1 JMH Associates © 2000, All rights reserved Chapter 12 Windows Sockets and Network Programming

2 JMH Associates © 2000, All rights reserved OBJECTIVESOBJECTIVES Upon completion of this chapter, you will be able to:  Understand the basic Windows Sockets API  Address portability issues between Berkeley and Windows Sockets  Use Windows Sockets over TCP/IP for peer-to-peer and client/server applications  Consider changes introduced by Windows Sockets 2  See how the Service Registration APOI provides protocol transparency

3 JMH Associates © 2000, All rights reserved WINDOWS SOCKETS (1 of 2) An extension of the Berkeley Sockets API  Into the Windows environment Porting of code already written for Berkeley Sockets  Windows stations easily integrated into TCP/IP networks Exceptions when sockets treated as file descriptors  Under UNIX  Also, extended functions with WSA prefix

4 JMH Associates © 2000, All rights reserved WINDOWS SOCKETS (2 of 2) Functions that manipulate files also work with sockets read()ioctl() write()close() Behave like overlapped Windows file handles Other network communication options  Named pipes  Remote Procedure Calls

5 JMH Associates © 2000, All rights reserved INITIALIZE THE WinSock DLL (1 of 2) int WSAStartup( WORD wVersionRequired, LPWSADATA lpWSAData);

6 JMH Associates © 2000, All rights reserved INITIALIZE THE WinSock DLL (2 of 2) wVersionRequired  Indicates the highest version of the WinSock DLL you need  Returns a non-zero value if the DLL cannot support the version you want  Low byte specifies the major version  High byte specifies the minor version  0x0101  version 1.1 lpWSAData points to a WSADATA structure that returns information on the configuration of the DLL WSAGetLastError() for error number

7 JMH Associates © 2000, All rights reserved ALLOCATE A SOCKET (1 of 3) Sockets are analogous to handles  A communication channel Call socket() to create (or open) a socket  Actually a HANDLE

8 JMH Associates © 2000, All rights reserved ALLOCATE A SOCKET (2 of 3)  Server: “Listening socket” for client connection requests typedef unsigned int SOCKET; SOCKET socket(int af, int type, int protocol);

9 JMH Associates © 2000, All rights reserved ALLOCATE A SOCKET (3 of 3)  af denotes the address family  PF_INET or AF_INET designates the Internet protocol  type specifies connection-oriented ( SOCK_STREAM ) or datagram communications ( SOCK_DGRAM )  protocol unnecessary for TCP/IP  Use 0 socket returns INVALID_SOCKET upon failure

10 JMH Associates © 2000, All rights reserved BIND (1 of 3) Next, bind the socket to its address and service endpoint int bind ( SOCKET s, const struct sockaddr *saddr, int namelen);  s is an “unbound” SOCKET returned by socket()  saddr specifies the address family and protocol-specific information  namelen is sizeof(sockaddr) Returns SOCKET_ERROR in case of error

11 JMH Associates © 2000, All rights reserved BIND (2 of 3) SOCKADDR structure struct sockaddr { u_short sa_family; char sa_data[14]; }; typedef struct sockaddr SOCKADDR, *PSPOCKADDR;

12 JMH Associates © 2000, All rights reserved BIND (3 of 3) sa_data is protocol-specific TCP/IP sockaddr_in : struct sockaddr_in { shortsin_family; // AF_INET u_shortsin_port; structin_addr sin_addr; //4-byte IP addr char sinzero [8]; }; typedef struct sockaddr_in SOCKADDR_IN, *PSOCKADDR_IN;

13 JMH Associates © 2000, All rights reserved BIND CONSIDERATIONS List of hosts (mapped to IP addresses) can be found in %SystemRoot%\system32\drivers\etc\hosts List of Services(mapped to services) can be found in %SystemRoot%\system32\drivers\etc\services If you bind to a specific IP address, you can only receive incoming packets over that IP address If you have more than one IP address, bind to hotnl(INADDR_ANY) “host to network long”

14 JMH Associates © 2000, All rights reserved BIND SETUP EXAMPLE (1 of 3) BOOL WINAPI WNetGetHostAddress( LPCSTR lpszHost, LPCSTR lpszService, LPCSTR lpszProto, LPSOCKADDR lpAddr) /* Fill in a SOCKADDR using host, protocol, service */ { LPHOSTENT lpHost; LPSERVENT lpServ; SOCKADDR_IN sin; ZeroMemory(&sin, sizeof(sin));

15 JMH Associates © 2000, All rights reserved BIND SETUP EXAMPLE (2 of 3) sin.sin_family = PF_INET; sin.sin_addr.s_addr = htonl(INADDR_ANY); if(lpszHost != NULL) { lpHost = gethostbyname(lpszHost); if(lpHost != NULL) { CopyMemory(&sin.sin_addr, lpHost->h_addr_list[0], lpHost->h_length); } lpServ = getservbyname(lpszService, lpszProto);

16 JMH Associates © 2000, All rights reserved BIND SETUP EXAMPLE (3 of 3) if(lpServ != NULL) { sin.sin_port = lpServ->s_port; ZeroMemory(sin.sin_zero, sizeof(sin.sin_zero)); CopyMemory(lpAddr, &sin, sizeof(SOCKADDR)); return TRUE; /* lpAddr is now ready for bind() */ } return FALSE; } The address returned by WNetGetHostAddress() can be passed directly to the bind() function

17 JMH Associates © 2000, All rights reserved listen () listen() makes server available for client connection  Socket goes from “bound” to “listening” state int listen(SOCKET s, int nQueueSize); nQueueSize indicates the number of connection requests you are willing to have queued at the socket  Up to SOMAXCON (5 for 1.1, “unlimited” in 2.0)

18 JMH Associates © 2000, All rights reserved accept () (1 of 2)  The call to listen() places the socket into the listening state  The server application calls accept()  Returning a “connected socket”  accept() blocks until a client request for a connection arrives  accept() return value gives the server a new socket for exchanging data

19 JMH Associates © 2000, All rights reserved accept () (2 of 2) SOCKET accept( SOCKET s, /* Listening socket */ LPSOCKADDR lpAddr, /* Find client details here */ LPINT lpnAddrLen /* Length of the returned structure */ );

20 JMH Associates © 2000, All rights reserved THE CLIENT SIDE (1 of 2) A client station wishing to connect to a server must also create a socket by calling socket() If it is not bound by an address, Windows Sockets will assign it a unique address to use for the duration of the connection

21 JMH Associates © 2000, All rights reserved THE CLIENT SIDE (2 of 2) int connect( SOCKET s, LPSOCKADDR lpName, int nNameLen); lpName points to a SOCKADDR structure designating the server machine name and port address

22 JMH Associates © 2000, All rights reserved EXCHANGE OF DATA (1 of 2)  Partner stations exchange data using send() and recv()  send() and recv() have identical arguments: int send (int recv ( SOCKET s, SOCKET s, LPSTR lpBuffer,LPSTR lpBuffer, int nBufferLen,int nBufferLen, int nFlags); int nFlags);

23 JMH Associates © 2000, All rights reserved EXCHANGE OF DATA (2 of 2)  nFlags == MSG_OOB indicates urgency  OOB for out-of-band  MSG_PEEK can be used to peek at the data without removing it  These are standard Berkeley Sockets calls  But read() and write() are more common under UNIX  Not atomic or message oriented  Loop until full message is received  Or sent, although incomplete send() is rare

24 JMH Associates © 2000, All rights reserved DATAGRAM SERVICE (1 of 2) Stations send and receive data using sendto() and recvfrom() Take the same arguments as send() and recv(), but add two to designate the partner station int sendto ( int recvfrom ( SOCKET s, SOCKET s, LPSTR lpBuffer, LPSTR lpBuffer, int nBufferLen, int nBufferLen, int nFlags, int nFlags, LPSOCKADDR lpAddr, LPSOCKADDR lpAddr, int nAddrLen); LPINT pnAddrLen);

25 JMH Associates © 2000, All rights reserved DATAGRAM SERVICE (2 of 2) With datagrams, the nFlags argument cannot be MSG_OOB You cannot send or receive urgent data

26 JMH Associates © 2000, All rights reserved CLOSING A SOCKET  In standard Berkeley Sockets, call close()  In Windows Sockets call void closesocket(SOCKET s);  For connection-oriented communications, the server side of the exchange closes the socket created by accept()  Not the one returned by socket()  Only when the server goes out of service should it close the listening socket  Finally, call void WSACleanup(void);  To break your connection to WSOCK32.DLL  This function is also non-portable

27 JMH Associates © 2000, All rights reserved SOCKETS SUMMARY (1 of 2) Connection Oriented Service ServerClientsocket() bind()connect() listen() accept() send()/recv() sendto()/recvfrom() closesocket()

28 JMH Associates © 2000, All rights reserved SOCKETS SUMMARY (2 of 2) Connectionless (Datagram) ServerClientsocket() listen() connect() send()/recv() sendto()/recvfrom() closesocket()

29 JMH Associates © 2000, All rights reserved BERKELEY vs WINDOWS SOCKETS Standard Berkeley Sockets calls will port to Windows Sockets, with these exceptions:  You must call WSAStartup() to initialize the sockets DLL  Though you can use UNIX-style read() and _write() to receive and send data, you must first convert the Windows socket to an operating system handle by calling _open_osfhandle()  In Sockets 1.1, you also have to call setsockopt() to force sockets to be opened as non-overlapped handles  You must use closesocket() (which is not portable), rather than close() (which is), to close a socket  You must call WSACleanup() to shut down the DLL

30 JMH Associates © 2000, All rights reserved OVERLAPPED I/O WITH WINDOWS SOCKETS (1 of 2) In WinSock 1.1, Windows opens sockets as overlapped file handles You can pass a socket to ReadFile() or WriteFile() without modification  Wait for an operation to complete by tying it to an event handle, and call WaitForSingleObject() WaitForMultipleObjects() or MsgWaitForMultipleObjects

31 JMH Associates © 2000, All rights reserved OVERLAPPED I/O WITH WINDOWS SOCKETS (2 of 2)  Use I/O completion routines with ReadFileEx() / WriteFileEx() and the extended wait functions WaitForSingleObjectEx(), WaitForMultipleObjectsEx(), and SleepEx()  Use an I/O completion port with ReadFile() / WriteFile(), CreateIoCompletionPort(), and GetQueuedCompletionStatus()

32 JMH Associates © 2000, All rights reserved WINDOWS SOCKETS 2 (1 of 2) Windows Sockets 2, available in NT 4.0, adds several areas of functionality Note: Use 1.1 for interoperability reasons  Standardized support for overlapped I/O  Scatter/gather I/O  Sending and receiving from non-contiguous buffers in memory

33 JMH Associates © 2000, All rights reserved WINDOWS SOCKETS 2 (2 of 2)  The ability to request quality of service from the Sockets support layer  Speed and reliability of transmission  The ability to organize sockets into groups  The quality of service of a socket group can be configured  It does not have to be done on a socket-by-socket basis  The sockets belonging to a group can be prioritized  Piggybacking of data onto connection requests  Multipoint connections (conference calls)

34 JMH Associates © 2000, All rights reserved STANDARDIZATION OF OVERLAPPED I/O (1 of 2)  The most important addition to Windows Sockets 2 is the standardization of overlapped I/O  Sockets are no longer created automatically as overlapped file handles  socket() will create a non-overlapped handle  To create an overlapped socket, call WSASocket() and explicitly ask for one

35 JMH Associates © 2000, All rights reserved STANDARDIZATION OF OVERLAPPED I/O (2 of 2) SOCKET WSAAPI WSASocket( int iAddressFamily, int iSocketType, int iProtocol, LPWSAPROTOCOL_INFO lpProtocolInfo, GROUP g, DWORD dwFlags);

36 JMH Associates © 2000, All rights reserved SCATTER/GATHER I/O (1 of 4) WinSock 2 adds the ability to collect and distribute data for transmission or reception from non-contiguous memory buffers typedef struct WSABUF { u_long len; char *buf; }WSABUF, *LPWSABUF;

37 JMH Associates © 2000, All rights reserved SCATTER/GATHER I/O (2 of 4)  buf points to the data  len is the number of bytes in this particular buffer  WSASend(), WSARecv(), WSASendTo(), and WSARecvFrom() take an array of WSABUF structures

38 JMH Associates © 2000, All rights reserved SCATTER/GATHER I/O (3 of 4) int WSARecv( SOCKET s, LPWSABUF lpRecvBuffers, DWORD dwBuffers, LPDWORD lpdwBytesReceived, LPDWORD lpdwFlags, LPWSAOVERLAPPED lpOverlapped, LPWSAOVERLAPPED_COMPLETION_ROUTINE lpCompletionRoutine);

39 JMH Associates © 2000, All rights reserved SCATTER/GATHER I/O (4 of 4)  lpRecvBuffers points to an array of WSABUF structures  dwBuffers is the number of structures in the array  When data arrives, the WinSock 2 drivers disperse it among the buffers passed

40 JMH Associates © 2000, All rights reserved LAB B–1 (1 of 2) Use Windows Sockets to connect clients (the client program) to a “command line server”  The clients take a command line and send it to a known server for execution  The server returns the results to the client over the socket The solution consists of two components:  Client.c  Run Client.exe in its own window  Server.c

41 JMH Associates © 2000, All rights reserved LAB B–1 (2 of 2)  Server.c is built as Server.exe and runs in its own window or is controlled with the job management commands from Module 5  Place the commands to be executed in the same directory as Server.exe  The header file, ClntSrvr.h, contains definitions used in the various programs, such as the message format  WSOCK32.LIB must be included when linking Challenge: Extend server to set up service name in services file and client finds it with WNetGetHostAddress