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.net无法下载图像。请求被阻止,为什么?(httpwebrequest)

httpwebrequest download image vb.net .net

memme · 技术社区 · 7 年前

在某些域上,我无法下载图像。该代码正在与其他域协同工作,但与一些its协同工作。我不知道为什么。我可以使用firefox或chrome等全浏览器下载图像,但不能使用httpwebrequest。我试图尽可能近距离地模拟全浏览器,但没有成功。

也许你能帮我找到错误?

错误为:

一个系统。网系统中发生WebException异常错误。dll。其他信息:基础连接已关闭: 发送时出现意外错误

在线:

    Dim httpWebResponse = DirectCast(httpWebRequest.GetResponse(), HttpWebResponse)

以下是故障下载示例代码:

    Dim httpWebRequest = DirectCast(WebRequest.Create("https://www.oglf.org/wp-content/uploads/2017/12/BestLEDTeethWhitening.jpg"), HttpWebRequest)
    httpWebRequest.UserAgent = "Mozilla/5.0 (Windows NT 6.3; WOW64; rv:31.0) Gecko/20100101 Firefox/31.0"
    httpWebRequest.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"
    httpWebRequest.Headers.Add(HttpRequestHeader.AcceptLanguage, "en-us,en;q=0.5")
    httpWebRequest.Referer = "https://www.oglf.org"
    httpWebRequest.AllowAutoRedirect = True
    httpWebRequest.KeepAlive = True

    Dim httpWebResponse = DirectCast(httpWebRequest.GetResponse(), HttpWebResponse)

    If (httpWebResponse.StatusCode <> HttpStatusCode.OK AndAlso httpWebResponse.StatusCode <> HttpStatusCode.Moved AndAlso httpWebResponse.StatusCode <> HttpStatusCode.Redirect) OrElse Not httpWebResponse.ContentType.StartsWith("image", StringComparison.OrdinalIgnoreCase) Then
        Return
    End If
    Using stream = httpWebResponse.GetResponseStream()
        Using fileStream = File.OpenWrite("c:\imagetest.jpg")
            Dim bytes = New Byte(4095) {}
            Dim read = 0
            Do
                If stream Is Nothing Then
                    Continue Do
                End If
                read = stream.Read(bytes, 0, bytes.Length)
                fileStream.Write(bytes, 0, read)
            Loop While read <> 0
        End Using
    End Using

1 回复 | 直到 7 年前

soohoonigan 7 年前

在这种情况下,问题是ssl连接协商失败。如果您不使用ssl进行连接对您没有任何影响,我只会使用以下方法:

Private Sub DownloadImage(ByVal source As String, destination As String)
    If source.StartsWith("https://") Then source = source.Replace("https://", "http://")
    Using wc As New System.Net.WebClient
        wc.DownloadFile(source, destination)
    End Using
End Sub

如果必须使用ssl,请尝试将TLS版本设置为1.2,因为某些网站需要,并且。net web client不默认为:

Private Sub DownloadImage(ByVal source As String, destination As String)
    System.Net.ServicePointManager.SecurityProtocol = Net.SecurityProtocolType.Tls12
    Using wc As New System.Net.WebClient
        wc.DownloadFile(source, destination)
    End Using
End Sub

调用时使用:

DownloadImage("https://www.oglf.org/wp-content/uploads/2017/12/BestLEDTeethWhitening.jpg", _
              "c:/tmp/test.jpg")