a what is a socket

b In socket programming, what goes on in the underlying () protocol when socket() is invoked successfully in an application program such as TCPEchoServer.c ?

#include /* for printf() and fprintf() */

#include /* for socket(), bind(), and connect() */

#include /* for sockaddr_in and inet_ntoa() */

#include /* for atoi() and exit() */

#include /* for memset() */

#include /* for close() */

#include"TCPEchoServer.h"

#define MAXPENDING 5 /* Maximum outstanding connection requests */

#define MAXBUF 100 //100

//void DieWithError(char *errorMessage); /* Error handling function */

//void HandleTCPClient(int clntSocket); /* TCP client handling function */

int main(int argc, char *argv[])

{

int servSock; /* Socket descriptor for server */

int clntSock; /* Socket descriptor for client */

struct sockaddr_in echoServAddr; /* Local address */

struct sockaddr_in echoClntAddr; /* Client address */

unsigned short echoServPort; /* Server port */

unsigned int clntLen; /* Length of client address data structure */

char buf[MAXBUF];

if (argc != 2) /* Test for correct number of arguments */

{

fprintf(stderr, "Usage: %s ", argv[0]);

exit(1);

}

echoServPort = atoi(argv[1]); /* First arg: local port */

/* Create socket for incoming connections */

if ((servSock = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)

DieWithError("socket() failed");

/* Construct local address structure */

memset(&echoServAddr, 0, sizeof(echoServAddr)); /* Zero out structure */

echoServAddr.sin_family = AF_INET; /* Internet address family */

echoServAddr.sin_addr.s_addr = htonl(INADDR_ANY); /* Any incoming interface */

echoServAddr.sin_port = htons(echoServPort); /* Local port */

/* Bind to the local address */

if (bind(servSock, (struct sockaddr *) &echoServAddr, sizeof(echoServAddr)) < 0)

DieWithError("bind() failed");

/* Mark the socket so it will listen for incoming connections */

if (listen(servSock, MAXPENDING) < 0)

DieWithError("listen() failed");

for (;;) /* Run forever */

{

/* Set the size of the in-out parameter */

clntLen = sizeof(echoClntAddr);

/* Wait for a client to connect */

if ((clntSock = accept(servSock, (struct sockaddr *) &echoClntAddr,

&clntLen)) < 0)

DieWithError("accept() failed");

/* clntSock is connected to a client! */

printf("Handling client %s ", inet_ntoa(echoClntAddr.sin_addr));

int ret=recv(clntSock,buf,MAXBUF-1,MSG_DONTWAIT);

if(ret==0)

{

close(clntSock);

}

HandleTCPClient(clntSock);

}

/* NOT REACHED */

}