LDOC Viewer Backend

This directory contains the backend implementation for the LDOC Viewer application.

The backend provides:

1. LDOC format implementation (reader and writer classes)
2. API endpoints for handling LDOC operations
3. Static file serving for the frontend

The LDOCWriter class handles the creation of LDOC containers:

• Compresses files using zlib
• Detects file types and MIME types
• Creates the LDOC manifest
• Assembles the final container with header, manifest, file data, and trailer

The LDOCReader class handles the extraction and inspection of LDOC containers:

• Parses the LDOC header
• Reads the manifest
• Extracts files from the container
• Provides metadata about the container and its contents

The backend exposes the following API endpoints:

• POST /api/encode: Creates an LDOC container from uploaded files
• POST /api/info: Returns metadata about an LDOC container
• POST /api/extract: Extracts all files from an LDOC container as a ZIP archive
• POST /api/view: Returns a list of files in an LDOC container with metadata
• POST /api/view/file: Returns the content of a specific file from an LDOC container

The backend includes helper functions for detecting file types:

• isTextFile: Determines if a file is a text file based on extension or MIME type
• isImageFile: Determines if a file is an image based on extension or MIME type
• isViewableFile: Determines if a file can be viewed in the browser

The LDOC format consists of:

1. Header (32 bytes):

   • Magic bytes "LDOC01" (6 bytes)
   • Version (1 byte)
   • Flags (1 byte)
   • Manifest length (4 bytes)
   • Manifest offset (8 bytes)
   • Trailer offset (8 bytes)
   • Reserved (4 bytes)

2. Manifest:

   • CBOR-encoded array of objects
   • Each object contains metadata about a file in the container

3. File Data:

   • Compressed file contents using zlib

4. Trailer:

   • JSON-encoded revision history