index.js•13 kB
import { mergeCapabilities, Protocol } from '../shared/protocol.js';
import { CallToolResultSchema, CompleteResultSchema, EmptyResultSchema, GetPromptResultSchema, InitializeResultSchema, LATEST_PROTOCOL_VERSION, ListPromptsResultSchema, ListResourcesResultSchema, ListResourceTemplatesResultSchema, ListToolsResultSchema, ReadResourceResultSchema, SUPPORTED_PROTOCOL_VERSIONS, ErrorCode, McpError } from '../types.js';
import Ajv from 'ajv';
/**
* An MCP client on top of a pluggable transport.
*
* The client will automatically begin the initialization flow with the server when connect() is called.
*
* To use with custom types, extend the base Request/Notification/Result types and pass them as type parameters:
*
* ```typescript
* // Custom schemas
* const CustomRequestSchema = RequestSchema.extend({...})
* const CustomNotificationSchema = NotificationSchema.extend({...})
* const CustomResultSchema = ResultSchema.extend({...})
*
* // Type aliases
* type CustomRequest = z.infer<typeof CustomRequestSchema>
* type CustomNotification = z.infer<typeof CustomNotificationSchema>
* type CustomResult = z.infer<typeof CustomResultSchema>
*
* // Create typed client
* const client = new Client<CustomRequest, CustomNotification, CustomResult>({
* name: "CustomClient",
* version: "1.0.0"
* })
* ```
*/
export class Client extends Protocol {
/**
* Initializes this client with the given name and version information.
*/
constructor(_clientInfo, options) {
var _a;
super(options);
this._clientInfo = _clientInfo;
this._cachedToolOutputValidators = new Map();
this._capabilities = (_a = options === null || options === void 0 ? void 0 : options.capabilities) !== null && _a !== void 0 ? _a : {};
this._ajv = new Ajv();
}
/**
* Registers new capabilities. This can only be called before connecting to a transport.
*
* The new capabilities will be merged with any existing capabilities previously given (e.g., at initialization).
*/
registerCapabilities(capabilities) {
if (this.transport) {
throw new Error('Cannot register capabilities after connecting to transport');
}
this._capabilities = mergeCapabilities(this._capabilities, capabilities);
}
assertCapability(capability, method) {
var _a;
if (!((_a = this._serverCapabilities) === null || _a === void 0 ? void 0 : _a[capability])) {
throw new Error(`Server does not support ${capability} (required for ${method})`);
}
}
async connect(transport, options) {
await super.connect(transport);
// When transport sessionId is already set this means we are trying to reconnect.
// In this case we don't need to initialize again.
if (transport.sessionId !== undefined) {
return;
}
try {
const result = await this.request({
method: 'initialize',
params: {
protocolVersion: LATEST_PROTOCOL_VERSION,
capabilities: this._capabilities,
clientInfo: this._clientInfo
}
}, InitializeResultSchema, options);
if (result === undefined) {
throw new Error(`Server sent invalid initialize result: ${result}`);
}
if (!SUPPORTED_PROTOCOL_VERSIONS.includes(result.protocolVersion)) {
throw new Error(`Server's protocol version is not supported: ${result.protocolVersion}`);
}
this._serverCapabilities = result.capabilities;
this._serverVersion = result.serverInfo;
// HTTP transports must set the protocol version in each header after initialization.
if (transport.setProtocolVersion) {
transport.setProtocolVersion(result.protocolVersion);
}
this._instructions = result.instructions;
await this.notification({
method: 'notifications/initialized'
});
}
catch (error) {
// Disconnect if initialization fails.
void this.close();
throw error;
}
}
/**
* After initialization has completed, this will be populated with the server's reported capabilities.
*/
getServerCapabilities() {
return this._serverCapabilities;
}
/**
* After initialization has completed, this will be populated with information about the server's name and version.
*/
getServerVersion() {
return this._serverVersion;
}
/**
* After initialization has completed, this may be populated with information about the server's instructions.
*/
getInstructions() {
return this._instructions;
}
assertCapabilityForMethod(method) {
var _a, _b, _c, _d, _e;
switch (method) {
case 'logging/setLevel':
if (!((_a = this._serverCapabilities) === null || _a === void 0 ? void 0 : _a.logging)) {
throw new Error(`Server does not support logging (required for ${method})`);
}
break;
case 'prompts/get':
case 'prompts/list':
if (!((_b = this._serverCapabilities) === null || _b === void 0 ? void 0 : _b.prompts)) {
throw new Error(`Server does not support prompts (required for ${method})`);
}
break;
case 'resources/list':
case 'resources/templates/list':
case 'resources/read':
case 'resources/subscribe':
case 'resources/unsubscribe':
if (!((_c = this._serverCapabilities) === null || _c === void 0 ? void 0 : _c.resources)) {
throw new Error(`Server does not support resources (required for ${method})`);
}
if (method === 'resources/subscribe' && !this._serverCapabilities.resources.subscribe) {
throw new Error(`Server does not support resource subscriptions (required for ${method})`);
}
break;
case 'tools/call':
case 'tools/list':
if (!((_d = this._serverCapabilities) === null || _d === void 0 ? void 0 : _d.tools)) {
throw new Error(`Server does not support tools (required for ${method})`);
}
break;
case 'completion/complete':
if (!((_e = this._serverCapabilities) === null || _e === void 0 ? void 0 : _e.completions)) {
throw new Error(`Server does not support completions (required for ${method})`);
}
break;
case 'initialize':
// No specific capability required for initialize
break;
case 'ping':
// No specific capability required for ping
break;
}
}
assertNotificationCapability(method) {
var _a;
switch (method) {
case 'notifications/roots/list_changed':
if (!((_a = this._capabilities.roots) === null || _a === void 0 ? void 0 : _a.listChanged)) {
throw new Error(`Client does not support roots list changed notifications (required for ${method})`);
}
break;
case 'notifications/initialized':
// No specific capability required for initialized
break;
case 'notifications/cancelled':
// Cancellation notifications are always allowed
break;
case 'notifications/progress':
// Progress notifications are always allowed
break;
}
}
assertRequestHandlerCapability(method) {
switch (method) {
case 'sampling/createMessage':
if (!this._capabilities.sampling) {
throw new Error(`Client does not support sampling capability (required for ${method})`);
}
break;
case 'elicitation/create':
if (!this._capabilities.elicitation) {
throw new Error(`Client does not support elicitation capability (required for ${method})`);
}
break;
case 'roots/list':
if (!this._capabilities.roots) {
throw new Error(`Client does not support roots capability (required for ${method})`);
}
break;
case 'ping':
// No specific capability required for ping
break;
}
}
async ping(options) {
return this.request({ method: 'ping' }, EmptyResultSchema, options);
}
async complete(params, options) {
return this.request({ method: 'completion/complete', params }, CompleteResultSchema, options);
}
async setLoggingLevel(level, options) {
return this.request({ method: 'logging/setLevel', params: { level } }, EmptyResultSchema, options);
}
async getPrompt(params, options) {
return this.request({ method: 'prompts/get', params }, GetPromptResultSchema, options);
}
async listPrompts(params, options) {
return this.request({ method: 'prompts/list', params }, ListPromptsResultSchema, options);
}
async listResources(params, options) {
return this.request({ method: 'resources/list', params }, ListResourcesResultSchema, options);
}
async listResourceTemplates(params, options) {
return this.request({ method: 'resources/templates/list', params }, ListResourceTemplatesResultSchema, options);
}
async readResource(params, options) {
return this.request({ method: 'resources/read', params }, ReadResourceResultSchema, options);
}
async subscribeResource(params, options) {
return this.request({ method: 'resources/subscribe', params }, EmptyResultSchema, options);
}
async unsubscribeResource(params, options) {
return this.request({ method: 'resources/unsubscribe', params }, EmptyResultSchema, options);
}
async callTool(params, resultSchema = CallToolResultSchema, options) {
const result = await this.request({ method: 'tools/call', params }, resultSchema, options);
// Check if the tool has an outputSchema
const validator = this.getToolOutputValidator(params.name);
if (validator) {
// If tool has outputSchema, it MUST return structuredContent (unless it's an error)
if (!result.structuredContent && !result.isError) {
throw new McpError(ErrorCode.InvalidRequest, `Tool ${params.name} has an output schema but did not return structured content`);
}
// Only validate structured content if present (not when there's an error)
if (result.structuredContent) {
try {
// Validate the structured content (which is already an object) against the schema
const isValid = validator(result.structuredContent);
if (!isValid) {
throw new McpError(ErrorCode.InvalidParams, `Structured content does not match the tool's output schema: ${this._ajv.errorsText(validator.errors)}`);
}
}
catch (error) {
if (error instanceof McpError) {
throw error;
}
throw new McpError(ErrorCode.InvalidParams, `Failed to validate structured content: ${error instanceof Error ? error.message : String(error)}`);
}
}
}
return result;
}
cacheToolOutputSchemas(tools) {
this._cachedToolOutputValidators.clear();
for (const tool of tools) {
// If the tool has an outputSchema, create and cache the Ajv validator
if (tool.outputSchema) {
try {
const validator = this._ajv.compile(tool.outputSchema);
this._cachedToolOutputValidators.set(tool.name, validator);
}
catch (_a) {
// Ignore schema compilation errors
}
}
}
}
getToolOutputValidator(toolName) {
return this._cachedToolOutputValidators.get(toolName);
}
async listTools(params, options) {
const result = await this.request({ method: 'tools/list', params }, ListToolsResultSchema, options);
// Cache the tools and their output schemas for future validation
this.cacheToolOutputSchemas(result.tools);
return result;
}
async sendRootsListChanged() {
return this.notification({ method: 'notifications/roots/list_changed' });
}
}
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