C# Receiving Packet in System.Sockets

问题

In my Client Server Application i wondered how to make a packet and send it to the server via the Client

Then on the server i recognize which packet is this and send the proper replay

but suddenly i got across this topic and it make me worry if i may fall in this problem

The Problem

One of the most common beginner mistakes for people designing protocols for TCP/IP is that they assume that message boundaries are preserved. For example, they assume a single "Send" will result in a single "Receive".

Some TCP/IP documentation is partially to blame. Many people read about how TCP/IP preserves packets - splitting them up when necessary and re-ordering and re-assembling them on the receiving side. This is perfectly true; however, a single "Send" does not send a single packet.

Local machine (loopback) testing confirms this misunderstanding, because usually when client and server are on the same machine they communicate quickly enough that single "sends" do in fact correspond to single "receives". Unfortunately, this is only a coincidence.

This problem usually manifests itself when attempting to deploy a solution to the Internet (increasing latency between client and server) or when trying to send larger amounts of data (requiring fragmentation). Unfortunately, at this point, the project is usually in its final stages, and sometimes the application protocol has even been published!

True story: I once worked for a company that developed custom client/server software. The original communications code had made this common mistake. However, they were all on dedicated networks with high-end hardware, so the underlying problem only happened very rarely. When it did, the operators would just chalk it up to "that buggy Windows OS" or "another network glitch" and reboot. One of my tasks at this company was to change the communication to include a lot more information; of course, this caused the problem to manifest regularly, and the entire application protocol had to be changed to fix it. The truly amazing thing is that this software had been used in countless 24x7 automation systems for 20 years; it was fundamentally broken and no one noticed.

So how could i send something like AUTH_CALC,VALUE1=10,VALUE2=12 packet and receive it from the server in a safe way...

And if you wanna an example of what i am doing here it is below

[CLIENT]

Send(Encoding.ASCII.GetBytes("1001:UN=user123&PW=123456")) //1001 is the ID

[SERVER]

private void OnReceivePacket(byte[] arg1, Wrapper Client)
{
    try
    {
        int ID;
        string V = Encoding.ASCII.GetString(arg1).Split(':')[0];
        int.TryParse(V, out ID);

        switch (ID)
        {
            case 1001://Login Packet
                AppendToRichEditControl("LOGIN PACKET RECEIVED");
                break;

            case 1002:
                //OTHER IDs
                break;

            default:
                break;
        }
    }
    catch { }         
}

So is this is a good way to structure a Message and handling it on the server ?

Also which is better encoding to use ASCII or UTF8 ?

回答1:

The best way you can do is by using length indicator. Suppose you are sending a file of 10000 bytes, first send the length of the file and receive the ack i.e "OK" string from other side, then keep on sending 10,000 bytes chunk by chunk(may be u can take 4096 bytes). Send 4096 bytes each time for two time and send 2000 odd bytes on the last chunk. On the receiver side there is no gauranty that for one send you will receive the whole 4096 bytes, so you need to wait until u get 4096 bytes and then proceed with next 4096 bytes.

来源：https://stackoverflow.com/questions/12326753/c-sharp-receiving-packet-in-system-sockets

标签

sockets

client-server