import asyncio
import uuid
import httpx
import uvicorn
from a2a.client import ClientConfig, ClientFactory
from a2a.server.agent_execution import AgentExecutor, RequestContext
from a2a.server.apps.jsonrpc.starlette_app import A2AStarletteApplication
from a2a.server.events import EventQueue, InMemoryQueueManager
from a2a.server.request_handlers.default_request_handler import DefaultRequestHandler
from a2a.server.tasks import InMemoryTaskStore
from a2a.types import (
AgentCapabilities, AgentCard, AgentSkill, Message, Role,
TaskState, TaskStatus, TaskStatusUpdateEvent, TextPart,
)
from galileo.otel import GalileoSpanProcessor, add_galileo_span_processor
from galileo_a2a import A2AInstrumentor
from langchain.agents import create_agent
from langchain_core.tools import tool
from langchain_openai import ChatOpenAI
from langgraph.graph import END, START, StateGraph
from opentelemetry.instrumentation.langchain import LangchainInstrumentor
from opentelemetry.sdk.trace import TracerProvider
from starlette.applications import Starlette
from typing_extensions import TypedDict
# --- Galileo tracing setup ---
provider = TracerProvider()
add_galileo_span_processor(provider, GalileoSpanProcessor())
A2AInstrumentor().instrument(tracer_provider=provider, agent_name="orchestrator")
LangchainInstrumentor().instrument(tracer_provider=provider)
llm = ChatOpenAI(model="gpt-4o-mini")
# --- Agent B: researcher (served over A2A) ---
@tool
def search_kb(query: str) -> str:
"""Search the travel knowledge base."""
if "paris" in query.lower():
return "Eiffel Tower 330m, Louvre 9.6M visitors/yr, 20 arrondissements."
return f"No results for: {query}"
researcher = create_agent(
llm, [search_kb],
system_prompt="Use search_kb to find facts, then summarize for a traveler.",
)
class ResearcherExecutor(AgentExecutor):
async def execute(self, ctx: RequestContext, queue: EventQueue) -> None:
result = await researcher.ainvoke({"messages": [("user", ctx.get_user_input())]})
await queue.enqueue_event(TaskStatusUpdateEvent(
task_id=ctx.task_id, context_id=ctx.context_id, final=True,
status=TaskStatus(
state=TaskState.completed,
message=Message(
message_id=str(uuid.uuid4()), role=Role.agent,
parts=[TextPart(text=result["messages"][-1].content or "")],
),
),
))
async def cancel(self, ctx: RequestContext, queue: EventQueue) -> None:
await queue.enqueue_event(TaskStatusUpdateEvent(
task_id=ctx.task_id, context_id=ctx.context_id, final=True,
status=TaskStatus(state=TaskState.canceled),
))
CARD = AgentCard(
name="researcher",
description="Travel researcher with tool use",
url="http://localhost:9867",
version="1.0.0",
capabilities=AgentCapabilities(streaming=True),
default_input_modes=["text/plain"],
default_output_modes=["text/plain"],
skills=[AgentSkill(id="qa", name="Q&A", description="Answer questions", tags=[])],
)
# --- Agent A: orchestrator (LangGraph) ---
class OrchestratorState(TypedDict):
user_query: str
research_query: str
response: str
plan: str
def build_orchestrator(client):
async def plan(state: OrchestratorState) -> dict:
prompt = (
"Formulate a travel research question."
" Reply with ONLY the question."
)
result = await create_agent(
llm, system_prompt=prompt,
).ainvoke({"messages": [("user", state["user_query"])]})
return {"research_query": result["messages"][-1].content}
async def delegate(state: OrchestratorState) -> dict:
msg = Message(
message_id=str(uuid.uuid4()), role=Role.user,
parts=[TextPart(text=state["research_query"])],
context_id="session-1",
)
async for event in client.send_message(msg):
if isinstance(event, tuple):
task = event[0]
is_done = (
task.status
and task.status.state == TaskState.completed
and task.status.message
)
if is_done:
text = getattr(
task.status.message.parts[0].root,
"text", "",
)
return {"response": text}
return {"response": ""}
async def synthesize(state: OrchestratorState) -> dict:
prompt = "Create a brief 3-day itinerary from the research."
user_msg = (
f"Research:\n{state['response']}"
"\n\nCreate itinerary."
)
result = await create_agent(
llm, system_prompt=prompt,
).ainvoke({"messages": [("user", user_msg)]})
return {"plan": result["messages"][-1].content}
graph = StateGraph(OrchestratorState)
graph.add_node("plan", plan)
graph.add_node("delegate", delegate)
graph.add_node("synthesize", synthesize)
graph.add_edge(START, "plan")
graph.add_edge("plan", "delegate")
graph.add_edge("delegate", "synthesize")
graph.add_edge("synthesize", END)
return graph.compile()
# --- Run both agents ---
async def main():
# Start Agent B
app = Starlette()
A2AStarletteApplication(
agent_card=CARD,
http_handler=DefaultRequestHandler(
agent_executor=ResearcherExecutor(),
task_store=InMemoryTaskStore(),
queue_manager=InMemoryQueueManager(),
),
).add_routes_to_app(app)
server = uvicorn.Server(uvicorn.Config(app, port=9867, log_level="warning"))
server_task = asyncio.create_task(server.serve())
await asyncio.sleep(1)
# Run Agent A
client = ClientFactory(
config=ClientConfig(
streaming=True,
httpx_client=httpx.AsyncClient(
timeout=httpx.Timeout(120),
),
),
).create(CARD)
result = await build_orchestrator(client).ainvoke({
"user_query": "Plan a 3-day trip to Paris",
"research_query": "",
"response": "",
"plan": "",
})
print(result["plan"])
server.should_exit = True
await server_task
provider.shutdown()
asyncio.run(main())
