[proxy] Prevent TLS stream from hanging

This change causes writer halves of a TLS stream to always flush after a
portion of bytes has been written by `std::io::copy`. Furthermore, some
cosmetic and minor functional changes are made to facilitate debug.

proxy/src/proxy.rs

@@ -6,7 +6,6 @@ use anyhow::bail;
 use tokio_postgres::NoTls;
 
 use rand::Rng;
-use std::io::Write;
 use std::{io, sync::mpsc::channel, thread};
 use zenith_utils::postgres_backend::Stream;
 use zenith_utils::postgres_backend::{PostgresBackend, ProtoState};
@@ -28,11 +27,13 @@ pub fn thread_main(
         println!("accepted connection from {}", peer_addr);
         socket.set_nodelay(true).unwrap();
 
-        thread::spawn(move || {
-            if let Err(err) = proxy_conn_main(state, socket) {
-                println!("error: {}", err);
-            }
-        });
+        thread::Builder::new()
+            .name("Proxy thread".into())
+            .spawn(move || {
+                if let Err(err) = proxy_conn_main(state, socket) {
+                    println!("error: {}", err);
+                }
+            })?;
     }
 }
 
@@ -158,6 +159,7 @@ impl ProxyConnection {
     fn handle_existing_user(&mut self) -> anyhow::Result<DatabaseInfo> {
         // ask password
         rand::thread_rng().fill(&mut self.md5_salt);
+
         self.pgb
             .write_message(&BeMessage::AuthenticationMD5Password(&self.md5_salt))?;
         self.pgb.state = ProtoState::Authentication; // XXX
@@ -250,51 +252,68 @@ databases without opening the browser.
 /// Create a TCP connection to a postgres database, authenticate with it, and receive the ReadyForQuery message
 async fn connect_to_db(db_info: DatabaseInfo) -> anyhow::Result<tokio::net::TcpStream> {
     let mut socket = tokio::net::TcpStream::connect(db_info.socket_addr()?).await?;
-    let config = db_info.conn_string().parse::<tokio_postgres::Config>()?;
+    let config = tokio_postgres::Config::from(db_info);
     let _ = config.connect_raw(&mut socket, NoTls).await?;
     Ok(socket)
 }
 
 /// Concurrently proxy both directions of the client and server connections
 fn proxy(
-    client_read: ReadStream,
-    client_write: WriteStream,
-    server_read: ReadStream,
-    server_write: WriteStream,
+    (client_read, client_write): (ReadStream, WriteStream),
+    (server_read, server_write): (ReadStream, WriteStream),
 ) -> anyhow::Result<()> {
-    fn do_proxy(mut reader: ReadStream, mut writer: WriteStream) -> io::Result<()> {
-        std::io::copy(&mut reader, &mut writer)?;
-        writer.flush()?;
-        writer.shutdown(std::net::Shutdown::Both)
+    fn do_proxy(mut reader: impl io::Read, mut writer: WriteStream) -> io::Result<u64> {
+        /// FlushWriter will make sure that every message is sent as soon as possible
+        struct FlushWriter<W>(W);
+
+        impl<W: io::Write> io::Write for FlushWriter<W> {
+            fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+                // `std::io::copy` is guaranteed to exit if we return an error,
+                // so we can afford to lose `res` in case `flush` fails
+                let res = self.0.write(buf);
+                if res.is_ok() {
+                    self.0.flush()?;
+                }
+                res
+            }
+
+            fn flush(&mut self) -> io::Result<()> {
+                self.0.flush()
+            }
+        }
+
+        let res = std::io::copy(&mut reader, &mut FlushWriter(&mut writer));
+        writer.shutdown(std::net::Shutdown::Both)?;
+        res
     }
 
     let client_to_server_jh = thread::spawn(move || do_proxy(client_read, server_write));
 
-    let res1 = do_proxy(server_read, client_write);
-    let res2 = client_to_server_jh.join().unwrap();
-    res1?;
-    res2?;
+    do_proxy(server_read, client_write)?;
+    client_to_server_jh.join().unwrap()?;
 
     Ok(())
 }
 
 /// Proxy a client connection to a postgres database
 fn proxy_pass(pgb: PostgresBackend, db_info: DatabaseInfo) -> anyhow::Result<()> {
-    let runtime = tokio::runtime::Builder::new_current_thread()
-        .enable_all()
-        .build()?;
-    let db_stream = runtime.block_on(connect_to_db(db_info))?;
-    let db_stream = db_stream.into_std()?;
-    db_stream.set_nonblocking(false)?;
+    let db_stream = {
+        // We'll get rid of this once migration to async is complete
+        let runtime = tokio::runtime::Builder::new_current_thread()
+            .enable_all()
+            .build()?;
 
-    let db_stream = zenith_utils::sock_split::BidiStream::from_tcp(db_stream);
-    let (db_read, db_write) = db_stream.split();
+        let stream = runtime.block_on(connect_to_db(db_info))?.into_std()?;
+        stream.set_nonblocking(false)?;
+        stream
+    };
 
-    let stream = match pgb.into_stream() {
+    let db = zenith_utils::sock_split::BidiStream::from_tcp(db_stream);
+
+    let client = match pgb.into_stream() {
         Stream::Bidirectional(bidi_stream) => bidi_stream,
         _ => bail!("invalid stream"),
     };
 
-    let (client_read, client_write) = stream.split();
-    proxy(client_read, client_write, db_read, db_write)
+    proxy(client.split(), db.split())
 }