uberbrady / CREST-fs

Cached Representation State Transfer File System. Mount "The Web" on your computer as a filesystem.

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It's more of a FAQ than a README, but here's what I've got.

What OS does this run on?
	I originally wrote it on Mac OS X. But that's probably rotted by now, and I think it may only run on Linux, which is where I use it.
What does this require?
	MacFuse is needed to be able to run filesystems in userspace on the Mac, and Fuse and uclibc are needed for the Linux version. You can probably
	hack the Makefile to not need it; I need static builds for my purposes.

Do I need a webdav server to use this crest thing?

	No. Well...no. The server protocol is really just HTTP, except for a special set of headers that are always set on every response. I deliberately did not use WebDAV. I think the only special thing you'll need is some additional headers (Which need to appear on all HTTP 200 responses, as well as redirects, and 404's, but not on 304's). Any webserver that does directory listings/index pages in a particular way should work. That particular way is: it should list relative links, and the href="" attribute should match the name for the link. Those 'entries' are considered 'rest resources' that can be listed. E.g.:
	<a href='resource1'>resource1</a> ...
	<a href='res2'>res2</a> ...
	That will display resource1 and res2 as usable file system resources.
	Other links on the page that are *not* relative, or whose names don't match their href's will *not* be listed. The default directory listing module in Apache displays links in this fashion.
	You *really* should have etags enabled on your server, or you will get horrible caching performance. Having it on directories will be nice as well, but requires some custom dirindex scripts. I have ended up building an entire PHP application to handle the various custom server responses. It's not huge, but it's a few pages of code.

How do I use it?
	./crestfs whereyouwanttomountit whereyouwanttocacheit 60 /dev/null
	then, you can cd to whereyouwanttomountit/example.com/mysubdir
	A feature that's now in heavy use will actually attempt to cache the contents 'underneath' the mountpoint by specifying the same directory twice.
	I usually run it with options of:
	and redirect stdout and stderr to files for debugging. It used to require -s and -f (to force single-threaded mode) but this is less often the case now. 
If you want to use HTTP Basic Authentication for some site on the web (right now only one site can be used), create a file and reference it instead of /dev/null in the command-line. The file should a few lines: the domain-name (and optional path elements) for which you want to authenticate, the next line should be your username, and the final line should be your password. This file need not exist when crestfs is launched (attempts to access password-protected files will simply fail). If the file is filled with the appropriate information later, crestfs should learn about it. If the contents of the file are changed (not simply filled-in from empty), I'm not sure it'll be caught properly.
Hey, I don't want The Whole Web, I just want *my* server. (server.com/sampledir/myfile1...)
	You'll still have to mount the web as a whole, but you can make a symlink -
	./crestfs mymountpoint /tmp/cachedir 60 /dev/null  # to mount the web normally, using a cachetime of 60
	ln -s mymountpoint/server.com/sampledir/ justmyserver # to have a 'justmyserver' "directory" which points to your server's directory
What features does it have?
	(NEW) File deletions use clever cache manipulations to avoid server round-trips, and extraneous (and sometimes even deadly) cache invalidations - but ONLY on 'manifest'-style directories.
	(NEW) Support for new leaf-chunking algorithm for writable filesystem - in manifest directories only, some etags may be blank, but etag matches on directories imply the CONTENTS (recursively!) of those directories are unchanged. This should really help performance a LOT.
	(NEW) File and directory creation are done asynchronously, speeding up apparent speed.
	(NEW) Symlinks to files and directories should work. Different type of HTTP Location: headers should be respected
	(NEW) All of the HTTP protocol stuff has been put into one file. Switching to a select() loop will be much easier soon.
	Directory Manifest support speeds access to all files
	Read-write access to a personal subtree of the filesystem.
	Cache-time is mount-time configurable with a command-line option - the amount of time that a resource will *always* be considered 'fresh' for, without requesting the resource from the web again. Interesting values for this are 60 as a reasonable default, and 2^31-1 (2147483647) as a near 'infinite' value (which means resources will only be grabbed once, then never requested again. Well, not for 1600 years, at least.).
	User-Agent header is now "CREST-fs/1.0"
	Threading support is in and seems to work OK.
	Anti-HotSpot pollution - since you're treating REST resources from the Web as actual files, when you go into a Starbucks and use their Wifi, every page you ask for gives you a redirect to a login page. Those redirects would normally be parsed as symlinks and could completely destroy your filesystem. Now, all filesystem-level 200's, 404's and 30x-series redirects require a special header to be set - "X-Bespin-Crest:" - it can be set to anything for now (the production server uses the word 'yes'), but will eventually be some kind of digital signature. This unfortunately makes using a stock Apache install far more difficult than it should be.
	HTTP/1.1 keepalive support is built and has improved performance dramatically.
	etags on directory listings will be respected (so later directory listings don't require another full GET)

	The cache file system looks almost exactly like the live filesystem, so you can boot off of it.
	Metadata for files (HTTP Headers section) is stored under .crestfs_metadata_rootnode/{PATH}
	a stat() on a file typically is implemented as a HEAD on the appropriate HTTP resource
	Directories are aggressively fetched when stat()'ed, as are files that have etags with them already.
	Files that are 'impossible' can be culled from being stat()'ed if they don't exist in one of their parents' directory entries.
	etags are stored and later fetches of files use them to avoid re-downloading unchanged files.
	HTTP redirects (that aren't your standard directory-redirects, which just add a '/' to the Location) are treated as symlinks
	Symlinks and directories are now cached normally, and the negative-directory entry caching system has been removed
	The bulk of the complexity is the get_resource() routine, which does the bulk of the work of managing caches and so on. The rest of the code
	is mostly just a shim to get it to work with FUSE.
	There's a test harness setup that allows testing get_resource() without the rest of FUSE, using simple command-line parameters.
	nonexistent files will create negative-caching entries, reducing server traffic
	The Anti-HotSpot Pollution system requires a lot of poking around at Apache to get working.
	Unexpected conditions in the cache directories will crash the filesystem.
	If you don't run crestfs in debug mode (-d) - sometimes it will hang for some bizarre reason.
	Directory listings can't be larger than 1MB
	Some of the static buffers are probably too small for practical use
	The Makefile is horrible and needs to probably be set up with 'autoconf' or something like it
	Magic numbers are used more than they should be, and this is Naughty.
	Disconnecting/reconnecting network access tends to screw everything up
	DNS lookups are obnoxious, but whaddyagonnado?
	DELETEs are still synchronous, and thus sluggish.
	Massive file copies can put 20000 files (I've seen 50k) in the .crestfs_pending_writes directory, which is pretty untenable
	HTTP connections are *not* pipelined, they're just kept-alive - and this heavily slows down creation of many small files


Cached Representation State Transfer File System. Mount "The Web" on your computer as a filesystem.


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