refactor: remove unnecesary httpx usage in http_helpers

src/a2a/client/transports/http_helpers.py

@@ -46,7 +46,7 @@ def get_http_args(context: ClientCallContext | None) -> dict[str, Any]:
     if context and context.service_parameters:
         http_kwargs['headers'] = context.service_parameters.copy()
     if context and context.timeout is not None:
-        http_kwargs['timeout'] = httpx.Timeout(context.timeout)
+        http_kwargs['timeout'] = context.timeout
     return http_kwargs
 
 
@@ -179,9 +179,12 @@ def __init__(
         url: str,
         **kwargs: Any,
     ) -> None:
-        headers = httpx.Headers(kwargs.pop('headers', None))
-        headers.setdefault('Accept', 'text/event-stream')
-        headers.setdefault('Cache-Control', 'no-store')
+        headers: dict[str, str] = dict(kwargs.pop('headers', None) or {})
+        present = {key.lower() for key in headers}
+        if 'accept' not in present:
+            headers['Accept'] = 'text/event-stream'
+        if 'cache-control' not in present:
+            headers['Cache-Control'] = 'no-store'
         self._request = client.build_request(
             method, url, headers=headers, **kwargs
         )

tests/client/transports/test_http_helpers.py

@@ -1,9 +1,12 @@
 import httpx
 import pytest
 
+from a2a.client.client import ClientCallContext
 from a2a.client.errors import A2AClientError
 from a2a.client.transports.http_helpers import (
+    _SSEEventSource,
     _default_sse_error_handler,
+    get_http_args,
     parse_sse_stream,
     send_http_stream_request,
 )
@@ -62,3 +65,49 @@ async def test_send_http_stream_request_non_sse(mocker):
         c async for c in send_http_stream_request(client, 'GET', 'http://test')
     ]
     assert chunks == ['plain error response']
+
+
+def test_get_http_args_passes_timeout_through_unwrapped():
+    """The timeout stays a bare float, for the client itself to wrap."""
+    http_kwargs = get_http_args(ClientCallContext(timeout=5.0))
+
+    assert http_kwargs['timeout'] == 5.0
+    assert not isinstance(http_kwargs['timeout'], httpx.Timeout)
+
+    request = httpx.AsyncClient().build_request(
+        'GET', 'http://test', **http_kwargs
+    )
+    assert request.extensions['timeout'] == {
+        'connect': 5.0,
+        'read': 5.0,
+        'write': 5.0,
+        'pool': 5.0,
+    }
+
+
+def test_sse_event_source_sets_default_stream_headers():
+    source = _SSEEventSource(httpx.AsyncClient(), 'GET', 'http://test')
+
+    assert source._request.headers['Accept'] == 'text/event-stream'
+    assert source._request.headers['Cache-Control'] == 'no-store'
+
+
+@pytest.mark.parametrize(
+    'caller_spelling', ['accept', 'Accept', 'ACCEPT', 'AcCePt']
+)
+def test_sse_event_source_keeps_caller_accept_whatever_its_case(
+    caller_spelling: str,
+):
+    """A caller's own Accept wins, and is never joined by a second one.
+
+    HTTP header names are case-insensitive, so matching the caller's
+    spelling exactly is not enough to detect that they already set one.
+    """
+    source = _SSEEventSource(
+        httpx.AsyncClient(),
+        'GET',
+        'http://test',
+        headers={caller_spelling: 'application/json'},
+    )
+
+    assert source._request.headers.get_list('accept') == ['application/json']

tests/client/transports/test_jsonrpc_client.py

@@ -245,7 +245,7 @@ async def test_send_message_with_timeout_context(
         mock_httpx_client.build_request.assert_called_once()
         _, kwargs = mock_httpx_client.build_request.call_args
         assert 'timeout' in kwargs
-        assert kwargs['timeout'] == httpx.Timeout(15.0)
+        assert kwargs['timeout'] == 15.0
 
 
 class TestGetTask:

tests/client/transports/test_rest_client.py

@@ -220,7 +220,7 @@ async def test_send_message_with_timeout_context(
         mock_build_request.assert_called_once()
         _, kwargs = mock_build_request.call_args
         assert 'timeout' in kwargs
-        assert kwargs['timeout'] == httpx.Timeout(10.0)
+        assert kwargs['timeout'] == 10.0
 
     @pytest.mark.asyncio
     async def test_url_serialization(