Error Handling for Invoke-RestMethod - Powershell - rest

Question

I have a powershell script using the Skytap API (REST). I would like to catch the error, if there is one, and try to display it.
For example, we are changing the IP:
Invoke-RestMethod -Uri https://cloud.skytap.com/configurations/XXXXXX/vms/YYYYYY/interfaces/ZZZZZZ?ip=10.0.0.1 -Method PUT -Headers $headers
If the IP is used somewhere else, I will get the 409 Conflict Error (Request is well-formed but conflicts with another resource or permission).
I would like to check if the error is 409 and then tell it to do something else about it.

Answer 1

This is somewhat awkward but the only way to do it as far as I know without doing something more complicated like using .NET's WebRequest and ConvertFrom-Json (or whatever data format you are expecting).
try {
Invoke-RestMethod ... your parameters here ...
} catch {
# Dig into the exception to get the Response details.
# Note that value__ is not a typo.
Write-Host "StatusCode:" $_.Exception.Response.StatusCode.value__
Write-Host "StatusDescription:" $_.Exception.Response.StatusDescription
}

Answer 2

I know you asked for Powershellv4, but since v6/v7 :
Try {
$WebRequestResult = Invoke-RestMethod -Uri $URL -Headers $Headers -Body $BodyJSON -Method $Method -ContentType $ContentType -SkipCertificateCheck
} Catch {
if($_.ErrorDetails.Message) {
Write-Host $_.ErrorDetails.Message
} else {
Write-Host $_
}
}

Answer 3

The Special Variable $? will solve this. It stands for $LASTEXITCODE = 0 (everything ok). It will ask for the Result Code from the previous Command.
Invoke-RestMethod -Uri https://cloud.skytap.com/configurations/XXXXXX/vms/YYYYYY/interfaces/ZZZZZZ?ip=10.0.0.1 -Method PUT -Headers $headers
if (!$?) {
throw $_.ErrorDetails.Message
}

Answer 4

Powershell 7 introduces the -SkipHttpErrorCheck parameter. This instructs the cmdlet to behave in a similar way to web requests in programming frameworks (i.e. where 404, 409, etc. are valid responses - the web request is successful but the server returned an error code).
This can be combined with the -StatusCodeVariable parameter. This instructs the cmdlet to insert the response code into a variable. However, the variable name is passed as a string (not as a reference). For example:
$scv = $null
Invoke-RestMethod ... -SkipHttpErrorCheck -StatusCodeVariable "scv"