Function detectImageDimensions

examples/pdf-server/server.ts:1911–1943

* Detect image dimensions from PNG or JPEG bytes.

(
      bytes: Buffer,
    )

     * Detect image dimensions from PNG or JPEG bytes.
     */
    function detectImageDimensions(
      bytes: Buffer,
    ): { width: number; height: number } | null {
      // PNG: width at offset 16 (4 bytes BE), height at offset 20 (4 bytes BE)
      if (
        bytes[0] === 0x89 &&
        bytes[1] === 0x50 &&
        bytes[2] === 0x4e &&
        bytes[3] === 0x47
      ) {
        if (bytes.length >= 24) {
          const width = bytes.readUInt32BE(16);
          const height = bytes.readUInt32BE(20);
          return { width, height };
        }
      }
      // JPEG: scan for SOF0/SOF2 markers (0xFF 0xC0 / 0xFF 0xC2)
      if (bytes[0] === 0xff && bytes[1] === 0xd8) {
        let offset = 2;
        while (offset < bytes.length - 8) {
          if (bytes[offset] !== 0xff) break;
          const marker = bytes[offset + 1];
          if (marker === 0xc0 || marker === 0xc2) {
            const height = bytes.readUInt16BE(offset + 5);
            const width = bytes.readUInt16BE(offset + 7);
            return { width, height };
          }
          const segLen = bytes.readUInt16BE(offset + 2);
          offset += 2 + segLen;
        }
      }
      return null;
    }

    /** Process a single interact command. Returns content parts and an isError flag. */
    async function processInteractCommand(