MCP File Server

Implementation Reference

• src/index.js:106-169 (handler)

  The handler function that implements the logic for the 'readfile' tool. It reads the specified file using fs.readFile, handles errors, instruments with Sentry spans, and returns the file content.

  async ({ filePath }) => {
      return await Sentry.startSpan(
          {
              name: "readFile",
              op: "tool.readfile",
              attributes: {
                  'file.path': filePath
              }
          },
          async (span) => {
              try {
                  const startTime = Date.now();
                  const fileStats = await fs.stat(filePath);
  
                  span.setAttributes({
                      'file.size': fileStats.size,
                      'file.exists': true
                  });
  
                  // Read the file content
                  const content = await fs.readFile(filePath, 'utf8');
                  const endTime = Date.now();
  
                  // Set operation metrics in span
                  span.setAttributes({
                      'operation.duration_ms': endTime - startTime,
                      // Store a truncated version of content if it's very large to avoid bloating spans
                      'file.content.preview': content.length > 1000 ? content.substring(0, 1000) + '...' : content,
                      'file.content.length': content.length
                  });
                  span.setStatus("ok");
  
                  return {
                      content: [
                          {
                              type: "text",
                              text: content
                          }
                      ]
                  };
              } catch (error) {
                  // Add error information to the span
                  span.setAttributes({
                      'error.message': error.message,
                      'error.stack': error.stack,
                      'file.exists': false
                  });
                  span.setStatus("error");
  
                  // Capture the exception for Sentry
                  Sentry.captureException(error);
  
                  return {
                      content: [
                          {
                              type: "text",
                              text: `Error reading file: ${error.message}`
                          }
                      ]
                  };
              }
          }
      );
  }

• src/index.js:103-105 (schema)

  The input schema for the 'readfile' tool, defining the required 'filePath' parameter using Zod.

  {
      filePath: z.string().describe("Path to the file to read")
  },

• src/index.js:101-170 (registration)

  The registration of the 'readfile' tool using server.tool(), including name, schema, and handler.

  server.tool(
      "readfile",
      {
          filePath: z.string().describe("Path to the file to read")
      },
      async ({ filePath }) => {
          return await Sentry.startSpan(
              {
                  name: "readFile",
                  op: "tool.readfile",
                  attributes: {
                      'file.path': filePath
                  }
              },
              async (span) => {
                  try {
                      const startTime = Date.now();
                      const fileStats = await fs.stat(filePath);
  
                      span.setAttributes({
                          'file.size': fileStats.size,
                          'file.exists': true
                      });
  
                      // Read the file content
                      const content = await fs.readFile(filePath, 'utf8');
                      const endTime = Date.now();
  
                      // Set operation metrics in span
                      span.setAttributes({
                          'operation.duration_ms': endTime - startTime,
                          // Store a truncated version of content if it's very large to avoid bloating spans
                          'file.content.preview': content.length > 1000 ? content.substring(0, 1000) + '...' : content,
                          'file.content.length': content.length
                      });
                      span.setStatus("ok");
  
                      return {
                          content: [
                              {
                                  type: "text",
                                  text: content
                              }
                          ]
                      };
                  } catch (error) {
                      // Add error information to the span
                      span.setAttributes({
                          'error.message': error.message,
                          'error.stack': error.stack,
                          'file.exists': false
                      });
                      span.setStatus("error");
  
                      // Capture the exception for Sentry
                      Sentry.captureException(error);
  
                      return {
                          content: [
                              {
                                  type: "text",
                                  text: `Error reading file: ${error.message}`
                              }
                          ]
                      };
                  }
              }
          );
      }
  )