I want to connect 2 clients to same server port using TCP IP. I have use the below code before bind:-
// Reuse already binded socket
int reuse=1;
setsockopt(m_iSocketId, SOL_SOCKET, SO_REUSEADDR, (char *)&reuse, sizeof(reuse))
listen(iSocketId, 2);
struct sockaddr clientAddr;
socklen_t length = sizeof(clientAddr);
int firstClientSocket = accept(iSocketId, &clientAddr, &length);
length = sizeof(clientAddr);
int secondClientSocket = accept(iSocketId, &clientAddr, &length);
After this code, you will have two client sockets to work with. Note, however that 'accept' function blocks until some client connects. In general, you should use some aync methods (e.g. select) to handle multiple clients.
SO_REUSEADDR is generally not intended for your purposes. It just tells the system that the listening port can be reused by multiple instances of the server. It's good for debugging, when your app doesn't close the socket properly upon exit. Otherwise the system might hold the port for some time, refusing to bind another socket to it.
And don't forget error handling on listen and accept calls =)
You don't need to set SO_REUSEADDR for this. You don't need to do anything special. Just create and connect as many sockets in the client as you need, and keep calling accept() in the server.
Related
I write a client, where i have to bind the client socket. This works fine. After that i try to connect the Socket and i get error 10048. (Address already in use.) I don't understand how this is possible.
I have to implement a client speaking with multiple server. Every server only accepts messages from a specific port. (every Server expects a different port). so i have to bind my client socket. The code above is to create one of these sockets.
My code works some times. But very often the connect gives me the error 10048, while the binding before was fine. I know that bind can give also the error 10048 if the socket is already in use. But it doesn't. It returns 0. So i guess the port is free. Immediate after binding i call connect and get error 10048. I do not understand why? At the moment of the binding the port was obviously free.
bool TEthernetSocket::Open()
{
WSADATA wsaData;
if (WSAStartup((MAKEWORD(2, 0)), &wsaData) == SOCKET_ERROR)
{
return IsConnected();
}
Socket = socket(AF_INET, SOCK_STREAM, 0); // TCP
if (Socket == INVALID_SOCKET)
{
return false;
}
//bind Socket
struct sockaddr_in sa_loc;
memset(&sa_loc, 0, sizeof(struct sockaddr_in));
sa_loc.sin_family = AF_INET;
sa_loc.sin_port = htons(ClientPort);
sa_loc.sin_addr.s_addr = inet_addr(IPClient.substr(0, 15).c_str());
CALL_TRACE_CB("ethernetSocket connected");
if (!(bind(Socket, (struct sockaddr*)&sa_loc, sizeof(struct
sockaddr))))
{
CALL_TRACE_CB("Bind works");
}
else
{
AnsiString msg = AnsiString().sprintf("EN: error socket Bind:
%d", WSAGetLastError());
CALL_ERROR_CB(ERROR_NO_PORT_HANDLE, msg.c_str());
Close();
}
// TCP
SOCKADDR_IN sAdd;
sAdd.sin_family = AF_INET;
sAdd.sin_port = htons(Port);
sAdd.sin_addr.s_addr = inet_addr(IP.substr(0, 15).c_str());
if (connect(Socket, (SOCKADDR*)&sAdd, sizeof(SOCKADDR_IN)) ==
SOCKET_ERROR)
{
AnsiString msg = AnsiString().sprintf("EN: error connect
errorcode: %d", WSAGetLastError());
}
}
I expect that bind() returns 10048 before connect returns this error, but actual only connect() returns this error
I have to implement a client speaking with multiple server. The server only accepts messages from a specific port, so i have to bind my client socket.
This is an unsolvable problem. When you make an outbound TCP connection, the combination of local IP address and port is reserved exclusively for that particular outbound TCP connection. If you need to make multiple outbound TCP connections from the same port, each will have to be bound to its own local IP address. That is going to be extremely inconvenient.
There are other problems too. Say you finish one connection and then try to start a new one. The new one will have the same local IP address, local port (since the server only tolerates one), remote IP address, and remote port. How will packets from the new connection be distinguished from old, stale packets from the old one?
This is why you get the error when you try to connect. It's not until all four parameters of the connection (local and remote address and local and remote port) are known that the collision with the prior connection is detectable. That's not known until you call connect.
You need to fix the server to ignore the source port. If that absolutely cannot be done, you'll have to adopt a wait and retry mechanism to handle collisions with past connections.
I'm in the process of writing a project for college involving writing a chat client and server using POSIX sockets and C++.
The clients are supposed to converse with each other using P2P, such as each client has his own open UDP socket through which he sends and recieves messages from/to other clients.
My problem is 2-fold:
My UDPSocket class constructor seems to be ignoring the port number completely, binding to port 65535 regardless of the parameter.
The port is binding to IP 255.255.255.255 rather than my own IP (10.0.0.3), or at least that's what i get when I call getpeername.
To the best of my knowledge passing INADDR_ANY should bind to my local address, and passing port number 0 should make the OS choose a free port, what am I doing wrong?
This is the constructor of my UDPSocket class:
UDPSocket::UDPSocket(int port){
socket_fd = socket (AF_INET, SOCK_DGRAM, 0);
// clear the s_in struct
bzero((char *) &in, sizeof(in)); /* They say you must do this */
//sets the sin address
in.sin_family = (short)AF_INET;
in.sin_addr.s_addr = htonl(INADDR_ANY); /* WILDCARD */
in.sin_port = htons((u_short)port);
fsize = sizeof(from);
//bind the socket on the specified address
if(bind(socket_fd, (struct sockaddr *)&in, sizeof(in))<0){
perror ("Error naming channel");
}
}
This is the initialization:
m_Socket = new UDPSocket(0);
And this is the method I use to retrieve the binded address: (UDPSocket inherits Socket)
std::string Socket::GetSocketAddress()
{
struct sockaddr_in addr;
int len = sizeof(addr);
getpeername(socket_fd, (struct sockaddr*)&addr, (socklen_t*)&len);
char ipAddressBuffer[50];
memset(ipAddressBuffer, 0, sizeof(ipAddressBuffer));
sprintf(ipAddressBuffer, "%s:%d", inet_ntoa(addr.sin_addr), ntohs(addr.sin_port));
return ipAddressBuffer;
}
Any help would be greatly appreciated,
Avi.
You're using getpeername , which gives you the remote address of a connected socket. If you check the return value of getpeername(), it should indicate failure.
You need to use getsockname() instead of getpeername() to get the address of your local socket
You need to check that getsockname() succeeds.
Note that your socket is bound to the special 0.0.0.0 address, which means "all local interfaces", so that's what getsockname() will also return.
Answering the more general question "How to set up peer-to-peer communications with UDP":
With UDP sockets, while you can use connect, you generally don't want to, as that restricts you to a single peer per socket. Instead, you want to use a single unconnected UDP socket in each peer with the sendto and recvfrom system calls to send and receive packets with a different address for each packet.
The sendto function takes a packet and a peer address to send it to, while the recvfrom function returns a packet and the peer address it came from. With a single socket, there's no need to multiplexing with select or poll -- you just call recvfrom to get the next packet from any source. When you get a packet, you also get the peer address to send packets (back) to.
On startup, your peer will create a single socket and bind it to INADDR_ANY (allowing it to receive packets on any interface or broadcast address on the machine) and either the specific port assigned to you program or port 0 (allowing the OS to pick any unused port). In the latter case, you'll need to use getsockname to get the port and report it to the user. Once the socket is set up, the peer program can sendto any peer it knows about, or recvfrom any peer at all (including those it does not yet know about).
So the only tricky part is bootstrapping -- getting the first packet(s) flowing so that peers can recieve them and figure out their peer addresses to talk to. One method is specifying peer addresses on the command line when you start each peer. You'll start the first one with no arguments (as it has no peers -- yet). It will just recvfrom (after socket setup) to get packets from peers. Start the second with the address of the first as an argument. It sends a packet (or several) to the first peer, which will then know about the new peer as soon as it gets the first packet. Now start a third client with the addresses of the first two on the command line...
I'm working on this project where the source and destination ports are specified for sending a message via a UDP socket in C++. I've got the TCP portion of the project working fine, but I don't understand how to specify both the source and destination ports when setting this up.
The way I would know how to do it is the "receiver" sets up a recvfrom() call, with the port that the "sender" will also use in the sendto() command... but it would need to be the same port.
So, given that I need port x on the "receiver" to talk to port y on the "sender", how would I do that?
Thanks
You can define a source port when you call bind on the sender side. For instance:
sockfd = socket(AF_INET, SOCK_STREAM, 0);
if (sockfd < 0) { /*error*/}
sockaddr_in sin;
sin.sin_family = AF_INET;
sin.sin_addr.s_addr = htonl(INADDR_ANY);
sin.sin_port = htons(source_port); // here
int res = bind(sockfd,(struct sockaddr*)&sin, sizeof(sin));
if (res < 0) { /*error*/}
And the destination port goes into the sockaddr parameter passed to sendto.
If this is one-to-one mapping, i.e. one source talks to one destination, then simply bind(2) the local port and connect(2) to the remote IP and port (contrary to common misconception you can connect UDP sockets). Do that on both sides (with appropriate remote and local IPs/ports of course), and now you can just use recv(2) and send(2) without explicit addressing.
If one side needs to wait for the other to send the first packet, then extract source address/port received with recvfrom(2), and then connect(2) to it.
If, on the other hand, one side acts as a multi-client server, then do same bind(2)/connect(2) dance on the client, but only do bind(2) to local port and then use recvfrom(2)/sendto(2) on the server.
If you need simultaneous duplex communication, then you should use sockets in blocking mode -- fcntl(...O_NONBLOCK...), and use select() to determine if your socket is writable or readable or both. Here is a nice example on how this can be done http://www.lowtek.com/sockets/select.html
I am trying to make a c++ program work which is written by somebody else. I am having hard time understanding it. I am not even %100 sure that we can use poll() with a UDP socket but the code I am refactoring, is using poll() to read from udp socket as follows:
fd.fd = m_bsocket;
fd.events = POLLIN;
iPollResult = poll(&fd, 1, iTimeout);
if(iPollResult > 0)
{
int iReceivedByteCount = recv(m_bsocket, p_pBuffer, p_iBufferSize, 0);
if(iReceivedByteCount > 0)
{
*p_pReadSize = iReceivedByteCount;
}
else
{
eReturnValue = UDP_READ_ERROR;
}
}
return eReturnValue;
I tried sending udp packets to this program using command line:
echo "123" | nc -u 127.0.0.1 25
It looks like poll() always times out and returns 0, therefore I can not read anything.
I also wrote a small c# program that sends udp datagram, but I can not receive the message. I am wondering what I am doing wrong...
While UDP sockets can be used to connect to another host, they are mostly used "connectionless". Reading your question and comments it makes no sense that you have a connected socket. Instead it should be connectionless as suggested by WouterH in his comment.
int sockfd = socket(AF_INET, SOCK_DGRAM, 0);
struct sockaddr_in sin = { 0 };
sin.sin_family = AF_INET;
sin.sin_port = htons(25);
sin.sin_addr.s_addr = INADDR_ANY;
bind(sockfd, (struct sockaddr *) &sin, sizeof(sin));
// Make socket non-blocking if needed
With the above code, whenever someone sends UDP packets to port 25 on any address of your host, your socket will intercept it. Use e.g. poll or select to know when data is available.
You don't need to call connect() as UDP is connectionless. You need to bind() the socket to the IP of the interface you are listening on or 0.0.0.0 (INADDR_ANY) for all interfaces. And when sending to a destination, use sendto().
For completeness: if you call connect() on a UDP socket, you are just setting a default destination for the send() function (then you can use send instead of sendto).
If you want to receive data, you always have to bind() the socket to the interface, or all interfaces. Beware that you will have to verify the source address from the messages you are receiving. So you might want to filter the sender by using recvfrom() and checking the source address.
I am hooking WSASend, and WSARecv in C++ using the same method I've used to hook the client's WSASend and WSARecv functions. In the client I am able to get the IP, Port, and Socket from the SOCKET structure passed by WSASend/WSARecv; however, for the server when I try to use getpeername or getsockname() they both return the error 10057 (Socket not connected)...
I'm fairly sure that the hook is correct on the server, since it prints the bytes successfully, and I'm also sure the socket SHOULD be valid seeing how client and server establish a successful connection.
Is there a way to resolve this problem by any other alternative methods? I've been looking around the internet to find a solution, but I haven't seen anyone with the same problem.
I've tried this:
sockaddr *address = new sockaddr;
int peer_len;
getpeername(s, address, &peer_len);
int err = WSAGetLastError();
if(err==0)
{
char *Str = inet_ntoa(((sockaddr_in*)address)->sin_addr);
printf("[%s", Str);
printf(":%d]",ntohs(((sockaddr_in*)address)->sin_port));
}
else
{
printf("Error %i\n",err);
}
(Using both getpeername and getsockname)Both result in the same socket not connected error.
I'm planning on using the packets the C++ dll gets and forward the information to the C# dll since it'll be easier to manage on that (for me anyways), but I'd need to distinguish each packet with it's socket id.
You can only do that on the connected socket, i.e. the one returned from the accept() call, not on the listening "server" socket.