fix(exporter): convert body to str as fallback

Author: lukaslihotzki-f

CHANGELOG.md

@@ -17,6 +17,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#4494](https://github.com/open-telemetry/opentelemetry-python/pull/4494))
 - Improve CI by cancelling stale runs and setting timeouts
   ([#4498](https://github.com/open-telemetry/opentelemetry-python/pull/4498))
+- Fix logging of objects which are convertible to strings
+  ([#4510](https://github.com/open-telemetry/opentelemetry-python/pull/4510))
 
 ## Version 1.31.0/0.52b0 (2025-03-12)
 

exporter/opentelemetry-exporter-otlp-proto-common/src/opentelemetry/exporter/otlp/proto/common/_internal/__init__.py

@@ -70,7 +70,9 @@ def _encode_resource(resource: Resource) -> PB2Resource:
 
 
 def _encode_value(
-    value: Any, allow_null: bool = False
+    value: Any,
+    allow_null: bool = False,
+    fallback: Optional[Callable[[Any], Any]] = None,
 ) -> Optional[PB2AnyValue]:
     if allow_null is True and value is None:
         return None
@@ -99,6 +101,8 @@ def _encode_value(
                 ]
             )
         )
+    elif fallback is not None:
+        return _encode_value(fallback(value), allow_null)
     raise Exception(f"Invalid type {type(value)} of value {value}")
 
 

exporter/opentelemetry-exporter-otlp-proto-common/src/opentelemetry/exporter/otlp/proto/common/_internal/_log_encoder/__init__.py

@@ -55,7 +55,7 @@ def _encode_log(log_data: LogData) -> PB2LogRecord:
         span_id=span_id,
         trace_id=trace_id,
         flags=int(log_data.log_record.trace_flags),
-        body=_encode_value(body, allow_null=True),
+        body=_encode_value(body, allow_null=True, fallback=str),
         severity_text=log_data.log_record.severity_text,
         attributes=_encode_attributes(log_data.log_record.attributes),
         dropped_attributes_count=log_data.log_record.dropped_attributes,

exporter/opentelemetry-exporter-otlp-proto-common/tests/test_log_encoder.py

@@ -69,6 +69,21 @@ def test_encode_no_body(self):
 
         self.assertEqual(encode_logs(sdk_logs), expected_encoding)
 
+    def test_encode_stringifiable(self):
+        class Stringifiable:
+            def __init__(self, data):
+                self.data = data
+            def __str__(self):
+                return self.data
+
+        sdk_logs, expected_encoding = self.get_test_logs()
+        for log in sdk_logs:
+            body = log.log_record.body
+            if isinstance(body, str):
+                log.log_record.body = Stringifiable(body)
+
+        self.assertEqual(encode_logs(sdk_logs), expected_encoding)
+
     def test_dropped_attributes_count(self):
         sdk_logs = self._get_test_logs_dropped_attributes()
         encoded_logs = encode_logs(sdk_logs)