Fix default handler return values to comply with MCP spec#247
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koic merged 1 commit intomodelcontextprotocol:mainfrom Mar 1, 2026
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The no-op handlers for `completion/complete`, `resources/subscribe`,
and `resources/unsubscribe` returned `nil`.
When a client accesses the expected response structure (e.g., `result[:completion][:values]`),
a `nil` result raises `NoMethodError`.
The MCP spec requires specific response structures even for no-op handlers.
Returning spec-compliant defaults ensures that clients receive valid responses without
requiring servers to explicitly override each handler.
`completion/complete` now returns `{ completion: { values: [], hasMore: false } }`.
ref: https://modelcontextprotocol.io/specification/2025-11-25/server/utilities/completion
`resources/subscribe` and `resources/unsubscribe` now return `{}` (empty result).
ref: https://modelcontextprotocol.io/specification/2025-11-25/server/resources#subscriptions
9 tasks
atesgoral
approved these changes
Mar 1, 2026
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Motivation and Context
The no-op handlers for
completion/complete,resources/subscribe, andresources/unsubscribereturnednil.When a client accesses the expected response structure (e.g.,
result[:completion][:values]), anilresult raisesNoMethodError.The MCP spec requires specific response structures even for no-op handlers. Returning spec-compliant defaults ensures that clients receive valid responses without requiring servers to explicitly override each handler.
completion/completenow returns{ completion: { values: [], hasMore: false } }.ref: https://modelcontextprotocol.io/specification/2025-11-25/server/utilities/completion
resources/subscribeandresources/unsubscribenow return{}(empty result). ref: https://modelcontextprotocol.io/specification/2025-11-25/server/resources#subscriptionsHow Has This Been Tested?
Added a repro test to verify the fix and prevent regression.
Breaking Changes
None.
Types of changes
Checklist