Decoding an encoded URI with .Net methods
The other day while working with an SSRS server, I found that the ‘Data feed’ option was returning an encoded uri string that did not work when used in my browser.
The parts causing issue were the following:
&rs%3AFormat=ATOM
&rc%3AItemPath=table
Decoding or escaping with .NET methods was the best option after searching for options, and a few decoding/escaping methods exist in .NET, so here are the comparisons for each:
$string = '&rs%3AFormat=ATOM&rc%3AItemPath=table'
[System.Net.WebUtility]::UrlDecode($string) # &rs:Format=ATOM&rc:ItemPath=table
[System.Web.HttpUtility]::UrlDecode($string) # &rs:Format=ATOM&rc:ItemPath=table
[System.Uri]::UnescapeDataString($string) # &rs:Format=ATOM&rc:ItemPath=table
[System.Web.HttpUtility]::HtmlDecode($string) # &rs%3AFormat=ATOM&rc%3AItemPath=table
[System.Net.WebUtility]::HtmlDecode($string) # &rs%3AFormat=ATOM&rc%3AItemPath=table
Target behaviour
Decoding the ‘&’ character
Decode & to &
Decoding the ‘:’ character
Decode rs%3A to rs:
Review
The tests show that none of the methods decode all parts that we need.
The first two using UrlDecode() methods behaved the same, both do not decode & and they have decoded : correctly.
The third using UnescapeDataString() method also behaved the same, not decoding & and decoding : correctly.
The last two using HtmlDecode() methods flipped the result, as it decoded & to &, and did not decode %3A to :.
To conclude
I needed to combine UrlDecode() and HtmlDecode() methods, and here are some suggestions.
Combine using a pipeline
$string = '&rs%3AFormat=ATOM&rc%3AItemPath=table'
$string | ForEach-Object {[System.Net.WebUtility]::HtmlDecode($_)} | ForEach-Object {[System.Net.WebUtility]::UrlDecode($_)}
# using the ForEach-Object alias '%'
$string | % {[System.Net.WebUtility]::HtmlDecode($_)} | % {[System.Net.WebUtility]::UrlDecode($_)}
Combine by nesting one method inside the other method
$string = '&rs%3AFormat=ATOM&rc%3AItemPath=table'
[System.Net.WebUtility]::UrlDecode([System.Net.WebUtility]::HtmlDecode($string))
# Switching the order has the same result
[System.Net.WebUtility]::HtmlDecode([System.Net.WebUtility]::UrlDecode($string))
But why System.Net.WebUtility and not System.Web.HttpUtility ?
System.Net.WebUtility is recommended over System.Web.HttpUtility because System.Net.WebUtility is part of the runtime, while System.Web.HttpUtility requires the System.Web.HttpUtility.dll assembly.
Microsoft suggest:
To encode or decode values outside of a web application, use the WebUtility class.
The System.Uri class also contains methods and properties that can be used for similar purposes.
The PowerShell ISE has System.Web.HttpUtility as part of it’s runtime, but it’s more correct to align with Windows PowerShell or Windows PowerShell Core.
References
https://learn.microsoft.com/en-us/dotnet/api/system.net.webutility
https://learn.microsoft.com/en-us/dotnet/api/system.web.httputility
https://learn.microsoft.com/en-us/dotnet/api/system.uri