Initial import. Most things seem working.

This includes an abortive attempt to do a gtk4 dialog (which I don't
think is possible, as gtk4 doesn't allow embedding toplevels anymore),
and an iced dialog, which I just never started writing.

async-xcb/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "async-xcb"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+async-io = "1.6"
+async-std = { version = "1.11", features = ["attributes"] }
+futures = "0.3"
+futures-lite = "1.12"
+nix = "0.23"
+# git source needed until extension event error resolution fix is released
+xcb = { git = "https://github.com/rust-x-bindings/rust-xcb", rev = "d09b5f91bc07d56673f1bc0d6c7ecd72b5ff7b3e" }

async-xcb/src/lib.rs

@@ -0,0 +1,49 @@
+use async_io::{Async, ReadableOwned};
+use futures::prelude::*;
+use futures_lite::ready;
+use nix::{fcntl::{fcntl, F_GETFL, F_SETFL, OFlag}, unistd::read};
+use std::{io, os::unix::io::AsRawFd, pin::Pin, sync::Arc, task::{Context, Poll}};
+
+pub struct AsyncConnection {
+    conn: Arc<Async<xcb::Connection>>,
+    readable: Option<ReadableOwned<xcb::Connection>>,
+}
+
+impl AsyncConnection {
+    pub fn new(conn: xcb::Connection) -> io::Result<Self> {
+        let flags = fcntl(conn.as_raw_fd(), F_GETFL)?;
+        fcntl(conn.as_raw_fd(), F_SETFL(OFlag::from_bits_truncate(flags) | OFlag::O_NONBLOCK))?;
+        Ok(Self {
+            conn: Arc::new(Async::new(conn)?),
+            readable: None,
+        })
+    }
+}
+
+impl AsyncRead for AsyncConnection {
+    fn poll_read(mut self: Pin<&mut Self>, cx: &mut Context<'_>, buf: &mut [u8]) -> Poll<std::io::Result<usize>> {
+        loop {
+            match read(self.conn.as_raw_fd(), buf) {
+                Err(nix::Error::EAGAIN) => (),
+                Err(err) => {
+                    self.readable = None;
+                    return Poll::Ready(Err(err.into()));
+                },
+                Ok(count) => {
+                    self.readable = None;
+                    return Poll::Ready(Ok(count));
+                }
+            }
+
+            if self.readable.is_none() {
+                self.readable = Some(Arc::clone(&self.conn).readable_owned());
+            }
+
+            if let Some(f) = &mut self.readable {
+                let res = ready!(Pin::new(f).poll(cx));
+                self.readable = None;
+                res?;
+            }
+        }
+    }
+}