fix: dev ui url works in sub-apps

src/google/adk/cli/adk_web_server.py

@@ -18,6 +18,7 @@
 from contextlib import asynccontextmanager
 import logging
 import os
+from pathlib import Path
 import time
 import traceback
 import typing
@@ -31,6 +32,7 @@
 from fastapi import HTTPException
 from fastapi import Query
 from fastapi.middleware.cors import CORSMiddleware
+from fastapi.responses import JSONResponse
 from fastapi.responses import RedirectResponse
 from fastapi.responses import StreamingResponse
 from fastapi.staticfiles import StaticFiles
@@ -44,6 +46,8 @@
 from opentelemetry.sdk.trace import TracerProvider
 from pydantic import Field
 from pydantic import ValidationError
+from starlette.responses import Response
+from starlette.staticfiles import PathLike
 from starlette.types import Lifespan
 from typing_extensions import override
 from watchdog.observers import Observer
@@ -196,6 +200,28 @@ class GetEventGraphResult(common.BaseModel):
   dot_src: str
 
 
+class ConfigInjectingStaticFiles(StaticFiles):
+  """
+  Custom StaticFiles that injects config.json for dev-ui.
+  Fixes https://github.com/google/adk-python/issues/2072
+  """
+
+  def __init__(self, *, directory: PathLike | None = None, base_url: Optional[str] = None, **kwargs):
+    super().__init__(directory=directory, **kwargs)
+    if base_url is None:
+      base_url = ""
+    self.base_url = base_url
+
+  async def get_response(self, path: str, scope) -> Response:
+    # Check if the request is for config.json
+    if Path(path).as_posix() == "assets/config/runtime-config.json":
+      config = {"backendUrl": self.base_url}
+      return JSONResponse(content=config)
+
+    # Otherwise, serve static files normally
+    return await super().get_response(path, scope)
+
+
 class AdkWebServer:
   """Helper class for setting up and running the ADK web server on FastAPI.
 
@@ -287,6 +313,7 @@ def get_fast_api_app(
           [Observer, "AdkWebServer"], None
       ] = lambda o, s: None,
       register_processors: Callable[[TracerProvider], None] = lambda o: None,
+      base_url: Optional[str] = None,
   ):
     """Creates a FastAPI app for the ADK web server.
 
@@ -303,6 +330,8 @@ def get_fast_api_app(
       tear_down_observer: Callback for cleaning up the file system observer.
       register_processors: Callback for additional Span processors to be added
         to the TracerProvider.
+      base_url: The base URL for the web-ui, useful if fastapi app is mounted as
+        a sub-application. If none is provided, the host is used in the frontend.
 
     Returns:
       A FastAPI app instance.
@@ -1013,7 +1042,12 @@ async def redirect_dev_ui_add_slash():
 
       app.mount(
           "/dev-ui/",
-          StaticFiles(directory=web_assets_dir, html=True, follow_symlink=True),
+          ConfigInjectingStaticFiles(
+              directory=web_assets_dir,
+              base_url=base_url,
+              html=True,
+              follow_symlink=True,
+          ),
           name="static",
       )
 

src/google/adk/cli/cli_tools_click.py

@@ -23,6 +23,7 @@
 import os
 import tempfile
 from typing import Optional
+from urllib.parse import urlparse
 
 import click
 from click.core import ParameterSource
@@ -616,18 +617,12 @@ def fast_api_common_options():
 
   def decorator(func):
     @click.option(
-        "--host",
+        "--base_url",
         type=str,
-        help="Optional. The binding host of the server",
-        default="127.0.0.1",
+        help="Optional. The base URL of the server.",
+        default="http://127\.0\.0\.1:8000",
         show_default=True,
     )
-    @click.option(
-        "--port",
-        type=int,
-        help="Optional. The port of the server",
-        default=8000,
-    )
     @click.option(
         "--allow_origins",
         help="Optional. Any additional origins to allow for CORS.",
@@ -719,8 +714,7 @@ def cli_web(
     eval_storage_uri: Optional[str] = None,
     log_level: str = "INFO",
     allow_origins: Optional[list[str]] = None,
-    host: str = "127.0.0.1",
-    port: int = 8000,
+    base_url="http://127.0.0.1:8000",
     trace_to_cloud: bool = False,
     reload: bool = True,
     session_service_uri: Optional[str] = None,
@@ -741,6 +735,9 @@ def cli_web(
     adk web --session_service_uri=[uri] --port=[port] path/to/agents_dir
   """
   logs.setup_adk_logger(getattr(logging, log_level.upper()))
+  parsed_url = urlparse(base_url)
+  host = parsed_url.hostname
+  port = parsed_url.port
 
   @asynccontextmanager
   async def _lifespan(app: FastAPI):
@@ -777,8 +774,7 @@ async def _lifespan(app: FastAPI):
       trace_to_cloud=trace_to_cloud,
       lifespan=_lifespan,
       a2a=a2a,
-      host=host,
-      port=port,
+      base_url=base_url,
       reload_agents=reload_agents,
   )
   config = uvicorn.Config(
@@ -810,8 +806,7 @@ def cli_api_server(
     eval_storage_uri: Optional[str] = None,
     log_level: str = "INFO",
     allow_origins: Optional[list[str]] = None,
-    host: str = "127.0.0.1",
-    port: int = 8000,
+    base_url="http://127.0.0.1:8000",
     trace_to_cloud: bool = False,
     reload: bool = True,
     session_service_uri: Optional[str] = None,
@@ -833,6 +828,9 @@ def cli_api_server(
   """
   logs.setup_adk_logger(getattr(logging, log_level.upper()))
 
+  parsed_url = urlparse(base_url)
+  host = parsed_url.hostname
+  port = parsed_url.port
   session_service_uri = session_service_uri or session_db_url
   artifact_service_uri = artifact_service_uri or artifact_storage_uri
   config = uvicorn.Config(
@@ -846,8 +844,7 @@ def cli_api_server(
           web=False,
           trace_to_cloud=trace_to_cloud,
           a2a=a2a,
-          host=host,
-          port=port,
+          base_url=base_url,
           reload_agents=reload_agents,
       ),
       host=host,

src/google/adk/cli/fast_api.py

@@ -27,9 +27,12 @@
 from fastapi import FastAPI
 from fastapi import UploadFile
 from fastapi.responses import FileResponse
+from fastapi.responses import JSONResponse
 from fastapi.responses import PlainTextResponse
+from fastapi.staticfiles import StaticFiles
 from opentelemetry.sdk.trace import export
 from opentelemetry.sdk.trace import TracerProvider
+from starlette.responses import Response
 from starlette.types import Lifespan
 from watchdog.observers import Observer
 
@@ -64,8 +67,7 @@ def get_fast_api_app(
     allow_origins: Optional[list[str]] = None,
     web: bool,
     a2a: bool = False,
-    host: str = "127.0.0.1",
-    port: int = 8000,
+    base_url: str = "http://127.0.0.1:8000",
     trace_to_cloud: bool = False,
     reload_agents: bool = False,
     lifespan: Optional[Lifespan[FastAPI]] = None,
@@ -189,7 +191,9 @@ def _parse_agent_engine_resource_name(agent_engine_id_or_resource_name):
   )
 
   # Callbacks & other optional args for when constructing the FastAPI instance
-  extra_fast_api_args = {}
+  extra_fast_api_args = dict(
+      base_url=base_url,
+  )
 
   if trace_to_cloud:
     from opentelemetry.exporter.cloud_trace import CloudTraceSpanExporter
@@ -352,7 +356,7 @@ async def _get_a2a_runner_async() -> Runner:
         logger.info("Setting up A2A agent: %s", app_name)
 
         try:
-          a2a_rpc_path = f"http://{host}:{port}/a2a/{app_name}"
+          a2a_rpc_path = f"{base_url}/a2a/{app_name}"
 
           agent_executor = A2aAgentExecutor(
               runner=create_a2a_runner_loader(app_name),

tests/unittests/cli/test_fast_api.py

@@ -24,6 +24,7 @@
 from unittest.mock import MagicMock
 from unittest.mock import patch
 
+from fastapi import FastAPI
 from fastapi.testclient import TestClient
 from google.adk.agents.base_agent import BaseAgent
 from google.adk.agents.run_config import RunConfig
@@ -432,8 +433,7 @@ def test_app(
         memory_service_uri="",
         allow_origins=["*"],
         a2a=False,  # Disable A2A for most tests
-        host="127.0.0.1",
-        port=8000,
+        base_url="http://127.0.0.1:8000",
     )
 
     # Create a TestClient that doesn't start a real server
@@ -607,8 +607,7 @@ def test_app_with_a2a(
           memory_service_uri="",
           allow_origins=["*"],
           a2a=True,
-          host="127.0.0.1",
-          port=8000,
+          base_url="http://127.0.0.1:8000",
       )
 
       client = TestClient(app)
@@ -897,5 +896,92 @@ def test_a2a_disabled_by_default(test_app):
   logger.info("A2A disabled by default test passed")
 
 
+def test_runtime_config_contains_base_url(test_app):
+  """Test that ./assets/config/runtime-config.json contains the base_url passed to the FastAPI app."""
+  # The test_app fixture configures the FastAPI app with base_url="http://127.0.0.1:8000"
+  expected_base_url = "http://127.0.0.1:8000"
+
+  # Make a request to the runtime config endpoint
+  response = test_app.get("/dev-ui/assets/config/runtime-config.json")
+
+  # Verify the response
+  assert response.status_code == 200
+  data = response.json()
+
+  # Verify the structure and content
+  assert isinstance(data, dict)
+  assert "backendUrl" in data
+  assert data["backendUrl"] == expected_base_url
+
+  logger.info(f"Runtime config test passed - base_url: {data['backendUrl']}")
+
+
+def test_runtime_config_with_custom_base_url(
+    mock_session_service,
+    mock_artifact_service,
+    mock_memory_service,
+    mock_agent_loader,
+    mock_eval_sets_manager,
+    mock_eval_set_results_manager,
+):
+  """Test that runtime-config.json contains a custom base_url when provided."""
+  custom_base_url = "https://example.com:9000/adk"
+
+  # Create a FastAPI app with a custom base_url
+  with (
+      patch("signal.signal", return_value=None),
+      patch(
+          "google.adk.cli.fast_api.InMemorySessionService",
+          return_value=mock_session_service,
+      ),
+      patch(
+          "google.adk.cli.fast_api.InMemoryArtifactService",
+          return_value=mock_artifact_service,
+      ),
+      patch(
+          "google.adk.cli.fast_api.InMemoryMemoryService",
+          return_value=mock_memory_service,
+      ),
+      patch(
+          "google.adk.cli.fast_api.AgentLoader",
+          return_value=mock_agent_loader,
+      ),
+      patch(
+          "google.adk.cli.fast_api.LocalEvalSetsManager",
+          return_value=mock_eval_sets_manager,
+      ),
+      patch(
+          "google.adk.cli.fast_api.LocalEvalSetResultsManager",
+          return_value=mock_eval_set_results_manager,
+      ),
+  ):
+    adk_app = get_fast_api_app(
+        agents_dir=".",
+        web=True,
+        session_service_uri="",
+        artifact_service_uri="",
+        memory_service_uri="",
+        allow_origins=["*"],
+        a2a=False,
+        base_url=custom_base_url,
+    )
+    app = FastAPI()
+    app.mount("/adk", adk_app)
+
+    client = TestClient(app)
+
+    # Make a request to the runtime config endpoint
+    response = client.get("/adk/dev-ui/assets/config/runtime-config.json")
+
+    # Verify the response contains the custom base_url
+    assert response.status_code == 200
+    data = response.json()
+    assert isinstance(data, dict)
+    assert "backendUrl" in data
+    assert data["backendUrl"] == custom_base_url
+
+    logger.info(f"Custom runtime config test passed - base_url: {data['backendUrl']}")
+
+
 if __name__ == "__main__":
   pytest.main(["-xvs", __file__])