1 jmh associates © 2000, all rights reserved chapter 12 windows sockets and network programming

1JMH Associates © 2000, All rights reserved

Chapter 12Chapter 12Chapter 12Chapter 12

Windows Sockets andNetwork Programming


OBJECTIVESOBJECTIVESOBJECTIVESOBJECTIVES

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


WINDOWS SOCKETS (1 of 2)WINDOWS SOCKETS (1 of 2)WINDOWS SOCKETS (1 of 2)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


WINDOWS SOCKETS (2 of 2)WINDOWS SOCKETS (2 of 2)WINDOWS SOCKETS (2 of 2)WINDOWS SOCKETS (2 of 2)

Functions that manipulate files also work with socketsread() ioctl()

write() close()

Behave like overlapped Windows file handles

Other network communication options Named pipes Remote Procedure Calls


INITIALIZE THE WinSock DLL (1 of 2)INITIALIZE THE WinSock DLL (1 of 2)INITIALIZE THE WinSock DLL (1 of 2)INITIALIZE THE WinSock DLL (1 of 2)

int WSAStartup(

WORD wVersionRequired,

LPWSADATA lpWSAData);


INITIALIZE THE WinSock DLL (2 of 2)INITIALIZE THE WinSock DLL (2 of 2)INITIALIZE THE WinSock DLL (2 of 2)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


ALLOCATE A SOCKET (1 of 3)ALLOCATE A SOCKET (1 of 3)ALLOCATE A SOCKET (1 of 3)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



Server: “Listening socket” for client connection requests

typedef unsigned int SOCKET;

SOCKET socket(int af,

int type, int protocol);



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


BIND (1 of 3)BIND (1 of 3)BIND (1 of 3)BIND (1 of 3)

Next, bind the socket to its address and service endpointint 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



SOCKADDR structure

struct sockaddr

{

u_short sa_family;

char sa_data[14];

};

typedef struct sockaddr SOCKADDR, *PSPOCKADDR;



sa_data is protocol-specific

TCP/IP sockaddr_in:

struct sockaddr_in{

short sin_family; // AF_INETu_short sin_port;struct in_addr sin_addr; //4-byte IP

addrchar sin zero [8];

};typedef struct sockaddr_in SOCKADDR_IN,

*PSOCKADDR_IN;


BIND CONSIDERATIONSBIND CONSIDERATIONSBIND CONSIDERATIONSBIND 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 tohotnl(INADDR_ANY) “host to network long”


BIND SETUP EXAMPLE (1 of 3)BIND SETUP EXAMPLE (1 of 3)BIND SETUP EXAMPLE (1 of 3)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));



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);



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


listen ()listen ()listen ()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)


accept ()accept () (1 of 2) (1 of 2)accept ()accept () (1 of 2) (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


accept ()accept () (2 of 2) (2 of 2)accept ()accept () (2 of 2) (2 of 2)

SOCKET accept(SOCKET s,

/* Listening socket */LPSOCKADDR lpAddr,

/* Find client details here */LPINT lpnAddrLen

/* Length of the returned structure */);


THE CLIENT SIDE (1 of 2)THE CLIENT SIDE (1 of 2)THE CLIENT SIDE (1 of 2)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


THE CLIENT SIDE (2 of 2)THE CLIENT SIDE (2 of 2)THE CLIENT SIDE (2 of 2)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


EXCHANGE OF DATA (1 of 2)EXCHANGE OF DATA (1 of 2)EXCHANGE OF DATA (1 of 2)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);


EXCHANGE OF DATA (2 of 2)EXCHANGE OF DATA (2 of 2)EXCHANGE OF DATA (2 of 2)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


DATAGRAM SERVICE (1 of 2)DATAGRAM SERVICE (1 of 2)DATAGRAM SERVICE (1 of 2)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);


DATAGRAM SERVICE (2 of 2)DATAGRAM SERVICE (2 of 2)DATAGRAM SERVICE (2 of 2)DATAGRAM SERVICE (2 of 2)

With datagrams, the nFlags argument cannot be MSG_OOB

You cannot send or receive urgent data


CLOSING A SOCKETCLOSING A SOCKETCLOSING A SOCKETCLOSING 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


SOCKETS SUMMARY (1 of 2)SOCKETS SUMMARY (1 of 2)SOCKETS SUMMARY (1 of 2)SOCKETS SUMMARY (1 of 2)

Connection Oriented Service

Server Client

socket() socket()bind() connect()listen()accept()

send()/recv()sendto()/recvfrom()closesocket() closesocket()


SOCKETS SUMMARY (2 of 2)SOCKETS SUMMARY (2 of 2)SOCKETS SUMMARY (2 of 2)SOCKETS SUMMARY (2 of 2)

Connectionless (Datagram)

Server Client

socket() socket()listen() connect()

send()/recv()sendto()/recvfrom()closesocket() closesocket()


BERKELEY vs WINDOWS SOCKETSBERKELEY vs WINDOWS SOCKETSBERKELEY vs WINDOWS SOCKETSBERKELEY 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


OVERLAPPED I/O WITH WINDOWS OVERLAPPED I/O WITH WINDOWS SOCKETS (1 of 2)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




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()


WINDOWS SOCKETS 2 (1 of 2)WINDOWS SOCKETS 2 (1 of 2)WINDOWS SOCKETS 2 (1 of 2)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


WINDOWS SOCKETS 2 (2 of 2)WINDOWS SOCKETS 2 (2 of 2)WINDOWS SOCKETS 2 (2 of 2)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)


STANDARDIZATION OFSTANDARDIZATION OFOVERLAPPED I/O (1 of 2)OVERLAPPED I/O (1 of 2)STANDARDIZATION OFSTANDARDIZATION OF

OVERLAPPED I/O (1 of 2)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


STANDARDIZATION OFSTANDARDIZATION OFOVERLAPPED I/O (2 of 2)OVERLAPPED I/O (2 of 2)STANDARDIZATION OFSTANDARDIZATION OF

OVERLAPPED I/O (2 of 2)OVERLAPPED I/O (2 of 2)

SOCKET WSAAPI WSASocket(

int iAddressFamily,

int iSocketType,

int iProtocol,

LPWSAPROTOCOL_INFO lpProtocolInfo,

GROUP g,

DWORD dwFlags);


SCATTER/GATHER I/O (1 of 4) SCATTER/GATHER I/O (1 of 4) SCATTER/GATHER I/O (1 of 4) 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;


SCATTER/GATHER I/O (2 of 4)SCATTER/GATHER I/O (2 of 4)SCATTER/GATHER I/O (2 of 4)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



int WSARecv(

SOCKET s,

LPWSABUF lpRecvBuffers,

DWORD dwBuffers,

LPDWORD lpdwBytesReceived,

LPDWORD lpdwFlags,

LPWSAOVERLAPPED lpOverlapped,

LPWSAOVERLAPPED_COMPLETION_ROUTINE

lpCompletionRoutine);



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


LAB B–1 (1 of 2)LAB B–1 (1 of 2)LAB B–1 (1 of 2)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


LAB B–1 (2 of 2)LAB B–1 (2 of 2)LAB B–1 (2 of 2)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

1 jmh associates © 2000, all rights reserved chapter 12 windows sockets and network programming

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