Powershell: Unable to find type when using PS 5 classes

问题

I'm using classes in PS with WinSCP Powershell Assembly. In one of the methods I'm using various types from WinSCP.

This works fine as long as I already have the assembly added - however, because of the way Powershell reads the script when using classes (I assume?), an error is throwed before the assembly could be loaded.

In fact, even if I put a Write-Host at the top, it will not load.

Is there any way of forcing something to run before the rest of the file is parsed?

Transfer() {
    $this.Logger = [Logger]::new()
    try {

        Add-Type -Path $this.Paths.WinSCP            
        $ConnectionType = $this.FtpSettings.Protocol.ToString()
        $SessionOptions = New-Object WinSCP.SessionOptions -Property @{
            Protocol = [WinSCP.Protocol]::$ConnectionType
            HostName = $this.FtpSettings.Server
            UserName = $this.FtpSettings.Username
            Password = $this.FtpSettings.Password
        }

Protocol = [WinSCP.Protocol]::$ConnectionType

Unable to find type [WinSCP.Protocol].

回答1:

As you've discovered, PowerShell refuses to run scripts that contains class definitions that reference then-unavailable (not-yet-loaded) types - the script parsing stage fails.

As of PSv5.1, even a using assembly statement at the top of a script does not help in this case, because in your case the type is referenced in the context of a PS class definition - this may get fixed in PowerShell Core, however; the required work is being tracked in this GitHub issue.

The proper solution is to create a script module (*.psm1) whose associated manifest (*.psd1) declares the assembly containing the referenced types a prerequisite, via the RequiredAssemblies key.

^{See alternative solution at the bottom if using modules is not an option.}

Here's a simplified walk-through:

Create test module tm as follows:

Create module folder ./tm and manifest (*.psd1) in it:

# Create module folder
mkdir ./tm

# Create manifest file that declares the WinSCP assembly a prerequisite.
# Modify the path to the assembly as needed; you may specify a relative path, but
# note that the path must not contain variable references (e.g., $HOME).
New-ModuleManifest ./tm/tm.psd1 -RootModule tm.psm1 `
  -RequiredAssemblies C:\path\to\WinSCPnet.dll

Create the script module file (*.psm1) in the module folder:

Create file ./tm/tm.psm1 with your class definition; e.g.:
```
class Foo {
  # Simply return the full name of the WinSCP type.
  [string] Bar() {
    return [WinSCP.Protocol].FullName
  }
}
```
Note: In the real world, modules are usually placed in one of the standard locations defined in $env:PSMODULEPATH, so that the module can be referenced by name only, without needing to specify a (relative) path.

Use the module:

PS> using module ./tm; (New-Object Foo).Bar()
WinSCP.Protocol

The using module statement imports the module and - unlike Import-Module - also makes the class defined in the module available to the current session.

Since importing the module implicitly loaded the WinSCP assembly thanks to the RequiredAssemblies key in the module manifest, instantiating class Foo, which references the assembly's types, succeeded.

If your use case doesn't allow the use of modules, you can use Invoke-Expression in a pinch, but note that it's generally better to avoid Invoke-Expression in the interest of robustness and so as to avoid security risks^[1] .

# Adjust this path as needed.
Add-Type -LiteralPath C:\path\to\WinSCPnet.dll

# By placing the class definition in a string that is invoked at *runtime*
# via Invoke-Expression, *after* the WinSCP assembly has been loaded, the
# class definition succeeds.
Invoke-Expression @'
class Foo {
  # Simply return the full name of the WinSCP type.
  [string] Bar() {
    return [WinSCP.Protocol].FullName
  }
}
'@

(New-Object Foo).Bar()

^{[1] It's not a concern in this case, but generally, given that Invoke-Expression can invoke any command stored in a string, applying it to strings not fully under your control can result in the execution of malicious commands.
This caveat applies to other language analogously, such as to Bash's built-in eval command.}

回答2:

Although it's not the solution per se, I worked around it. However, I'll leave the question open as it still stands

Instead of using WinSCP-types, I just use strings. Seeing as I already have enumerals that are identical to WinSCP.Protocol

Enum Protocols {
    Sftp
    Ftp
    Ftps
}

And have set Protocol in FtpSettings

$FtpSettings.Protocol = [Protocols]::Sftp

I can set the protocol like this

$SessionOptions = New-Object WinSCP.SessionOptions -Property @{
            Protocol = $this.FtpSettings.Protocol.ToString()
            HostName = $this.FtpSettings.Server
            UserName = $this.FtpSettings.Username
            Password = $this.FtpSettings.Password
        }

I used similar on [WinSCP.TransferMode]

$TransferOptions.TransferMode = "Binary" #[WinSCP.TransferMode]::Binary

回答3:

First, I would recommend mklement0's answer.

However, there is a bit of running around you can do to get much the same effect with a bit less work, which can be helpful in smaller projects or in the early stages.

It's possible to merely . source another ps1 file in your code which contains your classes referencing a not yet loaded library after you load the referenced assembly.

##########
MyClasses.ps1

Class myClass
{
     [3rdParty.Fancy.Object] $MyFancyObject
}

Then you can call your custom class library from your main script with a .

#######
MyMainScriptFile.ps1

#Load fancy object's library
Import-Module Fancy.Module #If it's in a module
Add-Type -Path "c:\Path\To\FancyLibrary.dll" #if it's in a dll you have to reference

. C:\Path\to\MyClasses.ps1

The original parsing will pass muster, the script will start, your reference will be added, and then as the script continues, the . sourced file will be read and parsed, adding your custom classes without issue as their reference library is in memory by the time the code is parsed.

It's still very much better to make and use a module with the proper manifest, but this will get by easy and is very easy to remember and use.

来源：https://stackoverflow.com/questions/42837447/powershell-unable-to-find-type-when-using-ps-5-classes

标签

powershell

winscp-net

add-type