Introduction

As often happens in the IT industry, terms get invented, and then used and abused. The term middleware is no exception. Arguably the first use of the term came out of the Internet Engineering Task Force (IETF) in the year 2000. Originally, the term was applied to any software which operates between the transport (that is, TCP/IP) and the application layer. More recently, especially with the acceptance of PHP Standard Recommendation number 7 (PSR-7), middleware, specifically in the PHP world, has been applied to the web client-server environment.

Note

The recipes in this section will make use of the concrete classes defined in Appendix, Defining PSR-7 Classes.