Add extra grpc header which is all lower case

According to https://httpwg.org/specs/rfc7540.html#HttpHeaders headers
in HTTP/2 (grpc transport) must all be lower case. Thus, using A2A via
grpc fails when using the HTTP header. Add specific all lowercase header
for gRPC.

Author: timn

src/a2a/extensions/common.py

@@ -4,6 +4,7 @@
 
 
 HTTP_EXTENSION_HEADER = 'X-A2A-Extensions'
+GRPC_EXTENSION_HEADER = 'x-a2a-extensions'
 
 
 def get_requested_extensions(values: list[str]) -> set[str]:

src/a2a/server/request_handlers/grpc_handler.py

@@ -23,7 +23,7 @@
 from a2a import types
 from a2a.auth.user import UnauthenticatedUser
 from a2a.extensions.common import (
-    HTTP_EXTENSION_HEADER,
+    GRPC_EXTENSION_HEADER,
     get_requested_extensions,
 )
 from a2a.grpc import a2a_pb2
@@ -76,7 +76,7 @@ def build(self, context: grpc.aio.ServicerContext) -> ServerCallContext:
             user=user,
             state=state,
             requested_extensions=get_requested_extensions(
-                _get_metadata_value(context, HTTP_EXTENSION_HEADER)
+                _get_metadata_value(context, GRPC_EXTENSION_HEADER)
             ),
         )
 
@@ -417,7 +417,7 @@ def _set_extension_metadata(
         if server_context.activated_extensions:
             context.set_trailing_metadata(
                 [
-                    (HTTP_EXTENSION_HEADER.lower(), e)
+                    (GRPC_EXTENSION_HEADER.lower(), e)
                     for e in sorted(server_context.activated_extensions)
                 ]
             )

tests/server/request_handlers/test_grpc_handler.py

@@ -5,7 +5,7 @@
 import pytest
 
 from a2a import types
-from a2a.extensions.common import HTTP_EXTENSION_HEADER
+from a2a.extensions.common import GRPC_EXTENSION_HEADER
 from a2a.grpc import a2a_pb2
 from a2a.server.context import ServerCallContext
 from a2a.server.request_handlers import GrpcHandler, RequestHandler
@@ -350,8 +350,8 @@ async def test_send_message_with_extensions(
         mock_grpc_context: AsyncMock,
     ) -> None:
         mock_grpc_context.invocation_metadata.return_value = grpc.aio.Metadata(
-            (HTTP_EXTENSION_HEADER.lower(), 'foo'),
-            (HTTP_EXTENSION_HEADER.lower(), 'bar'),
+            (GRPC_EXTENSION_HEADER.lower(), 'foo'),
+            (GRPC_EXTENSION_HEADER.lower(), 'bar'),
         )
 
         def side_effect(request, context: ServerCallContext):
@@ -379,8 +379,8 @@ def side_effect(request, context: ServerCallContext):
             mock_grpc_context.set_trailing_metadata.call_args.args[0]
         )
         assert set(called_metadata) == {
-            (HTTP_EXTENSION_HEADER.lower(), 'foo'),
-            (HTTP_EXTENSION_HEADER.lower(), 'baz'),
+            (GRPC_EXTENSION_HEADER.lower(), 'foo'),
+            (GRPC_EXTENSION_HEADER.lower(), 'baz'),
         }
 
     async def test_send_message_with_comma_separated_extensions(
@@ -390,8 +390,8 @@ async def test_send_message_with_comma_separated_extensions(
         mock_grpc_context: AsyncMock,
     ) -> None:
         mock_grpc_context.invocation_metadata.return_value = grpc.aio.Metadata(
-            (HTTP_EXTENSION_HEADER.lower(), 'foo ,, bar,'),
-            (HTTP_EXTENSION_HEADER.lower(), 'baz  , bar'),
+            (GRPC_EXTENSION_HEADER.lower(), 'foo ,, bar,'),
+            (GRPC_EXTENSION_HEADER.lower(), 'baz  , bar'),
         )
         mock_request_handler.on_message_send.return_value = types.Message(
             message_id='1',
@@ -415,8 +415,8 @@ async def test_send_streaming_message_with_extensions(
         mock_grpc_context: AsyncMock,
     ) -> None:
         mock_grpc_context.invocation_metadata.return_value = grpc.aio.Metadata(
-            (HTTP_EXTENSION_HEADER.lower(), 'foo'),
-            (HTTP_EXTENSION_HEADER.lower(), 'bar'),
+            (GRPC_EXTENSION_HEADER.lower(), 'foo'),
+            (GRPC_EXTENSION_HEADER.lower(), 'bar'),
         )
 
         async def side_effect(request, context: ServerCallContext):
@@ -450,6 +450,6 @@ async def side_effect(request, context: ServerCallContext):
             mock_grpc_context.set_trailing_metadata.call_args.args[0]
         )
         assert set(called_metadata) == {
-            (HTTP_EXTENSION_HEADER.lower(), 'foo'),
-            (HTTP_EXTENSION_HEADER.lower(), 'baz'),
+            (GRPC_EXTENSION_HEADER.lower(), 'foo'),
+            (GRPC_EXTENSION_HEADER.lower(), 'baz'),
         }