PSR7

PSR-7 is a PHP Standards Recommendation that defines a set of interfaces for representing HTTP messages, most notably requests and responses, along with supporting interfaces for URIs, streams, and uploaded files. It provides a standard contract to promote interoperability between PHP HTTP components and frameworks.

The design emphasizes immutability; instances of the interfaces are intended to be immutable, with operations that would modify state returning new instances. Core interfaces include RequestInterface, ResponseInterface, ServerRequestInterface, UriInterface, StreamInterface, and UploadedFileInterface. Implementations supply concrete behavior, while the interfaces describe how they should interact, including header management, message bodies, and URI handling.

PSR-7 does not prescribe concrete implementations. Instead, it offers the contract that libraries and frameworks can implement. Many PHP projects rely on PSR-7-compatible libraries for HTTP message handling, such as HTTP message implementations in Guzzle, Zend Diactoros, Laminas Diactoros, Nyholm PSR-7, and others; frameworks often integrate these pieces or provide adapters.

The standard is typically used in combination with other PSRs. PSR-17 provides factories for creating PSR-7 objects, PSR-18 defines a client interface for making HTTP requests using PSR-7 messages, and PSR-15 defines HTTP server request handlers that can consume PSR-7 messages. Middleware ecosystems also leverage PSR-7 to pass and transform messages along pipelines.

Versioning and status: PSR-7 has achieved broad adoption and is recognized as a foundational interface in PHP HTTP ecosystems. It continues to influence how HTTP messages are represented in PHP applications, alongside newer standards that complement or extend its functionality.