获取流长度时出现 WCF 异常

Question

我有一个返回流的 WCF Web 服务。在客户端，当我尝试使用下面的代码读取它时，我在“Byte[] buffer = new Byte[outputMessage.FileByteStream.Length];”行出现异常说 System.Notsupported。请告诉我我在这里做错了什么。

        FileMetaData metaData = new FileMetaData();
        metaData.ProductIDsArray = new string[] { "1", "2" };
        metaData.AuthenticationKey = "test";
        FileDownloadMessage inputParam = new FileDownloadMessage(metaData);
        FileTransferServiceClient obj = new FileTransferServiceClient();
        FileDownloadReturnMessage outputMessage = obj.DownloadFile(inputParam);
        Byte[] buffer = new Byte[outputMessage.FileByteStream.Length];
        int byteRead = outputMessage.FileByteStream.Read(buffer, 0, buffer.Length);
        Response.Buffer = false;

        Response.Buffer = false;
        Response.ContentType = "application/x-zip";
        Response.AppendHeader("content-length", buffer.Length.ToString());
        Stream outStream = Response.OutputStream;


        while (byteRead > 0)
        {
            outStream.Write(buffer, 0, buffer.Length);
            byteRead = outputMessage.FileByteStream.Read(buffer, 0, buffer.Length);
        }
        outputMessage.FileByteStream.Close();
        outStream.Close();

Answer 1

您正在读取的流不支持获取流的长度（很可能是因为在下载整个文件之前不会知道长度）。分块读取流 - 类似于 while 循环的方式，但有一个固定大小的缓冲区 - 一旦为 byteRead 返回 0，您就会知道您已经到达流的末尾。