I have this piece of code where a server socket is created and is set to listen on a particular port number say 5005. Now once the accept socket function returns the socket that gets created is copied into the m_Socket variable and finally i shutdown the server socket named SocServer which was created locally.
Now my question
Is it possible that the SocServer(created initially) and m_Socket(copied when accept returns) get the same number say 1500.
struct sockaddr_in ServerSock; // Socket address structure to bind the Port Number to listen to
char *localIP ;
SOCKET SocServer;
//To Set up the sockaddr structure
ServerSock.sin_family = AF_INET;
ServerSock.sin_addr.s_addr = INADDR_ANY
ServerSock.sin_port = htons(PortNumber);//port number of 5005
// To Create a socket for listening on PortNumber
if(( SocServer = socket( AF_INET, SOCK_STREAM, 0 )) == INVALID_SOCKET )
{
return FALSE;
}
//To bind the socket with wPortNumber
if(bind(SocServer,(sockaddr*)&ServerSock,sizeof(ServerSock))!=0)
{
return FALSE;
}
// To Listen for the connection on wPortNumber
if(listen(SocServer,SOMAXCONN)!=0)
{
return FALSE;
}
// Structure to get the IP Address of the connecting Entity
sockaddr_in insock;
int insocklen=sizeof(insock);
//To accept the Incoming connection on the wPortNumber
m_Socket=accept(SocServer,(struct sockaddr*)&insock,&insocklen);
//delete the server socket
if(SocServer != INVALID_SOCKET)
{
//To close and shutdown the Socserver
shutdown(SocServer, 2 );
closesocket(SocServer);
}
is it possible that Socserver and m_socket are the same because
as per my code the socket connection is established and for some other reason it gets closed and in TCPView it shows established for a while and then no connection at all.
Note: This happens only in some machines and is not reproducible always. Can any other network related issue be the cause.
Are you certain that the client who is connecting to your server did not close the connection? Also, you did not provide any function which uses the m_Socket so i cannot tell you if there is any problem while handling the incoming connection. I do not think that m_socket and SocServer may end up the same.
In this code:
m_Socket=accept(SocServer,(struct sockaddr*)&insock,&insocklen);
if(SocServer != INVALID_SOCKET)
why do you call accept() with what may apparently be a bad socket? And do you test the value you get back from accept() anywhere?
Related
I'm using winsocks and I am coding an IDS/Honeypot, this is just a small section of it, because at the moment I want the server to listen on multiple sockets (7) and accept the connections, but I've tried to dynamically create the sockets with an array (and the listener etc) but I am still having trouble - I've tried it multiple ways but so far, all I've managed to do is get it working successfully on ONE socket, and LISTEN to all sockets, but not accept them.
So, this was my last attempt but not sure, maybe I need to use threads or declare the sockets differently?
So far, in this small test code, I want:
Initialize server
listen on all 7 ports (1111,2222 ...etc)
Accept an incoming connection on ANY of them
display both messages on client/server
drop the connection
and continue
It's a little sloppy I know, but here is the code so far and I think you can see where I am going with it:
#include <iostream>
#include <winsock2.h>
#include <string>
#pragma comment(lib, "ws2_32.lib")
int main()
{
std::cout<<"Honeypot server [test #1] by Dreamwalker"<<std::endl;
WSADATA wsa;
SOCKET s[7] , new_socket[7];
struct sockaddr_in server , client;
int c, port[7] = {1111,2222,3333,4444,5555,6666,7777};
char *message;
std::cout<<"\nInitialising Winsock and other components...";
if (WSAStartup(MAKEWORD(2,2),&wsa) != 0)
{
std::cout<<"Failed. Error Code :"<<WSAGetLastError()<<std::endl;
return 1;
}
//!IMPORTANT: create multiple new sockets on different ports
int i = 0;
for( i = 0; i < 7; i++)
{
//Create socket
if((s[i] = socket(AF_INET , SOCK_STREAM , 0 )) == INVALID_SOCKET)
{
std::cout<<"Could not create socket : "<< WSAGetLastError()<<std::endl;
}
//Prepare the sockaddr_in structure
server.sin_family = AF_INET;
server.sin_addr.s_addr = INADDR_ANY;
server.sin_port = htons( port[i] );
//Bind
if( bind(s[i] ,(struct sockaddr *)&server , sizeof(server)) == SOCKET_ERROR)
{
std::cout<<"Bind failed with error code : "<< WSAGetLastError()<<std::endl;
}
/*!ALL CREATION CHECKING DONE, now create multiple sockets on the server
and listen for connections*/
c = sizeof(struct sockaddr_in);
listen(s[i] , SOMAXCONN);
}
///ALL INITIALIZED
std::cout<<"DONE!"<<std::endl;
//Listen/accept incoming connections
std::cout<<"Now listening for connections"<<std::endl;
new_socket[i] = accept(s[i] , (struct sockaddr *)&client, &c);
if (new_socket[i] == INVALID_SOCKET)
{
std::cout<<"accept failed with error code : "<< WSAGetLastError()<<std::endl;
}
//Accepted connection
else{
std::cout<<"Someone has connected to this machine!"<<std::endl;
message = "Hello Client , I have received your connection.\n";
send(new_socket[i] , message , strlen(message) , 0);
closesocket(s[i]);
}
std::cout<<"FINISHED"<<std::endl;
WSACleanup();
getchar();
return 0;
}
And now it's throwing a runtime error as well:
WSAENOTSOCK
10038
Socket operation on nonsocket.
An operation was attempted on something that is not a socket. Either the socket handle parameter did not reference a valid socket,
or for select, a member of an fd_set was not valid.
Which (including debugging) indicates that the socket isn't declared properly when creating on an array, advice?
You code to create/bind/listen is all good. Then:
new_socket[i] = accept(s[i] , (struct sockaddr *)&client, &c);
Firstly, by the time this runs you're outside the loop, and i is 7 which is past the end of the array of sockets, which is why you get the not-a-socket error.
Secondly, accept() is a blocking call, so you can't just call accept() on all the sockets from the same thread the way you did for listen. You need to either have a separate thread block in accept() for each of the ports, or find out which one has a client connection attempt in progress using e.g. select (or epoll - does Windows have that?), then accept() a client on that specific socket (but then you've still got to either create a thread to handle the client read/recvs and write/sends or use select/epoll to find out when there's input ready to read, or more space in output buffers for transmission). There's also a race condition to be wary of if you use select/epoll - a listening socket might signal readiness for accepting a client connection, but by the time you call accept() that connection attempt's failed and forgotten, then if the listening socket hasn't been set to non-blocking mode it'll hang there waiting for another client to connect to that specific socket. IMHO, this is a case where threading is actually easier.
I think it's more "Windowsy" to use IO Completion Ports (you might want to Google), but AFAIK they're totally unportable. Winsock's not an exact match for BSD sockets, but the porting or dual-support effort's small.
I want to implement a server c++ server program (under linux) using the standard (socket.h) library which shall accept only one active connection. My understanding of how to implement this is this (i have removed the error checking):
int port = 4711;
int MAXCONNECTIONS = 5;
int m_sock;
m_sock = socket ( AF_INET, SOCK_STREAM, 0 );
int on = 1;
setsockopt ( m_sock, SOL_SOCKET, SO_REUSEADDR, &on, sizeof ( on ) ) < 0
sockaddr_in m_addr;
m_addr.sin_family = AF_INET;
m_addr.sin_addr.s_addr = INADDR_ANY;
m_addr.sin_port = htons ( port );
bind ( m_sock, ( struct sockaddr * ) &m_addr,
sizeof ( m_addr ) );
listen ( m_sock, MAXCONNECTIONS );
// now accept new connection and get socket
int con_sock;
int addr_length = sizeof ( m_addr );
con_sock = accept ( m_sock, ( sockaddr * ) &m_addr, ( socklen_t * ) &addr_length );
This works so far in my code. But the first socket created will still accept connections. As far as I understand it I need to close the first socket now.
close ( m_sock );
This prevents new connections. But now I am unable to reastablish any connections when the first one blows. From my understand I would have to repeat the same procude as above.
What I encounter is that my code runs well until the accept where it would block and wait for connections but client connecting will receive "Connection refused" and I cannot see any LISTEN ports in netstat.
Do you have any ideas?
The option to accept other connections and close them immediately shall not be regarded here.
Just don't accept(2) new connections until you need to. Loop over accepting, processing client dialogue, and closing the connected socket.
To start with, try changing the second line of code (currently int MAXCONNECTIONS = 5;)
Firstly, let's differentiate between a listening socket and a connected socket. A listening socket is one on which the server listens, i.e. waits for clients. Once the call to accept returns, it means that the 3-way handshake with the client is complete and accept returns a connected socket. Connected socket is the one through which the actual communication with the client takes place.
In your example, m_sock is a listening socket and con_sock is the connected socket. When you are closing 'm_sock', you are actually closing the listening socket and therefore the server cannot accept any more connections and that is why the connection refused error on the client side.
If processing only one request at a time is your task, i guess what you need is an iterative server. You don't need to close the listening socket as the next request will be processed only after the previous one has been completely processed.
listen ( m_sock, MAXCONNECTIONS );
// now accept new connection and get socket
int con_sock;
int addr_length = sizeof ( m_addr );
for(;;)
{
con_sock = accept ( m_sock, ( sockaddr * ) &m_addr, ( socklen_t * ) &addr_length );
//do your task
close(con_sock);
}
If you want to refuse the connections to other connections while one request is being processed, you might want to reduce the backlog value to 1. This however will not send ECONNREFUSE error to the client but will just ignore the client request. However, when the server is idle, even then only one connection is what the server will have in its queue. (Not so sure why actually you would want to do this.)
I have a connection protocol that has been defined by our customer. Data are sent between two linux computers using UDP and TCP protocols. The IP addresses and ports are fixed on startup.
We are sending messages at 200 Hz and I have been using connect to save some time on the transmissions.
My problem is that if there is a communication error, I need to tear down the connections and reinitialise.
I have a problem with one of the UDP connections as it will not rebind to the required address and returns errno 22.
The code I am using is something like:
int
doConnect(int& sock, int local_port, char *local_ip, int remote_port, char *remote_ip)
{
sock = socket(PF_INET, SOCK_DGRAM, IPPROTO_UDP);
struct sockaddr_in addr;
memset(&addr, 0, sizeof(sockaddr_in);
addr.sin_family = AF_INET;
addr.sin_port = htons(local_port);
inet_pton(local_ip,&addr.sin_addr.s_addr);
if (0 > bind(sock, (struct sockaddr*)&addr, sizeof(addr)))
{
printf("Bind Error errno = %d\n", errno);
return ERR_BIND;
}
memset(&addr, 0, sizeof(sockaddr_in);
addr.sin_family = AF_INET;
addr.sin_port = htons(remote_port);
inet_pton(remote_ip,&addr.sin_addr.s_addr);
if (0 > connect(sock, (struct sockaddr*)&addr, sizeof(addr)))
{
printf("Connect Error errno = %d\n", errno);
return ERR_CONNECT;
}
return ERR_OK;
}
The way that this is used is like this:
int s1(-1), s2(-1);
doConnect(s1, 31003, "172.17.21.255", 31006, "172.17.21.1");
doConnect(s2, 31001, "172.17.21.3", 31004, "172.17.21.1");
When an error occurs
close(s1);
close(s2);
doConnect(s1, 31003, "172.17.21.255", 31006, "172.17.21.1");
doConnect(s2, 31001, "172.17.21.3", 31004, "172.17.21.1");
Here the local address is 172.17.21.3 and I am connecting to 172.17.21.1. s1 listens to a broadcast message.
s1 successfully reconnects to the remote machine, but s2 fails with error 22 from the call to bind.
I have tried explicitly calling bind and connect to an AF_UNSPEC address immediately before I close the socket. This doesn't solve the problem.
Are there any options that I should be using?
Perhaps you could try:
int val = 1;
setsockopt(sock, SOL_SOCKET, SO_REUSEADDR, &val, sizeof(val));
I also suggest you double check that you're not passing the same socket to the two consecutive doConnect() calls (as errno 22 = EINVAL, which in the case of bind() appears to mean that the socket is already bound to an address).
The underlying socket layer might hold the port & IP address still open, even after your call to close. Try some of the following:
do a sleep(10) (or more) between the close and the call to doConnect again
configure the sockets using setsockopt with the SO_LINGER set to off
This actually happens more commonly with TCP connections, but I see no reason UDP can't have this problem as well.
I have created a socket using the following lines of code.
Now i change the value of the socket i get like this
m_Socket++;
Even now the send recv socket functions succeeds without throwing SOCKET_ERROR.
I expect that it must throw error.
Am i doing something wrong.
struct sockaddr_in ServerSock; // Socket address structure to bind the Port Number to listen to
char *localIP ;
SOCKET SocServer;
//To Set up the sockaddr structure
ServerSock.sin_family = AF_INET;
ServerSock.sin_addr.s_addr = INADDR_ANY;
ServerSock.sin_port = htons(pLantronics->m_wRIPortNo);
// To Create a socket for listening on wPortNumber
if(( SocServer = socket( AF_INET, SOCK_STREAM, 0 )) == INVALID_SOCKET )
{
return FALSE;
}
//To bind the socket with wPortNumber
if(bind(SocServer,(sockaddr*)&ServerSock,sizeof(ServerSock))!=0)
{
return FALSE;
}
// To Listen for the connection on wPortNumber
if(listen(SocServer,SOMAXCONN)!=0)
{
return FALSE;
}
// Structure to get the IP Address of the connecting Entity
sockaddr_in insock;
int insocklen=sizeof(insock);
//To accept the Incoming connection on the wPortNumber
pLantronics->m_Socket=accept(SocServer,(struct sockaddr*)&insock,&insocklen);
if(pLantronics->m_Socket == INVALID_SOCKET)
{
shutdown(SocServer, 2 );
closesocket(SocServer );
return FALSE;
}
// To make socket non-blocking
DWORD dwNonBlocking = 1;
if(ioctlsocket( pLantronics->m_Socket, FIONBIO, &dwNonBlocking ))
{
shutdown(pLantronics->m_Socket, 2);
closesocket(pLantronics->m_Socket);
return FALSE;
}
pLantronics->m_sModemName = inet_ntoa(insock.sin_addr);
Now i do
m_Socket++;//change to some other number ideally expecting send recv to fail.
Even now the send recv socket functions succeeds without throwing SOCKET_ERROR.
I expect that it must throw error.
Am i doing something wrong.
It's because of the peculiar nature of Windows handles -- when created they are divisible by four and when used their two lowest bits are ignored. Incrementing a handle by one will make m_Socket refer to the same socket as before (only when you increment by four will the function return an error -- unless there is another handle with that value open).
You should not probe for open handles in this manner. While there are other ways to enumerate open handles, you shouldn't use them. Do not depend on the system to keep track of your handles -- track them yourself.
I have created a socket using the following lines of code and i get a valid socket and connection is established between the client and server machines. Is there a possibility that the socket becomes invalid due to network disturbances or any other reason.
If so how do we check whether the socket is valid or not.
SOCKET SocServer;
//To Set up the sockaddr structure
ServerSock.sin_family = AF_INET;
ServerSock.sin_addr.s_addr = INADDR_ANY
ServerSock.sin_port = htons(PortNumber);//port number of 5005
// To Create a socket for listening on PortNumber
if(( SocServer = socket( AF_INET, SOCK_STREAM, 0 )) == INVALID_SOCKET )
{
return FALSE;
}
//To bind the socket with wPortNumber
if(bind(SocServer,(sockaddr*)&ServerSock,sizeof(ServerSock))!=0)
{
return FALSE;
}
// To Listen for the connection on wPortNumber
if(listen(SocServer,SOMAXCONN)!=0)
{
return FALSE;
}
I know i can check for INVALID_SOCKET which in other words means the socket is 0. Is there any other way out because my SocServer will have a value say 2500, i want to check if this socket is valid.
Pass your socket to any one of the windows socket functions (eg. getsockopt()), if the socket is invalid, it will return SOCKET_ERROR while WSAGetLastError() will return WSAENOTSOCK.
It is important to note that INVALID_SOCKET does not equal 0(the actual value, which you should not use specifically is ((SOCKET)(~0))
The socket can become "invalid" when either side (expected or unexpected) disconnects, but not out of the blue due to network interferences (unless it disconnects, read above).
You can detect this by checking the return values of send() and recv() for -1 (SOCKET_ERROR)
The socket will not go invalid. But after you listen() you must accept() a connection. That connection may be lost at some point. It could be detected by a failure to write to the socket or recv() returning with error. Then you just recycle back to listen().
First, assuming that INVALID_SOCKET (which you don't show) is actually defined as 0 this is incorrect. socket returns -1 on failure like the other system calls (0 is a valid fd that could be returned).
Then once you accept a connection, your send/write or recv/read call will return -1. If you're trying to write, errno will be set to EPIPE to indicate the socket was closed (by your client). There's no way to just ask if a socket is closed.