Decompressing single files

Recreate a single file from a compressed file.

Overview

In this article, you’ll learn how to use AppleArchive to decompress a previously compressed file, and write the decompressed data to a file.

The code below decompresses the file generated using the steps explained in Compressing single files.

Create the file stream to read the source archive

The ArchiveByteStream class provides static factory methods that create streams for different functions. In this case, use fileStream(path:mode:options:permissions:) to create a byte stream that reads the source file:

let archiveFilePath = FilePath(NSTemporaryDirectory() + "myFile.pdf.lzfse")

guard let readFileStream = ArchiveByteStream.fileStream(
        path: archiveFilePath,
        mode: .readOnly,
        options: [ ],
        permissions: FilePermissions(rawValue: 0o644)) else {
    return
}
defer {
    try? readFileStream.close()
}

Create the file stream to write the decompressed file

You also use fileStream(path:mode:options:permissions:) to create the file stream that writes the decompressed file to the file system. In this case, use the writeOnly mode:

let destinationFilePath = FilePath(NSTemporaryDirectory() + "myFile_decompressed.pdf")

guard let writeFileStream = ArchiveByteStream.fileStream(
        path: destinationFilePath,
        mode: .writeOnly,
        options: [ .create ],
        permissions: FilePermissions(rawValue: 0o644)) else {
    return
}
defer {
    try? writeFileStream.close()
}

Create the decompression stream

Create the decompression stream. Specify the file-reading stream as the input stream that provides the compressed data:

guard let decompressStream = ArchiveByteStream.decompressionStream(readingFrom: readFileStream) else {
    print("unable to create compress stream")
    return
}
defer {
    try? decompressStream.close()
}

Decompress the source archive

Finally, call process(readingFrom:writingTo:) to write the output of the decompression stream to the file-writing stream:

do {
    _ = try ArchiveByteStream.process(readingFrom: decompressStream,
                                      writingTo: writeFileStream)
} catch {
    print("Handle `ArchiveByteStream.process` failed.")
}

On return, myFile_decompressed.pdf exists in NSTemporaryDirectory() and contains the decompressed contents of myFile.pdf.lzfse.