTTP Emitter

Emits PSR-7 responses to the PHP Server API.


To get started, install the http-emitter repository via the Composer package manager:

composer require zaphyr-org/http-emitter


Emitters play a crucial role in the process of emitting a PSR-7 response. This essential functionality is particularly relevant when your application operates under the context of a traditional PHP server API that utilizes output buffers, such as Apache, NGINX or php-fpm.

Usually, emitters are designed to carry out the following tasks during the response emission process:

  • Emit a response status line.
  • Emit all response headers.
  • Emit the response body.

Emitters are responsible for efficiently handling each of these critical steps, ensuring that the HTTP response is properly structured and compliant with the standard protocol. By executing these actions seamlessly, emitters contribute to the smooth and reliable communication between the server and the client, delivering the requested content efficiently and accurately.


Zaphyr\HttpEmitter\SapiEmitter serves as a component that takes in the response instance and leverages the built-in PHP function header() to emit both the headers and the status line. Subsequently, the emitter utilizes echo to emit the response body. This two-step process ensures that the response is properly constructed and sent to the client using standard PHP functionalities for handling HTTP responses:

$response = new Response();
$response->getBody()->write('Hello World!');

(new Zaphyr\HttpEmitter\SapiEmitter())->emit($response);

This repository does NOT come with a PSR-7 implementation out of the box. For a PSR-7 implementation, check out the HTTP Message repository.

Within its internal implementation, Zaphyr\HttpEmitter\SapiEmitter performs several crucial verifications to ensure the proper functioning and integrity of the response emission process:

  • Prevention of Headers Overwriting: Before sending the response headers using the header() function, the emitter checks whether any headers have already been sent earlier in the execution flow. If headers have been previously sent, it promptly raises an Zaphyr\HttpEmitter\Exceptions\HttpEmitterException exception.

  • Protection Against Output Interference: Additionally, the emitter takes precautions to prevent any interference with the output buffering mechanism. It checks whether any output has been sent prior to the response emission phase. If output has already been sent, which might occur if the application inadvertently echoes content before the response is ready, the emitter responds by raising an Zaphyr\HttpEmitter\Exceptions\HttpEmitterException exception. This safeguard ensures that the response body is isolated and not mixed with any other output, maintaining the integrity and clarity of the final response delivered to the client.

The Zaphyr\HttpEmitter\SapiEmitter possesses a versatile capability, making it capable of handling any response with ease, thereby consistently returning true as a result.


The Zaphyr\HttpEmitter\SapiStreamEmitter proves to be highly beneficial when there is a need to emit a Content-Range. The emitter detects the Content-Range header and emits only the bytes specified. A typical scenario where this emitter shines is when you want to stream a specific range of bytes from a file to a client. In such cases, the client can provide the following header as an example:

$response = (new Response())->withHeader('Content-Range', 'bytes 0-2/*');
$response->getBody()->write('hello world');

(new Zaphyr\HttpEmitter\SapiStreamEmitter())->emit($response);

This repository does NOT come with a PSR-7 implementation out of the box. For a PSR-7 implementation, check out the HTTP Message repository.

The Zaphyr\HttpEmitter\SapiStreamEmitter presents a constructor that accepts an integer argument, allowing you to specify the maximum buffer length for response emission. By default, if no value is provided, the emitter sets this maximum buffer length to 8192 bytes:

new Zaphyr\HttpEmitter\SapiStreamEmitter(8192);