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Beginning Winsock Programming - Simple TCP server

, 25 Feb 2002
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An introduction to WinSock programming. A simple TCP server is explained.

Introduction

The WinSock (Windows Sockets) API is a socket programming library for Microsoft Windows Operating Systems. It was originally based on Berkeley sockets. But several Microsoft specific changes were employed. In this article I shall attempt to introduce you to socket programming using WinSock, assuming that you have never done any kind of network programming on any Operating System.

If you only have a single machine, then don't worry. You can still program WinSock. You can use the local loop-back address called localhost with the IP address 127.0.0.1. Thus if you have a TCP server running on your machine, a client program running on the same machine can connect to the server using this loop-back address.

Simple TCP Server

In this article I introduce you to WinSock through a simple TCP server, which we shall create step by step. But before we begin, there are a few things that you must do, so that we are truly ready for starting our WinSock program

  • Initially use the VC++ 6.0 App Wizard to create a Win32 console application. 
  • Remember to set the option to add support for MFC
  • Open the file stdafx.h and add the following line :- #include <winsock2.h>
  • Also #include conio.h and iostream just after winsock2.h
  • Take Project-Settings-Link and add ws2_32.lib to the library modules list.

The main function

int _tmain(int argc, TCHAR* argv[], TCHAR* envp[])
{
    int nRetCode = 0;	
	
    cout << "Press ESCAPE to terminate program\r\n";
    AfxBeginThread(ServerThread,0);
    while(_getch()!=27);
	
    return nRetCode;
}

What we do in our main() is to start a thread and then loop a call to _getch(). _getch() simply waits till a key is pressed and returns the ASCII value of the character read. We loop till a value of 27 is returned, since 27 is the ASCII code for the ESCAPE key. You might be wondering that even if we press ESCAPE, the thread we started would still be active. Don't worry about that at all. When main() returns the process will terminate and the threads started by our main thread will also be abruptly terminated.

The ServerThread function

What I will do now is to list our ServerThread function and use code comments to explain what each relevant line of code does. Basically what our TCP server does is this. It listens on port 20248, which also happens to be my Code Project membership ID. Talk about coincidences. When a client connects, the server will send back a message to the client giving it's IP address and then close the connection and go back to accepting connections on port 20248. It will also print a line on the console where it's running that there was a connection from this particular IP address. All in all, an absolutely useless program, you might be thinking. In fact some of you might even think this is as useless as SNDREC32.EXE which comes with Windows. Cruel of those people I say.

UINT  ServerThread(LPVOID pParam)
{	
    cout << "Starting up TCP server\r\n";

    //A SOCKET is simply a typedef for an unsigned int.
    //In Unix, socket handles were just about same as file 
    //handles which were again unsigned ints.
    //Since this cannot be entirely true under Windows
    //a new data type called SOCKET was defined.
    SOCKET server;

    //WSADATA is a struct that is filled up by the call 
    //to WSAStartup
    WSADATA wsaData;

    //The sockaddr_in specifies the address of the socket
    //for TCP/IP sockets. Other protocols use similar structures.
    sockaddr_in local;

    //WSAStartup initializes the program for calling WinSock.
    //The first parameter specifies the highest version of the 
    //WinSock specification, the program is allowed to use.
    int wsaret=WSAStartup(0x101,&wsaData);

    //WSAStartup returns zero on success.
    //If it fails we exit.
    if(wsaret!=0)
    {
        return 0;
    }

    //Now we populate the sockaddr_in structure
    local.sin_family=AF_INET; //Address family
    local.sin_addr.s_addr=INADDR_ANY; //Wild card IP address
    local.sin_port=htons((u_short)20248); //port to use

    //the socket function creates our SOCKET
    server=socket(AF_INET,SOCK_STREAM,0);

    //If the socket() function fails we exit
    if(server==INVALID_SOCKET)
    {
        return 0;
    }

    //bind links the socket we just created with the sockaddr_in 
    //structure. Basically it connects the socket with 
    //the local address and a specified port.
    //If it returns non-zero quit, as this indicates error
    if(bind(server,(sockaddr*)&local,sizeof(local))!=0)
    {
        return 0;
    }

    //listen instructs the socket to listen for incoming 
    //connections from clients. The second arg is the backlog
    if(listen(server,10)!=0)
    {
        return 0;
    }

    //we will need variables to hold the client socket.
    //thus we declare them here.
    SOCKET client;
    sockaddr_in from;
    int fromlen=sizeof(from);

    while(true)//we are looping endlessly
    {
        char temp[512];

        //accept() will accept an incoming
        //client connection
        client=accept(server,
            (struct sockaddr*)&from,&fromlen);
		
        sprintf(temp,"Your IP is %s\r\n",inet_ntoa(from.sin_addr));

        //we simply send this string to the client
        send(client,temp,strlen(temp),0);
        cout << "Connection from " << inet_ntoa(from.sin_addr) <<"\r\n";
		
        //close the client socket
        closesocket(client);

    }

    //closesocket() closes the socket and releases the socket descriptor
    closesocket(server);

    //originally this function probably had some use
    //currently this is just for backward compatibility
    //but it is safer to call it as I still believe some
    //implementations use this to terminate use of WS2_32.DLL 
    WSACleanup();

    return 0;
}

Testing it out

Run the server and use telnet to connect to port 20248 of the machine where the server is running. If you have it on the same machine connect to localhost.

Sample Output

We see this output on the server

E:\work\Server\Debug>server
Press ESCAPE to terminate program
Starting up TCP server
Connection from 203.200.100.122
Connection from 127.0.0.1
E:\work\Server\Debug>

And this is what the client gets

nish@sumida:~$ telnet 202.89.211.88 20248
Trying 202.89.211.88...
Connected to 202.89.211.88.
Escape character is '^]'.
Your IP is 203.200.100.122
Connection closed by foreign host.
nish@sumida:~$

Conclusion

Well, in this article you learned how to create a simple TCP server. In further articles I'll show you more stuff you can do with WinSock including creating a proper TCP client among other things. If anyone has problems with compiling the code, mail me and I shall send you a zipped project. Thank you.

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

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About the Author

Nish Sivakumar

United States United States
Nish is a real nice guy who has been writing code since 1990 when he first got his hands on an 8088 with 640 KB RAM. Originally from sunny Trivandrum in India, he has been living in various places over the past few years and often thinks it’s time he settled down somewhere.
 
Nish has been a Microsoft Visual C++ MVP since October, 2002 - awfully nice of Microsoft, he thinks. He maintains an MVP tips and tricks web site - www.voidnish.com where you can find a consolidated list of his articles, writings and ideas on VC++, MFC, .NET and C++/CLI. Oh, and you might want to check out his blog on C++/CLI, MFC, .NET and a lot of other stuff - blog.voidnish.com.
 
Nish loves reading Science Fiction, P G Wodehouse and Agatha Christie, and also fancies himself to be a decent writer of sorts. He has authored a romantic comedy Summer Love and Some more Cricket as well as a programming book – Extending MFC applications with the .NET Framework.
 
Nish's latest book C++/CLI in Action published by Manning Publications is now available for purchase. You can read more about the book on his blog.
 
Despite his wife's attempts to get him into cooking, his best effort so far has been a badly done omelette. Some day, he hopes to be a good cook, and to cook a tasty dinner for his wife.

Comments and Discussions

 
QuestionProject File Pinmemberikurtoglu19-Jan-12 1:45 
Generalproject file Pinmembersheran aus17-Jun-11 20:29 
Generalproject file Pinmembersheran aus17-Jun-11 20:28 
GeneralCan you send me the project file? Pinmembercafukarfoo25-May-11 22:22 
GeneralMy vote of 5 Pinmemberzhllq@126.com25-Mar-11 6:49 
Generalneed zip file!!! Pinmemberaarthi krishnan15-Jul-10 2:30 
Generalthanks and i Pinmemberamir farkhondeh27-Jun-10 22:09 
Generalcode.zip Pinmemberneu_lake15-Mar-10 17:26 
QuestionError during compiling..... i m using windows Vista Pinmemberpratikmota4-Feb-10 10:15 
QuestionNot able to sniff TCP packet on windows Vista. But could do so on XP PinmemberAseem Sharma21-Dec-09 21:50 
GeneralWould you please send me a copy of the source code? Thank you a lot! Pinmemberbeyondfe29-Oct-09 17:06 
GeneralI will need the zip file too for this project. PinmemberYogesh Ithape27-Oct-09 2:28 
GeneralPlease mail me a project ZIP file PinmemberLintao Wang21-Oct-09 11:45 
Generalzip file Pinmemberboon8717-Sep-09 3:34 
Generalcode Pinmemberkufeji3-Aug-09 9:03 
Questioncould you give me help? Pinmemberzhaozhihong28-Jun-09 21:09 
General[Message Deleted] Pinmemberit.ragester2-Apr-09 21:54 
Questioncan you send me the zip file please? Pinmemberlovelr8-Oct-08 16:36 
GeneralVS2005 PinmemberAhmed Hozayen4-May-08 3:22 
GeneralThe source code PinmemberAhmed Hozayen24-Apr-08 5:34 
QuestionRe: The source code Pinmemberflik16-Oct-08 8:57 
Questionediting standard include file? Pinmemberbkelly1328-Dec-07 12:09 
AnswerRe: editing standard include file? PinmvpNishant Sivakumar28-Dec-07 13:31 
Questionlimiti access to localhost Pinmembersimonecristiano21-Oct-07 11:00 
GeneralExcellent ! Pinmemberquanghao30-Sep-07 21:56 
GeneralNo MFC [modified] PinmemberSam Hobbs26-Jul-07 21:37 
GeneralRe: No MFC Pinmemberjc kamaraj13-May-08 6:39 
QuestionProbblem while Connecting with localhost Pinmemberreena vade25-Jul-07 9:11 
AnswerRe: Probblem while Connecting with localhost PinmemberSam Hobbs26-Jul-07 21:01 
GeneralRe: Problem while Connecting with localhost Pinmemberreena vade30-Jul-07 23:51 
GeneralRe: Problem while Connecting with localhost PinmemberSam Hobbs13-Aug-07 18:37 
GeneralError when I use number port 80 PinmemberAntonio292923-May-07 4:49 
GeneralRe: Error when I use number port 80 Pinmemberzhaozhihong28-Jun-09 21:15 
Questionsgfs --- secured global file system Pinmemberarunwasgood5-Apr-07 2:38 
Generalsuperb PinmemberMember #139195622-Mar-07 0:25 
GeneralVery perfect Pinmembersaka-wind25-Jan-07 15:42 
QuestionIP Camera PinmemberBaalan714323-Jan-07 13:22 
AnswerRe: IP Camera Pinmember@netzgear@26-Mar-07 0:24 
QuestionWhat about accept errors? PinmemberChrisRibe11-Jan-07 5:03 
GeneralMessages Pinmemberjnhemley23-Nov-06 6:39 
Generalhtonl not used when setting local.sin_addr.s_addr Pinmembermbrezu213-Sep-06 22:24 
QuestionError While Compiling PinmemberMen_D_Men22-Aug-06 23:52 
AnswerRe: Error While Compiling Pinmembercristitomi23-Feb-07 2:29 
GeneralRe: Error While Compiling PinmemberDavid J Turner28-Apr-07 2:11 
GeneralRe: Error While Compiling Pinmembersameerlatif9-May-07 21:24 
GeneralRe: Error While Compiling PinmemberObli7-Nov-07 6:05 
GeneralUblele to compile with Win32 console application PinmemberSaikat_Glencoe11-May-06 19:48 
GeneralRe: Ublele to compile with Win32 console application Pinmembercristitomi23-Feb-07 2:32 
GeneralRe: Ublele to compile with Win32 console application PinmemberSam Hobbs26-Jul-07 20:53 
Questionhow can i download the source? Pinmemberliguosheng10-Apr-06 17:09 

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