Re: Making extensions available to multiple GRE applications

[Syd Logan]

Providing eveything any application may want was never the goal of the 
GRE as I understood it, rather, it was to provide everything all 
application must have. As such, the original intent of the GRE was to 
provide a factoring of components found in all mozilla apps at a rather 
low level. The layout engine, XPCOM,  networking code, and so forth fit 
into this category. A GRE is installed the first time a mozilla app is 
placed on a machine, and shared by compatible mozilla apps. It is also 
fixed in terms of its definition. The intent behind having a GRE is to 
save space on the hard disk, and to save time spent downloading and 
unpacking stuff at install time. One would not expect to see things in a 
GRE that were not absolutely fundamental, by this definition. GRE is 
"kernel" space, not "user" space (I use those terms loosely, but if you 
consider mozilla to be a platform, and then it almost makes sense to 
consider the GRE being kernel space and apps like a browser, mail 
client, or composer being user space).

Extensions seem to me to be in user space primarily because they are not 
universally essential.

Perhaps what is needed is an addition space, an "extensions" space that 
has additional stuff in it that is not "core" functionality, but might 
be shared nonetheless. But it would be good IMHO to make this space 
distinct from the GRE, for fear of the GRE becoming a kitchen sink that 
strays from the original goals.

If you are from a Unix persuation, GRE might be what you find in /lib, 
required by nearly every application, while extensions might be what is 
installed in /usr/lib.

syd

Benjamin Smedberg wrote:

I have filed and taken several bugs having to do with extensions and 
the GRE, and I would like to outline my plans for GRE extensions (and 
extensions in general) so that people may comment. Please reply to 
n.p.m.xpinstall, and not to the bugs, unless you have a patch or 
implementation comment. The overarching bug is bug 209439.

Definitions:
"extension" == a browser addon or utility (installed with XPInstall)
My plan has the following goals:

1) allow extensions to be registered with a GRE, so that they can be 
made available to multiple applications using the GRE
2) allow extensions to be installed into their own directories, 
instead of being installed in the same directory as an application
3) allow extensions (which use only frozen interfaces) to work with 
multiple versions of the GRE
4) allow extensions to be un-installed

Currently, extensions "piggyback" on top of an application's chrome 
and components directories. This makes it difficult/impossible to 
un-install extensions. Instead, it should not be difficult for 
extensions to maintain their own chrome and components locations.

Implementation-prerequisites:
1) The chrome: service needs to be extended to register arbitrary 
chrome directories (bug 210838)

Implementation:
Each extension would have an RDF file describing itself. The GRE would 
include an nsIExtensionManager service, which would allow applications 
to enumerate/discover available extensions, register extensions, and 
enable/disable extensions as necessary. The GRE would not contain any 
UI for extensions; any UI would be managed by applications. There 
would also be a little command-line utility with the GRE that would 
register extensions.

Extensions would not be enabled by default; instead, after the 
application initializes the GRE, it would need to use the 
nsIExtensionManager to enable the extensions that it wished to use.

Although every extension could use this mechanism, extensions meant 
for multiple applications would benefit most from this scheme. Some 
important examples would include:
DOM Inspector
Venkman
JSLib
tranformiix

I feel that GRE extensions are necessary, in order for the new roadmap 
to be implemented effectively.

--BDS

P.S. Can I also argue that there ought to be a second alpha before 
1.5beta? Not much of the current roadmap has been completed yet, and 
we're going to freeze 1.5a on Wednesday... how about another month and 
then 1.5a2?