When building the W3C Sample Code Library on a Windows platform (Windows 3.1 (32 bit), Windows 95, or Windows NT), you can decide on a set of different options to be enabled or disabled. This document describes the set of DLLs and how they can be built. C compilers on Windows platforms often have a notion of projects that define what files to include in the compilation and where to put the output. This document does not describe the process of creating projects as it depends on the compiler that you are using but refers you to your C compiler manuals.
Non-blocking network access can either be done using multiplexed I/O or
asynchronous I/O. Multiplexed I/O is based on an event loop with a
select() system call. The select() system call
is a function that scans a set of BSD like socket descriptors and returns
when one or more sockets are ready for either network read or
write. Asynchronous I/O is based on signals instead of a
select() call. Each time a socket is ready for a network operation,
for example read, a signal is generated. This signal can then be caught
by the application in an signal handler. Using the select()
call is called reactive whereas using signals is called
pro-active.
The W3C Sample Code Library supports both approaches under Windows, and therefore you must choose which model you prefer. The choice can depend on what type of application you are using and what other libraries you are using.
In this mode the Event Manager registers
all active sockets and passes them to a select() call which
then processes the registered sockets. When select() returns
the Event Manager dispatches the appropriate handlers as the sockets get
ready.
What to do:
Undefine WWW_WIN_ASYNC as a preprocessor directive when
generating the project for the Library. Please make sure that all
DLLs are compiled without this flag.
Here the Event Manager registers all
active sockets using WSAAsyncSelect which is part of the WinSock
API. When AsyncSelect() which is the asynchronous equivalent
to the select() returns, the Event Manager dispatches the results
of the AsyncSelect(). As the asynchronous select call needs
a windows handle, the Library creates a hidden window. This window
is not to be used explicitly by the application and the Library
closes the window when exiting.
What to do:
Define WWW_WIN_ASYNC as preprocessor directives when generating
the project for the Library.
A Windows application can use either a character based command line interface, or a graphic windows interface. Many MS-DOS applications do run as a simple command line tool which doesn't use GUI at all. Under Win32, there is a notion of a console application. This means that all user interaction happens through a standard DOS shell interface, with a FILE pointer like that in Unix. This does not exist under Win16, where a Windows window is required.
The Library supports both the console and the windows interface, and again you must choose what version you prefer. This is often something you have to decide as you are creating the project.
If you want to make a windows application then this is the mode to use. Eric Prud'hommeaux has provided a Windows application wrapper for the W3C Line Mode Browser which you can use in order to build the browser as a Windows application. This is found in www.c. Three other modules, scroll.c and lib.c provide the window for the application.
What to do: Define
_WINDOWS as preprocessor directives when generating the project for
the Library.
The console option is available only in Win32 in which case all user interaction happens through the Win32 console window. This model strongly resembles a Unix vt100 terminal interface.
What to do: Define
_CONSOLE as preprocessor directives when generating the project for
the Library.
Windows has a concept of both static and dynamic libraries, the latter also known as DLLs. It is out of scope here to describe the difference between DLLs and static libraries, but as DLLs is based on a lot more flexible memory model it is almost always the best solution for Windows applications.
The W3C Sample Code Library support both models in that if can be built as either one big static library or as a set of small DLLs. As mentioned, it is in almost all cases recommended to build DLLs instead of static libraries, and on Win16 it is required because a static library is too big.
The libraries may be build as one large static library. This is how libwww
is implemented on Unix platforms. Subsequent references to the various DLLs
may all be assumed to refer to the staticly linked libwww. Care has been
taken to insure that there are no #define conflicts where one
library would want a #define that would interfere with the modules
in other libraries. When building a static library, see the following sections
on Select Options and Input/Output
Options, accumulate all the #defines that are required,
and build the whole libwww with those #defines.
What to do:
Undefine WWW_WIN_DLL as preprocessor directives when generating
the project for the Library. Please note, that it is not recommended to staticly
link to the libraries if you are building a Win16 application as it creates
segment size problems.
The libwww can also be built as a set of DLLs that follows the modular architecture of the Library. This enables the application programmer to choose exactly what functionality should be enabled in the application. The boundaries between these DLLs are based on module interdependency and some assumptions regarding which modules may be replaced by the application. Unlike static linking, dynamic linking requires that all the modules in a DLL be replaced at once. This is because the DLL needs all internal references to be resolved at build time.
What to do: Define
WWW_WIN_DLL as preprocessor directives when generating the project
for the Library.
In addition to platform independent modules, there is a small Windows specific
DLL which implements the trace message generation. The DLL is called
windll.dll and contains also the definition of the global trace
flag definition.
windll.c - DLLMain to all DLLs.
wwwdll.c - instances of PTTYPrint and
WWW_TraceFlag. This is included in wwwdll so that it can export
the variables to the rest of the DLLs.
wwwdll.def, wwwutils.def, wwwcore.def
- def (exports) files for the DLLs of the same names.
What to do: Include
the windll.dll as a part of your project and make sure that it is built as
the first DLL.
The functions exported from a DLL are listed in the EXPORTS
section of a .def file. These can be found in the
windows directory. These may also be build
by the makeDefs.pl perl script,
see the description below. You can use the def files as a basis for generating
the DLL projects for your compiler.
What to do: Generate
the DLLs according to the def files so the exported interface is identical
to the set of functions defined in the actual c files included in the DLL.
Unfortunately, make files are not easily shared among different C compilers on Windows which complicates the distribution. We can not support all of them but we can give some hints which may help you to get going.
In the distribution file you can find a complete Microsoft Visual C++ 4.0 Project that builds libwww as a set of DLLs as described in the Library Internals. The easiest way to build the Library is to follow the directions in out installation guide.
We do not provide custum makefiles for this version anymore.
We do not provide custum makefiles for this version anymore.
The Borland C compiler has a different DLL interface where you need to use
the reserved word export in front of all methods and data objects
to be exported from a DLL. This is not currently the case but you can use
the makexprt.pl Perl script to
change the libwww code.
You can often use this project as the basis for porting the make file. The DLL description also various from compiler to compiler which can cause that you can't use the DLL def files directly. We try to make as generic solutions as possible but have limited resources to provide projects for multiple compilers.
makeDefs.pl is a perl 4 script
which takes a list of modules and generates a list of exports used by the
Windows DLLs. The module list may be taken from the appropriate header file
for the library, e.g. wwwutils.dll uses
wwwutils.def which is made from WWWUtils.html.
All def files included in the Library distribution file are automatically
kept up to date by using this script.
You can of course roll your own project instead of using the Makefiles provided by us. If you do so, then you should not that the WAIS gateway requires the freeWAIS library so if you don't have this then you can just take the WAIS module out of the project.