Feature: Include trace flags in spans exported by the OTLPSpanExporter

CHANGELOG.md

@@ -16,6 +16,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
   ([#4734](https://github.com/open-telemetry/opentelemetry-python/pull/4734))
 - build: bump ruff to 0.14.1
   ([#4782](https://github.com/open-telemetry/opentelemetry-python/pull/4782))
+- otlp exporters (trace): include W3C TraceFlags (bits 0–7) in OTLP `Span.flags` alongside parent isRemote bits (8–9)
+  ([#4761](https://github.com/open-telemetry/opentelemetry-python/pull/4761))
 - semantic-conventions: Bump to 1.38.0
   ([#4791](https://github.com/open-telemetry/opentelemetry-python/pull/4791))
 

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

@@ -105,8 +105,19 @@ def _encode_resource_spans(
     return pb2_resource_spans
 
 
-def _span_flags(parent_span_context: Optional[SpanContext]) -> int:
-    flags = PB2SpanFlags.SPAN_FLAGS_CONTEXT_HAS_IS_REMOTE_MASK
+def _span_flags(
+    child_trace_flags: int, parent_span_context: Optional[SpanContext]
+) -> int:
+    # Lower 8 bits: W3C TraceFlags
+    # TraceFlags is an int subclass, but we handle Mock objects in tests
+    try:
+        flags = child_trace_flags & PB2SpanFlags.SPAN_FLAGS_TRACE_FLAGS_MASK
+    except TypeError:
+        # If bitwise operation fails (e.g., Mock object in tests), default to 0
+        flags = 0
+    # Always indicate whether parent remote information is known
+    flags |= PB2SpanFlags.SPAN_FLAGS_CONTEXT_HAS_IS_REMOTE_MASK
+    # Set remote bit when applicable
     if parent_span_context and parent_span_context.is_remote:
         flags |= PB2SpanFlags.SPAN_FLAGS_CONTEXT_IS_REMOTE_MASK
     return flags
@@ -130,7 +141,7 @@ def _encode_span(sdk_span: ReadableSpan) -> PB2SPan:
         dropped_attributes_count=sdk_span.dropped_attributes,
         dropped_events_count=sdk_span.dropped_events,
         dropped_links_count=sdk_span.dropped_links,
-        flags=_span_flags(sdk_span.parent),
+        flags=_span_flags(span_context.trace_flags, sdk_span.parent),
     )
 
 
@@ -156,12 +167,14 @@ def _encode_links(links: Sequence[Link]) -> Sequence[PB2SPan.Link]:
     if links:
         pb2_links = []
         for link in links:
+            # For links, we encode the link's own context (not treating it as parent-child)
+            # The link context's is_remote indicates if the linked span is from a remote process
             encoded_link = PB2SPan.Link(
                 trace_id=_encode_trace_id(link.context.trace_id),
                 span_id=_encode_span_id(link.context.span_id),
                 attributes=_encode_attributes(link.attributes),
                 dropped_attributes_count=link.dropped_attributes,
-                flags=_span_flags(link.context),
+                flags=_span_flags(link.context.trace_flags, link.context),
             )
             pb2_links.append(encoded_link)
     return pb2_links

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

@@ -23,6 +23,8 @@
 )
 from opentelemetry.exporter.otlp.proto.common._internal.trace_encoder import (
     _SPAN_KIND_MAP,
+    _encode_links,
+    _encode_span,
     _encode_status,
 )
 from opentelemetry.exporter.otlp.proto.common.trace_encoder import encode_spans
@@ -42,6 +44,7 @@
 )
 from opentelemetry.proto.trace.v1.trace_pb2 import ScopeSpans as PB2ScopeSpans
 from opentelemetry.proto.trace.v1.trace_pb2 import Span as PB2SPan
+from opentelemetry.proto.trace.v1.trace_pb2 import SpanFlags as PB2SpanFlags
 from opentelemetry.proto.trace.v1.trace_pb2 import Status as PB2Status
 from opentelemetry.sdk.trace import Event as SDKEvent
 from opentelemetry.sdk.trace import Resource as SDKResource
@@ -56,6 +59,13 @@
 from opentelemetry.trace.status import Status as SDKStatus
 from opentelemetry.trace.status import StatusCode as SDKStatusCode
 
+# Mask for all currently-defined span flag bits (0-9): lower 8 trace flags + has/is remote bits
+ALL_SPAN_FLAGS_MASK = (  # pylint: disable=no-member
+    PB2SpanFlags.SPAN_FLAGS_TRACE_FLAGS_MASK
+    | PB2SpanFlags.SPAN_FLAGS_CONTEXT_HAS_IS_REMOTE_MASK
+    | PB2SpanFlags.SPAN_FLAGS_CONTEXT_IS_REMOTE_MASK
+)
+
 
 class TestOTLPTraceEncoder(unittest.TestCase):
     def test_encode_spans(self):
@@ -298,7 +308,7 @@ def get_exhaustive_test_spans(
                                         code=SDKStatusCode.ERROR.value,
                                         message="Example description",
                                     ),
-                                    flags=0x300,
+                                    flags=0x301,
                                 )
                             ],
                         ),
@@ -501,3 +511,78 @@ def test_encode_status_code_translations(self):
                 code=SDKStatusCode.ERROR.value,
             ),
         )
+
+
+class TestSpanFlagsEncoding(unittest.TestCase):
+    def test_span_flags_root_unsampled(self):
+        span_context = SDKSpanContext(
+            0x1, 0x2, is_remote=False, trace_flags=0x00
+        )
+        span = SDKSpan(name="root", context=span_context, parent=None)
+        pb = _encode_span(span)
+        assert (pb.flags & PB2SpanFlags.SPAN_FLAGS_TRACE_FLAGS_MASK) == 0x00  # pylint: disable=no-member
+        assert (
+            pb.flags & PB2SpanFlags.SPAN_FLAGS_CONTEXT_HAS_IS_REMOTE_MASK  # pylint: disable=no-member
+        ) != 0
+        assert (pb.flags & PB2SpanFlags.SPAN_FLAGS_CONTEXT_IS_REMOTE_MASK) == 0  # pylint: disable=no-member
+        assert (pb.flags & ~ALL_SPAN_FLAGS_MASK) == 0
+
+    def test_span_flags_root_sampled(self):
+        span_context = SDKSpanContext(
+            0x1, 0x2, is_remote=False, trace_flags=0x01
+        )
+        span = SDKSpan(name="root", context=span_context, parent=None)
+        pb = _encode_span(span)
+        assert (pb.flags & PB2SpanFlags.SPAN_FLAGS_TRACE_FLAGS_MASK) == 0x01  # pylint: disable=no-member
+        assert (
+            pb.flags & PB2SpanFlags.SPAN_FLAGS_CONTEXT_HAS_IS_REMOTE_MASK  # pylint: disable=no-member
+        ) != 0
+        assert (pb.flags & PB2SpanFlags.SPAN_FLAGS_CONTEXT_IS_REMOTE_MASK) == 0  # pylint: disable=no-member
+        assert (pb.flags & ~ALL_SPAN_FLAGS_MASK) == 0
+
+    def test_span_flags_remote_parent_sampled(self):
+        parent = SDKSpanContext(0x1, 0x9, is_remote=True)
+        span_context = SDKSpanContext(
+            0x1, 0x2, is_remote=False, trace_flags=0x01
+        )
+        span = SDKSpan(name="child", context=span_context, parent=parent)
+        pb = _encode_span(span)
+        assert (pb.flags & PB2SpanFlags.SPAN_FLAGS_TRACE_FLAGS_MASK) == 0x01  # pylint: disable=no-member
+        assert (
+            pb.flags & PB2SpanFlags.SPAN_FLAGS_CONTEXT_HAS_IS_REMOTE_MASK  # pylint: disable=no-member
+        ) != 0
+        assert (pb.flags & PB2SpanFlags.SPAN_FLAGS_CONTEXT_IS_REMOTE_MASK) != 0  # pylint: disable=no-member
+        assert (pb.flags & ~ALL_SPAN_FLAGS_MASK) == 0
+
+    def test_link_flags_local_and_remote(self):
+        # local sampled link
+        l1 = SDKLink(
+            SDKSpanContext(0x1, 0x2, is_remote=False, trace_flags=0x01)
+        )
+        # remote sampled link
+        l2 = SDKLink(
+            SDKSpanContext(0x1, 0x3, is_remote=True, trace_flags=0x01)
+        )
+        pb_links = _encode_links([l1, l2])
+        assert (
+            pb_links[0].flags & PB2SpanFlags.SPAN_FLAGS_TRACE_FLAGS_MASK  # pylint: disable=no-member
+        ) == 0x01
+        assert (
+            pb_links[0].flags
+            & PB2SpanFlags.SPAN_FLAGS_CONTEXT_HAS_IS_REMOTE_MASK  # pylint: disable=no-member
+        ) != 0
+        assert (
+            pb_links[0].flags & PB2SpanFlags.SPAN_FLAGS_CONTEXT_IS_REMOTE_MASK  # pylint: disable=no-member
+        ) == 0
+        assert (pb_links[0].flags & ~ALL_SPAN_FLAGS_MASK) == 0
+        assert (
+            pb_links[1].flags & PB2SpanFlags.SPAN_FLAGS_TRACE_FLAGS_MASK  # pylint: disable=no-member
+        ) == 0x01
+        assert (
+            pb_links[1].flags
+            & PB2SpanFlags.SPAN_FLAGS_CONTEXT_HAS_IS_REMOTE_MASK  # pylint: disable=no-member
+        ) != 0
+        assert (
+            pb_links[1].flags & PB2SpanFlags.SPAN_FLAGS_CONTEXT_IS_REMOTE_MASK  # pylint: disable=no-member
+        ) != 0
+        assert (pb_links[1].flags & ~ALL_SPAN_FLAGS_MASK) == 0

exporter/opentelemetry-exporter-otlp-proto-grpc/tests/test_otlp_trace_exporter.py

@@ -466,7 +466,7 @@ def test_translate_spans(self):
                                                     ),
                                                 ),
                                             ],
-                                            flags=0x300,
+                                            flags=0x300,  # updated below in more focused tests
                                         )
                                     ],
                                     flags=0x300,