(Go) Decompress Large Text File in Blocks

Decompresses a large text file in blocks, and compares the restored (decompressed) file with the original to make sure it's correct.

Chilkat Go Downloads Go Package for Windows, MacOS, Linux, Alpine Linux, Solaris

    // This example requires the Chilkat API to have been previously unlocked.
    // See Global Unlock Sample for sample code.

    // First, let's compress a text file.
    // We'll then decompress in blocks, and compare the decompressed with the original file.

    // Compress a text file:
    compress := chilkat.NewCompression()
    compress.SetAlgorithm("deflate")

    success := compress.CompressFile("qa_data/hamlet.xml","qa_data/hamlet_compressed.dat")
    if success != true {
        fmt.Println(compress.LastErrorText())
        compress.DisposeCompression()
        return
    }

    fac := chilkat.NewFileAccess()

    // Examine the uncompressed and compressed sizes:
    originalPath := "qa_data/hamlet.xml"
    // Note: The FileSize method returns a signed 32-bit integer.  If the file is potentially larger than 2GB, call FileSizeStr instead to return
    // the size of the file as a string, then convert to an integer value.
    fmt.Println("uncompressed size: ", *fac.FileSize(originalPath))
    fmt.Println("compressed size: ", *fac.FileSize("qa_data/hamlet_compressed.dat"))

    // Decompress in blocks..
    facSrc := chilkat.NewFileAccess()
    facDest := chilkat.NewFileAccess()

    facSrc.OpenForRead("qa_data/hamlet_compressed.dat")

    // If we compress in 32K chunks, find out how many blocks there will be.
    blockSize := 32768
    numBlocks := facSrc.GetNumBlocks(blockSize)

    // Open an output file for the decompressed data.
    restoredPath := "qa_output/hamlet_restored.xml"
    success = facDest.OpenForWrite(restoredPath)
    if success != true {
        fmt.Println(facDest.LastErrorText())
        compress.DisposeCompression()
        fac.DisposeFileAccess()
        facSrc.DisposeFileAccess()
        facDest.DisposeFileAccess()
        return
    }

    var decompressedStr *string = new(string)

    i := 0
    for i < numBlocks {
        compressedBytes = facSrc.ReadBlock(i,blockSize)
        if i == 0 {
            decompressedStr = compress.BeginDecompressString(compressedBytes)
        }
        else {
            decompressedStr = compress.MoreDecompressString(compressedBytes)
        }

        facDest.AppendText(*decompressedStr,"utf-8")

        i = i + 1
    }

    // At the very end, flush any remaining content, if any.
    decompressedStr = compress.EndDecompressString()
    facDest.AppendText(*decompressedStr,"utf-8")

    facSrc.FileClose()
    facDest.FileClose()

    // Examine the size of the restored file.
    fmt.Println("restored size: ", *fac.FileSize(restoredPath))

    // Compare the contents of the original with the restored.
    bEqualContents := fac.FileContentsEqual(restoredPath,originalPath)
    fmt.Println("Contents Equal: ", bEqualContents)

    compress.DisposeCompression()
    fac.DisposeFileAccess()
    facSrc.DisposeFileAccess()
    facDest.DisposeFileAccess()