[receiver/datadogreceiver] Include error when logging unmarshaling failures (open-telemetry#34515)

This helped us to identify empty buffer errors.

Author: Felipe Lopes

.chloggen/log-error-unmarshaling-failure.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: enhancement
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: datadogreceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: "Include error when logging unmarshaling failures in Datadog receiver."
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [34515]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

receiver/datadogreceiver/receiver.go

@@ -119,7 +119,7 @@ func (ddr *datadogReceiver) handleTraces(w http.ResponseWriter, req *http.Reques
 	ddTraces, err = translator.HandleTracesPayload(req)
 	if err != nil {
 		http.Error(w, "Unable to unmarshal reqs", http.StatusBadRequest)
-		ddr.params.Logger.Error("Unable to unmarshal reqs")
+		ddr.params.Logger.Error("Unable to unmarshal reqs", zap.Error(err))
 		return
 	}
 	for _, ddTrace := range ddTraces {
@@ -128,7 +128,7 @@ func (ddr *datadogReceiver) handleTraces(w http.ResponseWriter, req *http.Reques
 		err = ddr.nextTracesConsumer.ConsumeTraces(obsCtx, otelTraces)
 		if err != nil {
 			http.Error(w, "Trace consumer errored out", http.StatusInternalServerError)
-			ddr.params.Logger.Error("Trace consumer errored out")
+			ddr.params.Logger.Error("Trace consumer errored out", zap.Error(err))
 			return
 		}
 	}