Powershell确定永久移动（重定向）的资源的新URL

Question

我在Linux上使用AppImage使用Powershell Core v6-beta.5。有没有办法找出301重定向的“新”位置？

Invoke-WebRequest -Method HEAD http://SomethingThatThrows301.com/ -MaximumRedirection 0引发错误（Response status code does not indicate success: 301 (Moved Permanently)）。

虽然错误确实提到此举是301，但我仍然希望有一个适当的对象告诉我，以及新地址。

有办法吗？

Answer 1

^{注意：以下所有代码均可在所有受支持的平台上的Windows PowerShell和PowerShell Core中使用，默认情况下最多可进行50个重定向。}

假如说：

• 您不在乎特定的 3xx重定向状态代码，并且
• 您想知道最终目标URL（可能有重定向链）

使用以下内容：

[System.Net.HttpWebRequest]::Create('http://cnn.com').GetResponse().ResponseUri.AbsoluteUri

这样会产生结果（请注意目标网址的显示方式www.）：

http://www.cnn.com

以下是高级便捷功能Get-UrlRedirection的源代码，该功能打包了功能，既提供了最终目标URL的解析，又提供了重定向URL链的枚举。

示例调用：

> Get-UrlRedirection http://cnn.com
http://www.cnn.com

> Get-UrlRedirection -Enumerate http://microsoft.com/about
http://microsoft.com/about
https://microsoft.com/about
https://www.microsoft.com/about
https://www.microsoft.com/about/
https://www.microsoft.com/about/default.aspx
https://www.microsoft.com/en-us/about/

Function Get-UrlRedirection {
  [CmdletBinding()]
  Param (
    [Parameter(Mandatory, ValueFromPipeline)] [Uri] $Url,
    [switch] $Enumerate,
    [int] $MaxRedirections = 50 # Use same default as [System.Net.HttpWebRequest]
  )

  process {
    try {

      if ($Enumerate) { # Enumerate the whole redirection chain, from input URL to ultimate target,
                        # assuming the max. count of redirects is not exceeded.
        # We must walk the chain of redirections one by one.
        # If we disallow redirections, .GetResponse() fails and we must examine
        # the exception's .Response object to get the redirect target.
        $nextUrl = $Url
        $urls = @( $nextUrl.AbsoluteUri ) # Start with the input Uri
        $ultimateFound = $false
        # Note: We add an extra loop iteration so we can determine whether
        #       the ultimate target URL was reached or not.
        foreach($i in 1..$($MaxRedirections+1)) {
          Write-Verbose "Examining: $nextUrl"
          $request = [System.Net.HttpWebRequest]::Create($nextUrl)
          $request.AllowAutoRedirect = $False
          try {
            $response = $request.GetResponse()
            # Note: In .NET *Core* the .GetResponse() for a redirected resource
            #       with .AllowAutoRedirect -eq $False throws an *exception*.
            #       We only get here on *Windows*, with the full .NET Framework.
            #       We either have the ultimate target URL, or a redirection
            #       whose target URL is reflected in .Headers['Location']
            #       !! Syntax `.Headers.Location` does NOT work.
            $nextUrlStr = $response.Headers['Location']
            $response.Close()
            # If the ultimate target URL was reached (it was already
            # recorded in the previous iteration), and if so, simply exit the loop.
            if (-not $nextUrlStr) {
              $ultimateFound = $true
              break
            }
          } catch [System.Net.WebException] {
            # The presence of a 'Location' header implies that the
            # exception must have been triggered by a HTTP redirection 
            # status code (3xx). 
            # $_.Exception.Response.StatusCode contains the specific code
            # (as an enumeration value that can be case to [int]), if needed.
            # !! Syntax `.Headers.Location` does NOT work.
            $nextUrlStr = try { $_.Exception.Response.Headers['Location'] } catch {}
            # Not being able to get a target URL implies that an unexpected
            # error ocurred: re-throw it.
            if (-not $nextUrlStr) { Throw }
          }
          Write-Verbose "Raw target: $nextUrlStr"
          if ($nextUrlStr -match '^https?:') { # absolute URL
            $nextUrl = $prevUrl = [Uri] $nextUrlStr
          } else { # URL without scheme and server component
            $nextUrl = $prevUrl = [Uri] ($prevUrl.Scheme + '://' + $prevUrl.Authority + $nextUrlStr)
          }
          if ($i -le $MaxRedirections) { $urls += $nextUrl.AbsoluteUri }          
        }
        # Output the array of URLs (chain of redirections) as a *single* object.
        Write-Output -NoEnumerate $urls
        if (-not $ultimateFound) { Write-Warning "Enumeration of $Url redirections ended before reaching the ultimate target." }

      } else { # Resolve just to the ultimate target,
                # assuming the max. count of redirects is not exceeded.

                # Note that .AllowAutoRedirect defaults to $True.
        # This will fail, if there are more redirections than the specified 
        # or default maximum.
        $request = [System.Net.HttpWebRequest]::Create($Url)
        if ($PSBoundParameters.ContainsKey('MaxRedirections')) {
          $request.MaximumAutomaticRedirections = $MaxRedirections
        }
        $response = $request.GetResponse()
        # Output the ultimate target URL.
        # If no redirection was involved, this is the same as the input URL.
        $response.ResponseUri.AbsoluteUri
        $response.Close()

       }

      } catch {
        Write-Error $_ # Report the exception as a non-terminating error.
    }
  } # process

}

为了专注于代码，我省略了上面基于注释的帮助。这就是-只需将其直接粘贴在函数定义上方即可：

[System.Net.HttpWebRequest]::Create('http://cnn.com').GetResponse().ResponseUri.AbsoluteUri