Make inbound message handling concurrent after the initialization
handshake, so a slow or peer-awaiting handler no longer blocks other
messages on the same connection
fixes#176, #572
## Motivation and Context
Inbound messages were processed serially on the transport read loop. One
slow or peer-awaiting request handler (sampling, elicitation, roots)
blocked every later message on that connection, including the responses
and `notifications/cancelled` those handlers depend on which could
deadlock request/response flows.
## How Has This Been Tested?
New and old tests
## Breaking Changes
- after the handshake, inbound handlers may run concurrently (processing
stays serial during initialization). There is no opt-out flag by design,
concurrency is bounded by `maxConcurrentHandlers` /
`maxInFlightHandlers`.
- `ProtocolOptions` / `ClientOptions` / `ServerOptions` gain new
parameters with defaults
- `RequestHandlerExtra` is now a coroutine-context element and is no
longer user-constructible
## Types of changes
- [x] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [x] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update
## Checklist
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed
## refactor: Introduce AbstractClientTransport and simplify client
transport lifecycle
This PR unifies state management logic across client transports, except
for the websocket transport, as it needs more refactoring first and is
not the primary transport.
- Introduce `AbstractClientTransport` as base class for other client
transports.
- Migrate to `ClientTransportState` states with state machine,
streamline state management.
- Ensure proper cleanup and error handling consistency across transport
implementations.
- Add unit tests to validate `AbstractClientTransport` behavior and
state transitions.
- Update related documentation and API contract.
- Make sure `onClose` callback is called at most once
- fix
[StreamableHttpClientTransportTest.kt](https://github.com/modelcontextprotocol/kotlin-sdk/pull/516/changes#diff-b9fe8891d08a492448a7ed2dc782151c6a915ae1403a4d70c2034c6062c84cb5)
to throw `McpException` on connect when received invalid Json
## Motivation and Context
Unify lifecycle handling and eliminate duplication in client Transport
implementations.
## How Has This Been Tested?
Unit test, regression tests
## Breaking Changes
- `onClose` callback is now called only once
- send(...) will throw McpException with message "Transport is not
ready" when `ClientTransportState != Operational`
## Types of changes
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] Refactoring
- [ ] New feature (non-breaking change which adds functionality)
- [x] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update
## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed
## Additional context
See #517
# Update/Fix build workflow
- `macos-latest-xlarge` is no longer available. Switch to cheaper
runner: `macos-latest-xlarge` -> `macos-latest`
- Refactor build to run matrix job under Linux and macOS
- Tune caching GH caching
- Add junit and logger properties
- Downgrade Junit to 5.14.2
- Extract `ProcessBuilder` creation logic into helper functions
- Disable `StdioClientTransportTest` on windows temporary
## How Has This Been Tested?
CI
## Breaking Changes
Functionally - no. Outdated/broken TypeScript tests were disabled
## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [x] Bug fix (non-breaking change which fixes an issue)
- [x] CI Update
## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [ ] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [ ] My code follows the repository's style guidelines
- [ ] New and existing tests pass locally
- [ ] I have added appropriate error handling
- [ ] I have added or updated documentation as needed
## Additional context
GitHub actions workflows were blocked because the selected
"macos-latest-xlarge" runner, which is not available for the free
open-source plan. With "macos-latest" workflow works.
