Compressing single files

Compress a single file and store the result on the file system.

Overview

In this article, you’ll learn how to use AppleArchive to compress a single-source file, and write the compressed data to a file.

The code below compresses a file named myFile.pdf using the Algorithm.lzfse algorithm, and stores the result in a file named myFile.pdf.lzfse.

Create the file stream to read the source file

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 sourceFilePath = FilePath(NSTemporaryDirectory() + "myFile.pdf")

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

Create the file stream to write the compressed file

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

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

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

Create the compression stream

Create the compression stream, and specify the compression algorithm as lzfse. Specify the file-writing stream as the stream that receives the compressed data:

guard let compressStream = ArchiveByteStream.compressionStream(
        using: .lzfse,
        writingTo: writeFileStream) else {
    return
}
defer {
    try? compressStream.close()
}

Compress the source file

Finally, call process(readingFrom:writingTo:) to send the output of the file-reading stream to the compression stream. In turn, the compression stream sends its output to the file-writing stream:

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

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