make tokio dependency optional by adding alternative channel provider (async-channel)

Author: FlorianUekermann

h3/Cargo.toml

@@ -12,7 +12,8 @@ edition = "2018"
 bytes = "1"
 futures-util = { version = "0.3", default-features = false }
 http = "0.2.3"
-tokio = { version = "1", features = ["sync"] }
+tokio = { version = "1", features = ["sync"], optional = true }
+async-channel = { version = "1", optional = true }
 tracing = "0.1.18"
 fastrand = "1.7.0"
 
@@ -27,11 +28,14 @@ quinn = { version = "0.8.0", default-features = false, features = [
 quinn-proto = { version = "0.8.0", default-features = false }
 rcgen = "0.9"
 rustls = "0.20"
-tokio = { version = "1", features = ["rt", "macros", "io-util", "io-std"] }
+tokio = { version = "1", features = ["rt", "macros", "io-util", "io-std", "sync"] }
 tracing-subscriber = { version = "0.3", default-features = false, features = [
     "fmt",
     "ansi",
     "env-filter",
     "time",
     "tracing-log",
 ] }
+
+[features]
+default = ["tokio"]

h3/src/server.rs

@@ -61,7 +61,6 @@ use bytes::{Buf, BytesMut};
 use futures_util::future;
 use http::{response, HeaderMap, Request, Response, StatusCode};
 use quic::StreamId;
-use tokio::sync::mpsc;
 
 use crate::{
     connection::{self, ConnectionInner, ConnectionState, SharedStateRef},
@@ -74,6 +73,38 @@ use crate::{
 };
 use tracing::{error, trace, warn};
 
+#[cfg(all(feature = "tokio", not(feature = "async-channel")))]
+use tokio::sync::mpsc;
+
+#[cfg(feature = "async-channel")]
+mod mpsc {
+    use futures_util::StreamExt;
+    use std::task::{Context, Poll};
+
+    pub fn unbounded_channel<T>() -> (UnboundedSender<T>, UnboundedReceiver<T>) {
+        let (sender, receiver) = async_channel::unbounded();
+        (UnboundedSender(sender), UnboundedReceiver(receiver))
+    }
+
+    #[derive(Clone)]
+    pub struct UnboundedSender<T>(async_channel::Sender<T>);
+
+    impl<T> UnboundedSender<T> {
+        pub fn send(&self, msg: T) -> Result<(), async_channel::TrySendError<T>> {
+            self.0.try_send(msg)
+        }
+    }
+
+    #[derive(Clone)]
+    pub struct UnboundedReceiver<T>(async_channel::Receiver<T>);
+
+    impl<T> UnboundedReceiver<T> {
+        pub fn poll_recv(&mut self, cx: &mut Context) -> Poll<Option<T>> {
+            self.0.poll_next_unpin(cx)
+        }
+    }
+}
+
 /// Create a builder of HTTP/3 server connections
 ///
 /// This function creates a [`Builder`] that carries settings that can