Python: Fix replacing binary content data URIs

[Captain (po-et)]

Motivation and Context

Replacing ImageContent.data_uri after the object already contains data can raise a base64 error or store the entire URI as the payload. The MIME type also stays at its previous value. This affects applications that update an existing image before sending it to a multimodal model.

image = ImageContent(data=b"old_image", mime_type="image/jpeg", data_format="base64")
image.data_uri = "data:image/png;base64,bmV3X2ltYWdl"
# Expected: image.data == b"new_image", image.mime_type == "image/png"

Description

Always parse a replacement URI with DataUri.from_data_uri, as initialization and the first assignment already do. This replaces the payload, format and MIME type together. Parsing completes before assignment, so an invalid replacement leaves the previous content intact. The separate data setter and the data URI parser are unchanged.

Eight regressions cover replacing base64, bytes and ndarray-backed content with base64 or plain-text URIs, invalid replacement, and the ImageContent.to_dict() request payload. All eight fail on the base revision and pass with this fix.

Validation

• All contents unit tests: 402 passed.
• Repository-configured pre-commit checks for the three changed files: all applicable hooks passed.
• Independent Codex code review and rerun of the eight replacement regressions passed.
• git diff --check passed.

Validated on Python 3.12.14 / macOS arm64. The complete optional-provider test suite and live model calls were not run.

Contribution Checklist

• The change follows the contribution guidelines and configured formatting checks.
• Added regression tests and ran the affected contents unit suite.
• No public API signature changes.

AI disclosure: OpenAI Codex assisted with investigation, implementation, tests and independent review.

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[Copilot]

🟢 Approval recommended

The focused fix reuses established parsing behavior, includes targeted regression coverage, and has no identified blocking issues.

0 open findings

What changed in this PR

Fixes replacement of existing Python binary content through data_uri, keeping the payload, format, and MIME type consistent.

Changes:

• Uses the existing URI parser for every assignment.
• Adds eight regression cases covering replacements, invalid-input preservation, and image request serialization.

File	Description
python/​tests/​unit/​contents/​test_image_content.py	Verifies image replacement and request serialization.
python/​tests/​unit/​contents/​test_binary_content.py	Covers replacement formats and invalid-input preservation.
python/​semantic_kernel/​contents/​binary_content.py	Parses replacement URIs before assigning content.

🧠 Review effort: Balanced

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[PRABHU KIRAN VANDRANKI (VANDRANKI)]

Community review. This does not clear the merge gate.

The fix works and I think it is correct. I found one small gap, described last.

What I ran (upstream/main at 7a92cd4, a separate worktree, venv at C:/skv2, PR diff applied with git apply):

• python/tests/unit/contents on main with the PR's tests: 8 failed, 394 passed. With the binary_content.py change: 402 passed. The failing tests on main include test_replace_image_data_uri and test_replace_data_uri_invalid_preserves_existing_data.
• A probe of my own on main: ImageContent(data=b"old_image", ...) then image.data_uri = "data:image/png;base64,bmV3X2ltYWdl" raises binascii.Error: Only base64 data is allowed. On the PR the same code gives mime_type == "image/png", data == b"new_image", and to_dict() returns the new URI. That matches the description.
• The existing test_update_data_uri (setting data_uri on an empty BinaryContent) still passes, since that path already used DataUri.from_data_uri.

The invalid-URI test passes because from_data_uri runs before _data_uri is reassigned, so the old content stays. I read that in the diff and the test confirms it.

The gap: the setter does self.metadata.update(self._data_uri.parameters), which merges and never removes parameters from the previous URI. Probe on the PR: start from BinaryContent(data_uri="data:text/plain;foo=old;base64,b2xk"), then set data_uri = "data:image/jpeg;base64,bmV3". Result: mime_type is image/jpeg and data is b'new', but metadata is still {'foo': 'old'} and the new data_uri string is data:image/jpeg;foo=old;base64,bmV3. So a replacement URI with no parameters inherits the old URI's parameters. The PR's test_replace_data_uri always replaces foo=old with foo=new, so it does not catch this. Whether metadata given at construction (the test's {"source": "test"}) should survive is a design choice, so I would only drop the keys that came from the old URI's parameters, if the maintainers care about this case. I did not try a fix.

I did not run the full Python suite or the multimodal connectors that consume these URIs.