Scan QRCode MCP Server

Instructions

Implementation Reference

• src/services/qrcode-service.ts:46-57 (handler)

  Fetches the QR code image from the HTTP(S) URL, validates protocol, fetches and converts to buffer, then decodes using decodeQrFromBuffer.

  export async function decodeQrFromUrl(url: string): Promise<DecodeResult> {
    if (!/^https?:\/\//i.test(url)) {
      throw new Error('Only http(s) URLs are supported for imageUrl');
    }
    const res = await fetch(url);
    if (!res.ok) {
      throw new Error(`Failed to fetch image: ${res.status} ${res.statusText}`);
    }
    const arrayBuffer = await res.arrayBuffer();
    const buffer = Buffer.from(arrayBuffer);
    return decodeQrFromBuffer(buffer);
  }

• src/services/qrcode-service.ts:62-70 (handler)

  Main dispatcher function that routes to imageUrl decoder (decodeQrFromUrl) or dataUrl decoder based on input.

  export async function decodeQr(input: DecodeInput): Promise<DecodeResult> {
    if ('imageDataUrl' in input && input.imageDataUrl) {
      return decodeQrFromDataUrl(input.imageDataUrl);
    }
    if ('imageUrl' in input && input.imageUrl) {
      return decodeQrFromUrl(input.imageUrl);
    }
    throw new Error('Provide either imageDataUrl or imageUrl');
  }

• src/server.ts:72-78 (handler)

  MCP server handler for CallToolRequest of 'decode_qrcode_image_url': validates imageUrl arg and calls decodeQr service.

  if (name === 'decode_qrcode_image_url') {
    if (!args.imageUrl || typeof args.imageUrl !== 'string') {
      throw new Error('Missing required argument: imageUrl');
    }
    const result = await decodeQr({ imageUrl: args.imageUrl });
    return { content: [{ type: 'text', text: result.text }] };
  }

• src/server.ts:44-55 (registration)

  Registers the 'decode_qrcode_image_url' tool in ListToolsResponse with name, description, and inputSchema.

  {
    name: 'decode_qrcode_image_url',
    description: 'Decode a QR code from an HTTP(S) image URL',
    inputSchema: {
      type: 'object',
      required: ['imageUrl'],
      properties: {
        imageUrl: { type: 'string', description: 'HTTP(S) URL to the QR image.' },
      },
      additionalProperties: false,
    },
  },

• src/services/qrcode-service.ts:16-33 (helper)

  Low-level helper that loads image buffer with Jimp, prepares data for jsQR, detects and decodes the QR code.

  export async function decodeQrFromBuffer(buffer: Buffer): Promise<DecodeResult> {
    const image = await Jimp.read(buffer);
    const { data, width, height } = image.bitmap;
  
    // Jimp gives a Node Buffer; jsQR expects a Uint8ClampedArray in RGBA order (same layout as Canvas ImageData).
    const clamped = new Uint8ClampedArray(data.buffer, data.byteOffset, data.byteLength);
    const qr = (
      jsQR as unknown as (
        data: Uint8ClampedArray,
        width: number,
        height: number,
      ) => { data: string } | null
    )(clamped, width, height);
    if (!qr) {
      throw new Error('No QR code detected in image');
    }
    return { text: qr.data };
  }