Add MCP::Client::Stdio transport#262
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## Motivation and Context The `MCP::Client` currently only supports HTTP transport (`MCP::Client::HTTP`). To achieve parity with other MCP SDKs (Python, TypeScript, C#) which provide stdio client transports for spawning and communicating with server subprocesses, the Ruby SDK needs a stdio client transport. https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#stdio This enables building MCP clients that launch server processes and communicate via stdin/stdout using newline-delimited JSON-RPC 2.0 messages. ## How Has This Been Tested? Added tests for process spawning, protocol initialization handshake, notification handling, error handling, and transport close lifecycle. ## Additional context Enabled the `Lint/IncompatibleIoSelectWithFiberScheduler` cop in `.rubocop.yml` to detect accidental use of `IO.select` instead of `IO#wait_readable`.
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Motivation and Context
The
MCP::Clientcurrently only supports HTTP transport (MCP::Client::HTTP). To achieve parity with other MCP SDKs (Python, TypeScript, C#) which provide stdio client transports for spawning and communicating with server subprocesses, the Ruby SDK needs a stdio client transport.https://modelcontextprotocol.io/specification/2025-11-25/basic/transports#stdio
This enables building MCP clients that launch server processes and communicate via stdin/stdout using newline-delimited JSON-RPC 2.0 messages.
How Has This Been Tested?
Added tests for process spawning, protocol initialization handshake, notification handling, error handling, and transport close lifecycle.
Breaking Changes
None.
Types of changes
Checklist
Additional context
Enabled the
Lint/IncompatibleIoSelectWithFiberSchedulercop in.rubocop.ymlto detect accidental use ofIO.selectinstead ofIO#wait_readable.