Test: HTML Plug-ins - Class 3 MCQ

All the browsers support <object> element. It also defines an embedded object within the HTML document. It is used for embedding plug-ins like PDF readers, Flash Players, Java applets in the web page.

NPP_New function is called by the browser when an instance is created. There can exist multiple instances of the same plug-in. There are two conditions for it first if there are multiple embedded objects on a single page, second if several browser windows are open.

When the user leaves instance’s page or closes its window a plug-in instance is deleted. Then Gecko calls the function NPP_Destroy to inform plug-in that the instance is being deleted. Plug-in API calls and callbacks use main Navigator thread.

/Library/Internet Plug-Ins, ~/Library/Internet Plug-Ins, Plug-ins with the toolkit bundles, /System/Library/Frameworks/JavaVM.framework/Versions/Current/Resources, Profile directory/plugins are some of the directories in Mac OS X for plug-ins.

The plug-in file type depends on the platform. The file type in MS Windows is .DLL which is Dynamic Link Library files. Unix has .SO or .DSO files which are shared objects. MAC OS X has file PPC/x86/Universal loadable Mach-O bundle.

The plug-in DLL should contain FileExtents which specifies file extensions, ProductName which is for plug-in name, Language for the language which is in use, FileDescription for the description, MIMEType for the MIME types, FileOpenName for file open template.

There are three transmission modes that plug-in can select. In normal mode browser sends stream data sequentially to plug-in, in Random-access mode browser allows a plug-in to request specific ranges of bytes from anywhere in the stream. In File, mode browser saves data to a local file in cache and passes the file path to plug-in.

NPN_GetURL is a request for the browser to load a URL into a particular frame for display or browser window, or for delivering data of that URL to the plug-in instance in a new stream. NPN_PostURLNotify function notifies plug-in of a result when an operation completes.

NPN_Status is used to display a message on the status line. It makes the user feel that the plug-in is a part of the browser user interface, plug-in can emulate browser behavior by providing status line message.

There are plugin resources. ‘STR#’ 1 is associated with video or quicktime, MIME type is associated with str 128, aiff is associated with string 4, jpg is associated with string 6, image or jpeg is associated with string 5.

Browser calls various plug-in methods like NPP_Print, NPP_SetWindow, NPP_SetValue, NPP_HandleEvent, NPP_GetValue. NPP_SetValue is for setting the browser information, for delivering platform-specific event to instance browser calls NPP_HandleEvent method.

It is a convention that all of the browser specific functions have the prefix ‘”NPN” and all of the plug-in specific functions have the prefix “NPP”. Gecko calls plug-in API function NP_Initialize at the time when plug-in code first loaded.

When the last instance of a plug-in is deleted Gecko calls the function NP_Shutdown. The plug-in code is unloaded from memory. Plug-ins consume no resources when not loaded, it only consumes a little disk space.

When Gecko based browser starts, it checks certain directories for plugins. Windows have MOZ_PLUGIN_PATH, Profile directory\plugins, %APPDAT%/Mozilla\plugins, Plug-ins with toolkit bundles, HKEY_CURRENT_USER\Software\MozillaPlugins\*\Path are some of the directories in windows.

Profile directory/plugins, /usr/lib64/Mozilla/plugins, /usr/lib/Mozilla/plugins, ~/.mozilla/plugins are some of the directories in Linux for using plug-ins. /usr/lib64/firefox/plugins is for 64-bit Firefox.