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Old 10-09-2008, 09:44 PM   #1
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How to use poll() with non-blocking sockets

I have this project where I have to implement a simple port scanner in C++ for Linux. The program should take as input a target IP address, beginning port number, and ending port number. After recieving the above info, the program should display a list of open ports. I finally got it working but it takes a very long time to search a wide range of ports(100 to 1000). I was told that the run time would greatly decrease if I had several non -blocking sockets and apply poll() or use multi-threading(which is dificult so I heard). With this in mind, I am trying to find out how to open several non -blocking sockets and apply poll().However, I am confused about how to do this. Currently, after a user enters ip and the start and end ports I open a socket inside a for loop(goes from the start port to end port). Any advice/example would greatly be appreciated.
Old 10-10-2008, 12:48 PM   #2
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You could do this with poll, but personally, I don't know why you would not use select() instead and just add all of the sockets to the fd_sets for read and except.
Old 10-10-2008, 01:36 PM   #3
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info libc can tell you pretty much everything you need to know about your project. You just have to take the time to look through it and experiment with the code.
Old 10-12-2008, 09:55 AM   #4
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Thanks for the input! However, this is my first time working with sockets and isn't quite familiar with select(). By any chance can you give me input on adding select() to my program. Below is the code where I am opening a socket and checking if it is open/close:
for (port=start; port<=end; port++)

soc = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP); //created the tcp socket

    fcntl(soc,F_SETFL, O_NONBLOCK);
    memset( &servaddr, 0, sizeof(servaddr));
   servaddr.sin_family = AF_INET;
   servaddr.sin_port = htons(port); //set the portno

   hostaddr = gethostbyname( argv[1] ); //get the ip 1st argument
   memcpy(&servaddr.sin_addr, hostaddr->h_addr, hostaddr->h_length);
   conres = connect(sd, (struct sockaddr*)&servaddr, sizeof(servaddr));
   if (conres == -1)
   printf("Port %d is closed\n", port);
   printf("Port %d is open\n",port);
    return 0;
As noted at this time I am only opening one socket, where will I open more sockets. Should I open the sockets before the for loop. Any advice on this will be greatly appreciated!!!


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