refactor(core): extract Dispatcher; Protocol composes it#2130
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refactor(core): extract Dispatcher; Protocol composes it#2130felixweinberger wants to merge 1 commit into
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@modelcontextprotocol/client
@modelcontextprotocol/server
@modelcontextprotocol/express
@modelcontextprotocol/fastify
@modelcontextprotocol/hono
@modelcontextprotocol/node
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felixweinberger
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v2-stateless
This was referenced May 20, 2026
…or change)
Introduce `Dispatcher<ContextT>` (`packages/core/src/shared/dispatcher.ts`)
holding the request-handler registry, middleware chain, and `dispatch()`
entry point. `Protocol` now composes a `protected readonly dispatcher`
and delegates:
- `setRequestHandler` / `removeRequestHandler` / `assertCanSetRequestHandler`
- `fallbackRequestHandler` (now `dispatcher.fallbackHandler`)
- `_onrequest` invokes `dispatcher.dispatch(request, ctx)` for lookup,
middleware onion, and JSON-RPC response wrapping
The previous `_wrapHandler` override hook is replaced by `dispatcher.use()`:
- `Server` registers `_callToolResultMiddleware` (was `_wrapHandler` for tools/call)
- `Client` registers `_validationMiddleware` (was `_wrapHandler` for
elicitation/create + sampling/createMessage)
Same validation runs on the same paths; the observation point moves from
per-registration wrapping to per-dispatch middleware.
`dispatch()`'s catch block preserves `_onrequest`'s error behavior verbatim:
thrown errors surface their `code` (if a safe integer), `message`, and `data`.
No sanitization is introduced.
Tests:
- `dispatcher.test.ts` added (11 tests for setHandler/dispatch/middleware/error)
- `wrapHandler.test.ts` deleted (covered by rewritten customMethods test)
- `customMethods.test.ts` adapts one test from spying on `_wrapHandler` to
spying via middleware; same assertion (both 2-arg and 3-arg routes through)
No existing test assertions changed.
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Extracts
Dispatcher<Ctx>(handler map + middleware chain +dispatch()) fromProtocol.Protocolnow composes one;setRequestHandler/_onrequest/fallbackRequestHandlerdelegate. The_wrapHandleroverride hook becomesdispatcher.use(middleware).Zero behavior change.
dispatch()'s catch block preserves_onrequest's error mapping verbatim. No existing test assertions changed.Motivation and Context
Enabling refactor for SEP-2575:
_dispatchStateless(next PR) needs to invoke the same handler map + middleware that legacy_onrequestuses, without going through Protocol's session machinery.How Has This Been Tested?
pnpm test:all— count delta isdispatcher.test.ts(+11) andwrapHandler.test.ts(−1, redundant). No existing assertion changed.Breaking Changes
Protocol._wrapHandleroverride hook removed (was protected). Subclasses usethis.dispatcher.use(mw)instead.Types of changes
Checklist