@agentx-ai/notion-mcp-server/src/openapi-mcp-server/mcp/proxy.ts

AgentX MCP server for Notion API with user-friendly environment variables

import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import {
  CallToolRequestSchema,
  JSONRPCResponse,
  ListToolsRequestSchema,
  Tool,
} from "@modelcontextprotocol/sdk/types.js";
import { JSONSchema7 as IJsonSchema } from "json-schema";
import { OpenAPIToMCPConverter } from "../openapi/parser";
import { HttpClient, HttpClientError } from "../client/http-client";
import { OpenAPIV3 } from "openapi-types";
import { Transport } from "@modelcontextprotocol/sdk/shared/transport.js";

type PathItemObject = OpenAPIV3.PathItemObject & {
  get?: OpenAPIV3.OperationObject;
  put?: OpenAPIV3.OperationObject;
  post?: OpenAPIV3.OperationObject;
  delete?: OpenAPIV3.OperationObject;
  patch?: OpenAPIV3.OperationObject;
};

type NewToolDefinition = {
  methods: Array<{
    name: string;
    description: string;
    inputSchema: IJsonSchema & { type: "object" };
    returnSchema?: IJsonSchema;
  }>;
};

// import this class, extend and return server
export class MCPProxy {
  private server: Server;
  private httpClient: HttpClient;
  private tools: Record<string, NewToolDefinition>;
  private openApiLookup: Record<
    string,
    OpenAPIV3.OperationObject & { method: string; path: string }
  >;

  constructor(name: string, openApiSpec: OpenAPIV3.Document) {
    this.server = new Server(
      { name, version: "1.0.0" },
      { capabilities: { tools: {} } }
    );
    const baseUrl = openApiSpec.servers?.[0].url;
    if (!baseUrl) {
      throw new Error("No base URL found in OpenAPI spec");
    }
    this.httpClient = new HttpClient(
      {
        baseUrl,
        headers: this.parseHeadersFromEnv(),
      },
      openApiSpec
    );

    // Convert OpenAPI spec to MCP tools
    const converter = new OpenAPIToMCPConverter(openApiSpec);
    const { tools, openApiLookup } = converter.convertToMCPTools();
    this.tools = tools;
    this.openApiLookup = openApiLookup;

    this.setupHandlers();
  }

  private setupHandlers() {
    // Handle tool listing
    this.server.setRequestHandler(ListToolsRequestSchema, async () => {
      const tools: Tool[] = [];

      // Add methods as separate tools to match the MCP format
      Object.entries(this.tools).forEach(([toolName, def]) => {
        def.methods.forEach((method) => {
          const toolNameWithMethod = `${toolName}-${method.name}`;
          const truncatedToolName = this.truncateToolName(toolNameWithMethod);
          tools.push({
            name: truncatedToolName,
            description: method.description,
            inputSchema: method.inputSchema as Tool["inputSchema"],
          });
        });
      });

      return { tools };
    });

    // Handle tool calling
    this.server.setRequestHandler(CallToolRequestSchema, async (request) => {
      const { name, arguments: params } = request.params;

      // Find the operation in OpenAPI spec
      const operation = this.findOperation(name);
      if (!operation) {
        throw new Error(`Method ${name} not found`);
      }

      try {
        // Execute the operation
        const response = await this.httpClient.executeOperation(
          operation,
          params
        );

        // Convert response to MCP format
        return {
          content: [
            {
              type: "text", // currently this is the only type that seems to be used by mcp server
              text: JSON.stringify(response.data), // TODO: pass through the http status code text?
            },
          ],
        };
      } catch (error) {
        console.error("Error in tool call", error);
        if (error instanceof HttpClientError) {
          console.error(
            "HttpClientError encountered, returning structured error",
            error
          );
          const data = error.data?.response?.data ?? error.data ?? {};
          return {
            content: [
              {
                type: "text",
                text: JSON.stringify({
                  status: "error", // TODO: get this from http status code?
                  ...(typeof data === "object" ? data : { data: data }),
                }),
              },
            ],
          };
        }
        throw error;
      }
    });
  }

  private findOperation(
    operationId: string
  ): (OpenAPIV3.OperationObject & { method: string; path: string }) | null {
    return this.openApiLookup[operationId] ?? null;
  }

  private parseHeadersFromEnv(): Record<string, string> {
    const headers: Record<string, string> = {};

    // Get Notion API token
    const apiToken = process.env.NOTION_API_TOKEN;
    if (apiToken) {
      headers["Authorization"] = `Bearer ${apiToken}`;
    } else {
      console.warn(
        "NOTION_API_TOKEN environment variable is not set. API calls may fail."
      );
    }

    // Get Notion version (optional, defaults to 2022-06-28)
    const version = process.env.NOTION_VERSION || "2022-06-28";
    headers["Notion-Version"] = version;

    // Fallback to legacy OPENAPI_MCP_HEADERS for backward compatibility
    const headersJson = process.env.OPENAPI_MCP_HEADERS;
    if (headersJson) {
      try {
        const legacyHeaders = JSON.parse(headersJson);
        if (typeof legacyHeaders === "object" && legacyHeaders !== null) {
          // Merge legacy headers, but new headers take precedence
          Object.assign(headers, legacyHeaders);
        }
      } catch (error) {
        console.warn(
          "Failed to parse OPENAPI_MCP_HEADERS environment variable:",
          error
        );
      }
    }

    return headers;
  }

  private getContentType(headers: Headers): "text" | "image" | "binary" {
    const contentType = headers.get("content-type");
    if (!contentType) return "binary";

    if (contentType.includes("text") || contentType.includes("json")) {
      return "text";
    } else if (contentType.includes("image")) {
      return "image";
    }
    return "binary";
  }

  private truncateToolName(name: string): string {
    if (name.length <= 64) {
      return name;
    }
    return name.slice(0, 64);
  }

  async connect(transport: Transport) {
    // The SDK will handle stdio communication
    await this.server.connect(transport);
  }

  getServer() {
    return this.server;
  }
}