*Pipeline.getResults should close pipeline on error

Otherwise, it might be possible to panic when closing the pipeline if it
tries to read a connection that should be closed but still has a fatal
error on the wire.

#1920

pgconn/pgconn.go

@@ -2094,6 +2094,8 @@ func (p *Pipeline) getResults() (results any, err error) {
 	for {
 		msg, err := p.conn.receiveMessage()
 		if err != nil {
+			p.closed = true
+			p.err = err
 			p.conn.asyncClose()
 			return nil, normalizeTimeoutError(p.ctx, err)
 		}

pgconn/pgconn_test.go

@@ -3389,3 +3389,86 @@ func TestSNISupport(t *testing.T) {
 		})
 	}
 }
+
+// https://github.com/jackc/pgx/issues/1920
+func TestFatalErrorReceivedInPipelineMode(t *testing.T) {
+	t.Parallel()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 120*time.Second)
+	defer cancel()
+
+	steps := pgmock.AcceptUnauthenticatedConnRequestSteps()
+	steps = append(steps, pgmock.ExpectAnyMessage(&pgproto3.Parse{}))
+	steps = append(steps, pgmock.ExpectAnyMessage(&pgproto3.Describe{}))
+	steps = append(steps, pgmock.ExpectAnyMessage(&pgproto3.Parse{}))
+	steps = append(steps, pgmock.ExpectAnyMessage(&pgproto3.Describe{}))
+	steps = append(steps, pgmock.ExpectAnyMessage(&pgproto3.Parse{}))
+	steps = append(steps, pgmock.ExpectAnyMessage(&pgproto3.Describe{}))
+	steps = append(steps, pgmock.SendMessage(&pgproto3.RowDescription{Fields: []pgproto3.FieldDescription{
+		{Name: []byte("mock")},
+	}}))
+	steps = append(steps, pgmock.SendMessage(&pgproto3.ErrorResponse{Severity: "FATAL", Code: "57P01"}))
+	// We shouldn't get anything after the first fatal error. But the reported issue was with PgBouncer so maybe that
+	// causes the issue. Anyway, a FATAL error after the connection had already been killed could cause a panic.
+	steps = append(steps, pgmock.SendMessage(&pgproto3.ErrorResponse{Severity: "FATAL", Code: "57P01"}))
+
+	script := &pgmock.Script{Steps: steps}
+
+	ln, err := net.Listen("tcp", "127.0.0.1:")
+	require.NoError(t, err)
+	defer ln.Close()
+
+	serverKeepAlive := make(chan struct{})
+	defer close(serverKeepAlive)
+
+	serverErrChan := make(chan error, 1)
+	go func() {
+		defer close(serverErrChan)
+
+		conn, err := ln.Accept()
+		if err != nil {
+			serverErrChan <- err
+			return
+		}
+		defer conn.Close()
+
+		err = conn.SetDeadline(time.Now().Add(59 * time.Second))
+		if err != nil {
+			serverErrChan <- err
+			return
+		}
+
+		err = script.Run(pgproto3.NewBackend(conn, conn))
+		if err != nil {
+			serverErrChan <- err
+			return
+		}
+
+		<-serverKeepAlive
+	}()
+
+	parts := strings.Split(ln.Addr().String(), ":")
+	host := parts[0]
+	port := parts[1]
+	connStr := fmt.Sprintf("sslmode=disable host=%s port=%s", host, port)
+
+	ctx, cancel = context.WithTimeout(ctx, 59*time.Second)
+	defer cancel()
+	conn, err := pgconn.Connect(ctx, connStr)
+	require.NoError(t, err)
+
+	pipeline := conn.StartPipeline(ctx)
+	pipeline.SendPrepare("s1", "select 1", nil)
+	pipeline.SendPrepare("s2", "select 2", nil)
+	pipeline.SendPrepare("s3", "select 3", nil)
+	err = pipeline.Sync()
+	require.NoError(t, err)
+
+	_, err = pipeline.GetResults()
+	require.NoError(t, err)
+	_, err = pipeline.GetResults()
+	require.Error(t, err)
+
+	err = pipeline.Close()
+	require.Error(t, err)
+}