当我的构造函数接收大量字节时，如何在 PowerShell 脚本中使用 New-Object cmdlet？

Question

I am writing a PowerShell function/script (using the version that ships with Windows 10, which I believe is 5.0) to take in a GZip compressed Base64 string and decompress it, and then decode it under the assumption the original uncompressed/decoded string was Unicode encoded.

I am trying to instantiate a new object instance of type MemoryStream using this constructor and the New-Object cmdlet. It takes one parameter, which is an array of bytes.

PowerShell is unable to find a valid overload that accepts the array of bytes I am trying to pass as the constructor's parameter. I believe the issue is due to the array's relatively large length. Please see my code below:

Function DecompressString()
{
    param([parameter(Mandatory)][string]$TextToDecompress)
    
    try
    {
        $bytes = [Convert]::FromBase64String($TextToDecompress)

        $srcStreamParameters = @{
            TypeName = 'System.IO.MemoryStream'
            ArgumentList = ([byte[]]$bytes)
        }

        $srcStream = New-Object @srcStreamParameters
        $dstStream = New-Object -TypeName System.IO.MemoryStream
        
        $gzipParameters = @{
            TypeName = 'System.IO.Compression.GZipStream'
            ArgumentList = ([System.IO.Stream]$srcStream, [System.IO.Compression.CompressionMode]::Decompress)
        }
        
        $gzip = New-Object @gzipParameters
        $gzip.CopyTo($dstStream)
        $output = [Text.Encoding]::Unicode.GetString($dstStream.ToArray())
        Write-Output $output
    }
    catch
    {
        Write-Host "$_" -ForegroundColor Red
    }
    finally
    {
        if ($gzip -ne $null) { $gzip.Dispose() }
        if ($srcStream -ne $null) { $srcStream.Dispose() }
        if ($dstStream -ne $null) { $dstStream.Dispose() }
    }
}

DecompressString
$ExitPrompt = Read-Host -Prompt 'Press Enter to Exit'

The error message I get is: Cannot find an overload for "MemoryStream" and the argument count: "1764".

Can anyone please clarify how I can get the script interpreter to use the constructor correctly with a large byte array?

Answer 1

I thought I would share an answer to this question which I found very interesting, solution to the error has already been provided by Lance U. Matthews in his helpful comment, by adding the unary operator , before the $bytes assigned to the ArgumentList of New-Object , by doing so, the $bytes are passed as a single argument ( array of bytes ) and not as individual elements to the constructor of System.IO.MemoryStream :

$bytes = [Convert]::FromBase64String($compressedString)
$srcStreamParameters = @{
    TypeName     = 'System.IO.MemoryStream'
    ArgumentList = , $bytes
}

$srcStream = New-Object @srcStreamParameters

Beginning in PowerShell 5.0 and going forward, you can construct your memory stream with the following syntax, which is more efficient and straight forward:

$srcStream = [System.IO.MemoryStream]::new($bytes)

As for the functions ( Compress & Expand ), I would like to share my take on these cool functions.

• Required using statements and ArgumentCompleter for -Encoding Parameter.

using namespace System.Text
using namespace System.IO
using namespace System.IO.Compression
using namespace System.Collections
using namespace System.Management.Automation
using namespace System.Collections.Generic
using namespace System.Management.Automation.Language

Add-Type -AssemblyName System.IO.Compression

class EncodingCompleter : IArgumentCompleter {
    [IEnumerable[CompletionResult]] CompleteArgument (
        [string] $commandName,
        [string] $parameterName,
        [string] $wordToComplete,
        [CommandAst] $commandAst,
        [IDictionary] $fakeBoundParameters
    ) {
        [CompletionResult[]] $arguments = foreach($enc in [Encoding]::GetEncodings().Name) {
            if($enc.StartsWith($wordToComplete)) {
                [CompletionResult]::new($enc)
            }
        }
        return $arguments
    }
}

• Compression from string to Base64 GZip compressed string :

function Compress-GzipString {
    [cmdletbinding()]
    param(
        [Parameter(Mandatory, ValueFromPipeline)]
        [string] $String,

        [Parameter()]
        [ArgumentCompleter([EncodingCompleter])]
        [string] $Encoding = 'utf-8',

        [Parameter()]
        [CompressionLevel] $CompressionLevel = 'Optimal'
    )

    try {
        $enc       = [Encoding]::GetEncoding($Encoding)
        $outStream = [MemoryStream]::new()
        $gzip      = [GZipStream]::new($outStream, [CompressionMode]::Compress, $CompressionLevel)
        $inStream  = [MemoryStream]::new($enc.GetBytes($string))
        $inStream.CopyTo($gzip)
    }
    catch {
        $PSCmdlet.WriteError($_)
    }
    finally {
        $gzip, $outStream, $inStream | ForEach-Object Dispose
    }

    try {
        [Convert]::ToBase64String($outStream.ToArray())
    }
    catch {
        $PSCmdlet.WriteError($_)
    }
}

• Expansion from Base64 GZip compressed string to string :

function Expand-GzipString {
    [cmdletbinding()]
    param(
        [Parameter(Mandatory, ValueFromPipeline)]
        [string] $String,

        [Parameter()]
        [ArgumentCompleter([EncodingCompleter])]
        [string] $Encoding = 'utf-8'
    )

    try {
        $enc       = [Encoding]::GetEncoding($Encoding)
        $bytes     = [Convert]::FromBase64String($String)
        $outStream = [MemoryStream]::new()
        $inStream  = [MemoryStream]::new($bytes)
        $gzip      = [GZipStream]::new($inStream, [CompressionMode]::Decompress)
        $gzip.CopyTo($outStream)
        $enc.GetString($outStream.ToArray())
    }
    catch {
        $PSCmdlet.WriteError($_)
    }
    finally {
        $gzip, $outStream, $inStream | ForEach-Object Dispose
    }
}

And for the little Length comparison, querying the Loripsum API :

$loremIp = Invoke-RestMethod loripsum.net/api/10/long
$compressedLoremIp = Compress-GzipString $loremIp

$loremIp, $compressedLoremIp | Select-Object Length

Length
------
  8353
  4940

(Expand-GzipString $compressedLoremIp) -eq $loremIp # => Should be True

These 2 functions as well as Compression From File Path and Expansion from File Path can be found on this repo .