feat: Add MCP Elicitation support (#332)
* feat: implement MCP elicitation support for interactive user input Adds comprehensive elicitation functionality according to MCP 2025-06-18 specification: Core Features: - ElicitationAction enum (Accept, Decline, Cancel) - CreateElicitationRequestParam and CreateElicitationResult structures - Protocol version V_2025_06_18 with elicitation methods - Full JSON-RPC integration with method constants Capabilities Integration: - ElicitationCapability with schema validation support - ClientCapabilities builder pattern integration - enable_elicitation() and enable_elicitation_schema_validation() methods Handler Support: - create_elicitation method in ClientHandler and ServerHandler traits - Integration with existing request/response union types - Async/await compatible implementation Service Layer: - Basic create_elicitation method via macro expansion - Four convenience methods for common scenarios: * elicit_confirmation() - yes/no questions * elicit_text_input() - string input with optional requirements * elicit_choice() - selection from multiple options * elicit_structured_input() - complex data via JSON Schema Comprehensive Testing: - 11 test cases covering all functionality aspects - JSON serialization/deserialization validation - MCP specification compliance verification - Error handling and edge cases - Performance benchmarks - Capabilities integration tests All tests pass and code follows project standards. * feat: add typed elicitation API with enhanced error handling - Add new 'elicitation' feature that depends on 'client' and 'schemars' - Implement elicit<T>() method for type-safe elicitation with automatic schema generation - Remove convenience methods (elicit_confirmation, elicit_text_input, elicit_choice) - Add ElicitationError enum with detailed error variants: - Service: underlying service errors - UserDeclined: user cancelled or declined request - ParseError: response parsing failed with context - NoContent: no response content provided - Update documentation with comprehensive examples and error handling - Add comprehensive tests for typed elicitation and error handling * fix: correct elicitation direction to comply with MCP 2025-06-18 - Remove CreateElicitationRequest from ClientRequest - clients cannot initiate elicitation - Move elicit methods from client to server - servers now request user input - Add comprehensive direction tests verifying Server→Client→Server flow - Maintain CreateElicitationResult in ClientResult for proper responses - Update handlers to reflect correct message routing - Add elicitation feature flag for typed schema generation Fixes elicitation direction to match specification where servers request interactive user input from clients, not the reverse. * feat: add elicitation capability checking for server methods - Add supports_elicitation() method to check client capabilities - Add CapabilityNotSupported error variant to ElicitationError - Update elicit_structured_input() to check capabilities before execution - Update elicit<T>() method to check capabilities before execution - Add comprehensive tests for capability checking functionality - Tests verify that servers check client capabilities before sending elicitation requests - Ensures compliance with MCP 2025-06-18 specification requirement * fix: json rpc message schema * fix: doc tests * fix: cargo nightly fmt checks * fix: clippy * refactor: separate elicitation methods into dedicated impl block for RoleServer - Move (supports_elicitation, elicit_structured_input, elicit) to separate impl block - Move ElicitationError definition to elicitation methods section - Keep base methods (create_message, list_roots, notify_*) in main impl block with macro - Add section comments to distinguish general and elicitation-specific methods * revert: rollback LATEST protocol version to V_2025_03_26 * fix: remove protocol version assertions - Remove assertions for V_2025_06_18 protocol version * fix: fmt checks * feat: add timeout support for elicitation methods - Add peer_req_with_timeout macro variants for timeout-enabled methods - Implement create_elicitation_with_timeout() method - Implement elicit_with_timeout() for typed elicitation with timeout - Refactor elicit() to use elicit_with_timeout() internally - Add 8 comprehensive timeout tests covering validation, error handling, and realistic scenarios - Fix elicitation feature dependencies in Cargo.toml - Add proper feature gates for elicitation-specific code * feat: add timeout validation to prevent DoS attacks - Add InvalidTimeout error variant for comprehensive validation - Implement validate_timeout function with security limits (1ms-300s) - Integrate validation into peer_req_with_timeout macros - Add comprehensive security tests for timeout validation - Prevent DoS attacks through unreasonable timeout values * feat: separate UserDeclined and UserCancelled elicitation errors According to MCP specification and PR feedback, decline and cancel actions should be handled differently: - UserDeclined: explicit user rejection (clicked "Decline", "No", etc.) - UserCancelled: dismissal without explicit choice (closed dialog, Escape, etc.) Changes: - Split ElicitationError::UserDeclined into two distinct error types - Update error handling logic to map each ElicitationAction correctly - Improve documentation with proper action semantics - Add comprehensive tests for new error types and action mapping - Update examples to demonstrate proper error handling This provides better error granularity allowing servers to handle explicit declines vs cancellations appropriately as per MCP spec. * feat: add compile-time type safety for elicitation methods Add ElicitationSafe trait and elicit_safe\! macro to ensure elicit<T>() methods are only used with types that generate appropriate JSON object schemas, addressing type safety concerns from PR feedback. Features: - ElicitationSafe marker trait for compile-time constraints - elicit_safe\! macro for opt-in type safety declaration - Updated elicit<T> and elicit_with_timeout<T> to require ElicitationSafe bound - Comprehensive documentation with examples and rationale - Full test coverage for new type safety features This prevents common mistakes like: - elicit::<String>() - primitives not suitable for object schemas - elicit::<Vec<i32>>() - arrays don't match client expectations Breaking change: Existing code must add elicit_safe\!(TypeName) declarations for types used with elicit methods. This is an intentional safety improvement. * Revert "feat: add timeout validation to prevent DoS attacks" This reverts commit 829624212b4fb55ec32566329af7ec195c987ef5. * fix: correct doctest example in elicit_safe macro documentation - Remove invalid async/await usage in doctest example - Comment out the actual usage line to show intent without compilation errors - Maintain clear documentation of the macro's purpose and usage * refactor: remove redundant elicitation direction tests - Remove test_elicitation_not_in_client_request (duplicated functionality) - Remove redundant ServerRequest match in test_elicitation_direction_server_to_client - Direction compliance is already verified by the remaining comprehensive test - Reduces test fragility and maintenance burden * feat: add elicitation example with user name collection - Add elicitation server example demonstrating real MCP usage - Implement greet_user tool with context.peer.elicit::<T>() API - Show type-safe elicitation with elicit_safe! macro - Include reset_name tool and MCP Inspector instructions - Update examples documentation and dependencies * fix: add Default impl to ElicitationServer for clippy Resolves clippy::new_without_default warning by implementing Default trait for ElicitationServer struct.
This commit is contained in:
Andrei G
GitHub
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commit
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1 changed files with 2287 additions and 4 deletions
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@ -143,6 +143,7 @@ impl std::fmt::Display for ProtocolVersion {
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}
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impl ProtocolVersion {
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pub const V_2025_06_18: Self = Self(Cow::Borrowed("2025-06-18"));
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pub const V_2025_03_26: Self = Self(Cow::Borrowed("2025-03-26"));
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pub const V_2024_11_05: Self = Self(Cow::Borrowed("2024-11-05"));
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pub const LATEST: Self = Self::V_2025_03_26;
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@ -167,6 +168,7 @@ impl<'de> Deserialize<'de> for ProtocolVersion {
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match s.as_str() {
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"2024-11-05" => return Ok(ProtocolVersion::V_2024_11_05),
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"2025-03-26" => return Ok(ProtocolVersion::V_2025_03_26),
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"2025-06-18" => return Ok(ProtocolVersion::V_2025_06_18),
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_ => {}
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}
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Ok(ProtocolVersion(Cow::Owned(s)))
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@ -1173,6 +1175,75 @@ pub struct ListRootsResult {
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const_string!(RootsListChangedNotificationMethod = "notifications/roots/list_changed");
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pub type RootsListChangedNotification = NotificationNoParam<RootsListChangedNotificationMethod>;
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// =============================================================================
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// ELICITATION (INTERACTIVE USER INPUT)
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// =============================================================================
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// Method constants for elicitation operations.
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// Elicitation allows servers to request interactive input from users during tool execution.
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const_string!(ElicitationCreateRequestMethod = "elicitation/create");
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const_string!(ElicitationResponseNotificationMethod = "notifications/elicitation/response");
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/// Represents the possible actions a user can take in response to an elicitation request.
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///
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/// When a server requests user input through elicitation, the user can:
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/// - Accept: Provide the requested information and continue
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/// - Decline: Refuse to provide the information but continue the operation
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/// - Cancel: Stop the entire operation
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#[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Eq)]
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#[serde(rename_all = "lowercase")]
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#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
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pub enum ElicitationAction {
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/// User accepts the request and provides the requested information
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Accept,
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/// User declines to provide the information but allows the operation to continue
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Decline,
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/// User cancels the entire operation
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Cancel,
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}
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/// Parameters for creating an elicitation request to gather user input.
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///
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/// This structure contains everything needed to request interactive input from a user:
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/// - A human-readable message explaining what information is needed
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/// - A JSON schema defining the expected structure of the response
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#[derive(Debug, Serialize, Deserialize, Clone, PartialEq)]
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#[serde(rename_all = "camelCase")]
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#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
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pub struct CreateElicitationRequestParam {
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/// Human-readable message explaining what input is needed from the user.
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/// This should be clear and provide sufficient context for the user to understand
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/// what information they need to provide.
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pub message: String,
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/// JSON Schema defining the expected structure and validation rules for the user's response.
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/// This allows clients to validate input and provide appropriate UI controls.
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/// Must be a valid JSON Schema Draft 2020-12 object.
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pub requested_schema: JsonObject,
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}
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/// The result returned by a client in response to an elicitation request.
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///
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/// Contains the user's decision (accept/decline/cancel) and optionally their input data
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/// if they chose to accept the request.
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#[derive(Debug, Serialize, Deserialize, Clone, PartialEq)]
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#[serde(rename_all = "camelCase")]
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#[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
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pub struct CreateElicitationResult {
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/// The user's decision on how to handle the elicitation request
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pub action: ElicitationAction,
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/// The actual data provided by the user, if they accepted the request.
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/// Must conform to the JSON schema specified in the original request.
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/// Only present when action is Accept.
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#[serde(skip_serializing_if = "Option::is_none")]
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pub content: Option<Value>,
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}
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/// Request type for creating an elicitation to gather user input
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pub type CreateElicitationRequest =
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Request<ElicitationCreateRequestMethod, CreateElicitationRequestParam>;
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// =============================================================================
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// TOOL EXECUTION RESULTS
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// =============================================================================
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@ -1430,7 +1501,7 @@ ts_union!(
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);
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ts_union!(
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export type ClientResult = CreateMessageResult | ListRootsResult | EmptyResult;
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export type ClientResult = CreateMessageResult | ListRootsResult | CreateElicitationResult | EmptyResult;
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);
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impl ClientResult {
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@ -1445,7 +1516,8 @@ ts_union!(
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export type ServerRequest =
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| PingRequest
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| CreateMessageRequest
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| ListRootsRequest;
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| ListRootsRequest
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| CreateElicitationRequest;
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);
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ts_union!(
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@ -1470,6 +1542,7 @@ ts_union!(
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| ReadResourceResult
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| CallToolResult
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| ListToolsResult
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| CreateElicitationResult
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| EmptyResult
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;
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);
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