From 4d92fe4e5e9883ba594f90cd9675a89a75edc9e2 Mon Sep 17 00:00:00 2001
From: TimurDela <32736336+TimurDela@users.noreply.github.com>
Date: Wed, 1 Jun 2022 21:10:08 +0200
Subject: [PATCH] fix(inputs/modbus): #11105 fix requests starting with an
 omitted field (#11202)

---
 plugins/inputs/modbus/modbus_test.go | 67 ++++++++++++++++++++++++++++
 plugins/inputs/modbus/request.go     |  7 +--
 2 files changed, 71 insertions(+), 3 deletions(-)

diff --git a/plugins/inputs/modbus/modbus_test.go b/plugins/inputs/modbus/modbus_test.go
index 5e3d04523..5a7a7570d 100644
--- a/plugins/inputs/modbus/modbus_test.go
+++ b/plugins/inputs/modbus/modbus_test.go
@@ -1857,3 +1857,70 @@ func TestConfigurationPerRequestFail(t *testing.T) {
 		})
 	}
 }
+
+func TestRequestsStartingWithOmits(t *testing.T) {
+	modbus := Modbus{
+		Name:              "Test",
+		Controller:        "tcp://localhost:1502",
+		ConfigurationType: "request",
+		Log:               testutil.Logger{},
+	}
+	modbus.Requests = []requestDefinition{
+		{SlaveID: 1,
+			ByteOrder:    "ABCD",
+			RegisterType: "holding",
+			Fields: []requestFieldDefinition{
+				{
+					Name:      "holding-0",
+					Address:   uint16(0),
+					InputType: "INT16",
+					Omit:      true,
+				},
+				{
+					Name:      "holding-1",
+					Address:   uint16(1),
+					InputType: "UINT16",
+					Omit:      true,
+				},
+				{
+					Name:      "holding-2",
+					Address:   uint16(2),
+					InputType: "INT16",
+				},
+			},
+		},
+	}
+	require.NoError(t, modbus.Init())
+	require.NotEmpty(t, modbus.requests)
+	require.NotNil(t, modbus.requests[1])
+	require.Equal(t, uint16(0), modbus.requests[1].holding[0].address)
+
+	serv := mbserver.NewServer()
+	require.NoError(t, serv.ListenTCP("localhost:1502"))
+	defer serv.Close()
+
+	handler := mb.NewTCPClientHandler("localhost:1502")
+	require.NoError(t, handler.Connect())
+	defer handler.Close()
+	client := mb.NewClient(handler)
+	_, err := client.WriteMultipleRegisters(uint16(0), 3, []byte{0x00, 0x01, 0x00, 0x02, 0x00, 0x03})
+	require.NoError(t, err)
+
+	expected := []telegraf.Metric{
+		testutil.MustMetric(
+			"modbus",
+			map[string]string{
+				"type":     cHoldingRegisters,
+				"slave_id": strconv.Itoa(int(modbus.Requests[0].SlaveID)),
+				"name":     modbus.Name,
+			},
+			map[string]interface{}{"holding-2": int16(3)},
+			time.Unix(0, 0),
+		),
+	}
+
+	var acc testutil.Accumulator
+	require.NoError(t, modbus.Gather(&acc))
+	acc.Wait(len(expected))
+	testutil.RequireMetricsEqual(t, expected, acc.GetTelegrafMetrics(), testutil.IgnoreTime())
+}
diff --git a/plugins/inputs/modbus/request.go b/plugins/inputs/modbus/request.go
index 16e054b67..b3c5b62dc 100644
--- a/plugins/inputs/modbus/request.go
+++ b/plugins/inputs/modbus/request.go
@@ -13,10 +13,12 @@ func newRequest(f field, tags map[string]string) request {
 	r := request{
 		address: f.address,
 		length:  f.length,
-		fields:  []field{f},
+		fields:  []field{},
 		tags:    map[string]string{},
 	}
-
+	if !f.omit {
+		r.fields = append(r.fields, f)
+	}
 	// Copy the tags
 	for k, v := range tags {
 		r.tags[k] = v
@@ -63,6 +65,5 @@ func groupFieldsToRequests(fields []field, tags map[string]string, maxBatchSize
 		current = newRequest(f, tags)
 	}
 	requests = append(requests, current)
-
 	return requests
 }