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TCP client and server

This example illustrates a simple TCP server that accepts incoming client connections. Once a client connection is stablished, a thread is spawned to read data from the client and echo it back (if the echo option is not disabled).
Compile:
cl -o Server Server.c ws2_32.lib
Command line options:
server [-p:x] [-i:IP] [-o]
-p:x Port number to listen on
-i:str Interface to listen on
-o Receive only, don’t echo the data back

Client:
This sample is the echo client. It connects to the TCP server, sends data,
and reads data back from the server.
Compile:
cl -o Client Client.c ws2_32.lib
Command Line Options:

client [-p:x] [-s:IP] [-n:x] [-o]
-p:x Remote port to send to
-s:IP Server’s IP address or hostname
-n:x Number of times to send message
-o Send messages only; don’t receive

/*******************************************************
*     MYCPLUS Sample Code - http://www.mycplus.com     *
*                                                     *
*   This code is made available as a service to our   *
*      visitors and is provided strictly for the      *
*               purpose of illustration.              *
*                                                     *
* Please direct all inquiries to saqib at mycplus.com *
*******************************************************/

// Module Name: Client.c
//
// Description:
//    This sample is the echo client. It connects to the TCP server,
//    sends data, and reads data back from the server.
//
// Compile:
//    cl -o Client Client.c ws2_32.lib
//
// Command Line Options:
//    client [-p:x] [-s:IP] [-n:x] [-o]
//           -p:x      Remote port to send to
//           -s:IP     Server's IP address or hostname
//           -n:x      Number of times to send message
//           -o        Send messages only; don't receive
//
#include <winsock2.h>
#include <stdio.h>
#include <stdlib.h>

#define DEFAULT_COUNT       20
#define DEFAULT_PORT        5150
#define DEFAULT_BUFFER      2048
#define DEFAULT_MESSAGE     "This is a test of the emergency \
broadcasting system"

char  szServer[128],          // Server to connect to
      szMessage[1024];        // Message to send to sever
int   iPort     = DEFAULT_PORT;  // Port on server to connect to
DWORD dwCount   = DEFAULT_COUNT; // Number of times to send message
BOOL  bSendOnly = FALSE;         // Send data only; don't receive

//
// Function: usage:
//
// Description:
//    Print usage information and exit
//
void usage()
{
    printf("usage: client [-p:x] [-s:IP] [-n:x] [-o]\n\n");
    printf("       -p:x      Remote port to send to\n");
    printf("       -s:IP     Server's IP address or hostname\n");
    printf("       -n:x      Number of times to send message\n");
    printf("       -o        Send messages only; don't receive\n");
    ExitProcess(1);
}

//
// Function: ValidateArgs
//
// Description:
//    Parse the command line arguments, and set some global flags
//    to indicate what actions to perform
//
void ValidateArgs(int argc, char **argv)
{
    int                i;

    for(i = 1; i < argc; i++)
    {
        if ((argv[i][0] == '-') || (argv[i][0] == '/'))
        {
            switch (tolower(argv[i][1]))
            {
                case 'p':        // Remote port
                    if (strlen(argv[i]) > 3)
                        iPort = atoi(&argv[i][3]);
                    break;
                case 's':       // Server
                    if (strlen(argv[i]) > 3)
                        strcpy(szServer, &argv[i][3]);
                    break;
                case 'n':       // Number of times to send message
                    if (strlen(argv[i]) > 3)
                        dwCount = atol(&argv[i][3]);
                    break;
                case 'o':       // Only send message; don't receive
                    bSendOnly = TRUE;
                    break;
                default:
                    usage();
                    break;
            }
        }
    }
}

//
// Function: main
//
// Description:
//    Main thread of execution. Initialize Winsock, parse the
//    command line arguments, create a socket, connect to the
//    server, and then send and receive data.
//
int main(int argc, char **argv)
{
    WSADATA       wsd;
    SOCKET        sClient;
    char          szBuffer[DEFAULT_BUFFER];
    int           ret,
                  i;
    struct sockaddr_in server;
    struct hostent    *host = NULL;

    // Parse the command line and load Winsock
    //
    ValidateArgs(argc, argv);
    if (WSAStartup(MAKEWORD(2,2), &wsd) != 0)
    {
        printf("Failed to load Winsock library!\n");
        return 1;
    }
    strcpy(szMessage, DEFAULT_MESSAGE);
    //
    // Create the socket, and attempt to connect to the server
    //
    sClient = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
    if (sClient == INVALID_SOCKET)
    {
        printf("socket() failed: %d\n", WSAGetLastError());
        return 1;
    }
    server.sin_family = AF_INET;
    server.sin_port = htons(iPort);
    server.sin_addr.s_addr = inet_addr(szServer);
    //
    // If the supplied server address wasn't in the form
    // "aaa.bbb.ccc.ddd" it's a hostname, so try to resolve it
    //
    if (server.sin_addr.s_addr == INADDR_NONE)
    {
        host = gethostbyname(szServer);
        if (host == NULL)
        {
            printf("Unable to resolve server: %s\n", szServer);
            return 1;
        }
        CopyMemory(&server.sin_addr, host->h_addr_list[0],
            host->h_length);
    }
    if (connect(sClient, (struct sockaddr *)&server,
        sizeof(server)) == SOCKET_ERROR)
    {
        printf("connect() failed: %d\n", WSAGetLastError());
        return 1;
    }
    // Send and receive data
    //
    for(i = 0; i < dwCount; i++)
    {
        ret = send(sClient, szMessage, strlen(szMessage), 0);
        if (ret == 0)
            break;
        else if (ret == SOCKET_ERROR)
        {
            printf("send() failed: %d\n", WSAGetLastError());
            break;
        }
        printf("Send %d bytes\n", ret);
        if (!bSendOnly)
        {
            ret = recv(sClient, szBuffer, DEFAULT_BUFFER, 0);
            if (ret == 0)        // Graceful close
                break;
            else if (ret == SOCKET_ERROR)
            {
                printf("recv() failed: %d\n", WSAGetLastError());
                break;
            }
            szBuffer[ret] = '\0';
            printf("RECV [%d bytes]: '%s'\n", ret, szBuffer);
           }
    }
    closesocket(sClient);

    WSACleanup();
    return 0;
}
/************************ End of Client ********************/
/*******************************************************/
//--------------------------------------------------------------------------//
/*************************** Server ********************/
//
// Module Name: Server.c
//
// Description:
//    This example illustrates a simple TCP server that accepts
//    incoming client connections. Once a client connection is
//    established, a thread is spawned to read data from the
//    client and echo it back (if the echo option is not
//    disabled).
//
// Compile:
//    cl -o Server Server.c ws2_32.lib
//
// Command line options:
//    server [-p:x] [-i:IP] [-o]
//           -p:x      Port number to listen on
//           -i:str    Interface to listen on
//           -o        Receive only, don't echo the data back
//
#include <winsock2.h>

#include <stdio.h>
#include <stdlib.h>

#define DEFAULT_PORT        5150
#define DEFAULT_BUFFER      4096

int    iPort      = DEFAULT_PORT; // Port to listen for clients on
BOOL   bInterface = FALSE,	 // Listen on the specified interface
       bRecvOnly  = FALSE;   // Receive data only; don't echo back
char   szAddress[128];       // Interface to listen for clients on

//
// Function: usage
//
// Description:
//    Print usage information and exit
//
void usage()
{
    printf("usage: server [-p:x] [-i:IP] [-o]\n\n");
    printf("       -p:x      Port number to listen on\n");
    printf("       -i:str    Interface to listen on\n");
    printf("       -o        Don't echo the data back\n\n");
    ExitProcess(1);
}

//
// Function: ValidateArgs
//
// Description:
//    Parse the command line arguments, and set some global flags
//    to indicate what actions to perform
//
void ValidateArgs(int argc, char **argv)
{
    int i;

    for(i = 1; i < argc; i++)
    {
        if ((argv[i][0] == '-') || (argv[i][0] == '/'))
        {
            switch (tolower(argv[i][1]))
            {
                case 'p':
                    iPort = atoi(&argv[i][3]);
                    break;
                case 'i':
                    bInterface = TRUE;
                    if (strlen(argv[i]) > 3)
                        strcpy(szAddress, &argv[i][3]);
                    break;
                   case 'o':
		           bRecvOnly = TRUE;
                       break;
                default:
                    usage();
                    break;
            }
        }
    }
}

//
// Function: ClientThread
//
// Description:
//    This function is called as a thread, and it handles a given
//    client connection.  The parameter passed in is the socket
//    handle returned from an accept() call.  This function reads
//    data from the client and writes it back.
//
DWORD WINAPI ClientThread(LPVOID lpParam)
{
    SOCKET        sock=(SOCKET)lpParam;
    char          szBuff[DEFAULT_BUFFER];
    int           ret,
                  nLeft,
                  idx;

    while(1)
    {
        // Perform a blocking recv() call
        //
        ret = recv(sock, szBuff, DEFAULT_BUFFER, 0);
        if (ret == 0)        // Graceful close
            break;
        else if (ret == SOCKET_ERROR)
        {
            printf("recv() failed: %d\n", WSAGetLastError());
            break;
        }
        szBuff[ret] = '\0';
        printf("RECV: '%s'\n", szBuff);
        //
        // If we selected to echo the data back, do it
        //
        if (!bRecvOnly)
        {
            nLeft = ret;
            idx = 0;
			//
            // Make sure we write all the data
            //
            while(nLeft > 0)
            {
                ret = send(sock, &szBuff[idx], nLeft, 0);
                if (ret == 0)
                    break;
                else if (ret == SOCKET_ERROR)
                {
                    printf("send() failed: %d\n",
                        WSAGetLastError());
                    break;
                }
                nLeft -= ret;
                idx += ret;
               }
        }
    }
    return 0;
}

//
// Function: main
//
// Description:
//    Main thread of execution. Initialize Winsock, parse the
//    command line arguments, create the listening socket, bind
//    to the local address, and wait for client connections.
//
int main(int argc, char **argv)
{
    WSADATA       wsd;
    SOCKET        sListen,
                  sClient;
    int           iAddrSize;
    HANDLE        hThread;
    DWORD         dwThreadId;
    struct sockaddr_in local,
                       client;

    ValidateArgs(argc, argv);
    if (WSAStartup(MAKEWORD(2,2), &wsd) != 0)
    {
        printf("Failed to load Winsock!\n");
        return 1;
    }
    // Create our listening socket
    //
    sListen = socket(AF_INET, SOCK_STREAM, IPPROTO_IP);
    if (sListen == SOCKET_ERROR)
    {
        printf("socket() failed: %d\n", WSAGetLastError());
        return 1;
    }
    // Select the local interface and bind to it
    //
    if (bInterface)
    {
        local.sin_addr.s_addr = inet_addr(szAddress);
        if (local.sin_addr.s_addr == INADDR_NONE)
            usage();
    }
    else
        local.sin_addr.s_addr = htonl(INADDR_ANY);
    local.sin_family = AF_INET;
    local.sin_port = htons(iPort);

    if (bind(sListen, (struct sockaddr *)&local,
            sizeof(local)) == SOCKET_ERROR)
    {
        printf("bind() failed: %d\n", WSAGetLastError());
        return 1;
    }
    listen(sListen, 8);
    //
    // In a continous loop, wait for incoming clients. Once one
    // is detected, create a thread and pass the handle off to it.
    //
    while (1)
    {
        iAddrSize = sizeof(client);
        sClient = accept(sListen, (struct sockaddr *)&client,
                        &iAddrSize);
        if (sClient == INVALID_SOCKET)
        {
            printf("accept() failed: %d\n", WSAGetLastError());
            break;
        }
        printf("Accepted client: %s:%d\n",
            inet_ntoa(client.sin_addr), ntohs(client.sin_port));

        hThread = CreateThread(NULL, 0, ClientThread,
                    (LPVOID)sClient, 0, &dwThreadId);
        if (hThread == NULL)
        {
            printf("CreateThread() failed: %d\n", GetLastError());
            break;
        }
        CloseHandle(hThread);
    }
    closesocket(sListen);

    WSACleanup();
    return 0;
}

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