[Bug]: JSONDecodeError When trying A2AClient in Java to python A2A agent

[SR-Waivgen]

What happened?

Lib in build.gradle

implementation("io.github.a2asdk:a2a-java-sdk-client:0.2.5")

Steps I tried

1. I downloaded the repo for Python Helloworld A2A sample agent and started the server at port 9999 by referring this example link

2. Then I downloaded the Java helloworld example , I tried the below A2A client code in java to connect to Python A2A helloworld agent

A2A Client PoC – Java Example

package com.org;

import com.fasterxml.jackson.databind.ObjectMapper;
import io.a2a.A2A;
import io.a2a.client.A2AClient;
import io.a2a.spec.AgentCard;
import io.a2a.spec.Message;
import io.a2a.spec.MessageSendParams;
import io.a2a.spec.SendMessageResponse;

import java.util.HashMap;
import java.util.Map;

public class A2AClientPoc {
    private static final String SERVER_URL = "http://localhost:9999";
    private static final String MESSAGE_TEXT = "can you greet me ?";
    private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();

    public static void main(String[] args) {
        try {
            System.out.println("DEBUG: Starting client...");
            System.out.println("DEBUG: Connecting to server at: " + SERVER_URL);

            AgentCard finalAgentCard;

            System.out.println("DEBUG: Attempting to fetch public agent card...");
            AgentCard publicAgentCard = A2A.getAgentCard(SERVER_URL);
            System.out.println("DEBUG: Successfully fetched public agent card:");
            System.out.println(OBJECT_MAPPER.writeValueAsString(publicAgentCard));

            System.out.println("DEBUG: Using public agent card for client initialization (default).");
            finalAgentCard = publicAgentCard;

            if (publicAgentCard.supportsAuthenticatedExtendedCard()) {
                System.out.println("DEBUG: Public card supports authenticated extended card.");
                String extendedCardUrl = SERVER_URL + "/agent/authenticatedExtendedCard";
                System.out.println("DEBUG: Attempting to fetch from: " + extendedCardUrl);

                Map<String, String> authHeaders = new HashMap<>();
                authHeaders.put("Authorization", "Bearer dummy-token-for-extended-card");
                System.out.println("DEBUG: Using auth headers: " + authHeaders);

                try {
                    AgentCard extendedAgentCard = A2A.getAgentCard(
                            SERVER_URL,
                            "/agent/authenticatedExtendedCard",
                            authHeaders
                    );
                    System.out.println("DEBUG: Successfully fetched authenticated extended agent card:");
                    System.out.println(OBJECT_MAPPER.writeValueAsString(extendedAgentCard));
                    System.out.println("DEBUG: Using AUTHENTICATED EXTENDED agent card for client initialization.");
                    finalAgentCard = extendedAgentCard;
                } catch (Exception e) {
                    System.err.println("DEBUG: Failed to fetch extended card, using public card instead: " + e.getMessage());
                }
            } else {
                System.out.println("DEBUG: Public card does not indicate support for an extended card. Using public card.");
            }

            System.out.println("DEBUG: Creating A2A client with final agent card...");
            A2AClient client = new A2AClient(finalAgentCard);
            System.out.println("DEBUG: Client created successfully.");

            System.out.println("DEBUG: Creating message: '" + MESSAGE_TEXT + "'");
            Message message = A2A.toUserMessage(MESSAGE_TEXT);
            System.out.println("DEBUG: Message created with ID: " + message.getMessageId());

            MessageSendParams params = new MessageSendParams.Builder()
                    .message(message)
                    .build();

            System.out.println("DEBUG: MessageSendParams created.");
            System.out.println(OBJECT_MAPPER.writeValueAsString(params));

            System.out.println("DEBUG: Sending message to server...");
            SendMessageResponse response = client.sendMessage(params);

            System.out.println("DEBUG: Message sent successfully!");
            System.out.println("Message sent with ID: " + response.getId());
            System.out.println("Response: " + response.toString());

        } catch (Exception e) {
            System.err.println("DEBUG: An error occurred in main: " + e.getClass().getSimpleName());
            System.err.println("DEBUG: Error message: " + e.getMessage());
            System.err.println("DEBUG: Full stack trace:");
            e.printStackTrace();

            if (e.getMessage() != null && e.getMessage().contains("JSON")) {
                System.err.println("DEBUG: This appears to be a JSON parsing error.");
                System.err.println("DEBUG: Check if the server is running and returning valid JSON responses.");
                System.err.println("DEBUG: Server URL: " + SERVER_URL);
            }
        }
    }
}

3. When I run the above code I am getting the Json decode error .

Relevant Python Helloworld agent log output

DEBUG: HelloWorldAgentExecutor.__init__() called
DEBUG: HelloWorldAgentExecutor initialized with HelloWorldAgent
INFO:     Started server process [6668]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:9999 (Press CTRL+C to quit)
WARNING:  Unsupported upgrade request.
INFO:     127.0.0.1:53512 - "GET /.well-known/agent.json HTTP/1.1" 200 OK
WARNING:  Unsupported upgrade request.
INFO:     127.0.0.1:53513 - "GET /agent/authenticatedExtendedCard HTTP/1.1" 200 OK
WARNING:  Unsupported upgrade request.
Traceback (most recent call last):
  File "C:\Users\lapto\Music\AI\A2A\venv\Lib\site-packages\a2a\server\apps\jsonrpc\jsonrpc_app.py", line 204, in _handle_requests
    body = await request.json()
           ^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\lapto\Music\AI\A2A\venv\Lib\site-packages\starlette\requests.py", line 249, in json
    self._json = json.loads(body)
                 ^^^^^^^^^^^^^^^^
  File "C:\Users\lapto\AppData\Local\Programs\Python\Python312\Lib\json\__init__.py", line 346, in loads
    return _default_decoder.decode(s)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\lapto\AppData\Local\Programs\Python\Python312\Lib\json\decoder.py", line 338, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\lapto\AppData\Local\Programs\Python\Python312\Lib\json\decoder.py", line 356, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)
Request Error (ID: None): Code=-32700, Message='Expecting value: line 1 column 1 (char 0)'
INFO:     127.0.0.1:53514 - "POST / HTTP/1.1" 200 OK
WARNING:  Invalid HTTP request received.

Relevant Java A2A Client Log output

Caused by: io.a2a.spec.JSONParseError: Expecting value: line 1 column 1 (char 0)

Code of Conduct

• I agree to follow this project's Code of Conduct

[SR-Waivgen]

Hey @kabir / @fjuma , Is it possible to help me on this one pls ? I am waiting on this one to build a A2AClient in Java

[kabir]

For me it works fine.

I grabbed the latest a2a-samples, and went to the samples/python/agents/helloworld. I then installed everything:

[~/sourcecontrol/AI/a2aproject/a2a-samples/samples/python/agents/helloworld] 
% uv venv
Using CPython 3.13.3
Creating virtual environment at: .venv
Activate with: source .venv/bin/activate
(a2a-samples) 
[~/sourcecontrol/AI/a2aproject/a2a-samples/samples/python/agents/helloworld] 
% source .venv/bin/activate
(helloworld) 
[~/sourcecontrol/AI/a2aproject/a2a-samples/samples/python/agents/helloworld] 
% uv pip install -e .        
Resolved 55 packages in 284ms
      Built helloworld @ file:///Users/kabir/sourcecontrol/AI/a2aproject/a2a-samples/samples/python/agents/helloworld
Prepared 15 packages in 271ms
Installed 55 packages in 88ms
 + a2a-sdk==0.3.0
 + annotated-types==0.7.0
 .....

Then in the a2a-java project, first I ran io.a2a.examples.helloworld.HelloWorldClient in my IDE, and it worked fine.

Next I coped your class into that package and ran it in my IDE, and it seems to work:

Successfully fetched public agent card:
{"name":"Hello World Agent","description":"Just a hello world agent","url":"http://localhost:9999/","version":"1.0.0","capabilities":{"streaming":true,"pushNotifications":false,"stateTransitionHistory":false},"defaultInputModes":["text"],"defaultOutputModes":["text"],"skills":[{"id":"hello_world","name":"Returns hello world","description":"just returns hello world","tags":["hello world"],"examples":["hi","hello world"]}],"supportsAuthenticatedExtendedCard":true,"preferredTransport":"JSONRPC","protocolVersion":"0.3.0"}
Using public agent card for client initialization (default).
Public card supports authenticated extended card. Attempting to fetch from: http://localhost:9999/agent/authenticatedExtendedCard
Successfully fetched authenticated extended agent card:
{"name":"Hello World Agent - Extended Edition","description":"The full-featured hello world agent for authenticated users.","url":"http://localhost:9999/","version":"1.0.1","capabilities":{"streaming":true,"pushNotifications":false,"stateTransitionHistory":false},"defaultInputModes":["text"],"defaultOutputModes":["text"],"skills":[{"id":"hello_world","name":"Returns hello world","description":"just returns hello world","tags":["hello world"],"examples":["hi","hello world"]},{"id":"super_hello_world","name":"Returns a SUPER Hello World","description":"A more enthusiastic greeting, only for authenticated users.","tags":["hello world","super","extended"],"examples":["super hi","give me a super hello"]}],"supportsAuthenticatedExtendedCard":true,"preferredTransport":"JSONRPC","protocolVersion":"0.3.0"}
Using AUTHENTICATED EXTENDED agent card for client initialization.
Message sent with ID: 2eb3176e-344d-4713-9c96-4e9de7f8431a
Response: io.a2a.spec.SendMessageResponse@65987993

Process finished with exit code 0

On the server side, I see the following output (for both the above runs):

[~/sourcecontrol/AI/a2aproject/a2a-samples/samples/python/agents/helloworld] 
% uv run .
Uninstalled 7 packages in 16ms
Installed 12 packages in 11ms
/Users/kabir/sourcecontrol/AI/a2aproject/a2a-samples/samples/python/agents/helloworld/.venv/lib/python3.13/site-packages/google/protobuf/runtime_version.py:98: UserWarning: Protobuf gencode version 5.29.3 is exactly one major version older than the runtime version 6.31.1 at a2a.proto. Please update the gencode to avoid compatibility violations in the next runtime release.
  warnings.warn(
INFO:     Started server process [13146]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:9999 (Press CTRL+C to quit)
WARNING:  Unsupported upgrade request.
WARNING:  No supported WebSocket library detected. Please use "pip install 'uvicorn[standard]'", or install 'websockets' or 'wsproto' manually.
Deprecated agent card endpoint '/.well-known/agent.json' accessed. Please use '/.well-known/agent-card.json' instead. This endpoint will be removed in a future version.
INFO:     127.0.0.1:62459 - "GET /.well-known/agent.json HTTP/1.1" 200 OK
WARNING:  Unsupported upgrade request.
WARNING:  No supported WebSocket library detected. Please use "pip install 'uvicorn[standard]'", or install 'websockets' or 'wsproto' manually.
HTTP GET for authenticated extended card has been called by a client. This endpoint is deprecated in favor of agent/authenticatedExtendedCard JSON-RPC method and will be removed in a future release.
INFO:     127.0.0.1:62460 - "GET /agent/authenticatedExtendedCard HTTP/1.1" 200 OK
WARNING:  Unsupported upgrade request.
WARNING:  No supported WebSocket library detected. Please use "pip install 'uvicorn[standard]'", or install 'websockets' or 'wsproto' manually.
INFO:     127.0.0.1:62461 - "POST / HTTP/1.1" 200 OK
WARNING:  Unsupported upgrade request.
WARNING:  No supported WebSocket library detected. Please use "pip install 'uvicorn[standard]'", or install 'websockets' or 'wsproto' manually.
Deprecated agent card endpoint '/.well-known/agent.json' accessed. Please use '/.well-known/agent-card.json' instead. This endpoint will be removed in a future version.
INFO:     127.0.0.1:62481 - "GET /.well-known/agent.json HTTP/1.1" 200 OK
WARNING:  Unsupported upgrade request.
WARNING:  No supported WebSocket library detected. Please use "pip install 'uvicorn[standard]'", or install 'websockets' or 'wsproto' manually.
HTTP GET for authenticated extended card has been called by a client. This endpoint is deprecated in favor of agent/authenticatedExtendedCard JSON-RPC method and will be removed in a future release.
INFO:     127.0.0.1:62482 - "GET /agent/authenticatedExtendedCard HTTP/1.1" 200 OK
WARNING:  Unsupported upgrade request.
WARNING:  No supported WebSocket library detected. Please use "pip install 'uvicorn[standard]'", or install 'websockets' or 'wsproto' manually.
INFO:     127.0.0.1:62483 - "POST / HTTP/1.1" 200 OK
WARNING:  Unsupported upgrade request.
WARNING:  No supported WebSocket library detected. Please use "pip install 'uvicorn[standard]'", or install 'websockets' or 'wsproto' manually.
Deprecated agent card endpoint '/.well-known/agent.json' accessed. Please use '/.well-known/agent-card.json' instead. This endpoint will be removed in a future version.
INFO:     127.0.0.1:62513 - "GET /.well-known/agent.json HTTP/1.1" 200 OK
WARNING:  Unsupported upgrade request.
WARNING:  No supported WebSocket library detected. Please use "pip install 'uvicorn[standard]'", or install 'websockets' or 'wsproto' manually.
HTTP GET for authenticated extended card has been called by a client. This endpoint is deprecated in favor of agent/authenticatedExtendedCard JSON-RPC method and will be removed in a future release.
INFO:     127.0.0.1:62514 - "GET /agent/authenticatedExtendedCard HTTP/1.1" 200 OK
WARNING:  Unsupported upgrade request.
WARNING:  No supported WebSocket library detected. Please use "pip install 'uvicorn[standard]'", or install 'websockets' or 'wsproto' manually.
INFO:     127.0.0.1:62515 - "POST / HTTP/1.1" 200 OK
^CINFO:     Shutting down
INFO:     Waiting for application shutdown.
INFO:     Application shutdown complete.
INFO:     Finished server process [13146]
(helloworld) 

Maybe make sure you are using the latest version of a2a-samples, and a2a-java?

I see a commit in a2a-samples from Friday updating it to 0.3.0 of the spec. a2a-java is currently on 0.2.5, but we have a PR coming soon to update it to 0.3.0. Things have been moving fast, so it could be that the version of the specs in your versions of the two projects are out of sync perhaps.

Anyway, AIUI from 0.3.0 onwards there will be less breaking changes

[SR-Waivgen]

Hello @kabir

Thanks for answering.

Understood.But I am facing the issue still, I modified the helloworld code and implemented the simple agent using crewai using A2A.

For that agent I am facing the above issue that I mentioned.

Similar to helloworld agent I implemented the below :

main.py

import uvicorn
from a2a.server.apps import A2AStarletteApplication
from a2a.server.request_handlers import DefaultRequestHandler
from a2a.server.tasks import InMemoryTaskStore
from a2a.types import (
    AgentCapabilities,
    AgentCard,
    AgentSkill,
)
from  agent_executor import (
    PizzaOrderAgentExecutor
)
if __name__ == '__main__':
    # --8<-- [start:AgentSkill]
    skill = AgentSkill(
        id='pizza_order',
        name='Returns Pizza Order',
        description='just returns pizza order',
        tags=['pizza', 'order'],
        examples=['I want to order a pizza', 'Pizza order'],
    )
    # --8<-- [end:AgentSkill]
    extended_skill = AgentSkill(
        id='super_pizza_order',
        name='Returns a SUPER Pizza Order',
        description='A more enthusiastic pizza order, only for authenticated users.',
        tags=['pizza', 'super', 'extended'],
        examples=['super I want to order a pizza', 'give me a customer that ordered pepperoni pizza'],
    )
    # --8<-- [start:AgentCard]
    # This will be the public-facing agent card
    public_agent_card = AgentCard(
        name='Pizza Order Agent',
        description='Just a pizza ordering agent',
        url='http://localhost:10003/',
        version='1.0.0',
        default_input_modes=['text'],
        default_output_modes=['text'],
        capabilities=AgentCapabilities(streaming=True),
        skills=[skill],  # Only the basic skill for the public card
        supports_authenticated_extended_card=True,
    )
    # --8<-- [end:AgentCard]

    # This will be the authenticated extended agent card
    # It includes the additional 'extended_skill'
    specific_extended_agent_card = public_agent_card.model_copy(
        update={
            'name': 'Pizza Order Agent - Extended Edition',  # Different name for clarity
            'description': 'The full-featured pizza order agent for authenticated users.',
            'version': '1.0.1',  # Could even be a different version
            # Capabilities and other fields like url, default_input_modes, default_output_modes,
            # supports_authenticated_extended_card are inherited from public_agent_card unless specified here.
            'skills': [
                skill,
                extended_skill,
            ],  # Both skills for the extended card
        }
    )

    request_handler = DefaultRequestHandler(
        agent_executor=PizzaOrderAgentExecutor(),
        task_store=InMemoryTaskStore(),
    )

    server = A2AStarletteApplication(
        agent_card=public_agent_card,
        http_handler=request_handler,
        extended_agent_card=specific_extended_agent_card,
    )

    uvicorn.run(server.build(), host='0.0.0.0', port=10003)

agent_executor.py

import asyncio
from a2a.server.agent_execution import AgentExecutor, RequestContext
from a2a.server.events import EventQueue
from a2a.utils import new_agent_text_message
from crewai import Agent, Crew,Task


PIZZA_ORDERS = [
    {"id": 1, "pizza": "Margherita", "amount": 12.50, "customer": "John Doe"},
    {"id": 2, "pizza": "Pepperoni", "amount": 15.75, "customer": "Jane Smith"},
    {"id": 3, "pizza": "Vegetarian Supreme", "amount": 18.25, "customer": "Mike Johnson"},
    {"id": 4, "pizza": "Hawaiian", "amount": 16.00, "customer": "Sarah Wilson"},
    {"id": 5, "pizza": "Meat Lovers", "amount": 19.99, "customer": "David Brown"},
    {"id": 6, "pizza": "BBQ Chicken", "amount": 17.50, "customer": "Lisa Davis"},
    {"id": 7, "pizza": "Four Cheese", "amount": 14.25, "customer": "Tom Wilson"},
    {"id": 8, "pizza": "Supreme", "amount": 20.00, "customer": "Anna Johnson"}
]

# --8<-- [start:PizzaOrderAgent]
class PizzaOrderAgent:

    def __init__(self):
        self.pizza_agent=Agent(
            role='Pizza Order Assistant',
            goal='Find and analyze pizza orders based on user queries about amounts, pizza types, or customers',
            backstory="""You are a helpful pizza order assistant that can search through 
            pizza orders and find orders that match user criteria. You can search by amount 
            (within $2.00 range), pizza type, customer name, or provide general order information.
            Always format your responses clearly and include relevant order details.""",
            verbose=True,
            allow_delegation=False
        )
    """Pizza Order Agent."""
    def _create_pizza_search_task(self, query: str):
        """
        Create a simple CrewAI task for searching pizza orders.
        
        Args:
            query (str): User's search query
            
        Returns:
            Task: CrewAI task configured for pizza order search
        """
        
        task_description = f"""
        Search through the pizza orders based on the user's query: "{query}"
        
        Available pizza orders:
        {PIZZA_ORDERS}
        
        Help the user find relevant pizza orders and provide a clear response.
        Format your response with order details including ID, Pizza name, Amount, and Customer.
        """
        
        # Create and return the CrewAI task
        task = Task(
            description=task_description,
            agent=self.pizza_agent,  # Will be set by CrewAI when crew is created
            expected_output="A clear response with relevant pizza order information"
        )
        
        return task
    async def invoke(self, query: str) -> str:
        """
        📥 Handle a user query using CrewAI and return a response string.

        Args:
            query (str): What the user said (e.g., "find orders around $15")
            session_id (str): Helps group messages into a session

        Returns:
            str: Agent's reply with pizza order search results from CrewAI
        """
   
        
        try:
         
            # 🎯 Create a CrewAI task for the user query
            task = self._create_pizza_search_task(query)
            
            # 🚢 Create a CrewAI crew with our agent and task
            crew = Crew(
                agents=[self.pizza_agent],
                tasks=[task],
                verbose=True
            )
            
            # 🚀 Execute the crew and get results
            # Note: CrewAI's kickoff() is synchronous, so we run it in an executor
            loop = asyncio.get_event_loop()
            result = await loop.run_in_executor(None, crew.kickoff)
            
            # 📤 Return the CrewAI result
            response = str(result)
                   
            
            return response
            
        except Exception as e:
            # 🚫 Error handling
            error_msg = f"🚫 Sorry, I encountered an error while processing your pizza order search: {str(e)}"
            print(f"DEBUG: Error in PizzaOrderAgent.invoke(): {error_msg}")
            return error_msg




# --8<-- [start:PizzaOrderAgentExecutor_init]
class PizzaOrderAgentExecutor(AgentExecutor):
    """Test AgentProxy Implementation."""

    def __init__(self):
        print("DEBUG: PizzaOrderAgentExecutor.__init__() called")
        self.agent = PizzaOrderAgent()
        print("DEBUG: PizzaOrderAgentExecutor initialized with PizzaOrderAgent")

    # --8<-- [end:PizzaOrderAgentExecutor_init]
    # --8<-- [start:PizzaOrderAgentExecutor_execute]
    async def execute(
        self,
        context: RequestContext,
        event_queue: EventQueue,
    ) -> None:
        print("DEBUG: PizzaOrderAgentExecutor.execute() called")
        print(f"DEBUG: Request context: {context}")
        print(f"DEBUG: Event queue: {event_queue}")
        
        try:
            print("DEBUG: Calling agent.invoke()...")
            # result = await self.agent.invoke(context.get_user_input())
            result="Hello this is pizza order agent"
            print(f"DEBUG: Agent returned result: '{result}'")
            
            print("DEBUG: Creating agent text message...")
            message = new_agent_text_message(result)
            print(f"DEBUG: Created message: {message}")
            
            print("DEBUG: Enqueueing event...")
            await event_queue.enqueue_event(message)
            print("DEBUG: Event enqueued successfully")
            
        except Exception as e:
            print(f"DEBUG: Error in execute(): {e}")
            print(f"DEBUG: Error type: {type(e)}")
            raise

    # --8<-- [end:HelloWorldAgentExecutor_execute]

    # --8<-- [start:HelloWorldAgentExecutor_cancel]
    async def cancel(
        self, context: RequestContext, event_queue: EventQueue
    ) -> None:
        print("DEBUG: HelloWorldAgentExecutor.cancel() called")
        print("DEBUG: Cancel not supported - raising exception")
        raise Exception('cancel not supported')

    # --8<-- [end:HelloWorldAgentExecutor_cancel]

.env

OPENAI_API_KEY=<OPENAI_API_KEY>

requirements.txt

a2a-sdk==0.3.0
aiohappyeyeballs==2.6.1
aiohttp==3.12.15
aiosignal==1.4.0
annotated-types==0.7.0
anyio==4.10.0
appdirs==1.4.4
asttokens==3.0.0
attrs==25.3.0
backoff==2.2.1
bcrypt==4.3.0
blinker==1.9.0
build==1.3.0
cachetools==5.5.2
certifi==2025.8.3
cffi==1.17.1
charset-normalizer==3.4.2
chromadb==1.0.15
click==8.2.1
colorama==0.4.6
coloredlogs==15.0.1
crewai==0.152.0
cryptography==45.0.5
decorator==5.2.1
diskcache==5.6.3
distro==1.9.0
docstring_parser==0.17.0
durationpy==0.10
et_xmlfile==2.0.0
executing==2.2.0
fastapi==0.116.1
filelock==3.18.0
flatbuffers==25.2.10
frozenlist==1.7.0
fsspec==2025.7.0
google-api-core==2.25.1
google-auth==2.40.3
googleapis-common-protos==1.70.0
grpcio==1.74.0
h11==0.16.0
httpcore==1.0.9
httptools==0.6.4
httpx==0.28.1
httpx-sse==0.4.1
huggingface-hub==0.34.3
humanfriendly==10.0
idna==3.10
importlib_metadata==8.7.0
importlib_resources==6.5.2
instructor==1.10.0
ipython==9.4.0
ipython_pygments_lexers==1.1.1
jedi==0.19.2
Jinja2==3.1.6
jiter==0.10.0
json5==0.12.0
json_repair==0.25.2
jsonpickle==4.1.1
jsonref==1.1.0
jsonschema==4.25.0
jsonschema-specifications==2025.4.1
kubernetes==33.1.0
litellm==1.74.3
markdown-it-py==3.0.0
MarkupSafe==3.0.2
matplotlib-inline==0.1.7
mdurl==0.1.2
mmh3==5.2.0
mpmath==1.3.0
multidict==6.6.3
networkx==3.5
numpy==2.3.2
oauthlib==3.3.1
onnxruntime==1.22.0
openai==1.98.0
openpyxl==3.1.5
opentelemetry-api==1.36.0
opentelemetry-exporter-otlp-proto-common==1.36.0
opentelemetry-exporter-otlp-proto-grpc==1.36.0
opentelemetry-exporter-otlp-proto-http==1.36.0
opentelemetry-proto==1.36.0
opentelemetry-sdk==1.36.0
opentelemetry-semantic-conventions==0.57b0
orjson==3.11.1
overrides==7.7.0
packaging==25.0
parso==0.8.4
pdfminer.six==20250506
pdfplumber==0.11.7
pillow==11.3.0
portalocker==2.7.0
posthog==5.4.0
prompt_toolkit==3.0.51
propcache==0.3.2
proto-plus==1.26.1
protobuf==5.29.5
pure_eval==0.2.3
pyasn1==0.6.1
pyasn1_modules==0.4.2
pybase64==1.4.2
pycparser==2.22
pydantic==2.11.7
pydantic_core==2.33.2
Pygments==2.19.2
PyJWT==2.10.1
pypdfium2==4.30.0
PyPika==0.48.9
pyproject_hooks==1.2.0
pyreadline3==3.5.4
python-dateutil==2.9.0.post0
python-dotenv==1.1.1
pyvis==0.3.2
pywin32==311
PyYAML==6.0.2
referencing==0.36.2
regex==2025.7.34
requests==2.32.4
requests-oauthlib==2.0.0
rich==14.1.0
rpds-py==0.26.0
rsa==4.9.1
shellingham==1.5.4
six==1.17.0
sniffio==1.3.1
sse-starlette==3.0.2
stack-data==0.6.3
starlette==0.47.2
sympy==1.14.0
tenacity==9.1.2
tiktoken==0.9.0
tokenizers==0.21.4
tomli==2.2.1
tomli_w==1.2.0
tqdm==4.67.1
traitlets==5.14.3
typer==0.16.0
typing-inspection==0.4.1
typing_extensions==4.14.1
urllib3==2.5.0
uv==0.8.4
uvicorn==0.35.0
watchfiles==1.1.0
wcwidth==0.2.13
websocket-client==1.8.0
websockets==15.0.1
yarl==1.20.1
zipp==3.23.0

[kabir]

What does the JSON look like when it fails? And from just reading the above, I am not 100% clear on which call is failing

[SR-Waivgen]

Hey @kabir

I have given the client code that I ran and error log below. In the error log itself you can see the JSON of params then got stopped before sending message itself.

Is it a bug in sending JSON RPC request to the agent ? Because in the error log it's showing JSON Decode error

A2A Latest Java client code

package io.a2a.examples.helloworld;

import java.util.HashMap;
import java.util.Map;

import com.fasterxml.jackson.databind.ObjectMapper;
import io.a2a.client.A2AClient;
import io.a2a.A2A;
import io.a2a.spec.AgentCard;
import io.a2a.spec.Message;
import io.a2a.spec.MessageSendParams;
import io.a2a.spec.SendMessageResponse;

/**
 * A simple example of using the A2A Java SDK to communicate with an A2A server.
 * This example is equivalent to the Python example provided in the A2A Python SDK.
 */
public class HelloWorldClient {

    private static final String SERVER_URL = "http://localhost:10003";
    private static final String MESSAGE_TEXT = "how much is 10 USD in INR?";
    private static final ObjectMapper OBJECT_MAPPER = new ObjectMapper();

    public static void main(String[] args) {
        try {
            AgentCard finalAgentCard = null;
            AgentCard publicAgentCard = A2A.getAgentCard(SERVER_URL);
            System.out.println("Successfully fetched public agent card:");
            System.out.println(OBJECT_MAPPER.writeValueAsString(publicAgentCard));
            System.out.println("Using public agent card for client initialization (default).");
            finalAgentCard = publicAgentCard;

            if (publicAgentCard.supportsAuthenticatedExtendedCard()) {
                System.out.println("Public card supports authenticated extended card. Attempting to fetch from: " + SERVER_URL + "/agent/authenticatedExtendedCard");
                Map<String, String> authHeaders = new HashMap<>();
                authHeaders.put("Authorization", "Bearer dummy-token-for-extended-card");
                AgentCard extendedAgentCard = A2A.getAgentCard(SERVER_URL, "/agent/authenticatedExtendedCard", authHeaders);
                System.out.println("Successfully fetched authenticated extended agent card:");
                System.out.println(OBJECT_MAPPER.writeValueAsString(extendedAgentCard));
                System.out.println("Using AUTHENTICATED EXTENDED agent card for client initialization.");
                finalAgentCard = extendedAgentCard;
            } else {
                System.out.println("Public card does not indicate support for an extended card. Using public card.");
            }

            A2AClient client = new A2AClient(finalAgentCard);
            Message message = A2A.toUserMessage(MESSAGE_TEXT); // the message ID will be automatically generated for you
            MessageSendParams params = new MessageSendParams.Builder()
                .message(message)
                .build();
            System.out.println("PARAMS"+ OBJECT_MAPPER.writeValueAsString(params));
            SendMessageResponse response = client.sendMessage(params);
            System.out.println("RESPONSE"+ OBJECT_MAPPER.writeValueAsString(response));
            System.out.println("Message sent with ID: " + response.getId());
            System.out.println("Response: " + response.getResult());
        } catch (Exception e) {
            System.err.println("An error occurred: " + e.getMessage());
            e.printStackTrace();
        }
    }

} 

Error log in A2A Java Client

Successfully fetched public agent card:
{"name":"Pizza Order Agent","description":"Just a pizza ordering agent","url":"http://localhost:10003/","version":"1.0.0","capabilities":{"streaming":true,"pushNotifications":false,"stateTransitionHistory":false},"defaultInputModes":["text"],"defaultOutputModes":["text"],"skills":[{"id":"pizza_order","name":"Returns Pizza Order","description":"just returns pizza order","tags":["pizza","order"],"examples":["I want to order a pizza","Pizza order"]}],"supportsAuthenticatedExtendedCard":true,"preferredTransport":"JSONRPC","protocolVersion":"0.3.0"}
Using public agent card for client initialization (default).
Public card supports authenticated extended card. Attempting to fetch from: http://localhost:10003/agent/authenticatedExtendedCard
Successfully fetched authenticated extended agent card:
{"name":"Pizza Order Agent - Extended Edition","description":"The full-featured pizza order agent for authenticated users.","url":"http://localhost:10003/","version":"1.0.1","capabilities":{"streaming":true,"pushNotifications":false,"stateTransitionHistory":false},"defaultInputModes":["text"],"defaultOutputModes":["text"],"skills":[{"id":"pizza_order","name":"Returns Pizza Order","description":"just returns pizza order","tags":["pizza","order"],"examples":["I want to order a pizza","Pizza order"]},{"id":"super_pizza_order","name":"Returns a SUPER Pizza Order","description":"A more enthusiastic pizza order, only for authenticated users.","tags":["pizza","super","extended"],"examples":["super I want to order a pizza","give me a customer that ordered pepperoni pizza"]}],"supportsAuthenticatedExtendedCard":true,"preferredTransport":"JSONRPC","protocolVersion":"0.3.0"}
Using AUTHENTICATED EXTENDED agent card for client initialization.
PARAMS{"message":{"kind":"message","role":"user","parts":[{"kind":"text","text":"how much is 10 USD in INR?","kind":"text"}],"messageId":"c898934f-51f0-4a83-bbc2-132352a93f69","kind":"message"}}
An error occurred: Failed to send message: io.a2a.spec.A2AServerException: Expecting value: line 1 column 1 (char 0)
io.a2a.spec.A2AServerException: Failed to send message: io.a2a.spec.A2AServerException: Expecting value: line 1 column 1 (char 0)
	at io.a2a.client.A2AClient.sendMessage(A2AClient.java:176)
	at io.a2a.client.A2AClient.sendMessage(A2AClient.java:149)
	at io.a2a.examples.helloworld.HelloWorldClient.main(HelloWorldClient.java:52)
Caused by: io.a2a.spec.JSONParseError: Expecting value: line 1 column 1 (char 0)
	at io.a2a.spec.JSONRPCErrorDeserializer.deserialize(JSONRPCErrorDeserializer.java:49)
	at io.a2a.spec.JSONRPCErrorDeserializer.deserialize(JSONRPCErrorDeserializer.java:13)
	at com.fasterxml.jackson.databind.deser.SettableBeanProperty.deserialize(SettableBeanProperty.java:545)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeWithErrorWrapping(BeanDeserializer.java:570)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer._deserializeUsingPropertyBased(BeanDeserializer.java:440)
	at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.deserializeFromObjectUsingNonDefault(BeanDeserializerBase.java:1493)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserializeFromObject(BeanDeserializer.java:348)
	at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:185)
	at com.fasterxml.jackson.databind.deser.DefaultDeserializationContext.readRootValue(DefaultDeserializationContext.java:342)
	at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4905)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3848)
	at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3831)
	at io.a2a.util.Utils.unmarshalFrom(Utils.java:17)
	at io.a2a.client.A2AClient.unmarshalResponse(A2AClient.java:654)
	at io.a2a.client.A2AClient.sendMessage(A2AClient.java:174)
	... 2 more

Process finished with exit code 0

Error log in Python pizza agent

EBUG: PizzaOrderAgentExecutor.__init__() called
DEBUG: PizzaOrderAgentExecutor initialized with PizzaOrderAgent
INFO:     Started server process [4724]
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:10003 (Press CTRL+C to quit)
WARNING:  Unsupported upgrade request.
Deprecated agent card endpoint '/.well-known/agent.json' accessed. Please use '/.well-known/agent-card.json' instead. This endpoint will be removed in a future version.
INFO:     127.0.0.1:51110 - "GET /.well-known/agent.json HTTP/1.1" 200 OK
WARNING:  Unsupported upgrade request.
HTTP GET for authenticated extended card has been called by a client. This endpoint is deprecated in favor of agent/authenticatedExtendedCard JSON-RPC method and will be removed in a future release.
INFO:     127.0.0.1:51111 - "GET /agent/authenticatedExtendedCard HTTP/1.1" 200 OK
WARNING:  Unsupported upgrade request.
Traceback (most recent call last):
  File "C:\Users\lapto\OneDrive - Waivgen\Desktop\PizzaOrderingAgent\.venv\Lib\site-packages\a2a\server\apps\jsonrpc\jsonrpc_app.py", line 233, in _handle_requests
    body = await request.json()
           ^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\lapto\OneDrive - Waivgen\Desktop\PizzaOrderingAgent\.venv\Lib\site-packages\starlette\requests.py", line 250, in json        
    self._json = json.loads(body)
                 ^^^^^^^^^^^^^^^^
  File "C:\Users\lapto\AppData\Local\Programs\Python\Python312\Lib\json\__init__.py", line 346, in loads
    return _default_decoder.decode(s)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\lapto\AppData\Local\Programs\Python\Python312\Lib\json\decoder.py", line 338, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\lapto\AppData\Local\Programs\Python\Python312\Lib\json\decoder.py", line 356, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)
Request Error (ID: None): Code=-32700, Message='Expecting value: line 1 column 1 (char 0)'
INFO:     127.0.0.1:51112 - "POST / HTTP/1.1" 200 OK
WARNING:  Invalid HTTP request received.

[SR-Waivgen]

@kabir , Hello Kabir, Is there any update on above mentioned bug ?

[kabir]

@SR-Waivgen Hi I am just back from 2.5 weeks vacation. So there is a lot to catch up on! Will try to get to this later this week. If you don't hear anything, please don't hesitate to remind me again :-)

If you are able to push a repo with an example showing the problem, that will make it easier for me to run it

[SR-Waivgen]

@kabir sure kabir, I have already attached the code in above comment itself with respect to the file so it will be easier for you to copy and paste it .

Python Pizza A2A Agent

A2A agent

Java client code

Agent code

If this comment also not helpful , kindly ping here back

[kabir]

@SR-Waivgen A lot of things have changed since I went away. I've not had time to look at this issue yet since I am still catching up on everything.

But we have just merged #238 which is a big change to the clients, on top of some other big changes which happened while I was away.

So I think it could be good for you to try that with a built version of the a2a-java main branch (we will do 0.3.0 soon), and 0.3.0 of a2a-python, which has been released. That way we're not chasing errors in something old, which we won't fix.

If you still see the problem, then ideally please provide a GitHub repository with folders for:

• java - a pom and your classes so I can just build it and run in my IDE. This should reference 0.3.0.Beta1-SNAPSHOT which is a locally built version of a2a-java. Maybe make a note of the current SHA of the main branch you used too
• python - with your code and idiot-proof instructions for how to build/run it (I'm not super-well versed in Python)

Hopefully the above makes sense.