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fix: handle ping requests sent before initialize handshake - #745
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expect_response dropped a server ping while waiting for the initialize response, so the ping never got a reply. Answer it with an empty result during the initialize wait, the same way the server answers an early client ping. The server/discover wait still leaves it unanswered. Refs modelcontextprotocol#745 Fixes modelcontextprotocol#1362
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) * fix(client): answer a server ping during the initialize handshake expect_response dropped a server ping while waiting for the initialize response, so the ping never got a reply. Answer it with an empty result during the initialize wait, the same way the server answers an early client ping. The server/discover wait still leaves it unanswered. Refs #745 Fixes #1362 * test(client): drop duplicated discover ping comment * refactor(client): replace answer_ping bool with PreInitPing enum * test(client): assert notifications/initialized follows the ping response * refactor(client): match on PreInitPing instead of comparing it The compiler now flags this spot if PreInitPing gains a variant, and the PartialEq and Eq derives are no longer needed.
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Closes #488
Motivation and Context
The MCP spec explicitly permits clients to send
pingbefore theinitializerequest, but the Rust SDK was rejecting any such message with anExpectedInitializeRequesterror. This caused cross-SDK incompatibility with the TypeScript SDK, which probes connectivity with a ping before starting the handshake.How Has This Been Tested?
Two new integration tests were added.
Breaking Changes
None. The server now accepts an additional valid message sequence that was previously rejected in error.
Types of changes
Checklist