[Bug]: History Length = 0, is returning all the history

[anandsugumaran]

What happened?

As per the spec defined in website, historyLength=0 should not return any history. But we are getting all the history.

https://a2a-protocol.org/latest/specification/#323-stream-response

Relevant log output

curl -s -X POST "http://localhost:9000/" -H "Content-Type: application/json" -d '{
    "jsonrpc": "2.0",
    "method": "message/send",
    "params": {
        "message": {
            "messageId": "your-unique-message-id",
            "role": "user",
            "parts": [
                {"text": "What is 2+3 ?"}
            ]
        },
        "configuration": {
            "acceptedOutputModes": ["text/plain"],
			"historyLength":1
		}
    }'

{
    "id": 1,
    "jsonrpc": "2.0",
    "result": {
        "artifacts": [
            {
                "artifactId": "a67dace3-cd78-413e-badc-e0cf94507d18",
                "name": "agent_response",
                "parts": [
                    {
                        "kind": "text",
                        "text": "### Simple Math\n\n2 + 3 = **5**\n\nIf you have any questions about your finances, spending habits, budgeting, or would like to explore your account, I'm here to help!\n"
                    }
                ]
            }
        ],
        "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
        "history": [
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "your-unique-message-id",
                "parts": [
                    {
                        "kind": "text",
                        "text": "What is 2+3 ?"
                    }
                ],
                "role": "user",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            },
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "379b0031-cf8f-4354-93ea-f28a25e88f3c",
                "parts": [
                    {
                        "kind": "text",
                        "text": "###"
                    }
                ],
                "role": "agent",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            },
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "5ca7940e-36a1-4bea-bf02-3d2bdd1ca424",
                "parts": [
                    {
                        "kind": "text",
                        "text": " Simple Math\n\n2 + 3"
                    }
                ],
                "role": "agent",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            },
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "9d6739a1-95e5-4dc2-93c2-71a4f77fefc8",
                "parts": [
                    {
                        "kind": "text",
                        "text": " = **5**\n\nIf"
                    }
                ],
                "role": "agent",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            },
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "7865ceab-3c21-4f2c-bf56-7f3ed8054156",
                "parts": [
                    {
                        "kind": "text",
                        "text": " you have"
                    }
                ],
                "role": "agent",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            },
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "07e69ddb-c745-4ad7-8550-d7f6f4f2676e",
                "parts": [
                    {
                        "kind": "text",
                        "text": " any questions about your finances,"
                    }
                ],
                "role": "agent",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            },
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "e8e474b0-2c7d-4d73-a397-aa93f915c9ad",
                "parts": [
                    {
                        "kind": "text",
                        "text": " spending"
                    }
                ],
                "role": "agent",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            },
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "4ac5f332-5512-4b14-8e78-4bfaa29e2d5b",
                "parts": [
                    {
                        "kind": "text",
                        "text": " habits"
                    }
                ],
                "role": "agent",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            },
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "fcefe6a4-a50a-4b05-9dfd-8b65af250961",
                "parts": [
                    {
                        "kind": "text",
                        "text": ", bu"
                    }
                ],
                "role": "agent",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            },
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "55a6d3e0-9e10-49b9-91bb-480a56e319c4",
                "parts": [
                    {
                        "kind": "text",
                        "text": "dgeting, or woul"
                    }
                ],
                "role": "agent",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            },
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "49259de3-c2f9-4f5c-80d1-275fd3143d63",
                "parts": [
                    {
                        "kind": "text",
                        "text": "d like to explore"
                    }
                ],
                "role": "agent",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            },
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "258f271e-5833-481c-a269-3f17a54c426b",
                "parts": [
                    {
                        "kind": "text",
                        "text": " your"
                    }
                ],
                "role": "agent",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            },
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "ee6eff49-0c9b-4165-8473-a3379c3ae6ee",
                "parts": [
                    {
                        "kind": "text",
                        "text": " account, I'm here to"
                    }
                ],
                "role": "agent",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            },
            {
                "contextId": "51ee491d-28b8-4c32-9b2f-f7426b33f7ee",
                "kind": "message",
                "messageId": "83b174b4-b2ec-4e5a-ad0b-46e9b796c3c4",
                "parts": [
                    {
                        "kind": "text",
                        "text": " help!"
                    }
                ],
                "role": "agent",
                "taskId": "07f2a3b2-f498-438f-87b4-69fe60784e36"
            }
        ],
        "id": "07f2a3b2-f498-438f-87b4-6"
    }
}

Code of Conduct

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[lkawka]

Hi Anand,

You're right, the SDK should behave differently.

The root cause is that the specification was recently updated, and our current implementation has not yet integrated these changes. Specifically, there is an issue with differentiating between unset values and explicit 0 values in the current SDK version.

The latest specification addresses this by making the history_length field optional. We’re currently planning how to deal with the recent specification changes in the SDK and will then address this issue.

[anandsugumaran]

Hi @lkawka

Thanks for confirming. Will wait for this change in upcoming releases.