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Old 12-29-2002, 03:23 PM   #1
darkone
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Lightbulb Directory caching

Most graphical ftp clients are supporting directory caching nowdays (It's a great feature, as it reduces work/traffic done by both server & client) - However due lack of one simple ftp command, caching is currently very inaccurate.
What I'm suggesting is to add 'DATE' command (similar to SIZE) to read file's/directory's timestamp via control channel. This would allow client to determinate with simple check, wheter contents of directory have changed since last cache update.

Client Command: DATE <filename>
Server Response: 213 <file time low-order dword> <ft high-order dword> <system time low-order dword> <st high-order dword>

Client should turn caching off, if server replies with error on the first try (same as with REST).


Here are examples how it could/should be implemented:

Client enters directory for the first time:

CLIENT => SERVER: DATE . ("." = current directory)
SERVER => CLIENT: 213 0 0 0 1
... Client requests for directory list ...

Client enters cached directory (unmodifed):

CLIENT => SERVER: DATE .
SERVER => CLIENT: 213 0 0 0 2 (Client compares cached values to with new values - and notices directory has not changed)
... Client waits for next command ...

Client enters cached directory (modified):

CLIENT => SERVER: DATE .
SERVER => CLIENT: 213 1 0 0 2
... Client requests for directory list ...

*Note* Directory should not be cached, if 'System time' in server response is equal to or less than 'File time' - as it's possible (not very likely) that contents have changed since.

Server that doesn't support 'DATE':

CLIENT => SERVER: DATE .
SERVER => CLIENT: 500 'DATE': Command not understood
... Client requests for directory list ...


Any questions/comments?
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Old 01-03-2003, 02:02 PM   #2
Hetfield
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Yup, i totally agree with your suggestion. For me the directory caching is pretty much useless now
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Old 01-03-2003, 09:29 PM   #3
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I've never heard of DATE before. I wonder how many servers support it. Sounds like a good idea for our second generation caching.
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Old 01-07-2003, 09:23 PM   #4
darkone
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Heh, it actually doesn't exist in any rfc (atleast yet). Adding this feature is only ~10lines of code (on server side), so I'm quite confident that nearly all daemons that are still under development will support it. (I'll email wu-ftpd's development team asap, and ask what they think of it)
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client, command, date, directory, server

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