winsock bind ()

[logan]

Iam trying to send a message from my server app to the client app. The client app is connected to the server and the client and the server run on the same machine. What Iam doing is:

	SOCKET s;
	s = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP);
	if (s == INVALID_SOCKET)
	{
		return;
	}
	
	sockaddr_in sendto;
	sendto.sin_addr.s_addr = inet_addr ("127.0.0.1");
	sendto.sin_family = AF_INET;
	sendto.sin_port = htons (nPort);	//we only have the port address of the client

	if (bind (s, (sockaddr *)&sendto, sizeof (sendto)) == SOCKET_ERROR)
	{
		return;
	}

	char buffer [512];
	sprintf (buffer, "Hi!");
	if (send (s, buffer, strlen (buffer), 0) == SOCKET_ERROR)
	{
		int n = WSAGetLastError ();
		return;
	}

The above code doesnt work and WSAGetLastError () returns 0. Whats wrong with it? Cannt we bind a socket to a particular address and using that send a message?

[wildfrog]

Use bind(..) to bind the server socket to a local ip/port. To connect to a remote ip/port, use connect(...).

- petter

[philkr]

What you are trying to do is a peer-to-peer architecture.
If you want to have a client-server architecture, your server app has to listen() on a port and wait for a client to connect.
For peer-to-peer architecture you have to use UDP protocol. Simply change the second parameter of your socket() call to SOCK_DGRAM.

[Marc G]

[ moved thread ]

[MikeAThon]

I think you posted the server code. If so, then until a connection is established, there's no one to send() to.

bind() only binds a socket to an address; it's still premature to call send() on the socket. You need to call listen() so that the socket is set to listening mode and listens for incoming connections. You need to wait for a client to call connect() and thereby trigger the incoming connection to the server. Then the server needs to call accept() to accept the connection. Only then is it OK to call send().

Mike

[runesvend]

	SOCKET s;
	s = socket (AF_INET, SOCK_STREAM, IPPROTO_TCP);
	if (s == INVALID_SOCKET)
	{
		return;
	}
	
	sockaddr_in sendto;
	sendto.sin_addr.s_addr = inet_addr ("127.0.0.1");
	sendto.sin_family = AF_INET;
	sendto.sin_port = htons (nPort);	//we only have the port address of the client

	if (bind (s, (sockaddr *)&sendto, sizeof (sendto)) == SOCKET_ERROR)
	{
		return;
	}

	char buffer [512];
	sprintf (buffer, "Hi!");
	if (send (s, buffer, strlen (buffer), 0) == SOCKET_ERROR)
	{
		int n = WSAGetLastError ();
		return;
	}

If WSAGetLAstError returns 0 in the above code something is wrong. I don't think send returning SOCKET_ERROR and WSAGetLastError returnning 0 is possible.

Have you initialized the Winsock API with WSAStartup()?

[MikeAThon]

Good point. WSAGetLastError should have returned something like WSAENOTCONN.

Logan, are you certain that it returns 0?

Mike

[logan]

Thanks for the replies everyone.

I think you posted the server code. If so, then until a connection is established, there's no one to send() to.

The code is from the thread which is started by the server for a client. All clients are connected to the server. What Iam trying is that a client sends a message to the server which in turn forwards it to another client.

I tried a lot before posting here, one of the things that I did was to save the SOCKETS of all clients in a container and then send a message to a client using it's socket and it worked fine. So, my guess was maybe bind () doesn't initialize the socket properly.

Have you initialized the Winsock API with WSAStartup()?

Yes I have.

Logan, are you certain that it returns 0?

Yes it does.

I will try to post the project so that you guys can have a look.

One more question, what will happen to the message send to a client (which is connected to the server) but is waiting for some user input (like cin or scanf)? Once the client gets that input it starts looking for a message from server (recv is executed)? What I found is that the client gets the message once the input is over but what if the user takes lots of time for the input? Will the message be lost?

Regards.

[runesvend]

One more question, what will happen to the message send to a client (which is connected to the server) but is waiting for some user input (like cin or scanf)? Once the client gets that input it starts looking for a message from server (recv is executed)? What I found is that the client gets the message once the input is over but what if the user takes lots of time for the input? Will the message be lost?

If I understand you correctly, you're afraid of losing data on a socket because you're aren't receiving it as soon as it arrives. I can't imagine TCP throwing out data because new data has arrived, the most likely event is that it stops receiving new incoming data because its buffers are full.

You might want to read incoming data into your own buffer when it comes available. While the user is writing input you can recv() data into this buffer which you can then use later when needed. This would prevent your socket from blocking new incoming data because the TCP buffers are full. I'm not sure if Winsock will copy the data into its own buffers to avoid losing data, but implementing your own buffer is useful anyway IMO.

[sikorka]

problem is in line:
sendto.sin_port = htons (nPort); //we only have the port address of the client

probably nPort is Integer and its problem with conversion, you should try
sendto.sin_port = nPort;

[sikorka]

wrong
nPort should be unsigned int , propably you have integer
code with:
unsigned int nPort = 21111;
sendto.sin_port = htons(nPort);
works fine

[sunnypalsingh]

TCP Client and Server Interaction: