PowerShell的try块不释放文件句柄catch块

Question

我正在写尝试下载一个文件有两个文件的下载方法的脚本。我不打算进入出众的细节，但由此产生的功能看起来是这样的：

function Download-FileRobust($url, $targetFile) {
    try {
        Download-File $url $targetFile
    }
    catch {
        Download-FileWget $url $targetFile
    }
}

当Download-File函数失败，PowerShell不会放松，在位置$targetFile创建的文件句柄，并Download-FileWget不能写入到该位置。

我已经习惯了Python的，所以我花了相当一段时间才能找出问题。

对于其他两个函数的源代码，如下所示：

function Download-FileWget($url, $targetFile){
    $wgetDir = (Get-ChildItem -Path "$env:userprofile\Downloads\wget*win32").FullName
    if($env:Path -notlike "*$wgetDir*"){
        $env:Path = "$wgetDir;$env:Path"
    }
    Invoke-Expression "wget '$url' -O '$targetFile'"
}

function Download-File($url, $targetFile){
   $uri = New-Object "System.Uri" "$url"
   $request = [System.Net.HttpWebRequest]::Create($uri)
   $request.set_Timeout(15000) #15 second timeout
   $response = $request.GetResponse()
   $totalLength = [System.Math]::Floor($response.get_ContentLength()/1024)
   $responseStream = $response.GetResponseStream()
   $targetStream = New-Object -TypeName System.IO.FileStream -ArgumentList $targetFile, Create
   $buffer = new-object byte[] 10KB
   $count = $responseStream.Read($buffer,0,$buffer.length)
   $downloadedBytes = $count

   while ($count -gt 0){
       $targetStream.Write($buffer, 0, $count)
       $count = $responseStream.Read($buffer,0,$buffer.length)
       $downloadedBytes = $downloadedBytes + $count
       Write-Progress -activity "Downloading file '$($url.split('/') | Select -Last 1)'" -status "Downloaded ($([System.Math]::Floor($downloadedBytes/1024))K of $($totalLength)K): " -PercentComplete ((([System.Math]::Floor($downloadedBytes/1024)) / $totalLength)  * 100)

   }
   Write-Progress -activity "Finished downloading file '$($url.split('/') | Select -Last 1)'"
   $targetStream.Flush()
   $targetStream.Close()
   $targetStream.Dispose()
   $responseStream.Dispose()
}

Answer 1

里面的Download-File功能，你从来没有真正做任何事情，以确保$targetStream是正确的冲洗和处置。你需要用流在try/catch/finally块：

function Download-File {
    param([string]$url, [string]$targetFile)

    $uri = New-Object "System.Uri" "$url"
    $request = [System.Net.HttpWebRequest]::Create($uri)
    $request.set_Timeout(15000) #15 second timeout
    $response = $request.GetResponse()
    $totalLength = [System.Math]::Floor($response.get_ContentLength()/1024)
    $responseStream = $response.GetResponseStream()
    try {
        $targetStream = New-Object -TypeName System.IO.FileStream -ArgumentList $targetFile, Create
        try {
            $buffer = new-object byte[] 10KB
            $count = $responseStream.Read($buffer,0,$buffer.length)
            $downloadedBytes = $count

            while ($count -gt 0){
                $targetStream.Write($buffer, 0, $count)
                $count = $responseStream.Read($buffer,0,$buffer.length)
                $downloadedBytes = $downloadedBytes + $count
                Write-Progress -activity "Downloading file '$($url.split('/') | Select -Last 1)'" -status "Downloaded ($([System.Math]::Floor($downloadedBytes/1024))K of $($totalLength)K): " -PercentComplete ((([System.Math]::Floor($downloadedBytes/1024)) / $totalLength)  * 100)

            }
            Write-Progress -activity "Finished downloading file '$($url.split('/') | Select -Last 1)'"
        }
        catch {
            throw
        }
        finally {
            if($targetStream){
                $targetStream.Flush()
                $targetStream.Close()
                $targetStream.Dispose()
            }
        }
    }
    catch {
        throw
    }
    finally {
        $responseStream.Dispose()
    }
}