현대 프로토콜 2: A2A Modern Protocols 2: Agent2Agent

{
  "name": "Lamp Shop",
  "description": "Sells desk lamps, chairs and bookshelves. Negotiates the price with the buyer.",
  "supportedInterfaces": [
    { "url": "http://127.0.0.1:9999/", "protocolBinding": "JSONRPC", "protocolVersion": "1.0" }
  ],
  "version": "1.0.0",
  "capabilities": { "streaming": true },
  "defaultInputModes": ["text/plain"],
  "defaultOutputModes": ["application/json", "text/plain"],
  "skills": [
    {
      "id": "negotiate",
      "name": "Negotiate a purchase",
      "description": "Ask for an item, then send a price. The shop answers with a counteroffer or a receipt.",
      "tags": ["shopping", "negotiation"],
      "examples": ["I want to buy a lamp", "90"]
    }
  ]
}

python seller_agent.py               # http://127.0.0.1:9999

a2a card get http://127.0.0.1:9999
curl -s http://127.0.0.1:9999/.well-known/agent-card.json | python -m json.tool

(request
  :sender   (agent-identifier :name lamp-shop@shop.example)
  :receiver (set (agent-identifier :name df@platform.example))
  :language fipa-sl0
  :ontology FIPA-Agent-Management
  :protocol fipa-request
  :content
    "((action (agent-identifier :name df@platform.example)
        (register
          (df-agent-description
            :name (agent-identifier :name lamp-shop@shop.example)
            :protocols (set fipa-request)
            :languages (set fipa-sl0)
            :services (set (service-description
                             :name lamp-sale
                             :type furniture-seller))))))")

$ a2a send -a http://127.0.0.1:9999 "I want to buy a lamp"
Task:     a7b1e3f3-9530-4eb2-b84c-cac830752ff3
Context:  8718ea6a-4c6d-4ccc-a416-57ff708de2f2
Status:   input-required (2026-10-13T05:21:00Z)
  lamp: asking 130. Send your offer as a number.
History:
  [user] I want to buy a lamp

Resume:     a2a send --task-id a7b1e3f3-9530-4eb2-b84c-cac830752ff3 "<reply>"

a2a send -a http://127.0.0.1:9999 "I want to buy a lamp"     # input-required, asking 130
a2a send -a http://127.0.0.1:9999 --task-id <id> 80          # Counteroffer: 105
a2a send -a http://127.0.0.1:9999 --task-id <id> 105         # completed + receipt
a2a task get -a http://127.0.0.1:9999 <id> -o json           # TASK_STATE_COMPLETED
a2a send -a http://127.0.0.1:9999 --task-id <id> 110         # 끝난 task: 오류

python3 --version                    # 3.10 이상
mkdir a2a-lab && cd a2a-lab
python3 -m venv .venv
source .venv/bin/activate            # Windows: .venv\Scripts\activate
pip install "a2a-sdk[http-server]" uvicorn

# a2a CLI: macOS, Linux
brew tap a2aproject/a2a-cli https://github.com/a2aproject/a2a-cli
brew trust --formula a2aproject/a2a-cli/a2a   # Homebrew가 untrusted tap이라며 거절할 때
brew install a2a
# a2a CLI: Windows
winget install a2aproject.a2acli

a2a version                          # a2a 0.3.0

a2a server --echo --port 8080

$ a2a send -a http://localhost:8080 "hello A2A"
Task:     01a133e9-a808-741a-9718-61d315e93f75
Context:  01a133e9-a808-7501-949a-7f2576fb38af
Status:   completed (2026-10-13T15:18:33+09:00)
Artifacts:
  [01a133e9-a808-75b8-81eb-2483cf7cfcc9] hello A2A
History:
  [user] hello A2A

import uvicorn
from starlette.applications import Starlette

from a2a.helpers import get_message_text, new_task_from_user_message, new_text_part
from a2a.server.agent_execution import AgentExecutor
from a2a.server.request_handlers import DefaultRequestHandler
from a2a.server.routes import create_agent_card_routes, create_jsonrpc_routes
from a2a.server.tasks import InMemoryTaskStore, TaskUpdater
from a2a.types import AgentCapabilities, AgentCard, AgentInterface, AgentSkill


class Hello(AgentExecutor):
    async def execute(self, context, event_queue):
        task = new_task_from_user_message(context.message)  # every message starts a new task
        await event_queue.enqueue_event(task)
        up = TaskUpdater(event_queue=event_queue, task_id=task.id, context_id=task.context_id)
        text = get_message_text(context.message)
        await up.complete(up.new_agent_message(parts=[new_text_part(f"Hello! You said: {text}")]))

    async def cancel(self, context, event_queue):
        pass


card = AgentCard(
    name="Hello Agent",
    description="Says hello back.",
    version="1.0.0",
    default_input_modes=["text/plain"],
    default_output_modes=["text/plain"],
    capabilities=AgentCapabilities(),
    supported_interfaces=[AgentInterface(protocol_binding="JSONRPC", url="http://127.0.0.1:9000/", protocol_version="1.0")],
    skills=[AgentSkill(id="hello", name="Say hello", description="Replies to any message.", tags=["demo"])],
)
handler = DefaultRequestHandler(agent_executor=Hello(), task_store=InMemoryTaskStore(), agent_card=card)
app = Starlette(routes=create_agent_card_routes(card) + create_jsonrpc_routes(handler, "/"))

if __name__ == "__main__":
    uvicorn.run(app, host="127.0.0.1", port=9000)

python hello_agent.py

$ a2a card get http://127.0.0.1:9000
Name:         Hello Agent
Description:  Says hello back.
Version:      1.0.0
Interfaces:
  JSONRPC      http://127.0.0.1:9000/
Streaming:    false
Skills:
  hello                Say hello

$ a2a send -a http://127.0.0.1:9000 "hi there"
Task:     880a8f06-469f-47c8-95f8-f8d5cf439a40
Context:  d2932be2-8312-473d-b3a1-11626bc564dd
Status:   completed (2026-10-13T06:18:53Z)
  Hello! You said: hi there
History:
  [user] hi there

INFO:     127.0.0.1:57854 - "GET /.well-known/agent-card.json HTTP/1.1" 200 OK
INFO:     127.0.0.1:57854 - "POST / HTTP/1.1" 200 OK

"""A rule-based seller exposed as an A2A server (a2a-sdk 1.2.x, JSON-RPC binding).

    python seller_agent.py                       # lamp shop on :9999
    python seller_agent.py --config cards/b.json # another seller from a config file

No model inside: the seller asks for an offer (INPUT_REQUIRED), counters, and
either closes with a receipt artifact (COMPLETED) or walks away (REJECTED).
"""
import argparse
import json
import math
import re

import uvicorn
from starlette.applications import Starlette

from a2a.helpers import get_message_text, new_data_part, new_task_from_user_message, new_text_part
from a2a.server.agent_execution import AgentExecutor, RequestContext
from a2a.server.events import EventQueue
from a2a.server.request_handlers import DefaultRequestHandler
from a2a.server.routes import create_agent_card_routes, create_jsonrpc_routes
from a2a.server.tasks import InMemoryTaskStore, TaskUpdater
from a2a.types import AgentCapabilities, AgentCard, AgentInterface, AgentSkill

DEFAULT = {
    "name": "Lamp Shop",
    "description": "Sells desk lamps, chairs and bookshelves. Negotiates the price with the buyer.",
    "skill_description": "Ask for an item, then send a price. The shop answers with a counteroffer or a receipt.",
    "port": 9999,
    "reserve": {"lamp": 100, "chair": 180, "bookshelf": 260},
    "max_rounds": 3,
}


class Seller(AgentExecutor):
    def __init__(self, cfg):
        self.cfg = cfg
        self.open = {}  # task id -> {"item", "ask", "rounds"}

    async def execute(self, context: RequestContext, event_queue: EventQueue) -> None:
        task = context.current_task
        if task is None:
            task = new_task_from_user_message(context.message)
            await event_queue.enqueue_event(task)
        up = TaskUpdater(event_queue=event_queue, task_id=task.id, context_id=task.context_id)
        say = lambda text: up.new_agent_message(parts=[new_text_part(text)])
        text = get_message_text(context.message) or ""
        deal = self.open.get(task.id)

        if deal is None:  # first message: which item?
            item = next((k for k in self.cfg["reserve"] if k in text.lower()), None)
            if item is None:
                await up.reject(say("We only sell: " + ", ".join(self.cfg["reserve"]) + "."))
                return
            ask = math.ceil(self.cfg["reserve"][item] * 1.3)
            self.open[task.id] = {"item": item, "ask": ask, "rounds": 0}
            await up.requires_input(say(f"{item}: asking {ask}. Send your offer as a number."))
            return

        m = re.search(r"\d+", text)
        if m is None:
            await up.requires_input(say("Send your offer as a number."))
            return
        offer, reserve = int(m.group()), self.cfg["reserve"][deal["item"]]
        if offer >= reserve:
            receipt = {"seller": self.cfg["name"], "item": deal["item"], "price": offer}
            await up.add_artifact(parts=[new_data_part(receipt)], name="receipt")
            await up.complete(say(f"Deal: {deal['item']} at {offer}."))
            del self.open[task.id]
            return
        deal["rounds"] += 1
        if deal["rounds"] >= self.cfg["max_rounds"]:
            await up.reject(say(f"No deal at {offer}."))
            del self.open[task.id]
            return
        deal["ask"] = max(reserve, (offer + deal["ask"]) // 2)
        await up.requires_input(say(f"{offer} is too low. Counteroffer: {deal['ask']}."))

    async def cancel(self, context: RequestContext, event_queue: EventQueue) -> None:
        task = context.current_task
        self.open.pop(task.id, None)
        await TaskUpdater(event_queue=event_queue, task_id=task.id, context_id=task.context_id).cancel()


def build(cfg):
    url = f"http://127.0.0.1:{cfg['port']}/"
    card = AgentCard(
        name=cfg["name"],
        description=cfg["description"],
        version="1.0.0",
        default_input_modes=["text/plain"],
        default_output_modes=["application/json", "text/plain"],
        capabilities=AgentCapabilities(streaming=True),
        supported_interfaces=[AgentInterface(protocol_binding="JSONRPC", url=url, protocol_version="1.0")],
        skills=[AgentSkill(
            id="negotiate",
            name="Negotiate a purchase",
            description=cfg["skill_description"],
            tags=["shopping", "negotiation"],
            examples=["I want to buy a lamp", "90"],
        )],
    )
    handler = DefaultRequestHandler(agent_executor=Seller(cfg), task_store=InMemoryTaskStore(), agent_card=card)
    return Starlette(routes=create_agent_card_routes(card) + create_jsonrpc_routes(handler, "/"))


if __name__ == "__main__":
    ap = argparse.ArgumentParser()
    ap.add_argument("--config")
    ap.add_argument("--port", type=int)
    args = ap.parse_args()
    cfg = dict(DEFAULT)
    if args.config:
        cfg.update(json.load(open(args.config)))
    if args.port:
        cfg["port"] = args.port
    uvicorn.run(build(cfg), host="127.0.0.1", port=cfg["port"], log_level="warning")

python seller_agent.py               # http://127.0.0.1:9999

# 첫 메시지: 새 task가 생긴다
a2a send -a http://127.0.0.1:9999 "I want to buy a lamp"
# 같은 task에 이어 보내기
a2a send -a http://127.0.0.1:9999 --task-id <task id> 80
# 조회와 취소
a2a task get    -a http://127.0.0.1:9999 <task id>
a2a task cancel -a http://127.0.0.1:9999 <task id>
# 어느 명령이든 -o json을 붙이면 규격의 JSON 그대로 나온다

# 2번: A2A-Version 헤더 없이 보내기
curl -s http://127.0.0.1:9999/ -H 'Content-Type: application/json' -d '{
  "jsonrpc": "2.0", "id": 1, "method": "SendMessage",
  "params": {"message": {"role": "ROLE_USER", "messageId": "m0",
                         "parts": [{"text": "I want to buy a lamp"}]}}}'

$ curl (SendMessage without the A2A-Version header)
{"error":{"code":-32009,"message":"A2A version '0.3' is not supported by this handler. Expected version '1.0'.", ...}}

$ a2a send -a http://127.0.0.1:9999 --task-id <task> 80
Status:   input-required (2026-10-13T05:21:00Z)
  80 is too low. Counteroffer: 105.

$ a2a send -a http://127.0.0.1:9999 --task-id <task> 105
Task:     a7b1e3f3-9530-4eb2-b84c-cac830752ff3
Context:  8718ea6a-4c6d-4ccc-a416-57ff708de2f2
Status:   completed (2026-10-13T05:21:00Z)
  Deal: lamp at 105.
Artifacts:
  [receipt] {"item":"lamp","price":105,"seller":"Lamp Shop"}
History:
  [user] I want to buy a lamp
  [agent] lamp: asking 130. Send your offer as a number.
  [user] 80
  [agent] 80 is too low. Counteroffer: 105.
  [user] 105

$ a2a send -a http://127.0.0.1:9999 --task-id <task> 110 -o json
{
  "error": {
    "code": "A2ACLI_ERR_PROTOCOL",
    "message": "failed to send message: Task a7b1e3f3-... is in terminal state: TASK_STATE_COMPLETED",
    "a2aCode": "UNSUPPORTED_OPERATION"
  }
}
exit code 1

$ a2a send -a http://127.0.0.1:9999 "I want to buy a sofa"
Status:   rejected (2026-10-13T05:21:01Z)
  We only sell: lamp, chair, bookshelf.

$ a2a send ... "I want to buy a chair", then 100 three times
  100 is too low. Counteroffer: 180.
  100 is too low. Counteroffer: 180.
Status:   rejected (2026-10-13T05:21:01Z)
  No deal at 100.

$ a2a send ... "I want to buy a bookshelf", then a2a task cancel
Status:   canceled (2026-10-13T05:21:01Z)

a2a server --exec "claude -p --model haiku --system-prompt 'You are a furniture shop. You sell lamps. Answer in English, in one short sentence.'" \
  --name "Claude Shop" --port 8090

$ a2a send -a http://localhost:8090 "Do you sell lamps? How much?"
Task:     01a1341a-911a-7ba8-8341-deafdf73cdb8
Context:  01a1341a-911a-7cdc-8f74-74d95c6145dc
Status:   completed (2026-10-13T16:12:05+09:00)
Artifacts:
  [01a1341a-a9fd-76b6-a775-e1ba5074dbf3] Yes, we sell lamps, but I don't have their prices in front of me, so please check our current catalog or contact the shop for pricing.
History:
  [user] Do you sell lamps? How much?

claude -p --model haiku --tools "" --setting-sources "" --no-session-persistence
codex exec --skip-git-repo-check -

python scripts/trade_test_week06.py submissions/<학번>/week-06