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From Brandon Fosdick <b...@bfoz.net>
Subject Re: Bucket brigades and large files
Date Sat, 29 Oct 2005 05:02:19 GMT
Brandon Fosdick wrote:
> http://terran-bank.com/mod_dav_userdir_20051028.tar

So maybe I should explain the code a bit. First off, its all C++. Now we wait a sec for the
C folks to run away screaming...ok, good.

All of the database magic happens in class ServerConfig. It's an enourmous mess of a class.
Cleaning it up is on the ToDo list, after switching to prepared statements. (really, I have
a list, it's in OmniOutliner on my pbook) As the name implies, this class is created by the
usual create server config handler. All of the config directive handlers call set_X() methods
of ServerConfig.

repository.cc is what you think it is if you're familiar with mod_dav, but it mostly passes
stuff off to class resource_t, which then passes database requests to ServerConfig.
For those not familiar with mod_dav, every request starts with a call to get_resource(), which
is responsible for creating a structure that represents each DAV resource involved in the
request. In this case that structure is resource_t. 
deliver() is where the downloading happens. It creates a bucket brigade and dumps all of the
blocks from the database into the brigade. I have no idea if I did that right.

hooks.cc is where all of the hooks are registered. Nothing fancy there.

Locks, properties, etc are handled by the appropriately named files. Most of the handlers
pass through to a class method of some sort. That sounds like it would be slow, but almost
all of the class methods are inline, so its no worse than C. Most of these classes are fairly
straightforward. Locks are poorly implemented ATM.

stream_t in stream.h is where the upload magic happens. It serves as a buffer between mod_dav
and the database. Incoming bytes are buffered into 64K blocks before being written to MySQL.
This would be a great place to use prepared statements, but I haven't gotten around to it.
When I started this project I had never used them outside of PHP, and my focus was on getting
something working as quickly as possible.

apr_pool_base.h has a base class and a new() operator that helps with using pools. I can't
tell if the destructors are being called properly, but I haven't had any problems with memory
leaks, so maybe its working.

The sharp eyed will notice that I have a copy of mod_dav.h in the source. That's because the
official copy uses the namespace token in two places, and therefore barfs in C++. I sent an
email to the list about this several months ago and didn't get a response. So, I use a modified
copy.

I should point out that the usernames are constrained to be positive integers, but only because
that's what Terran Bank needs. At one point I was maintaining a fork that allowed real usernames,
but it fell by the side. Mainly because it was pointless, I think the only difference was
two functions in resource_t. Some day I'll add a compile-time config option.

That's the high level overview. Let me know if you want more.

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