wezterm/filedescriptor/README.md

The purpose of this crate is to make it a bit more ergonomic for portable applications that need to work with the platform level RawFd and RawHandle types.

Rather than conditionally using RawFd and RawHandle, the FileDescriptor type can be used to manage ownership, duplicate, read and write.

FileDescriptor

This is a bit of a contrived example, but demonstrates how to avoid the conditional code that would otherwise be required to deal with calling as_raw_fd and as_raw_handle:

use filedescriptor::{FileDescriptor, FromRawFileDescriptor};
use std::io::Write;

fn get_stdout() -> anyhow::Result<FileDescriptor> {
  let stdout = std::io::stdout();
  let handle = stdout.lock();
  FileDescriptor::dup(&handle)
}

fn print_something() -> anyhow::Result<()> {
   get_stdout()?.write(b"hello")?;
   Ok(())
}

Pipe

The Pipe type makes it more convenient to create a pipe and manage the lifetime of both the read and write ends of that pipe.

use filedescriptor::Pipe;
use std::io::{Read, Write};
use anyhow::Error;

let mut pipe = Pipe::new()?;
pipe.write.write(b"hello")?;
drop(pipe.write);

let mut s = String::new();
pipe.read.read_to_string(&mut s)?;
assert_eq!(s, "hello");

Socketpair

The socketpair function returns a pair of connected SOCK_STREAM sockets and functions both on posix and windows systems.

use std::io::{Read, Write};
use anyhow::Error;

let (mut a, mut b) = filedescriptor::socketpair()?;
a.write(b"hello")?;
drop(a);

let mut s = String::new();
b.read_to_string(&mut s)?;
assert_eq!(s, "hello");

Polling

The mio crate offers powerful and scalable IO multiplexing, but there are some situations where mio doesn't fit. The filedescriptor crate offers a poll(2) compatible interface suitable for testing the readiness of a set of file descriptors. On unix systems this is a very thin wrapper around poll(2), except on macOS where it is actually a wrapper around the select(2) interface. On Windows systems the winsock WSAPoll function is used instead.

use filedescriptor::*;
use anyhow::Error;
use std::time::Duration;
use std::io::{Read, Write};

let (mut a, mut b) = filedescriptor::socketpair()?;
let mut poll_array = [pollfd {
   fd: a.as_socket_descriptor(),
   events: POLLIN,
   revents: 0
}];
// sleeps for 20 milliseconds because `a` is not yet ready
assert_eq!(poll(&mut poll_array, Some(Duration::from_millis(20)))?, 0);

b.write(b"hello")?;

// Now a is ready for read
assert_eq!(poll(&mut poll_array, Some(Duration::from_millis(20)))?, 1);