Support server-to-client ping per MCP specification#358
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## Motivation and Context The MCP specification defines `ping` as a bidirectional utility: either party may issue it. https://modelcontextprotocol.io/specification/2025-11-25/basic/utilities/ping The previous PR added `MCP::Client#ping`. This PR adds the symmetric server-side send capability, `ServerSession#ping`. This aligns the Ruby SDK with the Python SDK (`ServerSession.send_ping`) and the TypeScript SDK (`Server.ping()`), both of which expose a server-initiated ping. In practice this enables a Ruby MCP server to health-check non-Ruby clients (e.g., Claude Desktop, the Python or TypeScript SDK client) during long-running tool operations. Scope is intentionally server-only: this PR does not add client-side inbound request dispatch, which is a larger refactor outside the ping utility. A Ruby `MCP::Client` therefore still cannot receive a server-initiated ping; that gap is tracked as a separate follow-up. ## How Has This Been Tested? New file `test/mcp/server_session_ping_test.rb` covers: - success (empty `result` returned) - `related_request_id` propagated through the transport when a session ID is set - `ValidationError` when the transport returns `nil` - `ValidationError` when the transport returns a non-Hash `result` - transport-level errors propagate unchanged - ping succeeds without any client capability declaration (per spec, ping has no capability gate) `test/mcp/server_context_test.rb` adds two tests for `ServerContext#ping` delegation (happy path and `NoMethodError` when the session lacks `#ping`). The existing server-side `ping` handler tests continue to pass unchanged. ## Breaking Changes None. `MCP::ServerContext#ping` and `MCP::Server::ValidationError` are purely additive.
atesgoral
approved these changes
May 22, 2026
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Motivation and Context
The MCP specification defines
pingas a bidirectional utility: either party may issue it. https://modelcontextprotocol.io/specification/2025-11-25/basic/utilities/pingThe previous PR added
MCP::Client#ping. This PR adds the symmetric server-side send capability,ServerSession#ping.This aligns the Ruby SDK with the Python SDK (
ServerSession.send_ping) and the TypeScript SDK (Server.ping()), both of which expose a server-initiated ping. In practice this enables a Ruby MCP server to health-check non-Ruby clients (e.g., Claude Desktop, the Python or TypeScript SDK client) during long-running tool operations.Scope is intentionally server-only: this PR does not add client-side inbound request dispatch, which is a larger refactor outside the ping utility. A Ruby
MCP::Clienttherefore still cannot receive a server-initiated ping; that gap is tracked as a separate follow-up.How Has This Been Tested?
New file
test/mcp/server_session_ping_test.rbcovers:resultreturned)related_request_idpropagated through the transport when a session ID is setValidationErrorwhen the transport returnsnilValidationErrorwhen the transport returns a non-Hashresulttest/mcp/server_context_test.rbadds two tests forServerContext#pingdelegation (happy path andNoMethodErrorwhen the session lacks#ping).The existing server-side
pinghandler tests continue to pass unchanged.Breaking Changes
None.
MCP::ServerContext#pingandMCP::Server::ValidationErrorare purely additive.Types of changes
Checklist