Method writeFileHeader

src/handlers/lzh/encoder.ts:40–113

(file: LHAFileInput)

  }

  private writeFileHeader(file: LHAFileInput): void {
    const timestamp = file.timestamp || new Date();
    const method = "-lh0-"; // Store method (no compression)
    const compressedData = file.data;
    const originalSize = file.data.length;
    const compressedSize = compressedData.length;
    const crc = this.calculateCRC16(file.data);

    // Prepare filename (ensure it's not too long)
    const filenameBytes = new TextEncoder().encode(file.filename);
    const filenameLength = Math.min(filenameBytes.length, 255);

    // Calculate header size (level 0)
    // 2 (header size + checksum) + 5 (method) + 4 (comp size) + 4 (orig size) + 
    // 2 (time) + 2 (date) + 1 (attr) + 1 (level) + 1 (name len) + name + 2 (crc)
    const baseHeaderSize = 2 + 5 + 4 + 4 + 2 + 2 + 1 + 1 + 1 + filenameLength + 2;
    const headerSize = baseHeaderSize - 2; // Size doesn't include the size byte itself and checksum

    const header = new Uint8Array(baseHeaderSize);
    let offset = 0;

    // Header size
    header[offset++] = headerSize;

    // Header checksum (calculate later)
    const checksumOffset = offset;
    header[offset++] = 0;

    // Method
    const methodBytes = new TextEncoder().encode(method);
    header.set(methodBytes, offset);
    offset += 5;

    // Compressed size
    this.writeDWord(header, offset, compressedSize);
    offset += 4;

    // Original size
    this.writeDWord(header, offset, originalSize);
    offset += 4;

    // MS-DOS timestamp
    const dosTime = this.dateToDosTime(timestamp);
    this.writeWord(header, offset, dosTime.time);
    offset += 2;
    this.writeWord(header, offset, dosTime.date);
    offset += 2;

    // Attributes (0x20 = archive bit)
    header[offset++] = 0x20;

    // Level (0)
    header[offset++] = 0x00;

    // Filename length
    header[offset++] = filenameLength;

    // Filename