File Split and Merge Utility Tool

1. Introduction

This Java application allows users to split large files into smaller parts and reconstruct them later. It features optional metadata generation for reliable merging, even if filenames are tampered.

2. Splitting Process

When a file is split using the SplitFile class:

• The user selects a file, an output directory, and number of chunks (2–100).
• A metadata file named metadata.part is generated by MetadataGenerator.
• Each chunk contains a 7-byte header:
  • 1 byte: Chunk index
  • 2 bytes: Magic number (short) — same across all parts
  • 4 bytes: Size of the chunk’s actual data
• The remaining bytes are raw file data.

3. Metadata File Structure

The metadata.part file is 271 bytes long, containing:

• 1 byte: Index = 0 (reserved to mark metadata file)
• 2 bytes: Magic number
• 256 bytes: Original filename (UTF-8, padded)
• 8 bytes: Original file size (long)
• 4 bytes: Number of chunks (int)

4. Merging Process

During merging via MergeFiles:

• If metadata is present:
  • Magic number and chunk count are read from metadata.
  • Each chunk’s index and magic number is verified against metadata.
  • All chunks (1 to N) are expected to be present.
• If metadata is absent:
  • The application infers the order from chunk headers alone.
  • All chunks must have a consistent magic number.
  • It validates that there are no missing or duplicate indices.

5. Tamper-Proof Mapping Using Headers

Each chunk includes a header containing its index and magic number. Even if a file is renamed, the index can be read via:

RandomAccessFile.readUnsignedByte(); // index
RandomAccessFile.readShort();       // magic number

6. Error Handling and Validation

• Duplicate indices or mismatched magic numbers will abort the merge.
• Missing chunks (based on metadata or index gaps) are detected.
• If the metadata is corrupt, the user can proceed using chunk headers alone.

7. Screenshots

Split Panel

Chunk files and metadata file after splitting

Merge Panel