c145876bb9
## Motivation and Context SEP-2575 (modelcontextprotocol/modelcontextprotocol#2575, merged for the 2026-07-28 spec release) makes MCP stateless, removing the `initialize`/`notifications/initialized` handshake in favor of per-request `_meta`-carried negotiation. The full lifecycle rewrite is unmerged in both the TypeScript SDK (the closed #2063/#2064/#2251 prototype stack, on hold since 2026-06-08) and the Python SDK, but two pieces of its wire contract stayed stable across every prototype iteration and are purely additive: - The `server/discover` method, which servers MUST implement: sessionless capability discovery returning `supportedVersions`, `capabilities`, `serverInfo`, and `instructions`. The new `Server#discover` handler reuses the same data `init` already builds, but is state-free and idempotent: it stores no client info, never marks a session initialized, and responds regardless of declared capabilities or initialization state (added to the no-capability group in `Methods.ensure_capability!`). `serverInfo` is returned unfiltered because discovery precedes version negotiation; the draft's `ttlMs`/`cacheScope` fields on `DiscoverResult` are left to the SEP-2549 work. On `StreamableHTTPTransport`, a `server/discover` POST is exempt from the `Mcp-Session-Id` requirement and the `MCP-Protocol-Version` header check, like `initialize`, so clients can probe a server with a bare POST in both stateful and stateless modes. - The error code vocabulary: the new `MCP::ErrorCodes` module exports `MISSING_REQUIRED_CLIENT_CAPABILITY = -32003` and `UNSUPPORTED_PROTOCOL_VERSION = -32004`. Constants only; nothing raises them yet (that belongs to the 2026-07-28 lifecycle work), and the existing inline `-32042` of `URLElicitationRequiredError` is intentionally left untouched. The removal of `initialize`, `ping`, and `logging/setLevel` that SEP-2575 also specifies is deliberately NOT implemented: the SDK targets protocol versions up to 2025-11-25, where those methods are required. Part of #389. ## How Has This Been Tested? - `test/mcp/server_test.rb`: `server/discover` returns the supported versions, the server's capabilities, server info, and instructions; it responds before `initialize` and with empty capabilities; it does not mark the session initialized (a subsequent `initialize` still succeeds); `instructions` is omitted when the server has none; and `define_custom_method(method_name: "server/discover")` now raises `MethodAlreadyDefinedError`. - `test/mcp/methods_test.rb`: `ensure_capability!` does not raise for `SERVER_DISCOVER` with empty capabilities. - `test/mcp/server/transports/streamable_http_transport_test.rb`: a `server/discover` POST without a session ID returns 200 with the discover result in both stateful and stateless modes, without issuing an `Mcp-Session-Id`. - New `test/mcp/error_codes_test.rb` pins the -32003/-32004 values. `bundle exec rake` (tests, RuboCop, and conformance baseline) passes. ## Breaking Changes None at the wire level for existing clients. One narrow API consequence: servers that previously registered their own `"server/discover"` handler via `define_custom_method` now get `MethodAlreadyDefinedError` because the method is built in.
85 lines
4.7 KiB
Ruby
85 lines
4.7 KiB
Ruby
# frozen_string_literal: true
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require "test_helper"
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require "mcp/methods"
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module MCP
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class MethodsTest < ActiveSupport::TestCase
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class << self
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def ensure_capability_raises_error_for(method, required_capability_name:, capabilities: {})
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test("ensure_capability! for #{method} raises an error if #{required_capability_name} capability is not present") do
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error = assert_raises(Methods::MissingRequiredCapabilityError) do
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Methods.ensure_capability!(method, capabilities)
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end
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assert_equal("Server does not support #{required_capability_name} (required for #{method})", error.message)
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end
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end
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def ensure_capability_does_not_raise_for(method, capabilities: {})
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test("ensure_capability! does not raise for #{method}") do
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assert_nothing_raised { Methods.ensure_capability!(method, capabilities) }
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end
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end
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end
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# Server methods and notifications
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ensure_capability_does_not_raise_for Methods::INITIALIZE
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# `server/discover` (SEP-2575) must respond regardless of declared capabilities.
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ensure_capability_does_not_raise_for Methods::SERVER_DISCOVER
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ensure_capability_raises_error_for Methods::PROMPTS_LIST, required_capability_name: "prompts"
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ensure_capability_raises_error_for Methods::PROMPTS_GET, required_capability_name: "prompts"
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ensure_capability_raises_error_for Methods::NOTIFICATIONS_PROMPTS_LIST_CHANGED, required_capability_name: "prompts"
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ensure_capability_raises_error_for Methods::NOTIFICATIONS_PROMPTS_LIST_CHANGED,
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required_capability_name: "prompts.listChanged",
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capabilities: { prompts: {} }
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ensure_capability_raises_error_for Methods::RESOURCES_LIST, required_capability_name: "resources"
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ensure_capability_raises_error_for Methods::RESOURCES_READ, required_capability_name: "resources"
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ensure_capability_raises_error_for Methods::RESOURCES_TEMPLATES_LIST, required_capability_name: "resources"
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ensure_capability_raises_error_for Methods::NOTIFICATIONS_RESOURCES_LIST_CHANGED, required_capability_name: "resources"
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ensure_capability_raises_error_for Methods::NOTIFICATIONS_RESOURCES_LIST_CHANGED,
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required_capability_name: "resources.listChanged",
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capabilities: { resources: {} }
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ensure_capability_raises_error_for Methods::RESOURCES_SUBSCRIBE, required_capability_name: "resources"
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ensure_capability_raises_error_for Methods::RESOURCES_SUBSCRIBE,
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required_capability_name: "resources.subscribe",
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capabilities: { resources: {} }
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ensure_capability_raises_error_for Methods::RESOURCES_UNSUBSCRIBE, required_capability_name: "resources"
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ensure_capability_raises_error_for Methods::RESOURCES_UNSUBSCRIBE,
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required_capability_name: "resources.subscribe",
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capabilities: { resources: {} }
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ensure_capability_raises_error_for Methods::NOTIFICATIONS_RESOURCES_UPDATED, required_capability_name: "resources"
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ensure_capability_raises_error_for Methods::NOTIFICATIONS_RESOURCES_UPDATED,
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required_capability_name: "resources.subscribe",
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capabilities: { resources: {} }
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ensure_capability_raises_error_for Methods::TOOLS_LIST, required_capability_name: "tools"
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ensure_capability_raises_error_for Methods::TOOLS_CALL, required_capability_name: "tools"
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ensure_capability_raises_error_for Methods::NOTIFICATIONS_TOOLS_LIST_CHANGED, required_capability_name: "tools"
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ensure_capability_raises_error_for Methods::NOTIFICATIONS_TOOLS_LIST_CHANGED,
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required_capability_name: "tools.listChanged",
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capabilities: { tools: {} }
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ensure_capability_raises_error_for Methods::LOGGING_SET_LEVEL, required_capability_name: "logging"
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ensure_capability_raises_error_for Methods::NOTIFICATIONS_MESSAGE, required_capability_name: "logging"
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ensure_capability_raises_error_for Methods::COMPLETION_COMPLETE, required_capability_name: "completions"
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# Client methods and notifications
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ensure_capability_does_not_raise_for Methods::NOTIFICATIONS_INITIALIZED
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ensure_capability_raises_error_for Methods::ROOTS_LIST, required_capability_name: "roots"
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ensure_capability_does_not_raise_for Methods::NOTIFICATIONS_ROOTS_LIST_CHANGED
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ensure_capability_raises_error_for Methods::SAMPLING_CREATE_MESSAGE, required_capability_name: "sampling"
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ensure_capability_raises_error_for Methods::ELICITATION_CREATE, required_capability_name: "elicitation"
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# Methods and notifications of both server and client
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ensure_capability_does_not_raise_for Methods::PING
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ensure_capability_does_not_raise_for Methods::NOTIFICATIONS_PROGRESS
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ensure_capability_does_not_raise_for Methods::NOTIFICATIONS_CANCELLED
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ensure_capability_does_not_raise_for Methods::NOTIFICATIONS_ELICITATION_COMPLETE
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end
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end
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