fix: keep existing header values while merging tracking headers for llm_request.config.http_options in Gemini.generate_content_async

PiperOrigin-RevId: 789013693

Author: xuanyang15

src/google/adk/models/google_llm.py

@@ -122,9 +122,9 @@ async def generate_content_async(
  if llm_request.config:
  if not llm_request.config.http_options:
  llm_request.config.http_options = types.HttpOptions()
- if not llm_request.config.http_options.headers:
- llm_request.config.http_options.headers = {}
- llm_request.config.http_options.headers.update(self._tracking_headers)
+ llm_request.config.http_options.headers = self._merge_tracking_headers(
+  llm_request.config.http_options.headers
+ )
 
  if stream:
  responses = await self.api_client.aio.models.generate_content_stream(
@@ -336,6 +336,23 @@ async def _preprocess_request(self, llm_request: LlmRequest) -> None:
  llm_request.config.system_instruction = None
  await self._adapt_computer_use_tool(llm_request)
 
+ def _merge_tracking_headers(self, headers: dict[str, str]) -> dict[str, str]:
+ """Merge tracking headers to the given headers."""
+ headers = headers or {}
+ for key, tracking_header_value in self._tracking_headers.items():
+ custom_value = headers.get(key, None)
+ if not custom_value:
+ headers[key] = tracking_header_value
+ continue
+
+ # Merge tracking headers with existing headers and avoid duplicates.
+ value_parts = tracking_header_value.split(' ')
+ for custom_value_part in custom_value.split(' '):
+ if custom_value_part not in value_parts:
+ value_parts.append(custom_value_part)
+ headers[key] = ' '.join(value_parts)
+ return headers
+
 
 def _build_function_declaration_log(
  func_decl: types.FunctionDeclaration,

tests/unittests/models/test_google_llm.py

@@ -403,7 +403,7 @@ async def mock_coro():
 
  for key, value in config_arg.http_options.headers.items():
  if key in gemini_llm._tracking_headers:
- assert value == gemini_llm._tracking_headers[key]
+ assert value == gemini_llm._tracking_headers[key] + " custom"
  else:
  assert value == custom_headers[key]