accept()

• if someone tries to connect to our socket and the connect() procedure was succesful, accept() returns a new socket file descriptor for this single connection. The "old" socket must be reachable for other Clients

#include <sys/types.h>
#include <sys/socket.h>

int accept(int sockfd, struct sockaddr *addr, socklen_t *addrlen); 

Parameters

• sockfd is the listen()ing socket descriptor.
• addr will usually be a pointer to a local struct sockaddr_storage
  • This is where the information about the incoming connection will go (and with it you can determine which host is calling you from which port).
• addrlen is a local integer variable that should be set to sizeof(struct sockaddr_storage) before its address is passed to accept()
  • accept() will not put more than that many bytes into addr. If it puts fewer in, it’ll change the value of addrlen to reflect that.

return values

• accept() returns -1 and sets errno

example

#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>

#define MYPORT "3490"  // the port users will be connecting to
#define BACKLOG 10     // how many pending connections queue holds

int main(void)
{
    struct sockaddr_storage their_addr;
    socklen_t addr_size;
    struct addrinfo hints, *res;
    int sockfd, new_fd;

    // !! don't forget your error checking for these calls !!

    // first, load up address structs with getaddrinfo():

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_UNSPEC;  // use IPv4 or IPv6, whichever
    hints.ai_socktype = SOCK_STREAM;
    hints.ai_flags = AI_PASSIVE;     // fill in my IP for me

    getaddrinfo(NULL, MYPORT, &hints, &res);

    // make a socket, bind it, and listen on it:

    sockfd = socket(res->ai_family, res->ai_socktype,
                                                 res->ai_protocol);
    bind(sockfd, res->ai_addr, res->ai_addrlen);
    listen(sockfd, BACKLOG);

    // now accept an incoming connection:

    addr_size = sizeof their_addr;
    new_fd = accept(sockfd, (struct sockaddr *)&their_addr,
                                                       &addr_size);

    // ready to communicate on socket descriptor new_fd!
    .
    .
    .