Python: reject non-base64 data URIs in detect_media_type_from_base64

[he-yufeng]

Problem

detect_media_type_from_base64 is part of the public API and its docstring documents that it raises ValueError on bad input. When given a data URI that has no ;base64, segment, though, it raises a bare IndexError instead:

from agent_framework import detect_media_type_from_base64

detect_media_type_from_base64(data_uri="data:image/svg+xml,<svg/>")
# IndexError: list index out of range

Per RFC 2397 a data URI can carry a URL-encoded (non-base64) payload, so data:image/svg+xml,<svg/>, data:text/plain,Hello, etc. are all valid URIs a caller can reasonably pass in. The function only understands base64 payloads, so the right outcome is the documented ValueError, not an opaque IndexError leaking from the internal split(";base64,", 1)[1].

Fix

Guard the split with the same check the rest of this module already uses. _get_data_bytes_as_str does if ";base64," not in uri: raise ContentError(...) before splitting, and _validate_uri checks for the comma before its split — this was the one spot that skipped the check. Now a URI without ;base64, raises a clear ValueError.

Test

Added test_detect_media_type_rejects_non_base64_data_uri, which asserts the three URIs above raise ValueError. It fails on main (the call raises IndexError, which the pytest.raises(ValueError) does not catch) and passes with this change. The existing detect_media_type_from_base64 test still passes.

[Copilot]

Pull request overview

This PR hardens the Python public API detect_media_type_from_base64 so that non-base64 data URIs (valid per RFC 2397, but unsupported by this helper) raise the documented ValueError instead of leaking an internal IndexError.

Changes:

• Add an explicit ";base64," presence check for data_uri inputs in detect_media_type_from_base64 and raise a clear ValueError when missing.
• Add a regression test ensuring several non-base64 data: URIs raise ValueError with a base64-related message.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
python/packages/core/agent_framework/_types.py	Adds validation to reject non-base64 data_uri inputs with a clear ValueError.
python/packages/core/tests/core/test_types.py	Adds regression coverage for non-base64 data URIs passed to detect_media_type_from_base64.