Proxy protocol support (#3)

Add proxy protocol support.

---------

Co-authored-by: Alcibiades <89996683+0xAlcibiades@users.noreply.github.com>
Co-authored-by: Dave Belvedere <90095005+dbelv@users.noreply.github.com>
Co-authored-by: Alcibiades Athens <alcibiades.eth@protonmail.com>

.gitignore

@@ -17,4 +17,4 @@ settings.yaml
 lcov.info
 
 # Ignore cargo lock for library
-Cargo.lock
+Cargo.lock

Cargo.toml

@@ -15,6 +15,7 @@ version = "0.5.3"
 default = []
 tls-rustls = ["arc-swap", "pin-project-lite", "rustls", "rustls-pemfile", "tokio/fs", "tokio/time", "tokio-rustls"]
 tls-openssl = ["openssl", "tokio-openssl", "pin-project-lite"]
+proxy-protocol = ["ppp", "pin-project-lite"]
 
 [dependencies]
 
@@ -37,6 +38,9 @@ tokio-openssl = { version = "0.6", optional = true }
 tokio-rustls = { version = "0.24", optional = true }
 tower-service = "0.3"
 
+## proxy-protocol
+ppp = { version = "2.2.0", optional = true }
+
 [dev-dependencies]
 axum = "0.6"
 hyper = { version = "0.14", features = ["full"] }

src/lib.rs

@@ -124,3 +124,7 @@ pub mod tls_openssl;
 #[doc(inline)]
 #[cfg(feature = "tls-openssl")]
 pub use self::tls_openssl::bind_openssl;
+
+#[cfg(feature = "proxy-protocol")]
+#[cfg_attr(docsrs, doc(cfg(feature = "proxy_protocol")))]
+pub mod proxy_protocol;

src/proxy_protocol/future.rs

@@ -0,0 +1,143 @@
+//! Future types for PROXY protocol support.
+use crate::accept::Accept;
+use crate::proxy_protocol::ForwardClientIp;
+use pin_project_lite::pin_project;
+use std::{
+    fmt,
+    future::Future,
+    io,
+    net::SocketAddr,
+    pin::Pin,
+    task::{Context, Poll},
+};
+use tokio::io::{AsyncRead, AsyncWrite};
+use tokio::time::Timeout;
+
+// A `pin_project` is a procedural macro used for safe field projection in conjunction
+// with the Rust Pin API, which guarantees that certain types will not move in memory.
+pin_project! {
+    /// This struct represents the future for the ProxyProtocolAcceptor.
+    /// The generic types are:
+    /// F: The future type.
+    /// A: The type that implements the Accept trait.
+    /// I: The IO type that supports both AsyncRead and AsyncWrite.
+    /// S: The service type.
+    pub struct ProxyProtocolAcceptorFuture<F, A, I, S>
+    where
+        A: Accept<I, S>,
+    {
+        #[pin]
+        inner: AcceptFuture<F, A, I, S>,
+    }
+}
+
+impl<F, A, I, S> ProxyProtocolAcceptorFuture<F, A, I, S>
+where
+    A: Accept<I, S>,
+    I: AsyncRead + AsyncWrite + Unpin,
+{
+    // Constructor for creating a new ProxyProtocolAcceptorFuture.
+    pub(crate) fn new(future: Timeout<F>, acceptor: A, service: S) -> Self {
+        let inner = AcceptFuture::ReadHeader {
+            future,
+            acceptor,
+            service: Some(service),
+        };
+        Self { inner }
+    }
+}
+
+// Implement Debug trait for ProxyProtocolAcceptorFuture to allow
+// debugging and logging.
+impl<F, A, I, S> fmt::Debug for ProxyProtocolAcceptorFuture<F, A, I, S>
+where
+    A: Accept<I, S>,
+    I: AsyncRead + AsyncWrite + Unpin,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("ProxyProtocolAcceptorFuture").finish()
+    }
+}
+
+pin_project! {
+    // AcceptFuture represents the internal states of ProxyProtocolAcceptorFuture.
+    // It can either be waiting to read the header or forward the client IP.
+    #[project = AcceptFutureProj]
+    enum AcceptFuture<F, A, I, S>
+    where
+        A: Accept<I, S>,
+    {
+        ReadHeader {
+            #[pin]
+            future: Timeout<F>,
+            acceptor: A,
+            service: Option<S>,
+        },
+        ForwardIp {
+            #[pin]
+            future: A::Future,
+            client_address: Option<SocketAddr>,
+        },
+    }
+}
+
+impl<F, A, I, S> Future for ProxyProtocolAcceptorFuture<F, A, I, S>
+where
+    A: Accept<I, S>,
+    I: AsyncRead + AsyncWrite + Unpin,
+    // Future whose output is a result with either a tuple of stream and optional address,
+    // or an io::Error.
+    F: Future<Output = Result<(I, Option<SocketAddr>), io::Error>>,
+{
+    type Output = io::Result<(A::Stream, ForwardClientIp<A::Service>)>;
+
+    // The main poll function that drives the future towards completion.
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+
+        loop {
+            // Check the current state of the inner future.
+            match this.inner.as_mut().project() {
+                AcceptFutureProj::ReadHeader {
+                    future,
+                    acceptor,
+                    service,
+                } => match future.poll(cx) {
+                    Poll::Ready(Ok(Ok((stream, client_address)))) => {
+                        let service = service.take().expect("future polled after ready");
+                        let future = acceptor.accept(stream, service);
+
+                        // Transition to the ForwardIp state after successfully reading the header.
+                        this.inner.set(AcceptFuture::ForwardIp {
+                            future,
+                            client_address,
+                        });
+                    }
+                    Poll::Ready(Ok(Err(e))) => return Poll::Ready(Err(e)),
+                    Poll::Ready(Err(timeout)) => {
+                        return Poll::Ready(Err(io::Error::new(io::ErrorKind::TimedOut, timeout)))
+                    }
+                    Poll::Pending => return Poll::Pending,
+                },
+                AcceptFutureProj::ForwardIp {
+                    future,
+                    client_address,
+                } => {
+                    return match future.poll(cx) {
+                        Poll::Ready(Ok((stream, service))) => {
+                            let service = ForwardClientIp {
+                                inner: service,
+                                client_address: *client_address,
+                            };
+
+                            // Return the successfully processed stream and service.
+                            Poll::Ready(Ok((stream, service)))
+                        }
+                        Poll::Ready(Err(e)) => Poll::Ready(Err(e)),
+                        Poll::Pending => Poll::Pending,
+                    };
+                }
+            }
+        }
+    }
+}