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Basic Echo Server
Created ~ 2024-03-04


This is a basic implementation of a server-client model using UNIX sockets (connects processes on the same machine).

The high level sequence of networking events are: server.c and client.c both create their respective sockets. The server binds to a file path, and listens for connections. The client connects and the server accepts. Then they exchange information through read() and write() operations. When the connection is broken, both programs close their sockets. The server also has the additional task of unlinking the socket file (deletes the name from filesystem).

The echo implementation includes:

  • user prompting for client (terminated with \n)
  • polling for server (waits for a write() from client to trigger read())
    • It will continuously loop if timeout, and its returned value is checked to determine if there has been any activity.

Resources and Links

Conceptual knowledge of what sockets are and how they are applied in connection-oriented server-client model was learned from IBM’s articles (I followed their diagram). Their articles are actually very holistic and can be read for general knowledge, despite it being written for their IBM i operating system.

Usage of the functions and structs were referenced with online man pages.

Dev Comments

I started with the man pages but I didn’t have a solid understanding of what sockets even were. So I found the IBM articles, then went back to the man pages. My first task was to create and bind a socket. Once I got that, I worked on connecting sockets, then exchanging data, and fixed it up to have the echo functionality. The EXIT_IF_ERR macro idea were taken from EVT-core.

I ran into some issues during development, mostly from a gap of knowledge about how to use UNIX sockets. In times like this, I tried to reference the man pages first to see if I missed something or if it could redirect me to another functions. Otherwise I would search on Google or use StackOverFlow.

I don’t remember every single issue I had, but here is a rough list of problems I was facing, the knowledge gap I had, and the resource that helped me:

  • I initially thought that the server and client would communicate through a file, like the client would write to a file that can read
    • Technically sockets are file (UNIX philosophy), but can’t be open and read in the traditional file sense.
  • bind() wouldn’t work because address was in use
    • apparently you have to unlink it