feat: make use of flagd-selector header in RPC mode (#396)

* feat(flagd): send flagd-selector header on RPC calls

RPC resolver now attaches the `flagd-selector` gRPC metadata header on every unary call and on the EventStream when a selector is configured, so the flagd server can serve the requested flag set. Brings the Python RPC resolver to parity with the Java and JS providers.

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

* refactor(flagd): precompute selector metadata and extract stream call args helper

Reduces listen() complexity below ruff C901 threshold while keeping the flagd-selector header wiring intact.

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

* fix(flagd): bump grpcio>=1.81.0 to match generated stubs

The flagd evaluation v2 generated stubs require grpcio>=1.81.0 (RuntimeError at import time otherwise). The pyproject constraint and lockfile were still pinned to 1.80.0, breaking CI on main.

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

* fix(flagd): widen metadata TypedDict and cover EventStream selector

- types.py: metadata is now variadic tuple[tuple[str, str], ...] to allow >1 entry and satisfy mypy.\n- tests: import FLAGD_SELECTOR_HEADER from the resolver instead of hardcoding, and add coverage for the EventStream listen() path (both with and without selector).

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

* fix(flagd): use contextlib.suppress to satisfy ruff S110/SIM105

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

* Update providers/openfeature-provider-flagd/src/openfeature/contrib/provider/flagd/resolvers/grpc.py

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>
Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

* style(flagd): apply ruff format to selector_metadata expression

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>

---------

Signed-off-by: Todd Baert <todd.baert@dynatrace.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

Author: toddbaert

providers/openfeature-provider-flagd/pyproject.toml

@@ -19,7 +19,7 @@ keywords = []
 dependencies = [
   "openfeature-sdk>=0.8.2",
   "openfeature-flagd-core>=1.0.0,<2",
-  "grpcio>=1.80.0",
+  "grpcio>=1.81.0",
   "protobuf>=6.30.0,<7.0.0",
   "pyyaml>=6.0.1",
   "cachebox>=5.1.0,<6.0.0",

providers/openfeature-provider-flagd/src/openfeature/contrib/provider/flagd/resolvers/grpc.py

@@ -32,6 +32,8 @@
 from ..flag_type import FlagType
 from .types import GrpcMultiCallableArgs
 
+FLAGD_SELECTOR_HEADER = "flagd-selector"
+
 if typing.TYPE_CHECKING:
     from google.protobuf.message import Message
 
@@ -71,6 +73,9 @@ def __init__(
         self._is_fatal = False
         self.channel = self._generate_channel(config)
         self.stub = evaluation_pb2_grpc.ServiceStub(self.channel)
+        self.selector_metadata: tuple[tuple[str, str], ...] | None = (
+            ((FLAGD_SELECTOR_HEADER, config.selector),) if config.selector else None
+        )
 
         self.thread: threading.Thread | None = None
         self.timer: threading.Timer | None = None
@@ -215,11 +220,17 @@ def emit_error(self) -> None:
             )
         )
 
-    def listen(self) -> None:
-        logger.debug("gRPC starting listener thread")
+    def _stream_call_args(self) -> GrpcMultiCallableArgs:
         call_args: GrpcMultiCallableArgs = {"wait_for_ready": True}
         if self.streamline_deadline_seconds > 0:
             call_args["timeout"] = self.streamline_deadline_seconds
+        if self.selector_metadata is not None:
+            call_args["metadata"] = self.selector_metadata
+        return call_args
+
+    def listen(self) -> None:
+        logger.debug("gRPC starting listener thread")
+        call_args = self._stream_call_args()
         request = evaluation_pb2.EventStreamRequest()
 
         # defining a never ending loop to recreate the stream
@@ -377,6 +388,8 @@ def _resolve(  # noqa: PLR0915 C901
             "timeout": self.deadline,
             "wait_for_ready": True,
         }
+        if self.selector_metadata is not None:
+            call_args["metadata"] = self.selector_metadata
         try:
             request: Message
             if flag_type == FlagType.BOOLEAN:

providers/openfeature-provider-flagd/src/openfeature/contrib/provider/flagd/resolvers/types.py

@@ -4,4 +4,4 @@
 class GrpcMultiCallableArgs(typing.TypedDict, total=False):
     timeout: float | None
     wait_for_ready: bool | None
-    metadata: tuple[tuple[str, str]] | None
+    metadata: tuple[tuple[str, str], ...] | None

providers/openfeature-provider-flagd/tests/test_grpc_resolver.py

@@ -0,0 +1,79 @@
+from contextlib import suppress
+from unittest.mock import MagicMock, Mock
+
+from openfeature.contrib.provider.flagd.config import Config
+from openfeature.contrib.provider.flagd.flag_type import FlagType
+from openfeature.contrib.provider.flagd.resolvers.grpc import (
+    FLAGD_SELECTOR_HEADER,
+    GrpcResolver,
+)
+from openfeature.schemas.protobuf.flagd.evaluation.v2 import evaluation_pb2
+
+
+def _make_resolver(selector):
+    config = Config(host="localhost", port=8013, tls=False)
+    config.selector = selector
+    resolver = GrpcResolver(
+        config=config,
+        emit_provider_ready=Mock(),
+        emit_provider_error=Mock(),
+        emit_provider_stale=Mock(),
+        emit_provider_configuration_changed=Mock(),
+    )
+    return resolver
+
+
+def test_unary_call_includes_selector_metadata_when_configured():
+    resolver = _make_resolver("test-selector")
+    mock_stub = MagicMock()
+    mock_stub.ResolveBoolean = Mock(
+        return_value=evaluation_pb2.ResolveBooleanResponse(value=True, reason="STATIC")
+    )
+    resolver.stub = mock_stub
+
+    resolver._resolve("flag", FlagType.BOOLEAN, False, None)
+
+    kwargs = mock_stub.ResolveBoolean.call_args.kwargs
+    assert kwargs.get("metadata") == ((FLAGD_SELECTOR_HEADER, "test-selector"),)
+
+
+def test_unary_call_omits_metadata_when_no_selector():
+    resolver = _make_resolver(None)
+    mock_stub = MagicMock()
+    mock_stub.ResolveBoolean = Mock(
+        return_value=evaluation_pb2.ResolveBooleanResponse(value=True, reason="STATIC")
+    )
+    resolver.stub = mock_stub
+
+    resolver._resolve("flag", FlagType.BOOLEAN, False, None)
+
+    kwargs = mock_stub.ResolveBoolean.call_args.kwargs
+    assert "metadata" not in kwargs
+
+
+def test_event_stream_includes_selector_metadata_when_configured():
+    resolver = _make_resolver("test-selector")
+    mock_stub = MagicMock()
+    mock_stub.EventStream = Mock(side_effect=Exception("break loop"))
+    resolver.stub = mock_stub
+    resolver.active = True
+
+    with suppress(Exception):
+        resolver.listen()
+
+    kwargs = mock_stub.EventStream.call_args.kwargs
+    assert kwargs.get("metadata") == ((FLAGD_SELECTOR_HEADER, "test-selector"),)
+
+
+def test_event_stream_omits_metadata_when_no_selector():
+    resolver = _make_resolver(None)
+    mock_stub = MagicMock()
+    mock_stub.EventStream = Mock(side_effect=Exception("break loop"))
+    resolver.stub = mock_stub
+    resolver.active = True
+
+    with suppress(Exception):
+        resolver.listen()
+
+    kwargs = mock_stub.EventStream.call_args.kwargs
+    assert "metadata" not in kwargs