Modify logic for message body on Microsoft.ApplicationInsights.MessageData to include default message for messages with empty body and export logs (#43091)

* Modify logic in PR (#43060) to include default message for messages with empty body and export logs

* Update CHANGELOG

* Update logic as per updated spec

* Addressed comments

Author: rads-1996

sdk/monitor/azure-monitor-opentelemetry-exporter/CHANGELOG.md

@@ -7,6 +7,8 @@
 ### Breaking Changes
 
 ### Bugs Fixed
+- Modified logic for message body on Microsoft.ApplicationInsights.MessageData to include default message for messages with empty body and export logs
+  ([#43091](https://github.com/Azure/azure-sdk-for-python/pull/43091))
 
 ### Other Changes
 

sdk/monitor/azure-monitor-opentelemetry-exporter/azure/monitor/opentelemetry/exporter/_constants.py

@@ -326,4 +326,7 @@ class _RP_Names(Enum):
 
 _DEFAULT_AAD_SCOPE = "https://monitor.azure.com//.default"
 
+# Default message for messages(MessageData) with empty body
+_DEFAULT_LOG_MESSAGE = "n/a"
+
 # cSpell:disable

sdk/monitor/azure-monitor-opentelemetry-exporter/azure/monitor/opentelemetry/exporter/export/logs/_exporter.py

@@ -18,6 +18,7 @@
 from azure.monitor.opentelemetry.exporter._constants import (
     _EXCEPTION_ENVELOPE_NAME,
     _MESSAGE_ENVELOPE_NAME,
+    _DEFAULT_LOG_MESSAGE,
 )
 from azure.monitor.opentelemetry.exporter._generated.models import (
     ContextTagKeys,
@@ -189,6 +190,9 @@ def _convert_log_to_envelope(log_data: LogData) -> TelemetryItem:
             severity_level=severity_level,  # type: ignore
             properties=properties,
         )
+        data.message = data.message.strip()
+        if len(data.message) == 0:
+            data.message = _DEFAULT_LOG_MESSAGE
         envelope.data = MonitorBase(base_data=data, base_type="MessageData")
 
     return envelope

sdk/monitor/azure-monitor-opentelemetry-exporter/tests/logs/test_logs.py

@@ -29,6 +29,7 @@
 from azure.monitor.opentelemetry.exporter._constants import (
     _APPLICATION_INSIGHTS_EVENT_MARKER_ATTRIBUTE,
     _MICROSOFT_CUSTOM_EVENT_NAME,
+    _DEFAULT_LOG_MESSAGE,
 )
 from azure.monitor.opentelemetry.exporter._generated.models import ContextTagKeys
 from azure.monitor.opentelemetry.exporter._utils import (
@@ -132,6 +133,20 @@ def setUpClass(cls):
             ),
             InstrumentationScope("test_name"),
         )
+        cls._log_data_empty_with_whitespaces = _logs.LogData(
+            _logs.LogRecord(
+                timestamp=1646865018558419456,
+                trace_id=125960616039069540489478540494783893221,
+                span_id=2909973987304607650,
+                severity_text="WARNING",
+                trace_flags=None,
+                severity_number=SeverityNumber.WARN,
+                body="  ",
+                resource=Resource.create(attributes={"asd": "test_resource"}),
+                attributes={"test": "attribute"},
+            ),
+            InstrumentationScope("test_name"),
+        )
         cls._log_data_event = _logs.LogData(
             _logs.LogRecord(
                 timestamp=1646865018558419456,
@@ -410,14 +425,21 @@ def test_log_to_envelope_log_none(self):
         envelope = exporter._log_to_envelope(self._log_data_none)
         self.assertEqual(envelope.name, "Microsoft.ApplicationInsights.Message")
         self.assertEqual(envelope.data.base_type, "MessageData")
-        self.assertEqual(envelope.data.base_data.message, "")
+        self.assertEqual(envelope.data.base_data.message, _DEFAULT_LOG_MESSAGE)
 
     def test_log_to_envelope_log_empty(self):
         exporter = self._exporter
         envelope = exporter._log_to_envelope(self._log_data_empty)
         self.assertEqual(envelope.name, "Microsoft.ApplicationInsights.Message")
         self.assertEqual(envelope.data.base_type, "MessageData")
-        self.assertEqual(envelope.data.base_data.message, "")
+        self.assertEqual(envelope.data.base_data.message, _DEFAULT_LOG_MESSAGE)
+    
+    def test_log_to_envelope_log_empty_with_whitespaces(self):
+        exporter = self._exporter
+        envelope = exporter._log_to_envelope(self._log_data_empty_with_whitespaces)
+        self.assertEqual(envelope.name, "Microsoft.ApplicationInsights.Message")
+        self.assertEqual(envelope.data.base_type, "MessageData")
+        self.assertEqual(envelope.data.base_data.message, _DEFAULT_LOG_MESSAGE)
 
     def test_log_to_envelope_log_complex_body(self):
         exporter = self._exporter