feat: Add dynamic tagging to gnmi plugin

plugins/inputs/gnmi/README.md

@@ -64,11 +64,23 @@ It has been optimized to support gNMI telemetry as produced by Cisco IOS XR (64-
 
     ## If suppression is enabled, send updates at least every X seconds anyway
     # heartbeat_interval = "60s"
+
+  #[[inputs.gnmi.subscription]]
+    # name = "descr"
+    # origin = "openconfig-interfaces"
+    # path = "/interfaces/interface/state/description"
+    # subscription_mode = "on_change"
+
+    ## If tag_only is set, the subscription in question will be utilized to maintain a map of
+    ## tags to apply to other measurements emitted by the plugin, by matching path keys
+    ## All fields from the tag-only subscription will be applied as tags to other readings,
+    ## in the format <name>_<fieldBase>.
+    # tag_only = true
 ```
 
 ## Example Output
 
 ```shell
-ifcounters,path=openconfig-interfaces:/interfaces/interface/state/counters,host=linux,name=MgmtEth0/RP0/CPU0/0,source=10.49.234.115 in-multicast-pkts=0i,out-multicast-pkts=0i,out-errors=0i,out-discards=0i,in-broadcast-pkts=0i,out-broadcast-pkts=0i,in-discards=0i,in-unknown-protos=0i,in-errors=0i,out-unicast-pkts=0i,in-octets=0i,out-octets=0i,last-clear="2019-05-22T16:53:21Z",in-unicast-pkts=0i 1559145777425000000
-ifcounters,path=openconfig-interfaces:/interfaces/interface/state/counters,host=linux,name=GigabitEthernet0/0/0/0,source=10.49.234.115 out-multicast-pkts=0i,out-broadcast-pkts=0i,in-errors=0i,out-errors=0i,in-discards=0i,out-octets=0i,in-unknown-protos=0i,in-unicast-pkts=0i,in-octets=0i,in-multicast-pkts=0i,in-broadcast-pkts=0i,last-clear="2019-05-22T16:54:50Z",out-unicast-pkts=0i,out-discards=0i 1559145777425000000
+ifcounters,path=openconfig-interfaces:/interfaces/interface/state/counters,host=linux,name=MgmtEth0/RP0/CPU0/0,source=10.49.234.115,descr/description=Foo in-multicast-pkts=0i,out-multicast-pkts=0i,out-errors=0i,out-discards=0i,in-broadcast-pkts=0i,out-broadcast-pkts=0i,in-discards=0i,in-unknown-protos=0i,in-errors=0i,out-unicast-pkts=0i,in-octets=0i,out-octets=0i,last-clear="2019-05-22T16:53:21Z",in-unicast-pkts=0i 1559145777425000000
+ifcounters,path=openconfig-interfaces:/interfaces/interface/state/counters,host=linux,name=GigabitEthernet0/0/0/0,source=10.49.234.115,descr/description=Bar out-multicast-pkts=0i,out-broadcast-pkts=0i,in-errors=0i,out-errors=0i,in-discards=0i,out-octets=0i,in-unknown-protos=0i,in-unicast-pkts=0i,in-octets=0i,in-multicast-pkts=0i,in-broadcast-pkts=0i,last-clear="2019-05-22T16:54:50Z",out-unicast-pkts=0i,out-discards=0i 1559145777425000000
 ```

plugins/inputs/gnmi/gnmi.go

@@ -56,6 +56,8 @@ type GNMI struct {
 	acc             telegraf.Accumulator
 	cancel          context.CancelFunc
 	wg              sync.WaitGroup
+	// Lookup/device+name/key/value
+	lookup map[string]map[string]map[string]interface{}
 
 	Log telegraf.Logger
 }
@@ -73,6 +75,9 @@ type Subscription struct {
 	// Duplicate suppression
 	SuppressRedundant bool            `toml:"suppress_redundant"`
 	HeartbeatInterval config.Duration `toml:"heartbeat_interval"`
+
+	// Mark this subscription as a tag-only lookup source, not emitting any metric
+	TagOnly bool `toml:"tag_only"`
 }
 
 // Start the http listener service
@@ -83,6 +88,7 @@ func (c *GNMI) Start(acc telegraf.Accumulator) error {
 	var request *gnmiLib.SubscribeRequest
 	c.acc = acc
 	ctx, c.cancel = context.WithCancel(context.Background())
+	c.lookup = make(map[string]map[string]map[string]interface{})
 
 	// Validate configuration
 	if request, err = c.newSubscribeRequest(); err != nil {
@@ -133,6 +139,11 @@ func (c *GNMI) Start(acc telegraf.Accumulator) error {
 			c.internalAliases[longPath] = name
 			c.internalAliases[shortPath] = name
 		}
+
+		if subscription.TagOnly {
+			// Create the top-level lookup for this tag
+			c.lookup[name] = make(map[string]map[string]interface{})
+		}
 	}
 	for alias, encodingPath := range c.Aliases {
 		c.internalAliases[encodingPath] = alias
@@ -297,6 +308,29 @@ func (c *GNMI) handleSubscribeResponseUpdate(address string, response *gnmiLib.S
 			}
 		}
 
+		// Update tag lookups and discard rest of update
+		subscriptionKey := tags["source"] + "/" + tags["name"]
+		if _, ok := c.lookup[name]; ok {
+			// We are subscribed to this, so add the fields to the lookup-table
+			if _, ok := c.lookup[name][subscriptionKey]; !ok {
+				c.lookup[name][subscriptionKey] = make(map[string]interface{})
+			}
+			for k, v := range fields {
+				c.lookup[name][subscriptionKey][path.Base(k)] = v
+			}
+			// Do not process the data further as we only subscribed here for the lookup table
+			continue
+		}
+
+		// Apply lookups if present
+		for subscriptionName, values := range c.lookup {
+			if annotations, ok := values[subscriptionKey]; ok {
+				for k, v := range annotations {
+					tags[subscriptionName+"/"+k] = v.(string)
+				}
+			}
+		}
+
 		// Group metrics
 		for k, v := range fields {
 			key := k
@@ -559,6 +593,18 @@ const sampleConfig = `
 
   ## If suppression is enabled, send updates at least every X seconds anyway
   # heartbeat_interval = "60s"
+
+  #[[inputs.gnmi.subscription]]
+    # name = "descr"
+    # origin = "openconfig-interfaces"
+    # path = "/interfaces/interface/state/description"
+    # subscription_mode = "on_change"
+
+    ## If tag_only is set, the subscription in question will be utilized to maintain a map of
+    ## tags to apply to other measurements emitted by the plugin, by matching path keys
+    ## All fields from the tag-only subscription will be applied as tags to other readings,
+    ## in the format <name>_<fieldBase>.
+    # tag_only = true
 `
 
 // SampleConfig of plugin

plugins/inputs/gnmi/gnmi_test.go

@@ -371,6 +371,126 @@ func TestNotification(t *testing.T) {
 				),
 			},
 		},
+		{
+			name: "tagged update pair",
+			plugin: &GNMI{
+				Log:      testutil.Logger{},
+				Encoding: "proto",
+				Redial:   config.Duration(1 * time.Second),
+				Subscriptions: []Subscription{
+					{
+						Name:             "oc-intf-desc",
+						Origin:           "openconfig-interfaces",
+						Path:             "/interfaces/interface/state/description",
+						SubscriptionMode: "on_change",
+						TagOnly:          true,
+					},
+					{
+						Name:             "oc-intf-counters",
+						Origin:           "openconfig-interfaces",
+						Path:             "/interfaces/interface/state/counters",
+						SubscriptionMode: "sample",
+					},
+				},
+			},
+			server: &MockServer{
+				SubscribeF: func(server gnmiLib.GNMI_SubscribeServer) error {
+					tagResponse := &gnmiLib.SubscribeResponse{
+						Response: &gnmiLib.SubscribeResponse_Update{
+							Update: &gnmiLib.Notification{
+								Timestamp: 1543236571000000000,
+								Prefix:    &gnmiLib.Path{},
+								Update: []*gnmiLib.Update{
+									{
+										Path: &gnmiLib.Path{
+											Origin: "",
+											Elem: []*gnmiLib.PathElem{
+												{
+													Name: "interfaces",
+												},
+												{
+													Name: "interface",
+													Key:  map[string]string{"name": "Ethernet1"},
+												},
+												{
+													Name: "state",
+												},
+												{
+													Name: "description",
+												},
+											},
+											Target: "",
+										},
+										Val: &gnmiLib.TypedValue{
+											Value: &gnmiLib.TypedValue_StringVal{StringVal: "foo"},
+										},
+									},
+								},
+							},
+						},
+					}
+					if err := server.Send(tagResponse); err != nil {
+						return err
+					}
+					if err := server.Send(&gnmiLib.SubscribeResponse{Response: &gnmiLib.SubscribeResponse_SyncResponse{SyncResponse: true}}); err != nil {
+						return err
+					}
+					taggedResponse := &gnmiLib.SubscribeResponse{
+						Response: &gnmiLib.SubscribeResponse_Update{
+							Update: &gnmiLib.Notification{
+								Timestamp: 1543236572000000000,
+								Prefix:    &gnmiLib.Path{},
+								Update: []*gnmiLib.Update{
+									{
+										Path: &gnmiLib.Path{
+											Origin: "",
+											Elem: []*gnmiLib.PathElem{
+												{
+													Name: "interfaces",
+												},
+												{
+													Name: "interface",
+													Key:  map[string]string{"name": "Ethernet1"},
+												},
+												{
+													Name: "state",
+												},
+												{
+													Name: "counters",
+												},
+												{
+													Name: "in-broadcast-pkts",
+												},
+											},
+											Target: "",
+										},
+										Val: &gnmiLib.TypedValue{
+											Value: &gnmiLib.TypedValue_IntVal{IntVal: 42},
+										},
+									},
+								},
+							},
+						},
+					}
+					return server.Send(taggedResponse)
+				},
+			},
+			expected: []telegraf.Metric{
+				testutil.MustMetric(
+					"oc-intf-counters",
+					map[string]string{
+						"path":                     "",
+						"source":                   "127.0.0.1",
+						"name":                     "Ethernet1",
+						"oc-intf-desc/description": "foo",
+					},
+					map[string]interface{}{
+						"in_broadcast_pkts": 42,
+					},
+					time.Unix(0, 0),
+				),
+			},
+		},
 	}
 
 	for _, tt := range tests {