Amazon S3：抛出状态为SendFailure的WebException - vb.NET

Question

我一直在开发一种服务，可以在AWS S3 Cloud Service上传/下载文件。以下代码运行正常，但我收到错误＆＃34; Web异常状态发送失败＆＃34;或＆＃34; 底层连接已关闭：发送上出现意外错误＆＃34;通常情况下。请在下面找到我检查过的链接列表。他们似乎都没有解决这个问题。任何帮助将不胜感激。

我检查的链接：

1. https://blogs.msdn.microsoft.com/jpsanders/2009/01/07/you-receive-one-or-more-error-messages-when-you-try-to-make-an-http-request-in-an-application-that-is-built-on-the-net-framework-2-0/
2. C# HttpWebRequest The underlying connection was closed: An unexpected error occurred on a send
3. https://forums.asp.net/t/2037197.aspx?C+HttpWebRequest+The+underlying+connection+was+closed+An+unexpected+error+occurred+on+a+send+

要上传的代码：

Private Shared Function Upload(ByVal S3Key As String, ByVal bucketName As String, ByRef client As IAmazonS3, ByVal filePath As String) As String
        Try
            Dim putRequest As New PutObjectRequest
            putRequest.BucketName = bucketName
            putRequest.Key = S3Key
            putRequest.FilePath = filePath
            putRequest.Metadata.Add("x-amz-meta-title", "someTitle")
            putRequest.Metadata.Add("Entity", "entity")
            putRequest.Metadata.Add("DocumentType", "docType")
            putRequest.Metadata.Add("UploadDate", DateTime.UtcNow.ToShortDateString())
            putRequest.Metadata.Add("Content-Type", "contentType")

            Dim response As PutObjectResponse = client.PutObject(putRequest)

        Catch amazonS3Exception As AmazonS3Exception
            If amazonS3Exception.ErrorCode IsNot Nothing AndAlso (amazonS3Exception.ErrorCode.Equals("InvalidAccessKeyId") OrElse amazonS3Exception.ErrorCode.Equals("InvalidSecurity")) Then
                Return "Invalid AWS Credentials"
            Else
                Return "Error occurred. Message:'{0}' when writing an object" + amazonS3Exception.Message
            End If
        End Try
    End Function

下载代码：

Public Function AWSFileDownload(ByVal fname As String, ByVal strFileType As Int32) As String
        Try
            Dim path As Path
            Dim data As String
            Dim awsAccessKey = System.Configuration.ConfigurationManager.AppSettings("AWSACCESSKEY")
            Dim awsSecretKey = System.Configuration.ConfigurationManager.AppSettings("AWSSECRETKEY")
            Dim bucketName_Documents = System.Configuration.ConfigurationManager.AppSettings("bucketName_Documents")
            Dim bucketName_OtherDocuments = System.Configuration.ConfigurationManager.AppSettings("bucketName_OtherDocuments")
            Dim S3Key As String = fname
            Dim type As String = ""
            Dim dest As String = ""
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12
            Using s3Client = New AmazonS3Client(awsAccessKey, awsSecretKey, RegionEndpoint.USEast1)

                Dim request As New GetObjectRequest()
                If (strFileType = "0") Then
                    request.BucketName = bucketName_OtherDocuments
                ElseIf (strFileType = "1") Then
                    request.BucketName = bucketName_Documents
                End If
                request.Key = S3Key
                Using response As GetObjectResponse = s3Client.GetObject(request)
                    Dim ext = Path.GetExtension(S3Key)
                    If Not IsDBNull(ext) Then
                        ext = LCase(ext)
                    End If
                    Select Case ext
                        Case ".htm", ".html"
                            type = "text/HTML"
                        Case ".txt"
                            type = "text/plain"
                        Case ".doc", ".rtf"
                            type = "Application/msword"
                        Case ".csv", ".xls"
                            type = "Application/x-msexcel"
                        Case ".docx"
                            type = "Application/vnd.openxmlformats-officedocument.wordprocessingml.document"
                        Case ".xlsx"
                            type = "Application/vnd.openxmlformats-officedocument.spreadsheetml.sheet"
                        Case Else
                            type = "text/plain"
                    End Select
                    dest = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), S3Key)
                    If Not File.Exists(dest) Then
                        response.WriteResponseStreamToFile(dest)
                    End If
                End Using
            End Using
            Response.ClearHeaders()
            Response.AppendHeader("content-disposition", "attachment; filename=" + S3Key)
            If type <> "" Then
                Response.ContentType = type
            End If
            Response.WriteFile(dest)
            Response.End()
        Catch amazonS3Exception As AmazonS3Exception
            If amazonS3Exception.ErrorCode IsNot Nothing AndAlso (amazonS3Exception.ErrorCode.Equals("InvalidAccessKeyId") OrElse amazonS3Exception.ErrorCode.Equals("InvalidSecurity")) Then
                Return "Invalid AWS Credentials"
            Else
                Return "Error occurred. Message:'{0}' when writing an object" + amazonS3Exception.Message
            End If
        End Try
    End Function