Class: MCP::Server::InputRequiredResult

Inherits:
Object
  • Object
show all
Defined in:
lib/mcp/server/input_required_result.rb

Overview

A multi round-trip input_required result (SEP-2322, MCP 2026-07-28). Handlers for tools/call, prompts/get, and resources/read may return one instead of their normal result to ask the client for additional input: input_requests maps server-assigned keys to embedded request shapes (elicitation/create, sampling/createMessage, or roots/list), and request_state is an opaque continuation string the client echoes back byte-exactly when it retries the original request with inputResponses under the same keys.

The server holds no memory between rounds: handlers re-run from the start on every retry and read the answers via server_context.input_responses / server_context.request_state (deterministic replay, matching the Python SDK). At least one of the two fields must be present; a request_state-only result is the load-shedding form ("retry later"). https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2322

Constant Summary collapse

EMBEDDABLE_METHODS = 
[
  Methods::ELICITATION_CREATE,
  Methods::SAMPLING_CREATE_MESSAGE,
  Methods::ROOTS_LIST,
].freeze

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(input_requests: nil, request_state: nil) ⇒ InputRequiredResult

Returns a new instance of InputRequiredResult.



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# File 'lib/mcp/server/input_required_result.rb', line 29

def initialize(input_requests: nil, request_state: nil)
  if (input_requests.nil? || input_requests.empty?) && request_state.nil?
    raise ArgumentError, "at least one of input_requests or request_state is required"
  end
  unless request_state.nil? || request_state.is_a?(String)
    raise ArgumentError, "request_state must be a String"
  end

  @input_requests = normalize_input_requests(input_requests)
  @request_state = request_state
  freeze
end

Instance Attribute Details

#input_requests ⇒ Object (readonly)

Returns the value of attribute input_requests.



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# File 'lib/mcp/server/input_required_result.rb', line 27

def input_requests
  @input_requests
end

#request_state ⇒ Object (readonly)

Returns the value of attribute request_state.



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# File 'lib/mcp/server/input_required_result.rb', line 27

def request_state
  @request_state
end

Instance Method Details

#missing_client_capabilities(declared) ⇒ Object

The subset of #required_client_capabilities the request did not declare. Per SEP-2575, servers MUST NOT rely on capabilities the client has not declared, so a non-empty return means the result must not be sent (-32021).



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# File 'lib/mcp/server/input_required_result.rb', line 68

def missing_client_capabilities(declared)
  missing = missing_subtree(required_client_capabilities, declared)
  prune_implied_form_elicitation(missing, declared)
end

#required_client_capabilities ⇒ Object

The client capabilities required to fulfill every embedded request, merged into one nested hash. The mapping matches the TypeScript SDK's requiredClientCapabilitiesForInputRequest: elicitation/create with mode: "url" requires elicitation.url, any other elicitation/create requires elicitation.form, sampling/createMessage with tools/toolChoice requires sampling.tools (plain sampling otherwise), and roots/list requires roots.



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# File 'lib/mcp/server/input_required_result.rb', line 59

def required_client_capabilities
  (@input_requests || {}).values.reduce({}) do |merged, entry|
    deep_merge(merged, entry_capability(entry))
  end
end

#to_h ⇒ Object 



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# File 'lib/mcp/server/input_required_result.rb', line 42

def to_h
  serialized_requests = @input_requests&.transform_values do |entry|
    { method: entry[:method], params: entry[:params] }.compact
  end

  {
    resultType: ResultType::INPUT_REQUIRED,
    inputRequests: serialized_requests,
    requestState: @request_state,
  }.compact
end