feat: add support for elicitation

Author: krtkvrm

mcp/client.go

@@ -56,6 +56,9 @@ type ClientOptions struct {
 	// Handler for sampling.
 	// Called when a server calls CreateMessage.
 	CreateMessageHandler func(context.Context, *ClientSession, *CreateMessageParams) (*CreateMessageResult, error)
+	// Handler for elicitation.
+	// Called when a server requests user input via Elicit.
+	ElicitationHandler func(context.Context, *ClientSession, *ElicitParams) (*ElicitResult, error)
 	// Handlers for notifications from the server.
 	ToolListChangedHandler      func(context.Context, *ClientSession, *ToolListChangedParams)
 	PromptListChangedHandler    func(context.Context, *ClientSession, *PromptListChangedParams)
@@ -119,6 +122,9 @@ func (c *Client) Connect(ctx context.Context, t Transport) (cs *ClientSession, e
 	if c.opts.CreateMessageHandler != nil {
 		caps.Sampling = &SamplingCapabilities{}
 	}
+	if c.opts.ElicitationHandler != nil {
+		caps.Elicitation = &ElicitationCapabilities{}
+	}
 
 	params := &InitializeParams{
 		ProtocolVersion: latestProtocolVersion,
@@ -255,6 +261,14 @@ func (c *Client) createMessage(ctx context.Context, cs *ClientSession, params *C
 	return c.opts.CreateMessageHandler(ctx, cs, params)
 }
 
+func (c *Client) elicit(ctx context.Context, cs *ClientSession, params *ElicitParams) (*ElicitResult, error) {
+	if c.opts.ElicitationHandler == nil {
+		// TODO: wrap or annotate this error? Pick a standard code?
+		return nil, &jsonrpc2.WireError{Code: CodeUnsupportedMethod, Message: "client does not support elicitation"}
+	}
+	return c.opts.ElicitationHandler(ctx, cs, params)
+}
+
 // AddSendingMiddleware wraps the current sending method handler using the provided
 // middleware. Middleware is applied from right to left, so that the first one is
 // executed first.
@@ -291,6 +305,7 @@ var clientMethodInfos = map[string]methodInfo{
 	methodPing:                      newMethodInfo(sessionMethod((*ClientSession).ping)),
 	methodListRoots:                 newMethodInfo(clientMethod((*Client).listRoots)),
 	methodCreateMessage:             newMethodInfo(clientMethod((*Client).createMessage)),
+	methodElicit:                    newMethodInfo(clientMethod((*Client).elicit)),
 	notificationToolListChanged:     newMethodInfo(clientMethod((*Client).callToolChangedHandler)),
 	notificationPromptListChanged:   newMethodInfo(clientMethod((*Client).callPromptChangedHandler)),
 	notificationResourceListChanged: newMethodInfo(clientMethod((*Client).callResourceChangedHandler)),

mcp/cmd.go

@@ -5,7 +5,7 @@
 package mcp
 
 import (
-	"context"
+	"context" <-
 	"fmt"
 	"io"
 	"os/exec"

mcp/protocol.go

@@ -893,7 +893,30 @@ type ResourceUpdatedNotificationParams struct {
 
 // TODO(jba): add CompleteRequest and related types.
 
-// TODO(jba): add ElicitRequest and related types.
+type ElicitParams struct {
+	// This property is reserved by the protocol to allow clients and servers to
+	// attach additional metadata to their responses.
+	Meta `json:"_meta,omitempty"`
+	// A human-readable message describing what information is being requested.
+	Message string `json:"message"`
+	// A JSON Schema object defining the structure of the requested data.
+	RequestedSchema *jsonschema.Schema `json:"requestedSchema"`
+}
+
+func (x *ElicitParams) GetProgressToken() any  { return getProgressToken(x) }
+func (x *ElicitParams) SetProgressToken(t any) { setProgressToken(x, t) }
+
+// The client's response to an elicitation/create request from the server.
+type ElicitResult struct {
+	// This property is reserved by the protocol to allow clients and servers to
+	// attach additional metadata to their responses.
+	Meta `json:"_meta,omitempty"`
+	// The action taken by the user: "accept", "decline", or "cancel".
+	Action string `json:"action"`
+	// The data provided by the user if action is "accept". This should conform
+	// to the requested schema.
+	Content map[string]any `json:"content,omitempty"`
+}
 
 // An Implementation describes the name and version of an MCP implementation, with an optional
 // title for UI representation.

mcp/server.go

@@ -628,6 +628,11 @@ func (ss *ServerSession) CreateMessage(ctx context.Context, params *CreateMessag
 	return handleSend[*CreateMessageResult](ctx, ss, methodCreateMessage, orZero[Params](params))
 }
 
+// Elicit sends an elicitation request to the client asking for user input.
+func (ss *ServerSession) Elicit(ctx context.Context, params *ElicitParams) (*ElicitResult, error) {
+	return handleSend[*ElicitResult](ctx, ss, methodElicit, orZero[Params](params))
+}
+
 // Log sends a log message to the client.
 // The message is not sent if the client has not called SetLevel, or if its level
 // is below that of the last SetLevel.