In what scenario would stdin come from a socket?

[smahm006]

Hello everyone,

I am a Python programmer trying to learn Rust. I like to learn by studying well made projects and for Rust I am using the ripgrep project to learn the language (Thank you BurntSushi for leaving this open source!)

I started with the grep-cli crate and just from digging into it's functions I realize there are a lot of low level concepts that I need to understand. The first function I started with is the "pub fn is_readable_stdin()" (in crates/cli/src/lib.rs) and that took me on a whole journey of a basic understanding what file descriptors are, how inter-process communications work and how everything is a file in Unix.

For now I understand why piping ( cat test.txt | rg "test file") and stdin redirection (rg "test file" < test.txt) make is_stdin_readable() true.

But there is also a check to see if stdin is coming from a socket (ft.is_socket()) but I am getting stuck trying to find an example where that would be applicable.

From https://unix.stackexchange.com/questions/16311/what-is-a-socket:

A socket is a pseudo-file that represents a network connection. Once a socket has been created (identifying the other host and port), writes to that socket are turned into network packets that get sent out, and data received from the network can be read from the socket.

And there are examples of opening a socket nc -lU socket.sock and writing to it socat -T 3 unix-connect:socket.sock 2 but I cannot find how to read from a socket, hence the question of the title.

[BurntSushi]

This is the commit that added the ft.is_socket() predicate: 020c545

The commit message also basically answers your question. It sounds like PowerShell uses a socket instead of a fifo. I do not know why it's implemented that way.

See also #1741, which is where the bug was originally reported.

[smahm006]

Ah makes sense, so generally stdin does not come from sockets.

Thanks for the clarification!

[BurntSushi]

Yeah it's definitely a strange case.