Start a simple local HTTP listener to receive test HTTP requests

Start-HttpListener.ps1

function Start-HttpListener {
    <#
    .SYNOPSIS
    Starts a local HTTP server and returns information about HTTP requests.

    .DESCRIPTION
    This function starts a local HTTP server, by default on http://localhost:10123/,
    and returns information about the first HTTP request received.

    To test this simple HTTP listener, try opening a second PowerShell session and
    sending a request using Invoke-RestMethod like this:

    $body = [pscustomobject]@{ Message = 'Hello world' } | ConvertTo-Json
    Invoke-RestMethod -Method Post -Uri 'http://localhost:10123/' -Body $body

    .PARAMETER Prefix
    Specifies the URI and path prefix for the HTTP server to listen on.

    .EXAMPLE
    Start-HttpListener | Select-Object -ExpandProperty Body

    Starts listening on http://localhost:10123/ and when a request is received,
    the body of the request is returned as a string.

    .EXAMPLE
    Start-HttpListener | ConvertTo-Json

    Starts listening on http://localhost:10123/ and when a request is received,
    a JSON object is returned with the remote client address, HTTP method, the
    full requested URL, the headers, and the body.

    .EXAMPLE
    (Start-HttpListener).Body | ConvertFrom-Json | ConvertTo-Json -Depth 100

    Starts listening on http://localhost:10123/ and when a request is received,
    the JSON body is reformatted and "pretty printed" as a string with consistent
    indentation.

    #>
    [CmdletBinding()]
    param (
        [Parameter()]
        [uri[]]
        $Prefix = 'http://localhost:10123/'
    )

    begin {
        Add-Type -AssemblyName System.Net
    }

    process {
        try {
            $listener = [Net.HttpListener]::new()
            $Prefix | ForEach-Object {
                $listener.Prefixes.Add($_)
            }
            $listener.Start()
            $context = $listener.GetContext()

            $request = $context.Request
            $headers = [ordered]@{}
            $request.Headers.Keys | Foreach-Object {
                $headers[$_] = $request.Headers[$_]
            }
            $reader = [io.streamreader]::new($request.InputStream)
            [pscustomobject]@{
                Client  = $request.RemoteEndPoint.ToString()
                Method  = $request.HttpMethod
                Url     = $request.Url
                Headers = $headers
                Body    = $reader.ReadToEnd()
            }

            $response = $context.Response
            $response.StatusCode = [int][net.httpstatuscode]::OK
            $response.StatusDescription = 'Status OK'
            $response.Close()
        } finally {
            if ($listener) {
                $listener.Dispose()
            }
        }
    }
}