Python: make SerializationMixin.from_dict enforce the documented type check#7256
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Python: make SerializationMixin.from_dict enforce the documented type check#7256he-yufeng wants to merge 1 commit into
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… check
from_dict resolved the expected type identifier from the payload itself
(_get_type_identifier(value) prefers value["type"]), so the mismatch
guard could never fire: any supplied 'type' matched itself, and a payload
like {"type": "function_tool", ...} silently deserialized into a Message,
getting its type rewritten on the next to_dict. The docstring has always
promised a ValueError on mismatch.
Resolve the identifier from the class instead, matching what to_dict
emits, so a mismatched or foreign 'type' now raises as documented.
Payloads without a 'type' field and dependency-injection lookups are
unchanged: in every previously valid case the class-resolved identifier
is the same string the payload carried.
Fixes microsoft#7255
Signed-off-by: Yufeng He <40085740+he-yufeng@users.noreply.github.com>
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Pull request overview
This PR fixes a correctness issue in the Python core serialization layer where SerializationMixin.from_dict() could not actually enforce its documented “type mismatch raises ValueError” behavior, allowing payloads with an incorrect "type" discriminator to deserialize into the wrong class (Fixes #7255).
Changes:
- Make
SerializationMixin.from_dict()derive the expected type identifier from the target class rather than the incoming payload, so the mismatch guard can trigger. - Add regression tests ensuring mismatched
"type"is rejected for bothfrom_dict()andfrom_json().
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/_serialization.py | Fixes the mismatch check by resolving the expected type identifier from the class instead of the payload. |
| python/packages/core/tests/core/test_serializable_mixin.py | Adds tests verifying mismatched "type" raises for both dict and JSON inputs. |
Comment on lines
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| if (supplied_type := value.get("type")) and supplied_type != type_id: | ||
| raise ValueError(f"Type mismatch: expected '{type_id}', got '{supplied_type}'") |
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Fixes #7255.
Problem
SerializationMixin.from_dictdocuments that a mismatchedtypefield raisesValueError, but the guard could never fire: it resolved the expected identifier viacls._get_type_identifier(value), and that helper prefers the payload's owntypefield when one is present. Any suppliedtypetherefore "matched" itself, and a payload like{"type": "function_tool", "role": "user", "contents": []}silently deserialized into aMessage, with the wrong type baked in until the nextto_dict()rewrote it.Fix
Resolve the expected identifier from the class (no payload), which is also what
to_dict()writes, so the mismatch guard now works as documented:In every previously valid case the class-resolved identifier is the same string the payload carried, so well-formed payloads (including no-
typepayloads anddependencies=injection, which keys on the same id) are unchanged. Classes that do polymorphic deserialization (Content, the file-access harness entries) overridefrom_dictthemselves and are unaffected.Tests
Two new tests in
test_serializable_mixin.py: mismatchedtyperaises on bothfrom_dictandfrom_json. Full file passes (28/28).pytest packages/core/tests/coreis green excepttest_feature_stage.py::test_feature_id_allows_lowercase_values, which fails identically on a cleanmaincheckout (pre-existing, unrelated). The exact repro from the issue now raisesType mismatch: expected 'message', got 'function_tool'.