Powershell 使用代理通过 HTTP 下载并检查远程文件大小在第二个文件上失败

Question

我有一个正在开发的 powershell 脚本，它将通过代理从 HTTP 服务器下载文件，并在服务器上包含 UN/PW。

我的文件下载正常，但有些文件非常大，所以我一直在添加一个函数来检查文件是否已更改（检查大小）。这适用于第一个文件。但它在这一行的第二个文件上超时：

$test = $wc2.OpenRead($source) | Out-Null)

下面列出了我的脚本的代码（不包括凭据）。我很感激有关如何正确关闭连接（因为我怀疑没有发生）或如何使用 Powershell 通过 HTTP 获取远程文件大小的建议。

Function getWebClient {
    $webClient = new-object System.Net.WebClient 

    $pxy = new-object System.Net.WebProxy $proxy  
    $pxy.Credentials = New-Object System.Net.NetworkCredential ("tnad\$proxy_un", "$proxy_pw") 
    $webClient.proxy=$pxy  
    $webClient.Headers.Add("user-agent", "Windows Powershell WebClient Header") 

    $WebClient.Credentials = New-Object System.Net.Networkcredential($un, $pw)

    return $WebClient
}

foreach ($ds in $datasetsTest) {
    Write-Host "Checking: $ds"
    $source = "$server$ds"
    $dest = "$destFolder$ds"

    #Test whether the destination file already exists, if it exists, compare file sizes.
    $destExists = Test-Path $dest

    if($destExists -eq $false) {
        Try {
            $wc1 = getWebClient
            $wc1.DownloadFile($source, $dest)
            $wc1.Dispose()
            Write-Host "File downloaded"  -foregroundcolor "green"
        } Catch {
            Write-Host "Downloading $ds failed..." -foregroundcolor "red"
        }
    } else {
        $localFileSize = (Get-Item $dest).length
        $wc2 = getWebClient
        $test = $wc2.OpenRead($source) | Out-Null
        $wc2.Dispose()

        $remoteFileSize = $wc2.ResponseHeaders["Content-Length"]

        Write-Host "Local file size: $localFileSize, remote file size: $remoteFileSize"
        if(!($localFileSize -eq $remoteFileSize)) {
            #file exists, but the server version changed...
            Try {
                Remove-Item $dest
                $wc3 = getWebClient
                $wc3.DownloadFile($source, $dest) 
                $wc3.Dispose($true)
                Write-Host "File downloaded"  -foregroundcolor "green"
            } Catch {
                Write-Host "Downloading $ds failed..." -foregroundcolor "red"
            }
        } else {
            Write-Host "Skipping, file exists and hasn't changed"  -foregroundcolor "magenta"
        }
    }
}

Answer 1

您的问题是由于 $test 变量被分配了空值。

当您构建变量 $test 时

$test = $wc2.OpenRead($source) | Out-Null

“| Out-Null”部分将结果清空，导致 null 被分配给 $test，删除它，您应该不会有问题。

作为关于关闭 System.Net.WebClient 连接的问题的旁白：您不需要执行任何操作，所有 HTTP 连接都会在需要时关闭，并且不应干扰建立第二个连接。开放的持久连接将允许在后续连接到同一 URL 时实现更及​​时、更高效的连接。有关持久 HTTP 连接的更多信息可以在此处找到。