webrtc/signalling: Fix potential hang and FD leak

If a peer connects via TCP and never initiates TLS, then the server
will get stuck in the accept loop. Spawn a task when accepting a TLS
connection, and timeout if it doesn't complete in 5 seconds.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1457>

net/webrtc/signalling/src/bin/server.rs

@@ -2,17 +2,20 @@
 
 use clap::Parser;
 use gst_plugin_webrtc_signalling::handlers::Handler;
-use gst_plugin_webrtc_signalling::server::Server;
+use gst_plugin_webrtc_signalling::server::{Server, ServerError};
 use tokio::io::AsyncReadExt;
 use tokio::task;
 use tracing_subscriber::prelude::*;
 
 use anyhow::Error;
+use std::time::Duration;
 use tokio::fs;
 use tokio::net::TcpListener;
 use tokio_native_tls::native_tls::TlsAcceptor;
 use tracing::{info, warn};
 
+const TLS_HANDSHAKE_TIMEOUT: Duration = Duration::from_secs(5);
+
 #[derive(Parser, Debug)]
 #[clap(about, version, author)]
 /// Program arguments
@@ -94,15 +97,20 @@ async fn main() -> Result<(), Error> {
 
         info!("Accepting connection from {}", address);
 
-        if let Some(ref acceptor) = acceptor {
-            let stream = match acceptor.accept(stream).await {
-                Ok(stream) => stream,
-                Err(err) => {
-                    warn!("Failed to accept TLS connection from {}: {}", address, err);
-                    continue;
+        if let Some(acceptor) = acceptor.clone() {
+            tokio::spawn(async move {
+                match tokio::time::timeout(TLS_HANDSHAKE_TIMEOUT, acceptor.accept(stream)).await {
+                    Ok(Ok(stream)) => server_clone.accept_async(stream).await,
+                    Ok(Err(err)) => {
+                        warn!("Failed to accept TLS connection from {}: {}", address, err);
+                        Err(ServerError::TLSHandshake(err))
+                    }
+                    Err(elapsed) => {
+                        warn!("TLS connection timed out {} after {}", address, elapsed);
+                        Err(ServerError::TLSHandshakeTimeout(elapsed))
+                    }
                 }
-            };
-            task::spawn(async move { server_clone.accept_async(stream).await });
+            });
         } else {
             task::spawn(async move { server_clone.accept_async(stream).await });
         }

net/webrtc/signalling/src/server/mod.rs

@@ -32,6 +32,10 @@ pub struct Server {
 pub enum ServerError {
     #[error("error during handshake {0}")]
     Handshake(#[from] async_tungstenite::tungstenite::Error),
+    #[error("error during TLS handshake {0}")]
+    TLSHandshake(#[from] tokio_native_tls::native_tls::Error),
+    #[error("timeout during TLS handshake {0}")]
+    TLSHandshakeTimeout(#[from] tokio::time::error::Elapsed),
 }
 
 impl Server {