Refactor to make starlette optional

Author: holtskinner

README.md

@@ -26,35 +26,28 @@ You can install the A2A SDK using either `uv` or `pip`.
 
 ### Using `uv`
 
-When you're working within a uv project or a virtual environment managed by uv, the preferred way to add packages is using uv add.
-
 ```bash
 uv add a2a-sdk
 ```
 
-### Using `pip`
-
-If you prefer to use pip, the standard Python package installer, you can install `a2a-sdk` as follows
+To include the optional HTTP server components (FastAPI, Starlette), install the `http-server` extra:
 
 ```bash
-pip install a2a-sdk
+uv add a2a-sdk[http-server]
 ```
 
-### Optional
-
-#### FastAPI-based A2A Server App
+### Using `pip`
 
-Using `a2a.server.apps.A2AFastAPIApplication` requires the FastAPI package, which is an optional dependency.
-With `uv`, it can be specified as follows:
+You can install `a2a-sdk` using pip, the standard Python package installer.
 
-```shell
-uv add a2a-sdk[fastapi]
+```bash
+pip install a2a-sdk
 ```
 
-Alternatively, a preferred version of the `fastapi` package can be added directly to the project:
+To include the optional HTTP server components (FastAPI, Starlette), install the `http-server` extra:
 
-```shell
-uv add fastapi
+```bash
+pip install a2a-sdk[http-server]
 ```
 
 ## Examples

pyproject.toml

@@ -14,8 +14,6 @@ dependencies = [
   "opentelemetry-api>=1.33.0",
   "opentelemetry-sdk>=1.33.0",
   "pydantic>=2.11.3",
-  "sse-starlette",
-  "starlette",
   "grpcio>=1.60",
   "grpcio-tools>=1.60",
   "grpcio_reflection>=1.7.0",
@@ -35,6 +33,9 @@ classifiers = [
   "License :: OSI Approved :: Apache Software License",
 ]
 
+[project.optional-dependencies]
+http-server = ["fastapi>=0.115.2", "sse-starlette", "starlette"]
+
 [project.urls]
 homepage = "https://google-a2a.github.io/A2A/"
 repository = "https://github.com/google-a2a/a2a-python"
@@ -51,7 +52,7 @@ python_functions = "test_*"
 addopts = "-ra --strict-markers"
 asyncio_mode = "strict"
 markers = [
-    "asyncio: mark a test as a coroutine that should be run by pytest-asyncio",
+  "asyncio: mark a test as a coroutine that should be run by pytest-asyncio",
 ]
 
 [build-system]
@@ -83,9 +84,8 @@ dev = [
   "types-requests",
   "pre-commit",
   "fastapi>=0.115.2",
-]
-fastapi = [
-    "fastapi>=0.115.2",
+  "sse-starlette",
+  "starlette",
 ]
 
 [[tool.uv.index]]

src/a2a/server/apps/jsonrpc/fastapi_app.py

@@ -2,11 +2,14 @@
 
 from typing import Any
 
-from a2a.server.apps.jsonrpc.fastapi_import_helpers import (
-    FastAPI,
-    Request,
-    Response,
-)
+
+try:
+    from fastapi import FastAPI, Request, Response
+except ImportError:
+    FastAPI = object
+    Request = object
+    Response = object
+
 from a2a.server.apps.jsonrpc.jsonrpc_app import (
     CallContextBuilder,
     JSONRPCApplication,

src/a2a/server/apps/jsonrpc/fastapi_import_helpers.py

@@ -16,7 +16,6 @@
 
 from a2a.auth.user import UnauthenticatedUser
 from a2a.auth.user import User as A2AUser
-from a2a.server.apps.jsonrpc.fastapi_import_helpers import FastAPI
 from a2a.server.context import ServerCallContext
 from a2a.server.request_handlers.jsonrpc_handler import JSONRPCHandler
 from a2a.server.request_handlers.request_handler import RequestHandler
@@ -45,6 +44,29 @@
 
 logger = logging.getLogger(__name__)
 
+try:
+    from fastapi import FastAPI
+    from sse_starlette.sse import EventSourceResponse
+    from starlette.applications import Starlette
+    from starlette.authentication import BaseUser
+    from starlette.requests import Request
+    from starlette.responses import JSONResponse, Response
+
+    _http_server_installed = True
+except ImportError:
+    _http_server_installed = False
+    # Define placeholder types for type hinting and to avoid import errors in other files.
+    # These will not be used at runtime if deps are missing, as __init__ will raise.
+    (
+        FastAPI,
+        EventSourceResponse,
+        Starlette,
+        BaseUser,
+        Request,
+        JSONResponse,
+        Response,
+    ) = (object,) * 7
+
 
 class StarletteUserProxy(A2AUser):
     """Adapts the Starlette User class to the A2A user representation."""
@@ -108,7 +130,7 @@ def __init__(
         extended_agent_card: AgentCard | None = None,
         context_builder: CallContextBuilder | None = None,
     ):
-        """Initializes the A2AStarletteApplication.
+        """Initializes the JSONRPCApplication.
 
         Args:
             agent_card: The AgentCard describing the agent's capabilities.
@@ -120,6 +142,10 @@ def __init__(
               ServerCallContext passed to the http_handler. If None, no
               ServerCallContext is passed.
         """
+        if not _http_server_installed:
+            raise ImportError(
+                'The `a2a-sdk[http-server]` package is required to use the `JSONRPCApplication`.'
+            )
         self.agent_card = agent_card
         self.extended_agent_card = extended_agent_card
         self.handler = JSONRPCHandler(

src/a2a/server/apps/jsonrpc/jsonrpc_app.py

@@ -2,8 +2,13 @@
 
 from typing import Any
 
-from starlette.applications import Starlette
-from starlette.routing import Route
+
+try:
+    from starlette.applications import Starlette
+    from starlette.routing import Route
+except ImportError:
+    Starlette = object
+    Route = object
 
 from a2a.server.apps.jsonrpc.jsonrpc_app import (
     CallContextBuilder,