StreamableHttp - GET request standalone SSE (#561)

tests/server/test_streamableHttp.py

@@ -541,3 +541,92 @@ def test_json_response(json_response_server, json_server_url):
     )
     assert response.status_code == 200
     assert response.headers.get("Content-Type") == "application/json"
+
+
+def test_get_sse_stream(basic_server, basic_server_url):
+    """Test establishing an SSE stream via GET request."""
+    # First, we need to initialize a session
+    mcp_url = f"{basic_server_url}/mcp"
+    init_response = requests.post(
+        mcp_url,
+        headers={
+            "Accept": "application/json, text/event-stream",
+            "Content-Type": "application/json",
+        },
+        json=INIT_REQUEST,
+    )
+    assert init_response.status_code == 200
+
+    # Get the session ID
+    session_id = init_response.headers.get(MCP_SESSION_ID_HEADER)
+    assert session_id is not None
+
+    # Now attempt to establish an SSE stream via GET
+    get_response = requests.get(
+        mcp_url,
+        headers={
+            "Accept": "text/event-stream",
+            MCP_SESSION_ID_HEADER: session_id,
+        },
+        stream=True,
+    )
+
+    # Verify we got a successful response with the right content type
+    assert get_response.status_code == 200
+    assert get_response.headers.get("Content-Type") == "text/event-stream"
+
+    # Test that a second GET request gets rejected (only one stream allowed)
+    second_get = requests.get(
+        mcp_url,
+        headers={
+            "Accept": "text/event-stream",
+            MCP_SESSION_ID_HEADER: session_id,
+        },
+        stream=True,
+    )
+
+    # Should get CONFLICT (409) since there's already a stream
+    # Note: This might fail if the first stream fully closed before this runs,
+    # but generally it should work in the test environment where it runs quickly
+    assert second_get.status_code == 409
+
+
+def test_get_validation(basic_server, basic_server_url):
+    """Test validation for GET requests."""
+    # First, we need to initialize a session
+    mcp_url = f"{basic_server_url}/mcp"
+    init_response = requests.post(
+        mcp_url,
+        headers={
+            "Accept": "application/json, text/event-stream",
+            "Content-Type": "application/json",
+        },
+        json=INIT_REQUEST,
+    )
+    assert init_response.status_code == 200
+
+    # Get the session ID
+    session_id = init_response.headers.get(MCP_SESSION_ID_HEADER)
+    assert session_id is not None
+
+    # Test without Accept header
+    response = requests.get(
+        mcp_url,
+        headers={
+            MCP_SESSION_ID_HEADER: session_id,
+        },
+        stream=True,
+    )
+    assert response.status_code == 406
+    assert "Not Acceptable" in response.text
+
+    # Test with wrong Accept header
+    response = requests.get(
+        mcp_url,
+        headers={
+            "Accept": "application/json",
+            MCP_SESSION_ID_HEADER: session_id,
+        },
+    )
+    assert response.status_code == 406
+    assert "Not Acceptable" in response.text