Socket, listen

[mattias1975]

I have made a socket program that is supposed to
receive some text from a client.
But there is something wrong when i call the
listen function. It returns -1.
Does anyone know whats wrong?

Mattias Westerberg



#include <winsock2.h>
#include <iostream.h>

#define BACKLOG 10

void main()
{
WORD wVersionRequested;
WSADATA wsaData;
int err;

wVersionRequested = MAKEWORD( 2, 2 );
err = WSAStartup( wVersionRequested, &wsaData );

if ( err != 0 )
cout << "could not find a usable WinSock DLL" << "\n";

if ( LOBYTE( wsaData.wVersion ) != 2 || HIBYTE( wsaData.wVersion ) != 2 ) {
WSACleanup( );
cout << "could not find a usable WinSock DLL" << "\n";
}

int sockfd, new_fd;
struct sockaddr_in my_addr;
struct sockaddr_in their_addr;
int sin_size;

if ((sockfd = socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) == -1) {
cout << "socket";
exit(1);
}

my_addr.sin_family = AF_INET;
my_addr.sin_addr.s_addr = inet_addr("xxx.xxx.x.x");
my_addr.sin_port = htons(321);

memset(&(my_addr.sin_zero), '\0', 8);

if (bind(sockfd, (struct sockaddr *)&my_addr, sizeof(struct sockaddr)) == -1) {
cout << "bind";
exit(1);
}

if (listen(sockfd, BACKLOG) == -1) {
cout << "listen";
exit(1);
}

char buf[100];
int numbytes;

while(1) {
sin_size = sizeof(struct sockaddr_in);
if ((new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size)) == -1) {
cout << "accept";
continue;
}

if ((numbytes=recv(sockfd, buf, 100, 0)) != -1) {
cout << buf;
break;
}
}
}

 

[timmay3141]

I think that ports 1-1000 or something are reserved, so you should use a bigger number. Other than that, I got it working, but I had to change some stuff so that you may not be able to do what you are trying to do. I don't have a much experience with sockets, so this may not help, but with these changes I can at least get past listen().

I changed:

socket(AF_INET, SOCK_RAW, IPPROTO_ICMP))

to

socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)

and changed:

my_addr.sin_addr.s_addr = inet_addr("xxx.xxx.x.x"); my_addr.sin_port = htons(321);

to

my_addr.sin_addr.s_addr = htonl(INADDR_ANY);
my_addr.sin_port = htons(3210);

Hope this helps.

 

[mingis]

I'm newby to sockets too, but few comments anyway:

1.
> I think that ports 1-1000 or something are reserved

I don't think so - you can easy listen on port 80, simulating HTTP server, for example.

2. inet_addr("xxx.xxx.x.x") looks suspicious. Probably I'm wrong, but idea of "listenning" is to accept messages comming from all hosts of the net - ADDR_ANY is commonly used in this place.

3. I'm not sure, what socket(AF_INET, SOCK_RAW, IPPROTO_ICMP)) means, but in your example listen() causes an error code 10045 meaning that requested operation (listenning) is not supported on such kind of socket or protocol.

 

[timmay3141]

Actually, I just checked my sockets book, and it does indeed say that you shouldn't use sockets 1-1000. I do know that I picked an arbitrary number under 1000 once and my program wouldn't work because of it. It might work, but it's generally safer to choose a number over 1000. I have heard this from many different sources, and I know it's true. Here's a link to another article that mentions this:

http://www.gamedev.net/reference/programming/features/ws2games/