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WSASIMPL.DLL: sample DLL over WinSock
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This DLL and the simple test program (SIMPLTST.EXE) are desribed
in Chapter 11, "DLLs over WinSock," in _Windows Sockets Network
Programming_ by Bob Quinn and Dave Shute (published by Addison-
Wesley, Reading, MA ISBN: 0-201-63372-8)
What it does: The WSASIMPL DLL rovides a simple API for
elemental network functionality using TCP: connect, send or receive
data, and disconnect.
What it illustrates: The main purpose of WSASIMPL is to
illustrate how to create a DLL that runs over WinSock, and prevents
reentrant messages from being sent to the application calling
the DLL over WinSock. It uses windows subclassing to capture keyboard
and mouse messages while blocking network operations are underway.
How to Use it: Here are short descriptions along with the
prototypes for the functions in the simplified WinSock API that
WSASIMPL.DLL provides:
SOCKET WINAPI ConnectTCP(LPSTR szDestination, LPSTR szService);
ConnectTCP() calls the WinSock WSAStartup() function to register
the task with the WinSock DLL, gets a socket handle with socket(),
resolves the destination host name or formats an address using
the GetAddr() function from the sample WINSOCKX library, and resolves
the destination service or formats the port number with the WINSOCKX
GetPort() function. When all these operations succeed, ConnectTCP()
returns a socket handle; when any step fails the function returns
INVALID_SOCKET.
int WINAPI SendData (SOCKET hSock, LPSTR lpOutBuf, int cbTotalToSend);
SendData() sends cbTotalToSend data bytes on the hSock socket
handle, from the buffer lpOutBuf. When it succeeds, it returns
the number of bytes sent, and when it fails it returns SOCKET_ERROR.
int WINAPI RecvData (SOCKET hSock, LPSTR lpInBuf, int cbTotalToRecv, int nTimeout);
RecvData() recieves up to cbTotalToRecv data bytes on the
hSock socket handle, into the buffer lpInBuf, until the nTimeout
period (in milliseconds) expires. It returns the number of bytes
received on success, and SOCKET_ERROR on failure (timeout is an
error condition).
int WINAPI CloseTCP (SOCKET hSock, LPSTR lpInBuf,int len);
CloseTCP() is almost the same function as CloseConn() in the
#WINSOCKX">WINSOCKX.LIB WinSock subroutine library.
It attempts a graceful close of the TCP connection on socket hSock
by calling shutdown() with how=1 to stop sends but allow
receives, then it calls recv() to read data (up to len)
into the buffer lpInBuf, if provided. When recv() fails with any
error, or returns 0 to indicate closure from the remote, CloseTCP()
then calls closesocket() to free the resources associated with
the socket handle.
The SIMPLTST sample application connects to an echo server, sends
data, and reads it back. The relevant code for this application
is as follows:
Known Problems: WSASIMPL.DLL subclasses the active window
when ConnectTCP() is called to avoid reentrant messages. We avoid
problems in our subclassed window procedure by noting receipt
of a WM_DESTROY message. Also note that because WSASIMPL.DLL uses
blocking operation mode, it imposes the typical limitations on
each task (e.g. while any blocking operation is outstanding, other
WinSock calls from the same task or thread fail with WSAEINPROGRESS).
File List:
WSASIMPL\SIMPLTST.DEF
WSASIMPL\SIMPLTST.ICO
WSASIMPL\SIMPLTST.RC
WSASIMPL\SIMPLTST.C
WSASIMPL\SIMPLTST.MAK Makefile for 16-bit simpltst.exe
WSASIMPL\SIMPLT32.MAK Makefile for 32-bit simplt32.exe
WSASIMPL\WSASIMPL.DEF
WSASIMPL\WSASIMPL.H
WSASIMPL\WSASIMPL.RC
WSASIMPL\WSASIMPL.C
WSASIMPL\WSASIMPL.MAK Makefile for 16-bit wsasimpl.dll
WSASIMPL\WSASMP32.MAK Makefile for 32-bit wsasmp32.dll
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NOTES:
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We used Microsoft Visual C++ enviroments (versions 1.52 for 16-bit,
and version 2.1 for 32-bit) to create most of the makefiles.
Unfortunately, because the paths are hard-coded in the file, you will
have to bring the project files (.mak) into the respective MS C++
environments to readjust things to the new directory, and even then
you will have to manually alter the project to access the library
files (the are in the root of the directory where you install the
samples).
All samples--including the sample DLL and static library--have a
number of other things in common:
- They all have 32-bit versions, and all 32-bit version names
end with "32" (16-bit versions don't have a number).
- They use the WSAperror() function from #WINSOCKX">WINSOCKX.LIB
to display error values and short descriptions when an unexpected
error occurs.
- They display error messages on any suspicious error condition.
They don't hide errors, but report them whenever they occur. As
we describe n a_c.htm">Appendix C: WinSock Error Reference,
these error messages should appear only when a "user fixable
error" occurs. If you get an error message from a sample
application for a non user-fixable error, then this may
indicate an anomoly in the WinSock implementation that your applications
may need to deal with. We show you the errors on purpose, to make
you aware of unexpected conditions.
- They have a minimal user interface, and do not have help (.HLP)
files available.
- They are meant to be played with. They are for exploration
and experimentation as well as to illustrate how to write WinSock
applications.
The icons used for each sample don't mean much, but they meet
the following three criteria:
- They each contain the socket from the official WinSock icon.
- Each one is colorful in its own unique and wonderful way.
- Each took under 10 minutes to create.
