fix(inputs.phpfpm): Check error before continue processing (#15176)

plugins/inputs/phpfpm/fcgi_client.go

@@ -29,7 +29,10 @@ func newFcgiClient(timeout time.Duration, h string, args ...interface{}) (*conn,
 		laddr := net.UnixAddr{Name: args[0].(string), Net: h}
 		con, err = net.DialUnix(h, nil, &laddr)
 	default:
-		err = errors.New("fcgi: we only accept int (port) or string (socket) params")
+		return nil, errors.New("fcgi: we only accept int (port) or string (socket) params")
+	}
+	if err != nil {
+		return nil, err
 	}
 
 	if timeout != 0 {
@@ -38,11 +41,7 @@ func newFcgiClient(timeout time.Duration, h string, args ...interface{}) (*conn,
 		}
 	}
 
-	fcgi := &conn{
-		rwc: con,
-	}
-
-	return fcgi, err
+	return &conn{rwc: con}, nil
 }
 
 func (c *conn) Request(env map[string]string, requestData string) (retout []byte, reterr []byte, err error) {

plugins/inputs/phpfpm/phpfpm_test.go

@@ -187,6 +187,35 @@ func TestPhpFpmTimeout_From_Fcgi(t *testing.T) {
 	require.GreaterOrEqual(t, time.Since(start), timeout)
 }
 
+// TestPhpFpmCrashWithTimeout_From_Fcgi show issue #15175: when timeout is enabled
+// and nothing is listenning on specified port, a nil pointer was dereferenced.
+func TestPhpFpmCrashWithTimeout_From_Fcgi(t *testing.T) {
+	tcp, err := net.Listen("tcp", "127.0.0.1:0")
+	require.NoError(t, err, "Cannot initialize test server")
+
+	tcpAddress := tcp.Addr().String()
+
+	// Yes close the tcp port now. The listenner is only used to find a free
+	// port and then make it free. This test hope that nothing will re-use the
+	// port in meantime.
+	tcp.Close()
+
+	const timeout = 200 * time.Millisecond
+
+	//Now we tested again above server
+	r := &phpfpm{
+		Urls:    []string{"fcgi://" + tcpAddress + "/status"},
+		Timeout: config.Duration(timeout),
+		Log:     &testutil.Logger{},
+	}
+	require.NoError(t, r.Init())
+
+	var acc testutil.Accumulator
+	require.Error(t, acc.GatherError(r.Gather))
+
+	require.Empty(t, acc.GetTelegrafMetrics())
+}
+
 func TestPhpFpmGeneratesMetrics_From_Socket(t *testing.T) {
 	// Create a socket in /tmp because we always have write permission and if the
 	// removing of socket fail when system restart /tmp is clear so