fix(server): validate elicitation form/url sub-capabilities in check_capability#2979
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…capability Connection.check_capability() only verified that the client declared elicitation at all, not whether specific sub-capabilities (form vs url) matched. Mirror the existing sampling sub-capability checks. Fixes modelcontextprotocol#2965
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Good fix! Validating each elicitation sub-capability (form/url) separately is more precise than the previous all-or-nothing check. The parametrized test matrix covering form-only, url-only, both, and mismatched cases is thorough. |
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Summary
Connection.check_capability()now validates elicitation sub-capabilities (form/url) when the caller specifies them, instead of only checking whether the client declared elicitation at all.Motivation
Fixes #2965.
When a client supports URL-mode elicitation only,
check_capability(ClientCapabilities(elicitation=ElicitationCapability(form=FormElicitationCapability())))incorrectly returnedTrue. The function only compared top-levelhave.elicitation is None, never inspecting individual sub-capabilities.This mirrors the existing
sampling.context/sampling.toolssub-capability checks in the same function.Changes
src/mcp/server/connection.py: Add nestedform/urlpresence checks under the elicitation branch.tests/server/test_connection.py: Add 6 parametrized regression cases covering form/url mismatch, match, and generic elicitation checks.Tests
uv run pytest tests/server/test_connection.py— 44 passeduv run ruff check src/mcp/server/connection.py tests/server/test_connection.py— cleanuv run ruff format --check src/mcp/server/connection.py tests/server/test_connection.py— cleanNotes
ServerSession.check_client_capability()delegates toConnection.check_capability(), so this fix applies to both APIs.