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DaleSeo
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Oct 16, 2026
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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DaleSeo
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Looks good, @gocamille. Just one extra comment before merging.
The compiler now flags this spot if PreInitPing gains a variant, and the PartialEq and Eq derives are no longer needed.
DaleSeo
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Fixes #1362
Motivation and Context
expect_responsenow answers a serverpingwith an empty result while the client waits for theinitializeresponse, instead of logging and dropping it. The reply goes straight onto the transport and a send failure becomes a transport error, matching how the server answers an early client ping (#745).expect_responsealso handles theserver/discoverwait, so it takes ananswer_pingflag:trueforinitialize,falsefor discover. Discover keeps ignoring the ping since 2026-07-28 has noping. Auto mode's fallback goes through the initialize path, so it answers there too.How Has This Been Tested?
client_answers_server_ping_during_initialize(test_client_initialization.rs): both sides on 2025-11-25. The server pings after readinginitializeand before sending the result, then checks the next message is the ping response and the one after isnotifications/initialized. Fails onmain.discover_startup_ignores_server_ping(test_client_lifecycle_modes.rs): the server pings before the discover result, and the next message it reads must be the client'stools/list. This passes onmaintoo; it's there so the flag can't leak into the discover path.Validation:
cargo test -p rmcp --features client --test test_client_initialization --test test_client_lifecycle_modes: passed (20 tests).cargo test -p rmcp --all-features: passed.cargo clippy --all-targets --all-features -- -D warningsandcargo +nightly fmt --all -- --check: clean.Breaking Changes
None.
Types of changes
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