Windows Sockets

Windows Sockets == winsock

Documentation available at

• http://papa.indstate.edu:8888/winsock-spec.html
• alt.winsock

What is winsock

Windows Sockets spec. defines a network programming interface to Microsoft Windows which is based on the "socket" paradigm.

Winsock was designed by a committee.

A standard API for all Windows TCP/IP programs.

How?

Windows DLL

Each vendor supplies its own WINSOCK.DLL

The DLL has to provide only the interface.

Actual network code can reside elsewhere.

Trumpet uses a windows program which is started by WINSOCK.DLL

PCTCP uses a network stack which is loaded at boot time.

What?

Winsock provides all of the "standard" Berkeley socket calls.

Additional functions were added for effiency reasons.

Only new mandatory calls:

• WSAStartup()
• WSACleanup()

MS Windows (tm)

Problems with Berkeley sockets under Windows:

• Windows is non-preemptive
• A call to a blocking function will freeze Windows
• Windows is message based. Does not translate well to Berkeley Sockets.
• sockets cannot be the same as file descriptors

Winsock differences

Asynchornous versions of blocking Berkeley socket calls:

Database lookup calls:

Berkeley                       Windows                                        
gethostbyaddr()                WSAAsyncGetHostByAddr()                        
gethostbyname()                WSAAsyncGetHostByName()                        
getprotobyname()               WSAAsyncGetProtoByName()                       
getprotobynumber()             WSAAsyncGetProtoByNumber()                     
getservbyname()                WSAAsyncGetServByName()                        
getservbyport()                WSAAsyncGetServByPort()                        

Other Windows-specific calls:

• WSAAsyncSelect()
• WSACancelAsyncRequest()
• WSACancelBlockingCall()
• WSACleanup()
• WSAGetLastError()
• WSAIsBlocking()
• WSASetBlockingHook()
• WSASetLastError()
• WSAStartup()
• WSAUnhookBlockingHook()

Winsock Data structures/types

SOCKET type

Typical BSD:

    s = socket(...);
    if (s == -1)
        { ... }

Winsock:

    s = socket(...);
    if (s == INVALID_SOCKET)
        { ... }

fd_set is NOT a bit-array under winsock.

MUST use FD_XXX calls (not macros...)

Errors

errno can lie!

Typical BSD:

    r = recv(...);
    if (r == -1 && errno == EWOULDBLOCK)
        {...}

Winsock:

    r = recv(...);
    if (r == -1 &&
            WSAGetLastError() == EWOULDBLOCK)
        {...}

Example WSA call

HANDLE PASCAL FAR WSAAsyncGetHostByAddr(
    HWND hWnd,
    unsigned int wMsg,
    const char FAR *addr,
    int len,
    int type,
    char FAR *buf,
    int buflen);

hWnd

The handle of the window which should receive a message when the asynchronous request completes.

wMsg

The message to be received when the asynchronous request completes.

addr

A pointer to the network address for the host. (network byte order!)

len

The length of the address

type

The type of the address (must be PF_INET) A pointer to the data area to receive the hostent data.

buf

Most be at least MAXGETHOSTSTRUCT bytes.

buflen

The size of data area buf above.