ConvertFrom-Json max length

Question

I have a problem using PowerShell v3 when converting JSON strings over 2MB in size. The default limit in JSON serializer used by PowerShell is set to 2MB which explains the error.

However when I deserialize object using ConvertFrom-Json on a smaller set (I got various data objects with smaller and bigger internal collections but those are the same objects) it returns very nice object with all properties which I can easily access.

To overcome the limitations of the serializer I tried to deserialize data by hand:

$jsser = New-Object System.Web.Script.Serialization.JavaScriptSerializer
$jsser.MaxJsonLength = $jsser.MaxJsonLength * 10
$jsser.RecursionLimit = 99    

$outObject = $jsser.DeserializeObject($json)

The object looks differently it seems that internal collections were not deserialized and when I try to execute properties they return empty results.

My questions:

1. Assumption is ConvertFrom-Json does some additional magic or somehow creates a template for the object before serialization. Any idea how to replicate it?

2. The object I get is always a PSCustomObject; if I get the object I want setup by ConvertFrom-Json is there anyway to use it as object type in JsonSerializer?

Answer 1

I had the same problem and was able to solve it like this:

[void][System.Reflection.Assembly]::LoadWithPartialName("System.Web.Extensions")        
$jsonserial= New-Object -TypeName System.Web.Script.Serialization.JavaScriptSerializer 
$jsonserial.MaxJsonLength  = 67108864
$Obj = $jsonserial.DeserializeObject($CourseTypesResponse)

You can use $jsonserial.MaxJsonLength to manipulate the MaxJsonLength property

source: https://social.technet.microsoft.com/Forums/windowsserver/en-US/833c99c1-d8eb-400d-bf58-38f7265b4b0e/error-when-converting-from-json?forum=winserverpowershell&prof=required

Answer 2

I had the same propblem when using Invoke-RestMethod and large JSON collections in the result. I ended up adapting the methods from Parsing json with PowerShell and Json.NET to convert JSON Collections to PowerShell Objects.

# .NET JSON Serializer 
$global:javaScriptSerializer = New-Object System.Web.Script.Serialization.JavaScriptSerializer
$global:javaScriptSerializer.MaxJsonLength = [System.Int32]::MaxValue
$global:javaScriptSerializer.RecursionLimit = 99

# Functions necessary to parse JSON output from .NET serializer to PowerShell Objects
function ParseItem($jsonItem) {
        if($jsonItem.PSObject.TypeNames -match "Array") {
                return ParseJsonArray($jsonItem)
        }
        elseif($jsonItem.PSObject.TypeNames -match "Dictionary") {
                return ParseJsonObject([HashTable]$jsonItem)
        }
        else {
                return $jsonItem
        }
}

function ParseJsonObject($jsonObj) {
        $result = New-Object -TypeName PSCustomObject
        foreach ($key in $jsonObj.Keys) {
                $item = $jsonObj[$key]
                if ($item) {
                        $parsedItem = ParseItem $item
                } else {
                        $parsedItem = $null
                }
                $result | Add-Member -MemberType NoteProperty -Name $key -Value $parsedItem
        }
        return $result
}

function ParseJsonArray($jsonArray) {
        $result = @()
        $jsonArray | ForEach-Object {
                $result += , (ParseItem $_)
        }
        return $result
}

function ParseJsonString($json) {
        $config = $javaScriptSerializer.DeserializeObject($json)
        return ParseJsonObject($config)
}