PowerShell

Decompress Large Text File in Blocks

See more Compression Examples

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

Add-Type -Path "C:\chilkat\ChilkatDotNet47-x64\ChilkatDotNet47.dll"

$success = $false

# 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 = New-Object Chilkat.Compression
$compress.Algorithm = "deflate"

$success = $compress.CompressFile("qa_data/hamlet.xml","qa_data/hamlet_compressed.dat")
if ($success -eq $false) {
    $($compress.LastErrorText)
    exit
}

$fac = New-Object Chilkat.FileAccess

# 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.
$("uncompressed size: " + $fac.FileSize($originalPath))
$("compressed size: " + $fac.FileSize("qa_data/hamlet_compressed.dat"))

# Decompress in blocks..
$facSrc = New-Object Chilkat.FileAccess
$facDest = New-Object Chilkat.FileAccess

$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 -eq $false) {
    $($facDest.LastErrorText)
    exit
}

# Assuming numBlocks > 1
$compress.FirstChunk = $true
$compress.LastChunk = $false

$i = 0
while ($i -lt $numBlocks) {
    $compressedBytes = $facSrc.ReadBlock($i,$blockSize)
    $decompressedStr = $compress.DecompressString($compressedBytes)

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

    $i = $i + 1

    $compress.FirstChunk = $false
    if ($i -eq ($numBlocks - 1)) {
        $compress.LastChunk = $true
    }

}

$facSrc.FileClose()
$facDest.FileClose()

# Examine the size of the restored file.
$("restored size: " + $fac.FileSize($restoredPath))

# Compare the contents of the original with the restored.
$bEqualContents = $fac.FileContentsEqual($restoredPath,$originalPath)
$("Contents Equal: " + $bEqualContents)