chore(inputs.gnmi): Add more response information for easier debugging (#15297)

plugins/inputs/gnmi/gnmi.go

@@ -27,10 +27,10 @@ import (
 var sampleConfig string
 
 // Define the warning to show if we cannot get a metric name.
-const emptyNameWarning = `Got empty metric-name for response, usually indicating
-configuration issues as the response cannot be related to any subscription.
-Please open an issue on https://github.com/influxdata/telegraf including your
-device model and the following response data:
+const emptyNameWarning = `Got empty metric-name for response (field %q), usually
+indicating configuration issues as the response cannot be related to any
+subscription.Please open an issue on https://github.com/influxdata/telegraf
+including your device model and the following response data:
 %+v
 This message is only printed once.`
 

plugins/inputs/gnmi/handler.go

@@ -3,6 +3,7 @@ package gnmi
 import (
 	"context"
 	"crypto/tls"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -237,7 +238,11 @@ func (h *handler) handleSubscribeResponseUpdate(acc telegraf.Accumulator, respon
 		if name == "" {
 			h.log.Debugf("No measurement alias for gNMI path: %s", field.path)
 			if !h.emptyNameWarnShown {
-				h.log.Warnf(emptyNameWarning, response.Update)
+				if buf, err := json.Marshal(response); err == nil {
+					h.log.Warnf(emptyNameWarning, field.path, string(buf))
+				} else {
+					h.log.Warnf(emptyNameWarning, field.path, response.Update)
+				}
 				h.emptyNameWarnShown = true
 			}
 		}