WCF Rest 服务下载文件“信号量异常”

问：

我遇到了使用 WCF rest 序列从服务器下载文件的问题。在 localhost 上一切正常，但是当我从静态 ip 公开 api 时，远程计算机无法下载大文件 （500Mb）。

以下是我到目前为止的测试场景：

1. 使用 webHttpBinding。
2. 当 transferMode = “buffered” 时，文件正在传输，但 byteArraylength 除外。
3. 当 transferMode = “streamed” 时，文件在远程浏览器上开始下载，但在服务器端之间停止，存在“信号量超时期限已过期”的例外。

服务合同

<ServiceContract>
Public Interface IService   
    <OperationContract()>
    <WebGet(UriTemplate:="File/{Param}", ResponseFormat:=WebMessageFormat.Json, BodyStyle:=WebMessageBodyStyle.Bare)>
    Function FileDownloadRequest(Param As String) As Stream
End Interface

<ServiceBehavior(InstanceContextMode:=InstanceContextMode.Single, ConcurrencyMode:=ConcurrencyMode.Multiple, UseSynchronizationContext:=False)>
Public Class RequestHandler
    Implements IService

Private Function FileDownloadRequest(Param As String) As Stream Implements IService.FileDownloadRequest
        Dim _FileName As String = RootFolder & "\" & Param
        Try
            ReqLogs.Add("<<-- Download request recieved for " & _FileName)
            '
            'Header Set For CORS
            '
            WebOperationContext.Current.OutgoingResponse.Headers.Add("Access-Control-Allow-Origin", "*")            
            If File.Exists(_FileName) Then
                WebOperationContext.Current.OutgoingResponse.Headers("Content-Disposition") = "attachment; filename=" + "Report Data.csv"
                WebOperationContext.Current.OutgoingResponse.ContentType = "application/octet-stream"
                WebOperationContext.Current.OutgoingResponse.StatusCode = Net.HttpStatusCode.OK

                Dim _FStream As New FileStream(_FileName, FileMode.Open, FileAccess.Read)
                WebOperationContext.Current.OutgoingResponse.ContentLength = _FStream.Length
                ReqLogs.Add("<<-- Download processing..... ++ " & _FStream.Length.ToString)
                Return _FStream
            Else
                ReqLogs.Add("---- File not found to download !!!")
                Throw New Exception("File not found to download")
            End If
        Catch ex As Exception
            ReqLogs.Add("Download event error: " & ex.Message)
            WebOperationContext.Current.OutgoingResponse.StatusCode = Net.HttpStatusCode.InternalServerError
            Return Nothing
        End Try
    End Function

End Class