[v12] Make ProtoPostgres support PROXY protocol

lib/multiplexer/multiplexer.go

@@ -496,19 +496,13 @@ func (m *Mux) detect(conn net.Conn) (*Conn, error) {
 
 			proxyLine = newProxyLine
 			// repeat the cycle to detect the protocol
-		case ProtoTLS, ProtoSSH, ProtoHTTP:
+		case ProtoTLS, ProtoSSH, ProtoHTTP, ProtoPostgres:
 			return &Conn{
 				protocol:  proto,
 				Conn:      conn,
 				reader:    reader,
 				proxyLine: proxyLine,
 			}, nil
-		case ProtoPostgres:
-			return &Conn{
-				protocol: proto,
-				Conn:     conn,
-				reader:   reader,
-			}, nil
 		}
 	}
 	// if code ended here after three attempts, something is wrong

lib/multiplexer/multiplexer_test.go

@@ -538,8 +538,9 @@ func TestMux(t *testing.T) {
 		defer cancel()
 
 		mux, err := New(Config{
-			Context:  ctx,
-			Listener: listener,
+			Context:                     ctx,
+			Listener:                    listener,
+			EnableExternalProxyProtocol: true,
 		})
 		require.NoError(t, err)
 		go mux.Serve()
@@ -548,20 +549,36 @@ func TestMux(t *testing.T) {
 		// register listener before establishing frontend connection
 		dblistener := mux.DB()
 
-		// Connect to the listener and send Postgres SSLRequest which is what
-		// psql or other Postgres client will do.
-		conn, err := net.Dial("tcp", listener.Addr().String())
-		require.NoError(t, err)
-		defer conn.Close()
+		check := func(t *testing.T, expectedAddr string, proxyLine []byte) {
+			// Connect to the listener and send Postgres SSLRequest which is what
+			// psql or other Postgres client will do.
+			conn, err := net.Dial("tcp", listener.Addr().String())
+			require.NoError(t, err)
+			defer conn.Close()
 
-		frontend := pgproto3.NewFrontend(pgproto3.NewChunkReader(conn), conn)
-		err = frontend.Send(&pgproto3.SSLRequest{})
-		require.NoError(t, err)
+			_, err = conn.Write(sampleProxyV2Line)
+			require.NoError(t, err)
+
+			frontend := pgproto3.NewFrontend(pgproto3.NewChunkReader(conn), conn)
+			err = frontend.Send(&pgproto3.SSLRequest{})
+			require.NoError(t, err)
 
-		// This should not hang indefinitely since we set timeout on the mux context above.
-		conn, err = dblistener.Accept()
-		require.NoError(t, err, "detected Postgres connection")
-		require.Equal(t, ProtoPostgres, conn.(*Conn).Protocol())
+			// This should not hang indefinitely since we set timeout on the mux context above.
+			dbConn, err := dblistener.Accept()
+			require.NoError(t, err, "detected Postgres connection")
+			require.Equal(t, ProtoPostgres, dbConn.(*Conn).Protocol())
+			if expectedAddr != "" {
+				require.Equal(t, expectedAddr, dbConn.RemoteAddr().String())
+			}
+		}
+
+		t.Run("without proxy line", func(t *testing.T) {
+			check(t, "", nil)
+		})
+
+		t.Run("with proxy line", func(t *testing.T) {
+			check(t, "127.0.0.1:12345", sampleProxyV2Line)
+		})
 	})
 
 	// WebListener verifies web listener correctly multiplexes connections