feat(outputs.mqtt): enhance routing capabilities (#12224)

plugins/outputs/mqtt/README.md

@@ -39,8 +39,13 @@ See the [CONFIGURATION.md][CONFIGURATION.md] for more details.
 
   ## MQTT Topic for Producer Messages
   ## MQTT outputs send metrics to this topic format:
-  ## <topic_prefix>/<hostname>/<pluginname>/ (e.g. prefix/web01.example.com/mem)
-  topic_prefix = "telegraf"
+  ## {{ .TopicPrefix }}/{{ .Hostname }}/{{ .PluginName }}/{{ .Tag "tag_key" }}
+  ## (e.g. prefix/web01.example.com/mem/some_tag_value)
+  ## Each path segment accepts either a template placeholder, an environment variable, or a tag key
+  ## of the form `{{.Tag "tag_key_name"]]`. Empty path elements as well as special MQTT characters
+  ## (such as `+` or `#`) are invalid to form the topic name and will lead to an error.
+  ## In case a tag is missing in the metric, that path segment omitted for the final topic.
+  topic = "telegraf/{{ .Hostname }}/{{ .PluginName }}"
 
   ## QoS policy for messages
   ## The mqtt QoS policy for sending messages.

plugins/outputs/mqtt/mqtt.go

@@ -30,7 +30,8 @@ type MQTT struct {
 	Password    string   `toml:"password"`
 	Database    string
 	Timeout     config.Duration `toml:"timeout"`
-	TopicPrefix string          `toml:"topic_prefix"`
+	TopicPrefix string          `toml:"topic_prefix" deprecated:"1.25.0;use 'topic' instead"`
+	Topic       string          `toml:"topic"`
 	QoS         int             `toml:"qos"`
 	ClientID    string          `toml:"client_id"`
 	tls.ClientConfig
@@ -41,6 +42,7 @@ type MQTT struct {
 
 	client     Client
 	serializer serializers.Serializer
+	generator  *TopicNameGenerator
 
 	sync.Mutex
 }
@@ -58,6 +60,15 @@ func (*MQTT) SampleConfig() string {
 	return sampleConfig
 }
 
+func (m *MQTT) Init() error {
+	var err error
+	m.generator, err = NewTopicNameGenerator(m.TopicPrefix, m.Topic)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 func (m *MQTT) Connect() error {
 	m.Lock()
 	defer m.Unlock()
@@ -91,24 +102,17 @@ func (m *MQTT) Write(metrics []telegraf.Metric) error {
 	if len(metrics) == 0 {
 		return nil
 	}
+
 	hostname, ok := metrics[0].Tags()["host"]
 	if !ok {
 		hostname = ""
 	}
-
 	metricsmap := make(map[string][]telegraf.Metric)
-
 	for _, metric := range metrics {
-		var t []string
-		if m.TopicPrefix != "" {
-			t = append(t, m.TopicPrefix)
+		topic, err := m.generator.Generate(hostname, metric)
+		if err != nil {
+			return fmt.Errorf("topic name couldn't be generated due to error: %w", err)
 		}
-		if hostname != "" {
-			t = append(t, hostname)
-		}
-
-		t = append(t, metric.Name())
-		topic := strings.Join(t, "/")
 
 		if m.BatchMessage {
 			metricsmap[topic] = append(metricsmap[topic], metric)

plugins/outputs/mqtt/mqtt_test.go

@@ -2,8 +2,10 @@ package mqtt
 
 import (
 	"fmt"
+	"github.com/influxdata/telegraf/metric"
 	"path/filepath"
 	"testing"
+	"time"
 
 	"github.com/stretchr/testify/require"
 	"github.com/testcontainers/testcontainers-go/wait"
@@ -49,12 +51,13 @@ func TestConnectAndWriteIntegration(t *testing.T) {
 	}
 
 	// Verify that we can connect to the MQTT broker
-	err := m.Connect()
-	require.NoError(t, err)
+	require.NoError(t, m.Init())
+
+	// Verify that we can connect to the MQTT broker
+	require.NoError(t, m.Connect())
 
 	// Verify that we can successfully write data to the mqtt broker
-	err = m.Write(testutil.MockMetrics())
-	require.NoError(t, err)
+	require.NoError(t, m.Write(testutil.MockMetrics()))
 }
 
 func TestConnectAndWriteIntegrationMQTTv3(t *testing.T) {
@@ -76,12 +79,13 @@ func TestConnectAndWriteIntegrationMQTTv3(t *testing.T) {
 	}
 
 	// Verify that we can connect to the MQTT broker
-	err := m.Connect()
-	require.NoError(t, err)
+	require.NoError(t, m.Init())
+
+	// Verify that we can connect to the MQTT broker
+	require.NoError(t, m.Connect())
 
 	// Verify that we can successfully write data to the mqtt broker
-	err = m.Write(testutil.MockMetrics())
-	require.NoError(t, err)
+	require.NoError(t, m.Write(testutil.MockMetrics()))
 }
 
 func TestConnectAndWriteIntegrationMQTTv5(t *testing.T) {
@@ -103,10 +107,108 @@ func TestConnectAndWriteIntegrationMQTTv5(t *testing.T) {
 	}
 
 	// Verify that we can connect to the MQTT broker
-	err := m.Connect()
-	require.NoError(t, err)
+	require.NoError(t, m.Init())
+	require.NoError(t, m.Connect())
 
 	// Verify that we can successfully write data to the mqtt broker
-	err = m.Write(testutil.MockMetrics())
-	require.NoError(t, err)
+	require.NoError(t, m.Write(testutil.MockMetrics()))
+}
+
+func TestMQTTTopicGenerationTemplateIsValid(t *testing.T) {
+	tests := []struct {
+		name          string
+		topic         string
+		expectedError string
+	}{
+		{
+			name:          "a valid pattern is accepted",
+			topic:         "this/is/valid",
+			expectedError: "",
+		},
+		{
+			name:          "an invalid pattern is rejected",
+			topic:         "this/is/#/invalid",
+			expectedError: "found forbidden character # in the topic name this/is/#/invalid",
+		},
+		{
+			name:          "an invalid pattern is rejected",
+			topic:         "this/is/+/invalid",
+			expectedError: "found forbidden character + in the topic name this/is/+/invalid",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			m := &MQTT{
+				Topic: tt.topic,
+			}
+			err := m.Init()
+			if tt.expectedError != "" {
+				require.ErrorContains(t, err, tt.expectedError)
+			} else {
+				require.NoError(t, err)
+			}
+		})
+	}
+}
+
+func TestGenerateTopicName(t *testing.T) {
+	s := serializers.NewInfluxSerializer()
+	m := &MQTT{
+		Servers:    []string{"tcp://localhost:502"},
+		serializer: s,
+		KeepAlive:  30,
+		Log:        testutil.Logger{},
+	}
+	tests := []struct {
+		name    string
+		pattern string
+		want    string
+	}{
+		{
+			name:    "matches default legacy format",
+			pattern: "telegraf/{{ .Hostname }}/{{ .PluginName }}",
+			want:    "telegraf/hostname/metric-name",
+		},
+		{
+			name:    "respect hardcoded strings",
+			pattern: "this/is/a/topic",
+			want:    "this/is/a/topic",
+		},
+		{
+			name:    "allows the use of tags",
+			pattern: "{{ .TopicPrefix }}/{{ .Tag \"tag1\" }}",
+			want:    "prefix/value1",
+		},
+		{
+			name:    "uses the plugin name when no pattern is provided",
+			pattern: "",
+			want:    "metric-name",
+		},
+		{
+			name:    "ignores tag when tag does not exists",
+			pattern: "{{ .TopicPrefix }}/{{ .Tag \"not-a-tag\" }}",
+			want:    "prefix",
+		},
+		{
+			name:    "ignores empty forward slashes",
+			pattern: "double//slashes//are//ignored",
+			want:    "double/slashes/are/ignored",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			m.Topic = tt.pattern
+			m.TopicPrefix = "prefix"
+			met := metric.New(
+				"metric-name",
+				map[string]string{"tag1": "value1"},
+				map[string]interface{}{"value": 123},
+				time.Date(2022, time.November, 10, 23, 0, 0, 0, time.UTC),
+			)
+			require.NoError(t, m.Init())
+			actual, err := m.generator.Generate("hostname", met)
+			require.NoError(t, err)
+			require.Equal(t, tt.want, actual)
+		})
+	}
 }

plugins/outputs/mqtt/sample.conf

@@ -13,8 +13,13 @@
 
   ## MQTT Topic for Producer Messages
   ## MQTT outputs send metrics to this topic format:
-  ## <topic_prefix>/<hostname>/<pluginname>/ (e.g. prefix/web01.example.com/mem)
-  topic_prefix = "telegraf"
+  ## {{ .TopicPrefix }}/{{ .Hostname }}/{{ .PluginName }}/{{ .Tag "tag_key" }}
+  ## (e.g. prefix/web01.example.com/mem/some_tag_value)
+  ## Each path segment accepts either a template placeholder, an environment variable, or a tag key
+  ## of the form `{{.Tag "tag_key_name"]]`. Empty path elements as well as special MQTT characters
+  ## (such as `+` or `#`) are invalid to form the topic name and will lead to an error.
+  ## In case a tag is missing in the metric, that path segment omitted for the final topic.
+  topic = "telegraf/{{ .Hostname }}/{{ .PluginName }}"
 
   ## QoS policy for messages
   ## The mqtt QoS policy for sending messages.

plugins/outputs/mqtt/topic_name_generator.go

@@ -0,0 +1,58 @@
+package mqtt
+
+import (
+	"fmt"
+	"strings"
+	"text/template"
+
+	"github.com/influxdata/telegraf"
+)
+
+type TopicNameGenerator struct {
+	Hostname    string
+	TopicPrefix string
+	PluginName  string
+	metric      telegraf.Metric
+	template    *template.Template
+}
+
+func NewTopicNameGenerator(topicPrefix string, topic string) (*TopicNameGenerator, error) {
+	tt, err := template.New("topic_name").Parse(topic)
+	if err != nil {
+		return nil, err
+	}
+	for _, p := range strings.Split(topic, "/") {
+		if strings.ContainsAny(p, "#+") {
+			return nil, fmt.Errorf("found forbidden character %s in the topic name %s", p, topic)
+		}
+	}
+	return &TopicNameGenerator{TopicPrefix: topicPrefix, template: tt}, nil
+}
+
+func (t *TopicNameGenerator) Tag(key string) string {
+	tagString, _ := t.metric.GetTag(key)
+	return tagString
+}
+
+func (t *TopicNameGenerator) Generate(hostname string, m telegraf.Metric) (string, error) {
+	t.Hostname = hostname
+	t.metric = m
+	t.PluginName = m.Name()
+	var b strings.Builder
+	err := t.template.Execute(&b, t)
+	if err != nil {
+		return "", err
+	}
+	var ts []string
+	for _, p := range strings.Split(b.String(), "/") {
+		if p != "" {
+			ts = append(ts, p)
+		}
+	}
+	topic := strings.Join(ts, "/")
+	// This is to keep backward compatibility with previous behaviour where the plugin name was always present
+	if topic == "" {
+		return m.Name(), nil
+	}
+	return topic, nil
+}