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From Jon Moore <j...@apache.org>
Subject thoughts on httpclient decorators
Date Fri, 01 Jun 2012 14:07:51 GMT
As we've seen, we've run into a couple of problems with some of our
decorators for the DefaultHttpClient where underlying backends do
non-transparent things (ranging from decompressing content bodies without
updating response headers, to following redirects). I do think the
decorators provide a nice way to layer the overall functionality from a
codebase point of view, but I think they are brittle because they rely on
unenforceable assumptions (e.g. that backend clients that get injected
behave transparently).

I think the solution to this is to continue using the decorators, but hide
them from most users--in other words, reimplementing the DefaultHttpClient
as a stack of decorators that get enabled/disabled by configuration. In
other words, a user should be able to "new DefaultHttpClient()" and get
something that is capable of caching, following redirects, and handling
compression (per configuration).

I think this looks like:
(1) generate a decorator for redirect following
(2) create a new class (BasicHttpClient?) that is essentially
DefaultHttpClient minus the redirect logic
(3) reimplement DefaultHttpClient so that it generates and configures a
stack of RedirectFollowingHttpClient, DecompressingHttpClient,
CachingHttpClient, BasicHttpClient (this might mean needing to pull the
httpclient-cache module into the httpclient module)
(4) add warning documentation on the DecompressingHttpClient and
CachingHttpClient about needing to wire them up correctly (this should
probably happen first, actually)

I suspect there are actually other decorators lurking in there too
(authentication? cookie handling?).

I think this potentially gives us a clean way to layer in
functionality--implement it as a decorator and then figure out where in the
stack is the right/safe way to add it. Opting into the new functionality is
a matter of turning it on in the config for DefaultHttpClient, which is far
simpler for users to do.

Thoughts?

Jon

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