ISAPI
Encyclopedia
The Internet Server Application Programming Interface (ISAPI) is an N-tier API
of Internet Information Services
(IIS), Microsoft
's collection of Windows
-based web server services. The most prominent application of IIS and ISAPI is Microsoft's web server
.
The ISAPI has also been implemented by Apache
's mod_isapi module so that server-side web applications written for Microsoft's IIS can be used with Apache, and other third-party web servers like Zeus Web Server
offer ISAPI interfaces.
Microsoft
's web server application software is called Internet Information Services
, which is made up of a number of "sub-applications" and is very configurable. ASP.NET
is one such slice of IIS, allowing a programmer to write web applications in his or her choice of programming language (VB.NET, C#, J#) that's supported by the Microsoft .NET CLR
. ISAPI is a much lower-level programming system, giving much better performance, at the expense of simplicity. While Microsoft is generally credited with the creation of the ISAPI specification, it was actually co-developed by Process Software and Microsoft with input from a small number of other vendors.
ISAPI applications can be written using any language which allows the export of standard C functions, for instance C, C++, Delphi. There are a couple of libraries available which help to ease the development of ISAPI applications, and in Delphi Pascal the Intraweb components for web-application development. MFC
includes classes for developing ISAPI applications. Additionally, there is the ATL Server
technology which includes a C++ library dedicated to developing ISAPI applications.
that are loaded into a process that is controlled by IIS. Clients can access ISAPI extensions in the same way they access a static HTML page. Certain file extensions or a complete folder or site can be mapped to be handled by an ISAPI extension.
Filters are implemented as DLLs and can be registered on an IIS server on a site level or a global level (i.e., they apply to all sites on an IIS server). Filters are initialised when the worker process is started and listens to all requests to the site on which it is installed.
Common tasks performed by ISAPI filters include:
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
of Internet Information Services
Internet Information Services
Internet Information Services – formerly called Internet Information Server – is a web server application and set of feature extension modules created by Microsoft for use with Microsoft Windows. It is the most used web server after Apache HTTP Server. IIS 7.5 supports HTTP, HTTPS,...
(IIS), Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
's collection of Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
-based web server services. The most prominent application of IIS and ISAPI is Microsoft's web server
Web server
Web server can refer to either the hardware or the software that helps to deliver content that can be accessed through the Internet....
.
The ISAPI has also been implemented by Apache
Apache HTTP Server
The Apache HTTP Server, commonly referred to as Apache , is web server software notable for playing a key role in the initial growth of the World Wide Web. In 2009 it became the first web server software to surpass the 100 million website milestone...
's mod_isapi module so that server-side web applications written for Microsoft's IIS can be used with Apache, and other third-party web servers like Zeus Web Server
Zeus Web Server
Zeus Web Server is a proprietary web server for Unix and Unix-like platforms . Support for AIX, Tru64, and Mac OS X was dropped on 10 June 2008....
offer ISAPI interfaces.
Microsoft
Microsoft
Microsoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
's web server application software is called Internet Information Services
Internet Information Services
Internet Information Services – formerly called Internet Information Server – is a web server application and set of feature extension modules created by Microsoft for use with Microsoft Windows. It is the most used web server after Apache HTTP Server. IIS 7.5 supports HTTP, HTTPS,...
, which is made up of a number of "sub-applications" and is very configurable. ASP.NET
ASP.NET
ASP.NET is a Web application framework developed and marketed by Microsoft to allow programmers to build dynamic Web sites, Web applications and Web services. It was first released in January 2002 with version 1.0 of the .NET Framework, and is the successor to Microsoft's Active Server Pages ...
is one such slice of IIS, allowing a programmer to write web applications in his or her choice of programming language (VB.NET, C#, J#) that's supported by the Microsoft .NET CLR
Common Language Runtime
The Common Language Runtime is the virtual machine component of Microsoft's .NET framework and is responsible for managing the execution of .NET programs. In a process known as just-in-time compilation, the CLR compiles the intermediate language code known as CIL into the machine instructions...
. ISAPI is a much lower-level programming system, giving much better performance, at the expense of simplicity. While Microsoft is generally credited with the creation of the ISAPI specification, it was actually co-developed by Process Software and Microsoft with input from a small number of other vendors.
ISAPI applications
ISAPI consists of two components: Extensions and Filters. These are the only two types of applications that can be developed using ISAPI. Both Filters and Extensions must be compiled into DLL files which are then registered with IIS to be run on the web server.ISAPI applications can be written using any language which allows the export of standard C functions, for instance C, C++, Delphi. There are a couple of libraries available which help to ease the development of ISAPI applications, and in Delphi Pascal the Intraweb components for web-application development. MFC
Microsoft Foundation Class Library
The Microsoft Foundation Class Library is a library that wraps portions of the Windows API in C++ classes, including functionality that enables them to use a default application framework...
includes classes for developing ISAPI applications. Additionally, there is the ATL Server
ATL Server
ATL Server is a technology originally developed by Microsoft for developing web based applications. It uses a tag replacement engine written in C++ to render web pages...
technology which includes a C++ library dedicated to developing ISAPI applications.
Extensions
ISAPI Extensions are true applications that run on IIS. They have access to all of the functionality provided by IIS. ISAPI extensions are implemented as DLLsDynamic-link library
Dynamic-link library , or DLL, is Microsoft's implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems...
that are loaded into a process that is controlled by IIS. Clients can access ISAPI extensions in the same way they access a static HTML page. Certain file extensions or a complete folder or site can be mapped to be handled by an ISAPI extension.
Filters
ISAPI filters are used to modify or enhance the functionality provided by IIS. They always run on an IIS server and filter every request until they find one they need to process. Filters can be programmed to examine and modify both incoming and outgoing streams of data. Internally programmed and externally configured priorities determine in which order filters are called.Filters are implemented as DLLs and can be registered on an IIS server on a site level or a global level (i.e., they apply to all sites on an IIS server). Filters are initialised when the worker process is started and listens to all requests to the site on which it is installed.
Common tasks performed by ISAPI filters include:
- Changing request data (URLs or headers) sent by the client
- Controlling which physical file gets mapped to the URL
- Controlling the user name and password used with anonymous or basic authentication
- Modifying or analyzing a request after authentication is complete
- Modifying a response going back to the client
- Running custom processing on "access denied" responses
- Running processing when a request is complete
- Run processing when a connection with the client is closed
- Performing special logging or traffic analysis.
- Performing custom authentication.
- Handling encryption and compression.
Common ISAPI applications
This is a list of common ISAPI applications implemented as ISAPI extensions:- Active Server PagesActive Server PagesActive Server Pages , also known as Classic ASP or ASP Classic, was Microsoft's first server-side script engine for dynamically-generated Web pages. Initially released as an add-on to Internet Information Services via the Windows NT 4.0 Option Pack Active Server Pages (ASP), also known as Classic...
(ASP), installed as standard - ASP.NETASP.NETASP.NET is a Web application framework developed and marketed by Microsoft to allow programmers to build dynamic Web sites, Web applications and Web services. It was first released in January 2002 with version 1.0 of the .NET Framework, and is the successor to Microsoft's Active Server Pages ...
, installed as standard on IIS 6.0 onwards - ColdFusion, later versions of ColdFusion are installable on IIS
- PerlPerlPerl is a high-level, general-purpose, interpreted, dynamic programming language. Perl was originally developed by Larry Wall in 1987 as a general-purpose Unix scripting language to make report processing easier. Since then, it has undergone many changes and revisions and become widely popular...
ISAPI (aka Perliis), available for free to install - PHPPHPPHP is a general-purpose server-side scripting language originally designed for web development to produce dynamic web pages. For this purpose, PHP code is embedded into the HTML source document and interpreted by a web server with a PHP processor module, which generates the web page document...
, available for free to install.
ISAPI Development
ISAPI applications can be developed using any development tool that can generate a Win32 DLL. Wizards for generating ISAPI framework applications have been available in Microsoft development tools since Visual C++ 4.0.See also
- Internet Information ServicesInternet Information ServicesInternet Information Services – formerly called Internet Information Server – is a web server application and set of feature extension modules created by Microsoft for use with Microsoft Windows. It is the most used web server after Apache HTTP Server. IIS 7.5 supports HTTP, HTTPS,...
- ATL ServerATL ServerATL Server is a technology originally developed by Microsoft for developing web based applications. It uses a tag replacement engine written in C++ to render web pages...
- SAPIServer Application Programming InterfaceIn computer science, the Server Application Programming Interface is the generic term used to designate direct module interfaces to web server applications such as the Apache HTTP Server, Microsoft IIS, or iPlanet...
- C++C++C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
- PHPPHPPHP is a general-purpose server-side scripting language originally designed for web development to produce dynamic web pages. For this purpose, PHP code is embedded into the HTML source document and interpreted by a web server with a PHP processor module, which generates the web page document...
- FastCGI: An alternative way of interfacing a web server with application codeFastCGIFastCGI is a protocol for interfacing interactive programs with a web server. FastCGI is a variation on the earlier Common Gateway Interface ; FastCGI's main aim is to reduce the overhead associated with interfacing the web server and CGI programs, allowing a server to handle more web page...