ProxySettings: Long ProxyServerExceptions result in an error

[Seth401]

Details of the scenario you tried and the problem that is occurring

Using a very "long" ProxyServerExceptions list will lead to an error while trying to apply the configuration. The reason is that the length of the ProxyServerExceptions string currently can't exceed 255 characters as it's converted to a byte.

Verbose logs showing the problem

I'm only including the relevant part.

VERBOSE: [AD]:                            [[ProxySettings]Longbypass] Test-TargetResource: Checking the computer proxy settings to ensure 'Present'.
VERBOSE: [AD]:                            [[ProxySettings]Longbypass] Test-TargetResource: Checking that the computer proxy settings 'DefaultConnectionSettings' are in the desired state.
VERBOSE: [AD]:                            [[ProxySettings]Longbypass] Test-ProxySettings: The proxy setting 'ProxyServerExceptions' value 'b1.com;*.web2.com;*.web3.com;*.web4.com;*.' does not match the desired value '*.example1.com;*.example2.com;*.example3.
com;*.example4.com;*.example5.com;*.example6.com;*.example7.com;*.example8.com;*.example9.com;*.example10.com;*.example11.com;*.example12.com;*.example13.com;*.example14.com;*.example15.com;*.example16.com;*.example17.com'.
VERBOSE: [AD]:                            [[ProxySettings]Longbypass] Test-TargetResource: Computer proxy settings 'DefaultConnectionSettings' are not in the desired state.
VERBOSE: [AD]:                            [[ProxySettings]Longbypass] Test-TargetResource: Checking that the computer proxy settings 'SavedLegacySettings' are in the desired state.
VERBOSE: [AD]:                            [[ProxySettings]Longbypass] Test-ProxySettings: The proxy setting 'ProxyServerExceptions' value 'b1.com;*.web2.com;*.web3.com;*.web4.com;*.' does not match the desired value '*.example1.com;*.example2.com;*.example3.
com;*.example4.com;*.example5.com;*.example6.com;*.example7.com;*.example8.com;*.example9.com;*.example10.com;*.example11.com;*.example12.com;*.example13.com;*.example14.com;*.example15.com;*.example16.com;*.example17.com'.
VERBOSE: [AD]:                            [[ProxySettings]Longbypass] Test-TargetResource: Computer proxy settings 'SavedLegacySettings' are not in the desired state.
VERBOSE: [AD]: LCM:  [ End    Test     ]  [[ProxySettings]Longbypass]  in 0.2190 seconds.
VERBOSE: [AD]: LCM:  [ Start  Set      ]  [[ProxySettings]Longbypass]
VERBOSE: [AD]:                            [[ProxySettings]Longbypass] Set-TargetResource: Applying the computer proxy settings to ensure 'Present'.
VERBOSE: [AD]:                            [[ProxySettings]Longbypass] Set-TargetResource: Enabling computer proxy settings.
Cannot convert value "262" to type "System.Byte". Error: "Value was either too large or too small for an unsigned byte."
    + CategoryInfo          : InvalidArgument: (:) [], CimException
    + FullyQualifiedErrorId : InvalidCastIConvertible
    + PSComputerName        : localhost

Suggested solution to the issue

The responsible line within the ProxySettings DSC resource directly uses the string length. If this exceeds 255 it can't be converted to a byte.
https://github.com/PowerShell/NetworkingDsc/blob/e714098d02654dfa8a3aed6b44430c68cea9fdbf/Modules/NetworkingDsc/DSCResources/MSFT_ProxySettings/MSFT_ProxySettings.psm1#L655

As far as I can tell those 4 bytes can be used to indicate the length but as it is little endian hex you need to convert it to hex and reverse the order for each pair. The following would only be a patch for the write, I didn't check the read but it likely needs to be adjusted as well.

There probably is a better solution to do the conversion.

655c655,662
<         $proxySettings += @($ProxyServerExceptionsString.Length, 0x0, 0x0, 0x0)
---
> 	  $hex = '{0:x8}' -f $ProxyServerExceptionsString.Length
>         $ProxyServerExceptionsStringLength = @()
>         $ProxyServerExceptionsStringLength += @("0x"+($hex[6..7] -join ''))
>         $ProxyServerExceptionsStringLength += @("0x"+($hex[4..5] -join ''))
>         $ProxyServerExceptionsStringLength += @("0x"+($hex[2..3] -join ''))
>         $ProxyServerExceptionsStringLength += @("0x"+($hex[0..1] -join ''))
> 
>         $proxySettings += [Byte[]][Int[]]$ProxyServerExceptionsStringLength

The DSC configuration that is used to reproduce the issue (as detailed as possible)

Using a value of 17 generates a ProxyServerExceptions list that results in a string that's 262 character long. Using a value of 16 results in a string that's 246 characters long.

Configuration LongProxyExample
{
    $bypass = 1..17 | %{ "*.example$_.com" }
    Import-DSCResource -ModuleName NetworkingDsc

    Node localhost
    {
        ProxySettings Longbypass
        {
            IsSingleInstance       = 'Yes'
            ProxyServerExceptions  = $bypass
        }
    }
}

The operating system the target node is running

OsName               : Microsoft Windows Server 2016 Standard
OsOperatingSystemSKU : StandardServerEdition
OsArchitecture       : 64-bit
WindowsBuildLabEx    : 14393.1794.amd64fre.rs1_release.171008-1615
OsLanguage           : en-US
OsMuiLanguages       : {en-US}

Version and build of PowerShell the target node is running

Name                           Value
----                           -----
PSVersion                      5.1.14393.1884
PSEdition                      Desktop
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   10.0.14393.1884
CLRVersion                     4.0.30319.42000
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1

Version of the DSC module that was used ('dev' if using current dev branch)

6.3.0.0

[PlagueHO]

Great catch and thanks for raising this @Seth401 - looks like this one shouldn't be too tough to fix. Happy to take PRs from the community - but otherwise I'll try and get to it as soon as I can (got a few other repos I'm looking after).