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Sockets

Sockets. The Standard Network Programming API. Agenda. Evolution API Components (Sockets/Winsock) Protocol Configuration Tools. Evolution. Mid 80’s  Berkley Sockets 1991  birds-of-a-feather 1992  Winsock 1.0 1993  Winsock 1.1 Now  2.0+. Winsock vs. “Berkley” Sockets.

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Sockets

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  1. Sockets The Standard Network Programming API

  2. Agenda • Evolution • API Components (Sockets/Winsock) • Protocol Configuration • Tools

  3. Evolution Mid 80’s  Berkley Sockets 1991  birds-of-a-feather 1992  Winsock 1.0 1993  Winsock 1.1 Now  2.0+

  4. Winsock vs. “Berkley” Sockets • Berkley Sockets were the original socket implementation • Berkley Sockets == X-Platform • Work on any TCP/IP stack • Unix / Linux • Consoles • Mac • Windows • Winsock specific begins with “WSA” • Winsock specific • WSAStartup() • WSAAsynch…() • Generic Sockets • socket() • recvfrom()

  5. Winsock 2.0 • QoS (Quality of Service) • Reserve bandwidth • Multicast • Conserves bandwidth by allowing send lists. • One packet to multiple recipients. • Requires multicast aware hardware • Overlapped I/O • High performance I/O model • !!! NOT PORTABLE !!! • IPv6 (making provisions for) • Expanded address space • IPSec (Data Encryption)

  6. File I/O “Stream” Similarities • Winsock 2.n added “Unified I/O” • MSDN mentions deprecation • Socket Handle == File Handle • CreateFile(…) • ReadFile(…) / WriteFile(…) • CloseFile(…) • Serial I/O same • Com Handle == File Handle

  7. Sockets API Components Init Connect Service Disconnect DeInit

  8. InitializationWinsock Specific • Winsock2.h • Include this header • WS2_32.lib • Link to this library • WSAStartup ( in ReqVer, out VerInfo ) • Can succeed even if is doesn’t support your requested version in it’s entirety. BAH!!! • View VerInfo to make certain the version. • Should provision for fallback. • WSACleanup () • Close all sockets before calling this function. • Make sure no pending blocking sockets. • WSAGetLastError () • Call this to determine extended error information on error from any Winsock method. • Does not work until successful return from WSAStartup ().

  9. Domain Name ResolutionFunctions • gethostbyname (char *domainName) • Deprecated • WSAAsyncGetHostByName (char *) • Deprecated • getaddrinfo ( char *domainName, …) • New to Winsock 2 • Reverse lookups also available • IPDomain • getnameinfo() Winsock 2 • gethostbyaddr() Winsock 1 (deprecated)

  10. Create SocketSpecifying Protocol • socket (in family, in stream, in protocol) • Address Family: • AF_INET • Stream: (Connected or Connectionless) • SOCK_STREAM • SOCK_DGRAM • SOCK_RAW • Protocol: • IPPROTO_TCP • IPPROTO_UDP • Returns an unconnected handle to a socket. • closesocket (socket) • Closes connection • Releases the resources

  11. ConnectInitiate a connection • connect ( socket, addr, addrlen) • socket = handle created with call to ‘socket’ • addr = port & IP of place to connect. • must specify the address family in the addr struct. • addrlen = sizeof(addr). • WSAConnect(…) • Supports Quality of Service . • Facilitates initial data packet transfer upon connect.

  12. BindSpecify “Incoming” Address • bind ( in socket, in address, in sizeof(address) ) • Socket = socket handle • Address • family = AF_INET • sin_port = htons( port # ) • sin_addr.s_addr = htonl (ADDR_ANY) • Can specify IP if more than one NIC and want specific one. • Fails if IP/port combo in use. Keep track of ports in use in app and try unused one. May have to cycle through a few. • Implicit bind done on connect(). You must bind before an accept(). • Cannot rebind.

  13. ListenListen for a connection requests • listen ( in socket, in backlog ) • socket • Backlog • # of pending connections allowed before additional connections are refused. • Call listen() once to set listening state. • Returns immediately. • To stop listening on the socket, close it. • closesocket ( socket ).

  14. AcceptAccepting a connection • newSock accept ( in socket, out addr, in sizeof(addr)) • Socket • One you are listening on. • newSocket • New socket created by the accept() method. Use this socket to send() / recv() on the new connection. • NOTE • This is NOT the socket you passed to listen(). It is a brand spanking new socket. • Addr • Address of connection accepted (filled out by the accept function). • Steps • socket () • bind () • listen () • accept () • Loop on accept() until you have all the connections you want, then close the socket passed to listen().

  15. SendSending Data • send ( socket, buff, bufflen, flags) • Flags • MSG_OOB • Priority message. Can’t use with UDP • Used with connection based e.g., TCP • sendto (…, addr, sizeof(addr)) • Addr = address to send to. Overrides bind() if socket was bound. • Used with connectionless e.g., UDP • WSASend (ditto send, overlap struct, OL funk) • Use with overlapped I/O • WSASendTo (…) • Use with overlapped I/O

  16. ReceiveReceiving Data • recv (sock, buff, bufflen, flags) • Buff = incoming data • Bufflen = number of bytes in buffer or bytes to receive (whichever is less) • Flags • MSG_PEEK • Leave data in system buffers. Inefficient • MSG_OOB • Get out-of-band packets • recvfrom (…) • UDP version • WSARecv (…) • Overlapped version • WSARecvFrom (…) • Overlapped version • WSARecvEx (…) • Adds protocol for large messages via. MSG_PARTIAL notification. Normally handled by application with standard socket’s recv(). • Not used with overlapped I/O.

  17. Protocol Configuration Socket Options I/O Control

  18. Socket Options • (get/set)sockopt (sock, sol*, so*, val, sizeof(val)) • “sol” socket option level • SOL_SOCKET • Generic Level • IPPROTO_TCP • TCP/IP specific • “so” Common Sock Options • SO_BROADCAST • SO_KEEPALIVE • SO_MAX_MSG_SIZE • SO_RCVBUF • SO_RCVTIMEO • SO_SNDBUF • Much more • Multicast group membership management

  19. I/O Control • ioctlsocket (sock, command, arg) • FIONBIO • On/Off non-blocking mode (blocking is default) • Additional Multicast configuration • Set Keep Alive interval • Flush send buffer • And more… • WSAIoctl (…) • Overlapped version

  20. Tools Getting the Job Done!!! Making Development Easier

  21. Tools • Shims • DLL that sits between Winsock and IP stack, or IP stack and device driver. • Let’s you monkey with everything. • Hacker tool • Ping • App that sends an ICMP message to an IP. • Reports round trip time. • Good for determining average latency and general internet connection state. • Trace Route • App that sends a packet to an IP. • Reports hops and time between hops. • Good for locating problematic net hardware • NetStat • App that reports all packet activity • Ipconfig/winifcfg • App that reports local IP addresses • Sniffers • Similar to SHIMS, but often a piece of hardware • Can sit between NIC and cable, or attach to cable anywhere • Expensive equipment, time consuming to learn and use effectively

  22. Socket Wrappers • Platform SDKs • Special O/S specific e.g. xbox achievement, session, … • Speech • Middle Ware • Server Components • Lobby Client • Tested Architecture • High Performance (really?) • Encryption Schemes • Compression Schemes • Standard/Flexible Message Format • X-Platform • Flexible API • See references link on class web site for venders

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