PSR http Message
A PSR that provides a set of common interfaces for HTTP messages
...HTTP messages are typically abstracted from the end-user consumer, but as developers, we typically need to know how they are structured and how to access or manipulate them in order to perform our tasks, whether that might be making a request to an HTTP API, or handling an incoming request. The first line of a request is the "request line", and contains, in order, the HTTP request method, the request target (usually either an absolute URI or a path on the web server), and the HTTP protocol version.