Cover by Francesco Cesarini, Simon Thompson

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Chapter 15. Socket Programming

Although distributed Erlang might be a first step in allowing programs on remote machines to communicate with each other, we sometimes have to rely on lower-level mechanisms and standardized protocols. Sockets allow programs written in any language to exchange data on different computers by exchanging byte streams transmitted using the protocols of the Internet Protocol (IP) Suite.

Whereas sockets are used to create a byte-oriented communication stream between programs possibly running on different machines, ports, which we cover in the next chapter, will do the same for programs running on the same machine. Byte streams, which in Erlang can be viewed as either binaries or integer lists, often follow standards and application-level protocols that allow programs written independently of each other to interact with each other.

Examples of socket-based communication include communication between web browsers and servers, instant messaging (IM) clients, email servers and clients, and peer-to-peer applications. The Erlang distribution itself is based on nodes communicating with each other through sockets.

Erlang can hide the raw packets from the user, providing user-friendly APIs to User Datagram Protocol (UDP) and Transmission Control Protocol (TCP). These are contained in the two library modules gen_udp, a connectionless, less reliable, packet-based communication protocol, and gen_tcp, which provides a connection-oriented communication channel. Both of these ...

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