[fhgffy]

Motivation & Context

Sending or returning a zero-byte attachment through A2A raises ValueError. Content.from_data() accepts empty bytes, but the A2A URI parser rejects the resulting empty base64 payload.

Description & Review Guide

• What are the major changes? Allow zero payload characters in the existing A2A URI pattern. Add empty-payload cases and exercise A2AAgent.run() in both streaming modes; extend the executor test to check empty and nonempty binary parts.
• What is the impact of these changes? Empty attachments reach the A2A transport as raw binary parts. Existing media-type, parameter, encoding and character checks still apply.
• What do you want reviewers to focus on? Whether empty binary content survives conversion in both directions without relaxing the other URI checks.

Related Issue

Fixes #9054

Automated triage reproduced the issue; maintainer agreement to implement it has not been recorded.

AI Assistance

• No material AI assistance was used.
• This is an AI-assisted contribution. I reviewed, understood, and verified all submitted content and accept responsibility for it.

AI assistance details: AI assisted the issue analysis, implementation, regression tests, and PR description. The reported checks were run against the checkout.

Contribution Checklist

• The code builds clean without any errors or warnings (source distribution and wheel built).
• All unit tests pass, and I have added new tests where possible (195 A2A unit tests passed, 96% package coverage; five added empty-payload cases fail on the unchanged source. Broader workspace and live-agent tests were not run. Existing compatibility tests emit 14 deprecation warnings).
• The PR follows the Contribution Guidelines (Native pre-commit hooks, Ruff checks and formatting, source Pyright and all five package test-type checkers passed).
• This PR links to an agreed issue with no competing open PR, or the Related Issue section documents a trivial-change or repository-automation exception.
• This is not a breaking change. Public signatures and nonempty attachment handling are unchanged.

[Copilot]

Copilot review overview

🟢 Approval recommended

The narrowly scoped parser change preserves existing validation and has targeted regression coverage for both affected conversion paths.

Review effort: Balanced
Findings: None

What changed in this PR

Fixes #9054 by allowing zero-byte attachments through Python’s A2A integration without changing other URI validation rules.

Changes:

• Allow empty base64 payloads in the URI parser.
• Add regression coverage for parsing, both client streaming modes, and executor binary output.

File	Description
python/​packages/​a2a/​tests/​test_utils.py	Tests empty payloads with and without media-type parameters.
python/​packages/​a2a/​tests/​test_a2a_executor.py	Checks empty and nonempty raw binary output.
python/​packages/​a2a/​tests/​test_a2a_agent.py	Tests empty attachments in both streaming modes.
python/​packages/​a2a/​agent_framework_a2a/​_utils.py	Allows zero payload characters in data URIs.

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