TCP客户端到服务器通信 [英] TCP Client to Server communication

问题描述

我要找的是Windows Form VB.Net上的一个简单的TCPClient / Listner示例。我是新手和微软TCPClient / Listner类的例子不是我正在寻找。我正在寻找的是TCPClient发送消息和TCPListener获取消息，并发回一个消息我有你的消息？

帮助将是巨大的。我有一些代码，但只是发送消息到服务器，而不是从服务器回到客户端..
任何帮助将非常感谢..

解决方案

TCP通信是所谓的基于流的，这意味着它不处理任何数据包。

您可以例如发送：

您好！

您好吗？

但您可能会收到：

>

或：

您是吗？

）

要解决这个问题，您必须应用名为length-prefixing的东西。长度前缀（或长度前缀）意味着在发送消息之前，将其长度（字符数量）放在其开头。这可以由终端读取，然后终端将根据其长度读取每个消息，因此部分消息或消息集中在一起不会有问题。

这是不是最简单的事情，但我创建了两个类，将为你做所有这一切。请参阅下面的示例，了解如何使用它们进行简单的基于消息的通信。

链接到来源：

All I'm looking for is a simple TCPClient/Listner example on Windows Form VB.Net. I'm a newbie and Microsoft TCPClient/Listner class examples are not what I am looking for. All I am looking is for the TCPClient to send a message and for a TCPListener to get the message and to send a message back "I got your message" ?

A little help would be great. I have some codes, but is only to send message to server and not back from server to client.. Any help will be very appreciated..

解决方案

TCP communication is what's called stream-based, which means it doesn't handle any packets. Due to this messages that are received can be partial or lumped together.

You could for example send:

Hello!

How are you?

But you might receive:

Hello!How are you?

or:

Hello!How ar

e you?

(or something similar)

To fix this you must apply something called "length-prefixing". Length-prefixing (or length prefixing) means that before you send a message, you put it's length (amount of characters) in the beginning of it. This can then be read by the endpoint which will then read each message according to it's length, thus there will be no problems with partial messages or messages lumped together.

This is not the most simple thing to do, but I've created two classes that will do all that for you. See the examples below on how to use them for simple message-based communication.

Link to source: http://www.mydoomsite.com/sourcecodes/ExtendedTcpClient.zip

Link to C# source : http://www.mydoomsite.com/sourcecodes/ExtendedTcpClient%20CSharp.zip

Example usage

Note that in those examples Client does not refer to the client side, but to the TcpClient.

Server side

1. First declare a new variable for ExtendedTcpClient, and be sure to include WithEvents in the declaration.

   Dim WithEvents Client As ExtendedTcpClient
   

2. Then you will need a TcpListener and a Timer to check for incoming connections.

   Dim Listener As New TcpListener("0.0.0.0", 5555) 'Listen for any connection on port 5555.
   Dim WithEvents Tmr As New System.Windows.Forms.Timer
   

3. Then you need to subscribe to the timer's Tick event.

   Private Sub Tmr_Tick(sender As System.Object, e As System.EventArgs) Handles Tmr.Tick
   
   End Sub
   

   In there you check for incoming connections via the Listener.Pending() method. When you are to accept a connection you first declare a new instance of the ExtendedTcpClient. The class requires to have a form as it's owner, in this application Me is the current form.
   Then you use the ExtendedTcpClient.SetNewClient() method with Listener.AcceptTcpClient() as it's argument to apply the TcpClient from the listener. Put this code in the Tmr_Tick sub:

   If Listener.Pending() = True Then
       Client = New ExtendedTcpClient(Me)
       Client.SetNewClient(Listener.AcceptTcpClient())
   End If
   

   Now the client and server are connected to each other.

4. Now you need to subscribe to the PacketReceived event of the client. Create a sub like so:

   Private Sub Client_PacketReceived(sender As Object, e As ExtendedTcpClient.PacketReceivedEventArgs) Handles Client.PacketReceived
   
   End Sub
   

   All received data are presented in an array of bytes. In the PacketReceived sub you can output the received packet as text into a TextBox. Just check if the packet header is PlainText and then you can convert the received packets contents (which is an array of bytes, accessed via e.Packet.Contents) to a string and put it in the TextBox.

   If e.Packet.Header = TcpMessagePacket.PacketHeader.PlainText Then
       TextBox1.AppendText("Message recieved: " & System.Text.Encoding.Default.GetString(e.Packet.Contents) & Environment.NewLine)
   End If
   

   System.Text.Encoding.Default.GetString() will convert a byte array to normal text.

5. In the PacketReceived sub you can also make it send "Message received" to the client.

   Dim ResponsePacket As New TcpMessagePacket(System.Text.Encoding.Default.GetBytes("Message received."), TcpMessagePacket.PacketHeader.PlainText)
   ResponsePacket.Send(Client.Client) 'Get the ExtendedTcpClient's underlying TcpClient.
   

6. Lastly, when closing the form you just need to disconnect the client.

   Private Sub ServerWindow_FormClosing(sender As Object, e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
       If Client IsNot Nothing Then Client.Disconnect()
   End Sub
   

And that's it for the server side.

---

Client side

1. For the client side you will do pretty much the same as the server side, though you won't be needing a TcpListener nor a Timer.

   Dim Client As New ExtendedTcpClient(Me) 'The current form as it's owner.
   

2. Connect to the server via the IP and port you've given the listener.

   Client.Connect("127.0.0.1", 5555) 'Connects to localhost (your computer) at port 5555.
   

3. Now if you want to send text to the server you'd do something like this (in for example a button):

   Dim MessagePacket As New TcpMessagePacket(System.Text.Encoding.Default.GetBytes(TextBox2.Text), TcpMessagePacket.PacketHeader.PlainText)
   MessagePacket.Send(Client.Client)
   

   TextBox2 includes the text you want to send.

4. Lastly, you will need to subscribe to the PacketReceived event here too to check for responses from the server. In there you receive text just like the server does.

   Private Sub Client_PacketReceived(sender As Object, e As ExtendedTcpClient.PacketReceivedEventArgs) Handles Client.PacketReceived
       If e.Packet.Header = TcpMessagePacket.PacketHeader.PlainText Then
           TextBox1.AppendText(System.Text.Encoding.Default.GetString(e.Packet.Contents) & Environment.NewLine) 'Prints for example "Message received." from the server.
       End If
   End Sub
   

And now everything should be working!

Link to a complete example project (only client-to-server): http://www.mydoomsite.com/sourcecodes/TCP%20Messaging%20System.zip

Link to C# example: http://www.mydoomsite.com/sourcecodes/CSharp%20TCP%20Messaging%20System.zip

If you want to add more headers to the class (the headers indicates to you what type of packet it is), just open TcpMessagePacket.vb and add more values in the PacketHeader enum (located in the region called Constants).

Hope this helps!

---

Screenshot from the example project

(Click the image for larger resolution)

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