Asynchronous Pluggable Protocol

An APP enables customized transfer protocols for your Web browser.

An Asynchronous Pluggable Protocol (APP) creates extensions for Internet Explorer. The address bar of your browser starts with “http://.” This shows that the browser is using the Hypertext Transfer Protocol (HTTP). APPs provide other protocols for this space.


Developers can copy an existing protocol, such as HTTP, modify it and re-register it as a new pluggable protocol. An example of a pluggable protocol is “about.” This displays descriptive HTML pages stored on the computer. This protocol displayed the “about” text if the referenced page was not found in earlier versions of Internet Explorer (before version 6).


APPs cannot override existing available protocols. HTTP is embedded in the browser’s definition files, for example. You can, however, write your own version, which will be activated by a call in the address bar. Write an APP called XTTP, for example. You will still be able to access HTTP by typing “http://” at the beginning of an address, but you would access your new protocol by typing the address of a website beginning with “xttp://.”


It would be extremely complicated to create an alternative protocol for downloading websites. Many Web pages require a combination of protocols depending on whether they contain relative, virtual or absolute links. Don’t ignore these requirements, since they will cause “permission denied” errors when each protocol tries to access the same resources.

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