PR Summary

Fis #12764

This PR addresses 12764 by using persistent HTTP connections when Invoke-WebRequest uses the -Session variable. It does this by

1. Tracking the HttpClient object in the saved WebRequestSession.
2. Monitoring properties in WebRequestSession and rebuilding the HttpClient if they are changed. This is done to ensure that existing scripts that might tweak parameters between invocations of IWR actually apply the changes so they will behave in a backwards compatible manner. When anything that impacts the HttpClient is changed, the persistent connection is abandoned by disposing the HttpClient and underlying HttpClientHandler and constructing a new one. A warning is logged when this occurs as it has a performance impact (though no worse than the existing behaviour).
3. To support point 2, many parameters are stored as internal set-only properties in the WebRequestSession so changes between invocations that would require a new connection can be detected and the handler rebuilt appropriately.

PR Context

This PR makes a considerable difference to performance when using Invoke-WebRequest or Invoke-RestMethod with sessions when multiple requests are made to the same host. This is particularly evident for HTTPS requests, as each HTTPS connection can take hundreds of milliseconds to establish.

This PR as written passes existing tests in WebCmdlets.Tests.ps1 and additional WebSession tests that verify the HttpClient is rebuilt when appropriate.

The PR provides as much backwards compatibility as possible at the expense of the complexity of tracking how the HttpClient used in the WebSession was constructed and recreating the HttpClient in the case it would have been constructed differently between invocations in scripts that assume it is okay to change parameters between invocations with the same WebSession.

This PR squashes the commits in the original PR#19173 following multiple round of reviews by Ilya (@iSazonov) and CarloToso on a previous version of the PR. PR#19173 has been withdrawn due to number of commits and volume of review comments.

Performance Impact

Performance impact of maintaining HTTP connection persistence is measured by comparing PowerShell 7.3.3 with this PR using this simple script:

(Measure-Command {
    $null =Invoke-WebRequest https://postman-echo.com/get?i=1 -SessionVariable Session
    1..10 | ForEach-Object {
            $null =Invoke-WebRequest https://postman-echo.com/get?i=$_ -WebSession $Session
    }
}).ToString()

PowerShell 7.3.3

00:00:08.3019013

PR Branch

00:00:03.4589770

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: or [ WIP ] to the beginning of the title (the WIP bot will keep its status check at Pending while the prefix is present) and remove the prefix when the PR is ready.
• Breaking changes
  • None
  • OR
  • Experimental feature(s) needed
    • Experimental feature name(s):
• User-facing changes
  • Not Applicable
  • OR
  • Documentation needed
    • Issue filed:
• Testing - New and feature
  • N/A or can only be tested interactively
  • OR
  • Make sure you've added a new test if existing tests do not effectively test the code changed
• Tooling
  • I have considered the user experience from a tooling perspective and don't believe tooling will be impacted.
  • OR
  • I have considered the user experience from a tooling perspective and opened an issue in the relevant tool repository. This may include:
    • Impact on PowerShell Editor Services which is used in the PowerShell extension for VSCode
      (which runs in a different PS Host).
      • Issue filed:
    • Impact on Completions (both in the console and in editors) - one of PowerShell's most powerful features.
      • Issue filed:
    • Impact on PSScriptAnalyzer (which provides linting & formatting in the editor extensions).
      • Issue filed:
    • Impact on EditorSyntax (which provides syntax highlighting with in VSCode, GitHub, and many other editors).
      • Issue filed: