add `--debug-echo` option for P4 end servers to run a simulated P5 TCP echo server

This makes it possible to debug with only 4 processes instead of 5.

docs/how-to/test-ptth-quic.md

@@ -4,9 +4,11 @@
 
 - Open 3 terminals in `prototypes/quic_demo`
 - Use `export RUST_LOG=quic_demo_relay_server=debug` to enable debug logging
-for the terminal that will run the relay server
+for the terminal that will run the relay server (P3)
 - Use `export RUST_LOG=quic_demo_end_server=debug` for the terminal that
-will run the end server
+will run the end server (P4)
+- Use `export RUST_LOG=quic_demo_client=debug` for the terminal that
+will run the client (P2)
 
 When the relay server is running, use curl to get the list of connected
 end servers: `curl 127.0.0.1:4004`
@@ -15,6 +17,8 @@ end servers: `curl 127.0.0.1:4004`
 
 - Start a relay `cargo run --bin quic_demo_relay_server`
 - Verify that the relay has no end servers connected 
-- Start an end server `cargo run --bin quic_demo_end_server`
+- Start an end server `cargo run --bin quic_demo_end_server -- --debug-echo`
 - Verify that the end server connected
-
+- Start a client `cargo run --bin quic_demo_client`
+- Connect to the client and verify that the debug echo server is running
+`nc 127.0.0.1 30381`

prototypes/quic_demo/src/bin/quic_demo_end_server.rs

@@ -10,21 +10,23 @@ struct Opt {
 	relay_addr: Option <String>,
 	#[structopt (long)]
 	server_id: Option <PeerId>,
+	#[structopt (long)]
+	debug_echo: bool,
 }
 
 #[tokio::main]
 async fn main () -> anyhow::Result <()> {
 	tracing_subscriber::fmt::init ();
 	
-	let opt = Opt::from_args ();
+	let opt = Arc::new (Opt::from_args ());
 	
 	let server_cert = tokio::fs::read ("quic_server.crt").await?;
-	let relay_addr = opt.relay_addr.unwrap_or_else (|| String::from ("127.0.0.1:30380")).parse ()?;
+	let relay_addr = opt.relay_addr.clone ().unwrap_or_else (|| String::from ("127.0.0.1:30380")).parse ()?;
 	let endpoint = make_client_endpoint ("0.0.0.0:0".parse ()?, &[&server_cert])?;
 	
 	trace! ("Connecting to relay server");
 	
-	let server_id = opt.server_id.unwrap_or_else (|| "bogus_server".to_string ());
+	let server_id = opt.server_id.clone ().unwrap_or_else (|| "bogus_server".to_string ());
 	
 	let quinn::NewConnection {
 		mut bi_streams,
@@ -37,11 +39,12 @@ async fn main () -> anyhow::Result <()> {
 	loop {
 		let (relay_send, relay_recv) = bi_streams.next ().await.ok_or_else (|| anyhow::anyhow! ("Relay server didn't open a bi stream"))??;
 		
-		tokio::spawn (handle_bi_stream (relay_send, relay_recv));
+		tokio::spawn (handle_bi_stream (Arc::clone (&opt), relay_send, relay_recv));
 	}
 }
 
 async fn handle_bi_stream (
+	opt: Arc <Opt>,
 	relay_send: quinn::SendStream,
 	mut relay_recv: quinn::RecvStream,
 ) -> anyhow::Result <()>
@@ -50,13 +53,14 @@ async fn handle_bi_stream (
 		protocol::P3ToP4Stream::NewPtthConnection {
 			client_id,
 			..
-		} => handle_new_ptth_connection (relay_send, relay_recv, client_id).await?,
+		} => handle_new_ptth_connection (opt, relay_send, relay_recv, client_id).await?,
 	}
 	
 	Ok (())
 }
 
 async fn handle_new_ptth_connection (
+	opt: Arc <Opt>,
 	mut relay_send: quinn::SendStream,
 	mut relay_recv: quinn::RecvStream,
 	_client_id: String,
@@ -73,6 +77,12 @@ async fn handle_new_ptth_connection (
 	
 	debug! ("Started PTTH connection");
 	
+	if opt.debug_echo {
+		relay_send.write (b"Connected to P4=P5 debug echo server\n").await?;
+		debug! ("Relaying bytes using internal debug echo server (P4=P5)");
+		tokio::io::copy (&mut relay_recv, &mut relay_send).await?;
+	}
+	else {
 		let stream = TcpStream::connect (("127.0.0.1", p4_to_p5_req.port)).await?;
 		let (local_recv, local_send) = stream.into_split ();
 		
@@ -86,6 +96,7 @@ async fn handle_new_ptth_connection (
 		}.build ();
 		
 		ptth_conn.wait_for_close ().await?;
+	}
 	
 	Ok (())
 }