Using extensible stream-oriented I/O buffers

Extensible buffers are those buffers that dynamically increase their size when new data is written to them. They are usually used to read data from sockets when the size of the incoming message is unknown.

Some application layer protocols do not define the exact size of the message. Instead, the boundary of the message is represented by a specific sequence of symbols at the end of the message itself or by a transport protocol service message end of file (EOF) issued by the sender after it finishes sending the message.

For example, according to the HTTP protocol, the header section of the request and response messages don't have a fixed length and its boundary is represented by a sequence of four ASCII symbols, <CR><LF><CR><LF>, which is part of the message. In such cases, dynamically extensible buffers and functions that can work with them, which are provided by the Boost.Asio library, are very useful.

In this recipe, we will...