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使用Net.Sockets.TcpListener和Net.Sockets.TcpClient

作者:昆明飞华工贸有限公司 来源:www.kmfhgm.com    未知发布时间:2017-09-07 12:54:22
使用Net.Sockets.TcpListener和Net.Sockets.TcpClient进行图片传输时如何精确控制 在dotnet平台Net.Sockets.TcpListener和Net.Sockets.TcpClient已经为我们封装了所有Socket关于tcp部分,操作也更为简单,面向数据流。使用TcpClient的GetStream方法获取数据流后可以方便的对数据流进行读写操作,就如同本地磁盘的文件读写一样,使得程序员在设计程序时更为便捷简单。

但如果你使用过这两个对象进行数据传输的时候,你会发现问题也随之而来——GetStream获取的数据流是一个永无止境的Stream,你无法获取它的具体长度。

来看一下微软MSDN关于这两个对象的例程:

Shared Sub Connect(server As [String], message As [String]) Try ' Create a TcpClient. ' Note, for this client to work you need to have a TcpServer ' connected to the same address as specified by the server, port ' combination. Dim port As Int32 = 13000 Dim client As New TcpClient(server, port) ' Translate the passed message into ASCII and store it as a Byte array. Dim data As [Byte]() = System.Text.Encoding.ASCII.GetBytes(message) ' Get a client stream for reading and writing. ' Stream stream = client.GetStream(); Dim stream As NetworkStream = client.GetStream() ' Send the message to the connected TcpServer. stream.Write(data, 0, data.Length) Console.WriteLine("Sent: {0}", message) ' Receive the TcpServer.response. ' Buffer to store the response bytes. data = New [Byte](256) {} ' String to store the response ASCII representation. Dim responseData As [String] = [String].Empty ' Read the first batch of the TcpServer response bytes. Dim bytes As Int32 = stream.Read(data, 0, data.Length) responseData = System.Text.Encoding.ASCII.GetString(data, 0, bytes) Console.WriteLine("Received: {0}", responseData) ' Close everything. stream.Close() client.Close() Catch e As ArgumentNullException Console.WriteLine("ArgumentNullException: {0}", e) Catch e As SocketException Console.WriteLine("SocketException: {0}", e) End Try Console.WriteLine(ControlChars.Cr + " Press Enter to continue...") Console.Read() End Sub 'Connect 你不得不去指定一个固定尺寸的缓冲区来接收数据,如果实际发送的数据超出了这个长度,你可能无法接收到全部完整的数据,而如果发送的数据少于缓冲区的大小,那么很显然你的内存会比别人消耗的更快。更为严重的时,如果你要发送一副图片,图片容量可能根据内容的不同而各有千秋,容量也不止256Byte这么小,该如何精确控制缓冲区呢?


其实我们可以很容易的解决这个问题,就像很多文件格式所做的事情一样,我们可以在Stream的前几个字节写入实际有效数据的长度,然后根据这个长度来分配内存,再读取内容,专题系统,我所做的客户端与服务器之间传递屏幕的源代码如下:


"----------------客户端----------------

Public Class Form1 Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick Dim tcpc As New Net.Sockets.TcpClient Dim slens(7) As Byte Try tcpc.Connect("127.0.0.1", 2099) If tcpc.Connected Then For i = 0 To 7 slens(i) = tcpc.GetStream.ReadByte Next Dim buf(BitConverter.ToUInt64(slens, 0)) As Byte Me.Text = buf.Length tcpc.GetStream.Read(buf, 0, buf.Length) Dim mem As New IO.MemoryStream(buf) Dim bmp As New Bitmap(mem) Me.PictureBox1.Image = bmp tcpc.Close() End If Catch ex As Exception Finally tcpc.Close() End Try End Sub Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load End Sub End Class


'------------服务器---------------- Public Class Form1 Private Sub BackgroundWorker1_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork Dim tcps As New Net.Sockets.TcpListener(2099) tcps.Start() While True Dim slen As UInt64 Dim slens(7) As Byte Dim tcpc As Net.Sockets.TcpClient tcpc = tcps.AcceptTcpClient '创建图片 Dim bmp As New Bitmap(Screen.PrimaryScreen.Bounds.Width, Screen.PrimaryScreen.Bounds.Height) bmp.SetResolution(1, 1) Dim gph As Graphics = Graphics.FromImage(bmp) gph.CopyFromScreen(New Point(0, 0), New Point(0, 0), bmp.Size) gph.Flush() '存入内存 Dim mem As New IO.MemoryStream bmp.Save(mem, Drawing.Imaging.ImageFormat.Tiff) '文件长度 slen = mem.Length slens = BitConverter.GetBytes(slen) '发送长度 For i = 0 To 7 tcpc.GetStream.WriteByte(slens(i)) Next '发送内容 tcpc.GetStream.Write(mem.ToArray, 0, mem.Length) tcpc.Close() End While End Sub Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load Me.BackgroundWorker1.RunWorkerAsync() End Sub End Class


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