ConvertFrom-Json : Error during serialization or deserialization using the JSON JavaScriptSerializer

Question

I have an API and when I run the PowerShell script:

Invoke-WebRequest 'https://api.tfl.gov.uk/Place/Type/OysterTicketShop'|ConvertFrom-Json

I get the error:

ConvertFrom-Json : Error during serialization or deserialization using the JSON JavaScriptSerializer. The length of the string exceeds the value set on the maxJsonLength property. Parameter name: input At line:2 char:72 + Invoke-WebRequest 'https://api.tfl.gov.uk/Place/Type/OysterTicketShop'|ConvertFr ... + ~~~~~~~~~ + CategoryInfo : NotSpecified: (:) [ConvertFrom-Json], ArgumentException + FullyQualifiedErrorId : System.ArgumentException,Microsoft.PowerShell.Commands.ConvertFromJsonCommand

My understanding is the API is quite large but I haven't been able to resolve the issue.

I tried using:

Invoke-WebRequest 'https://api.tfl.gov.uk/Place/Type/OysterTicketShop'|ConvertFrom-Json 
[void][System.Reflection.Assembly]::LoadWithPartialName("System.Web.Extensions")
$jsonserial= New-Object -TypeName System.Web.Script.Serialization.JavaScriptSerializer 
$jsonserial.MaxJsonLength = $somevalue 
$Obj = $jsonserial.DeserializeObject($rawtext) 
$jsonserial.MaxJsonLength = [int]::MaxValue

I still got the same error.

I edited and formatted the code. Please check if I removed or added some whitespace that is harmful. — ypercubeᵀᴹ
– ypercubeᵀᴹ, Commented Oct 1, 2017 at 18:54

Parrish · Accepted Answer · 2017-10-01 21:07:02Z

2

Welp, if you follow the logic above, you are trying to convert the webrequest object from JSON which it is not. If the body is what is in JSON then you need to do the following.

ConvertFrom-Json (Invoke-WebRequest 'https://api.tfl.gov.uk/Place/Type/OysterTicketShop').Content

That is about it.

answered Oct 1, 2017 at 21:07

Parrish

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Comments

David · Accepted Answer · 2017-10-01 20:14:42Z

A couple of issues here.

Invoke-WebRequest 'https://api.tfl.gov.uk/Place/Type/OysterTicketShop'|ConvertFrom-Json

You are still using the same method here. And then it seems like you have pasted some somewhat relevant code under it. What does $rawtext and $somevalue hold?

$jsonserial.MaxJsonLength = $somevalue 
$Obj = $jsonserial.DeserializeObject($rawtext) 
$jsonserial.MaxJsonLength = [int]::MaxValue

There is no need to change MaxJsonLength twice, especially not after the deserialization.

You want to remove the ConvertFrom-Json cmdlet because of the length limit and use the webrequest response for the JavaScriptSerializer.

$url = "https://api.tfl.gov.uk/Place/Type/OysterTicketShop"
[void][System.Reflection.Assembly]::LoadWithPartialName("System.Web.Extensions")
$jsonserial = New-Object -TypeName System.Web.Script.Serialization.JavaScriptSerializer
$jsonserial.MaxJsonLength = [int]::MaxValue
#Because of SSL requirements
[Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
#Getting webresponse/JSON data, stored in a varibale
$content = (Invoke-WebRequest $url).Content
#Deserializing the JSON data
$Obj = $jsonserial.DeserializeObject($content)

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