[exporter/splunkhec] drop empty log events (open-telemetry#34871)

**Description:**
Drop empty log events

Log records with no body are dropped by Splunk on reception as they
contain no log message, albeit they may have attributes.
  
This PR removes those logs from consideration to be exported.
  
This is in tune with the behavior of splunkhecreceiver, which refuses
HEC events with no event (open-telemetry#19769)

Author: atoulme

.chloggen/drop_empty_events.yaml

@@ -0,0 +1,34 @@
+# 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: splunkhecexporter
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Drop empty log events
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [34871]
+
+# (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: |
+  Log records with no body are dropped by Splunk on reception
+  as they contain no log message, albeit they may have attributes.
+  
+  This PR removes those logs from consideration to be exported.
+  
+  This is in tune with the behavior of splunkhecreceiver, which refuses HEC events with no event (#19769)
+
+
+# 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: []

exporter/splunkhecexporter/client.go

@@ -205,6 +205,10 @@ func (c *client) fillLogsBuffer(logs plog.Logs, buf buffer, is iterState) (iterS
 				} else {
 					// Parsing log record to Splunk event.
 					event := mapLogRecordToSplunkEvent(rl.Resource(), logRecord, c.config)
+					if event == nil {
+						// TODO record this drop as a metric
+						continue
+					}
 
 					// JSON encoding event and writing to buffer.
 					var err error

exporter/splunkhecexporter/logdata_to_splunk.go

@@ -24,6 +24,12 @@ const (
 )
 
 func mapLogRecordToSplunkEvent(res pcommon.Resource, lr plog.LogRecord, config *Config) *splunk.Event {
+	body := lr.Body().AsRaw()
+	if body == nil || body == "" {
+		// events with no body are rejected by Splunk.
+		return nil
+	}
+
 	host := unknownHostName
 	source := config.Source
 	sourcetype := config.SourceType
@@ -83,11 +89,6 @@ func mapLogRecordToSplunkEvent(res pcommon.Resource, lr plog.LogRecord, config *
 		return true
 	})
 
-	body := lr.Body().AsRaw()
-	if body == nil {
-		body = ""
-	}
-
 	return &splunk.Event{
 		Time:       nanoTimestampToEpochMilliseconds(lr.Timestamp()),
 		Host:       host,

exporter/splunkhecexporter/logdata_to_splunk_test.go

@@ -187,14 +187,13 @@ func Test_mapLogRecordToSplunkEvent(t *testing.T) {
 				config.SourceType = "sourcetype"
 				return config
 			},
-			wantSplunkEvents: []*splunk.Event{
-				commonLogSplunkEvent("", 0, map[string]any{}, "unknown", "source", "sourcetype"),
-			},
+			wantSplunkEvents: []*splunk.Event{},
 		},
 		{
 			name: "with span and trace id",
 			logRecordFn: func() plog.LogRecord {
 				logRecord := plog.NewLogRecord()
+				logRecord.Body().SetStr("foo")
 				logRecord.SetSpanID([8]byte{0, 0, 0, 0, 0, 0, 0, 50})
 				logRecord.SetTraceID([16]byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 100})
 				return logRecord
@@ -207,7 +206,7 @@ func Test_mapLogRecordToSplunkEvent(t *testing.T) {
 				return config
 			},
 			wantSplunkEvents: func() []*splunk.Event {
-				event := commonLogSplunkEvent("", 0, map[string]any{}, "unknown", "source", "sourcetype")
+				event := commonLogSplunkEvent("foo", 0, map[string]any{}, "unknown", "source", "sourcetype")
 				event.Fields["span_id"] = "0000000000000032"
 				event.Fields["trace_id"] = "00000000000000000000000000000064"
 				return []*splunk.Event{event}
@@ -329,10 +328,7 @@ func Test_mapLogRecordToSplunkEvent(t *testing.T) {
 				config.SourceType = "sourcetype"
 				return config
 			},
-			wantSplunkEvents: []*splunk.Event{
-				commonLogSplunkEvent("", ts, map[string]any{"custom": "custom"},
-					"myhost", "myapp", "myapp-type"),
-			},
+			wantSplunkEvents: []*splunk.Event{},
 		},
 		{
 			name: "with array body",
@@ -449,13 +445,7 @@ func commonLogSplunkEvent(
 
 func Test_emptyLogRecord(t *testing.T) {
 	event := mapLogRecordToSplunkEvent(pcommon.NewResource(), plog.NewLogRecord(), &Config{})
-	assert.Zero(t, event.Time)
-	assert.Equal(t, event.Host, "unknown")
-	assert.Zero(t, event.Source)
-	assert.Zero(t, event.SourceType)
-	assert.Zero(t, event.Index)
-	assert.Equal(t, "", event.Event)
-	assert.Empty(t, event.Fields)
+	assert.Nil(t, event)
 }
 
 func Test_nanoTimestampToEpochMilliseconds(t *testing.T) {