ruby-sdk/test/mcp/server_cancellation_test.rb
Koichi ITO 6d42cf7826 Fix an incorrect result: null response to an id-bearing notification message
## Motivation and Context

A JSON-RPC notification carries no id and must not receive any response.
When a client erroneously sent a notification-only method such as `notifications/cancelled` with an id,
the server replied with a successful `result: null`, which is neither a valid MCP result nor
a legal reply to a notification.

Such a message is now treated as a request for a method that has no request handler and rejected with
Method not found, matching the behavior of the TypeScript and Python SDKs. A well-formed notification
that omits the id continues to receive no response.

Fixes #434.

## How Has This Been Tested?

Added regression tests covering id-bearing `notifications/cancelled`, `notifications/initialized`,
and `notifications/progress`, a batch that mixes an id-bearing notification with other messages,
custom `notifications/*` methods, and the same case over the HTTP transport.

## Breaking Changes

None for spec-conformant clients, which never put an id on a notification.
The only behavioral change is that a malformed id-bearing notification now receives a Method not found error
instead of a spurious `result: null`.
2026-07-01 01:55:15 +09:00

717 lines
25 KiB
Ruby

# frozen_string_literal: true
require "test_helper"
module MCP
class ServerCancellationTest < ActiveSupport::TestCase
include InstrumentationTestHelper
class MockTransport < Transport
attr_reader :requests, :notifications, :cancelled_request_ids
def initialize(server)
super
@requests = []
@notifications = []
@cancelled_request_ids = []
end
def send_request(method, params = nil, **_kwargs)
@requests << { method: method, params: params }
{}
end
def send_notification(method, params = nil, **_kwargs)
@notifications << { method: method, params: params }
true
end
def cancel_pending_request(request_id, reason: nil)
@cancelled_request_ids << request_id
end
def send_response(response); end
def open; end
def close; end
def handle_request(request); end
end
setup do
configuration = MCP::Configuration.new
configuration.instrumentation_callback = instrumentation_helper.callback
@server = Server.new(name: "test_server", version: "1.0.0", configuration: configuration)
@mock_transport = MockTransport.new(@server)
@server.transport = @mock_transport
@session = ServerSession.new(server: @server, transport: @mock_transport, session_id: "sess-1")
end
test "cooperative cancellation via server_context suppresses response" do
observed_cancelled = false
@server.define_tool(name: "slow") do |server_context:|
20.times do
break if server_context.cancelled?
sleep(0.01)
end
observed_cancelled = server_context.cancelled?
Tool::Response.new([{ type: "text", text: "ok" }])
end
request_id = 42
call_thread = Thread.new do
@session.handle(
jsonrpc: "2.0",
id: request_id,
method: Methods::TOOLS_CALL,
params: { name: "slow", arguments: {} },
)
end
sleep(0.02) until @session.lookup_in_flight(request_id)
@session.handle(
jsonrpc: "2.0",
method: Methods::NOTIFICATIONS_CANCELLED,
params: { requestId: request_id, reason: "user aborted" },
)
response = call_thread.value
assert observed_cancelled, "tool handler should observe cancellation"
assert_nil response, "cancelled request must not emit a JSON-RPC response"
end
test "tool raising CancelledError via raise_if_cancelled! suppresses the JSON-RPC response" do
@server.define_tool(name: "raising") do |server_context:|
50.times do
server_context.raise_if_cancelled!
sleep(0.01)
end
Tool::Response.new([{ type: "text", text: "ok" }])
end
request_id = 99
call_thread = Thread.new do
@session.handle(
jsonrpc: "2.0",
id: request_id,
method: Methods::TOOLS_CALL,
params: { name: "raising", arguments: {} },
)
end
sleep(0.02) until @session.lookup_in_flight(request_id)
@session.handle(
jsonrpc: "2.0",
method: Methods::NOTIFICATIONS_CANCELLED,
params: { requestId: request_id, reason: "raised" },
)
response = call_thread.value
assert_nil response, "raise_if_cancelled! must result in no JSON-RPC response"
end
test "CancelledError raised from nested server-to-client call suppresses response" do
@server.define_tool(name: "nesting") do |**|
# Simulate a transport-level CancelledError coming back from a nested
# send_request (e.g. sampling/createMessage after parent was cancelled).
raise MCP::CancelledError.new(request_id: "nested-xyz", reason: "parent aborted")
end
response = @session.handle(
jsonrpc: "2.0",
id: 123,
method: Methods::TOOLS_CALL,
params: { name: "nesting", arguments: {} },
)
assert_nil response, "CancelledError propagating from a nested call must suppress the JSON-RPC response"
end
test "cancellation with unknown request id is silently ignored" do
response = @session.handle(
jsonrpc: "2.0",
method: Methods::NOTIFICATIONS_CANCELLED,
params: { requestId: "does-not-exist" },
)
assert_nil response
end
test "id-bearing notifications/cancelled is rejected with Method not found, not result: null" do
response = @session.handle(
jsonrpc: "2.0",
id: 1001,
method: Methods::NOTIFICATIONS_CANCELLED,
)
assert_equal 1001, response[:id]
refute response.key?(:result)
assert_equal JsonRpcHandler::ErrorCode::METHOD_NOT_FOUND, response.dig(:error, :code)
end
test "id-bearing notifications/initialized is rejected with Method not found" do
response = @session.handle(
jsonrpc: "2.0",
id: 1002,
method: Methods::NOTIFICATIONS_INITIALIZED,
)
assert_equal 1002, response[:id]
refute response.key?(:result)
assert_equal JsonRpcHandler::ErrorCode::METHOD_NOT_FOUND, response.dig(:error, :code)
end
test "id-bearing notifications/progress is rejected with Method not found" do
response = @session.handle(
jsonrpc: "2.0",
id: 1003,
method: Methods::NOTIFICATIONS_PROGRESS,
params: { progressToken: "tok", progress: 1 },
)
assert_equal 1003, response[:id]
refute response.key?(:result)
assert_equal JsonRpcHandler::ErrorCode::METHOD_NOT_FOUND, response.dig(:error, :code)
end
test "well-formed notifications/initialized still receives no response" do
response = @session.handle(
jsonrpc: "2.0",
method: Methods::NOTIFICATIONS_INITIALIZED,
)
assert_nil response
end
test "id-bearing notification mixed into a batch yields only its Method not found error" do
responses = @session.handle([
{ jsonrpc: "2.0", method: Methods::NOTIFICATIONS_CANCELLED, params: { requestId: "x" } },
{ jsonrpc: "2.0", id: 2001, method: Methods::NOTIFICATIONS_CANCELLED },
{ jsonrpc: "2.0", id: 2002, method: Methods::PING },
])
cancelled_error = responses.find { |response| response[:id] == 2001 }
assert_equal JsonRpcHandler::ErrorCode::METHOD_NOT_FOUND, cancelled_error.dig(:error, :code)
ping_response = responses.find { |response| response[:id] == 2002 }
assert_equal({}, ping_response[:result])
# The well-formed notification carries no id and contributes no response.
assert_equal 2, responses.size
end
test "id-bearing custom notifications/* method is rejected with Method not found" do
called = false
@server.define_custom_method(method_name: "notifications/custom") { called = true }
response = @session.handle(
jsonrpc: "2.0",
id: 3001,
method: "notifications/custom",
)
assert_equal JsonRpcHandler::ErrorCode::METHOD_NOT_FOUND, response.dig(:error, :code)
refute called
end
test "well-formed custom notifications/* method is dispatched without a response" do
called = false
@server.define_custom_method(method_name: "notifications/custom") { called = true }
response = @session.handle(
jsonrpc: "2.0",
method: "notifications/custom",
)
assert_nil response
assert called
end
test "duplicate cancellation for the same in-flight request is idempotent" do
@server.define_tool(name: "slow_dup") do |server_context:|
20.times do
break if server_context.cancelled?
sleep(0.01)
end
Tool::Response.new([{ type: "text", text: "ok" }])
end
request_id = 51
call_thread = Thread.new do
@session.handle(
jsonrpc: "2.0",
id: request_id,
method: Methods::TOOLS_CALL,
params: { name: "slow_dup", arguments: {} },
)
end
sleep(0.02) until @session.lookup_in_flight(request_id)
first = @session.handle(
jsonrpc: "2.0",
method: Methods::NOTIFICATIONS_CANCELLED,
params: { requestId: request_id, reason: "first" },
)
second = @session.handle(
jsonrpc: "2.0",
method: Methods::NOTIFICATIONS_CANCELLED,
params: { requestId: request_id, reason: "second" },
)
response = call_thread.value
assert_nil first
assert_nil second, "duplicate cancel must not emit a response"
assert_nil response, "cancelled request must not emit a response"
end
test "cancellation arriving after the request already completed is silently ignored" do
@server.define_tool(name: "quick") do
Tool::Response.new([{ type: "text", text: "done" }])
end
request_id = 61
response = @session.handle(
jsonrpc: "2.0",
id: request_id,
method: Methods::TOOLS_CALL,
params: { name: "quick", arguments: {} },
)
assert response, "the tool should have completed successfully before the cancel arrives"
assert_nil @session.lookup_in_flight(request_id), "completed request must be unregistered"
late = @session.handle(
jsonrpc: "2.0",
method: Methods::NOTIFICATIONS_CANCELLED,
params: { requestId: request_id, reason: "late" },
)
assert_nil late, "late cancel for a completed request must be silently ignored"
end
test "initialize request cannot be cancelled" do
init_params = {
protocolVersion: Configuration::LATEST_STABLE_PROTOCOL_VERSION,
clientInfo: { name: "test", version: "1.0" },
capabilities: {},
}
response = @session.handle(
jsonrpc: "2.0",
id: "init-1",
method: Methods::INITIALIZE,
params: init_params,
)
assert response, "initialize returns a response"
assert response[:result][:protocolVersion]
# The initialize request is not registered in the in-flight map.
assert_nil @session.lookup_in_flight("init-1")
end
test "ServerSession#cancel_request sends notification and cancels pending" do
@session.cancel_request(request_id: "req-9", reason: "timeout")
notification = @mock_transport.notifications.last
assert_equal Methods::NOTIFICATIONS_CANCELLED, notification[:method]
assert_equal "req-9", notification[:params][:requestId]
assert_equal "timeout", notification[:params][:reason]
assert_includes @mock_transport.cancelled_request_ids, "req-9"
end
test "parent cancellation propagates to nested server-to-client requests" do
@session.instance_variable_set(:@client_capabilities, { elicitation: {} })
parent_request_id = 101
cancellation = @session.register_in_flight(parent_request_id)
# Simulate a nested sampling/elicitation send via ServerSession. The transport
# is expected to receive `parent_cancellation:` and `server_session:` kwargs so
# it can install an `on_cancel` hook. Here we assert those kwargs are forwarded.
recorded = {}
(class << @mock_transport; self; end).define_method(:send_request) do |method, _params = nil, **kwargs|
recorded[:method] = method
recorded[:kwargs] = kwargs
{}
end
@session.create_form_elicitation(
message: "ignored",
requested_schema: { type: "object", properties: {} },
related_request_id: parent_request_id,
)
assert_equal Methods::ELICITATION_CREATE, recorded[:method]
assert_equal parent_request_id, recorded[:kwargs][:related_request_id]
assert_same cancellation, recorded[:kwargs][:parent_cancellation]
assert_same @session, recorded[:kwargs][:server_session]
end
test "cancellation reason is recorded in instrumentation data" do
recorded_data = nil
@server.configuration.instrumentation_callback = ->(data) { recorded_data = data }
@server.define_tool(name: "slow_with_reason") do |server_context:|
50.times do
break if server_context.cancelled?
sleep(0.01)
end
Tool::Response.new([{ type: "text", text: "ok" }])
end
request_id = 77
call_thread = Thread.new do
@session.handle(
jsonrpc: "2.0",
id: request_id,
method: Methods::TOOLS_CALL,
params: { name: "slow_with_reason", arguments: {} },
)
end
sleep(0.02) until @session.lookup_in_flight(request_id)
@session.handle(
jsonrpc: "2.0",
method: Methods::NOTIFICATIONS_CANCELLED,
params: { requestId: request_id, reason: "explicit reason string" },
)
call_thread.value
assert recorded_data
assert recorded_data[:cancelled]
assert_equal "explicit reason string", recorded_data[:cancellation_reason]
end
# Helper for the non-tools cancellation regression tests below. Spawns a background
# request, waits for the in-flight entry, sends `notifications/cancelled`, and
# returns [response, thread_result_flag_yielded_by_block].
def drive_cancellation(request_id:, method:, params:)
result_flag = { observed: false }
call_thread = Thread.new do
@session.handle(jsonrpc: "2.0", id: request_id, method: method, params: params)
end
sleep(0.02) until @session.lookup_in_flight(request_id)
yield(result_flag) if block_given?
@session.handle(
jsonrpc: "2.0",
method: Methods::NOTIFICATIONS_CANCELLED,
params: { requestId: request_id, reason: "caller aborted" },
)
[call_thread.value, result_flag]
end
test "resources/read handler that opts in to server_context observes cancellation" do
observed = false
@server.resources_read_handler do |_params, server_context:|
50.times do
break if server_context.cancelled?
sleep(0.01)
end
observed = server_context.cancelled?
[{ uri: "test://resource", text: "done" }]
end
response, = drive_cancellation(
request_id: 201,
method: Methods::RESOURCES_READ,
params: { uri: "test://resource" },
)
assert observed, "resources/read handler should observe cancellation via server_context"
assert_nil response, "cancelled resources/read must not emit a JSON-RPC response"
end
test "completion/complete handler that opts in to server_context observes cancellation" do
observed = false
@server.capabilities[:completions] = {}
@server.completion_handler do |_params, server_context:|
50.times do
break if server_context.cancelled?
sleep(0.01)
end
observed = server_context.cancelled?
{ completion: { values: ["v"], hasMore: false } }
end
# completion/complete requires a known ref; register a dummy prompt.
@server.define_prompt(name: "dummy") { MCP::Prompt::Result.new(messages: []) }
response, = drive_cancellation(
request_id: 202,
method: Methods::COMPLETION_COMPLETE,
params: { ref: { type: "ref/prompt", name: "dummy" }, argument: { name: "arg", value: "" } },
)
assert observed, "completion/complete handler should observe cancellation via server_context"
assert_nil response, "cancelled completion/complete must not emit a JSON-RPC response"
end
test "prompts/get template that opts in to server_context observes cancellation" do
observed = false
prompt_class = Class.new(MCP::Prompt) do
prompt_name "slow_prompt"
define_singleton_method(:template) do |_args, server_context:|
50.times do
break if server_context.cancelled?
sleep(0.01)
end
observed = server_context.cancelled?
MCP::Prompt::Result.new(messages: [])
end
end
@server.prompts[prompt_class.name_value] = prompt_class
# Share `observed` between the closure above and the test scope.
@server.singleton_class.define_method(:_test_observed) { observed }
response, = drive_cancellation(
request_id: 203,
method: Methods::PROMPTS_GET,
params: { name: "slow_prompt" },
)
assert observed, "prompt template should observe cancellation via server_context"
assert_nil response, "cancelled prompts/get must not emit a JSON-RPC response"
end
test "send_to_transport (notifications) works with a custom transport that only implements the abstract signature" do
# Regression: `ServerSession#send_to_transport` must not assume the
# transport's `send_notification` accepts the new kwargs
# (`session_id:` / `related_request_id:`). Custom transports that
# implement the abstract `Transport#send_notification(method, params = nil)`
# contract must keep working - this is exercised via `cancel_request` /
# `send_peer_cancellation` which the cancellation feature relies on.
minimal_transport = Class.new(Transport) do
attr_reader :recorded
def initialize(server)
super
@recorded = []
end
def send_notification(method, params = nil)
@recorded << [method, params]
true
end
def send_request(method, params = nil)
@recorded << [method, params]
{}
end
def send_response(_); end
def open; end
def close; end
end.new(@server)
session = ServerSession.new(server: @server, transport: minimal_transport)
assert_nothing_raised do
session.cancel_request(request_id: "req-1", reason: "timeout")
end
recorded = minimal_transport.recorded.last
assert_equal Methods::NOTIFICATIONS_CANCELLED, recorded[0]
assert_equal "req-1", recorded[1][:requestId]
assert_equal "timeout", recorded[1][:reason]
end
test "send_to_transport_request works with a custom transport that only implements the abstract signature" do
# Regression: `ServerSession#send_to_transport_request` must not assume
# the transport's `send_request` accepts the new kwargs
# (`session_id:` / `related_request_id:` / `parent_cancellation:` /
# `server_session:`). Custom transports that implement the abstract
# `Transport#send_request(method, params = nil)` contract must keep working.
minimal_transport = Class.new(Transport) do
attr_reader :recorded
def initialize(server)
super
@recorded = []
end
def send_request(method, params = nil)
@recorded << [method, params]
{} # fake response
end
def send_notification(method, params = nil)
@recorded << [method, params]
true
end
def send_response(_); end
def open; end
def close; end
end.new(@server)
session = ServerSession.new(server: @server, transport: minimal_transport)
session.instance_variable_set(:@client_capabilities, { sampling: {} })
assert_nothing_raised do
session.create_sampling_message(
messages: [{ role: "user", content: { type: "text", text: "hi" } }],
max_tokens: 10,
)
end
recorded = minimal_transport.recorded.last
assert_equal Methods::SAMPLING_CREATE_MESSAGE, recorded[0]
refute_nil recorded[1]
end
test "tool with positional `server_context` parameter is not auto-opted-in" do
# Regression: `accepts_server_context?` (used by tool/prompt dispatch) must
# require `server_context` as a *keyword* parameter. A tool whose `call`
# signature is `def self.call(arg, server_context)` (positional name collision)
# would previously have been opt-in, and `tool.call(**args, server_context: ctx)`
# would have blown up or passed the wrapped Hash to the wrong slot.
tool = Class.new(MCP::Tool) do
tool_name "positional_collision"
input_schema(properties: { a: { type: "string" } }, required: ["a"])
class << self
def call(a, server_context)
[a, server_context]
end
end
end
@server.tools[tool.name_value] = tool
# Should dispatch without `server_context:` kwarg - the positional arg collision
# must NOT trigger opt-in. The tool receives only its declared positional (a).
response = @session.handle(
jsonrpc: "2.0",
id: 303,
method: Methods::TOOLS_CALL,
params: { name: "positional_collision", arguments: { a: "hello" } },
)
# Because the tool signature isn't opt-in, `tool.call(**args)` is called
# (without `server_context:`). The method has `server_context` as a required
# positional, so missing it raises ArgumentError - caught as an internal error.
# The key assertion is that we do NOT pass `server_context:` kwarg that would
# flow into the positional slot as a Hash.
assert response.dig(:error), "dispatch should not silently inject server_context kwarg"
end
test "handler with positional `server_context` parameter is not auto-opted-in" do
# Regression: `handler_declares_server_context?` must require `server_context`
# as a *keyword* parameter. A positional parameter that happens to be named
# `server_context` (rare but possible) would previously have been treated as
# opt-in, and the dispatch site would call `handler.call(params, server_context: ctx)`
# - the second positional argument would become the Hash `{server_context: ctx}`,
# which is never what the user intended.
received_args = nil
@server.define_custom_method(method_name: "custom/positional_name") do |params, server_context|
received_args = [params, server_context]
{ ok: true }
end
response = @session.handle(
jsonrpc: "2.0",
id: 302,
method: "custom/positional_name",
params: { hello: "world" },
)
assert_equal [{ hello: "world" }, nil],
received_args,
"positional `server_context` must receive the single `params` argument, not an auto-wrapped context"
assert_equal({ ok: true }, response[:result])
end
test "handler with **kwargs-only signature is not auto-opted-in to server_context" do
# Regression: a block like `|**opts|` would have triggered opt-in under the
# looser `accepts_server_context?` check used by tools, and the dispatch site
# would then call `handler.call(params, server_context:)` - but a proc that
# only declares `**opts` cannot accept the positional `params` (lambdas raise
# ArgumentError, non-lambda procs silently drop it). The stricter
# `handler_declares_server_context?` check requires `server_context` as a
# named keyword to opt in, so a kwargs-only handler receives only `params`.
received_positional = nil
@server.define_custom_method(method_name: "custom/kwargs_only") do |params, **_opts|
received_positional = params
{ ok: true }
end
response = @session.handle(
jsonrpc: "2.0",
id: 301,
method: "custom/kwargs_only",
params: { hello: "world" },
)
assert_equal({ hello: "world" }, received_positional)
assert_equal({ ok: true }, response[:result])
end
test "custom method handler that opts in to server_context observes cancellation" do
observed = false
@server.define_custom_method(method_name: "custom/slow") do |_params, server_context:|
50.times do
break if server_context.cancelled?
sleep(0.01)
end
observed = server_context.cancelled?
{ ok: true }
end
response, = drive_cancellation(
request_id: 204,
method: "custom/slow",
params: {},
)
assert observed, "custom method handler should observe cancellation via server_context"
assert_nil response, "cancelled custom method must not emit a JSON-RPC response"
end
test "send_peer_cancellation routes notification on parent stream via related_request_id" do
recorded_notifications = []
(class << @mock_transport; self; end).define_method(:send_notification) do |method, params = nil, **kwargs|
recorded_notifications << { method: method, params: params, kwargs: kwargs }
true
end
@session.send_peer_cancellation(
nested_request_id: "nested-1",
related_request_id: 42,
reason: "parent aborted",
)
notif = recorded_notifications.last
assert_equal Methods::NOTIFICATIONS_CANCELLED, notif[:method]
assert_equal "nested-1", notif[:params][:requestId]
assert_equal "parent aborted", notif[:params][:reason]
# Crucially, the cancel notification targets the parent's stream, not the GET SSE stream.
assert_equal 42, notif[:kwargs][:related_request_id]
end
end
end