Persistent proxy and off-line web apps
Jon Smirl
solution for implementing off-line web apps. This mail describes the
basic concept. I'm all for any input on the easiest way to achieve
this using the Mozilla code base. I'm working towards a solution that
could be shipped with Firefox if all the kinks can be worked out.
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The concept is fairly simple, you run a proxy server on the local
machine. Mozilla is set up to always talk to the local proxy server.
The proxy server also implements FastCGI. Domains can download
sandboxed Javascript and run it as a FastCGI app off from the proxy
server. The proxy server will intercept requests for the domain and
route then through the FCGI app first before sending them on out to
the Internet.
This model provides a transparent solution for offline web apps.
Domains can be assigned space and given access to storage or sqlite.
You could build a local version of gmail that would have exactly the
same UI as the Internet one. When reconnecting to the Internet the app
can sync up with the main servers.
The proxy server is always running, it is a separate app from the
browser. This provides for long running programs like RSS polling or a
chat client. It can also be used to manage things like replication of
large amounts of photos/music back to web servers. The proxy server
can be designed to use low levels of memory when not active.
Another idea would be to split web apps with a MVC (model, view,
controller) architecture. The model code stays back on the main server
and the controller code is migrated into the proxy sandbox if
available. The MVC split is much more powerful than the current AJAX
system since it provides a clean way to save a lot of state info.
This design is well suited to the XULrunner / Firefox shift planned
for next year. With a XULrunner based FIrefox it 's not too hard to
build the proxy server and fastcgi layer using the XULrunner
components. The separate proxy model can equally serve IE, Mozilla or
any other browser.
What do you think? The concept is a blend of Net Nanny and Akami's
edge services. Is this something worth pursuing or has it already been
tried and I never noticed?
Brendan points out BEA's alchemy proposal.... I go read about it ...
Alchemy is beating around the same bush but not quite exactly the same
concept. He didn't generalize enough. He structures the data store and
synchronization and assumes you want a data store and synchronization.
He also talks about calling back to web services. It is not clear if
he intended for any server to download code into Alchemy or if the
code has to come via BEA.
I was working from an entirely general view point. The proxy talks
standardized FCGI to the local FCGI app. This app is migratory, it can
run at the server or on the client. I posted the code for serving FCGI
via xpcshell on the js-eng list. Each domain is isolated into it's own
process, that makes it easy to apply cross site scripting controls.
There is no required structure for the FCGI code. It can access the
safe Javascript/XPCOM API and do what it wants. There needs to be a UI
via the browser for limiting how much disk space the FCGI app can
consume, but it can do what it wants with that disk space - keep logs
or run a sqllite db in it. If you want to synchronize, supply your own
code. You can always chose to install non-safe FCGI app versions too.
Something like xmlhttprequest can pragmatically talk to the server
from the FCGI app or just open up a socket to the server assuming that
the cross-site scripting rules are applied. Some apps may choose to
run entirely on the local system. Off-line apps need to have a special
mode if they can't contact the remote server.
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Jon Smirl
jons...@gmail.com