RE: MIME type filter ?

From: ADELINE E InfoRstTel[SMTP:Emmanuel.Adeline@socgen.com]
Sent: Wednesday, 22 April 1998 3:06
Subject: MIME type filter ?

>Is it possible to block documents which have some particular MIME types?
> am looking preferably for a solution not involving much source
modification.
>by the way, would it be a good idea to extend ACL filtering to MIME types?

The answer is yes and no.

Yes, because you could block the well-known file extensions of certain MIME
type with Squids existing ACL mechanisms

e.g. .PDF for Acrobat files which are *almost* always MIME type
application/pdf, so block the .PDF extensions via a URL regex.

No, because not all types act in such well known and predictable ways.

e.g. Microsoft Word (.DOC) could be application/msword on one server or it
could really be a README.DOC text file of type text/plain on another.

Given that Squid doesn't know the MIME type until it has already queried the
destination web server (or upstream / sibling caches), it is not a part of
the caching methodology that could be easily implemented, and would result
in Squid doing a check first, then either continuing the HTTP transfer, or
dumping it altogether. You could do a cursory "HEAD" request, then based on
the Content-Type: header decide to proceed with the GET or POST. It would
sort of fall down for CGI-BIN scripts and the like though, so its actual
application is very limited IMHO. Either means of "sniffing" the MIME type
involves a TCP/IP session creation and teardown, which are somewhat
expensive and would slow down the actual transfer of data (on a second
session) by the time it takes to do this.

Jason

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end
Received on Tue Apr 21 1998 - 19:27:40 MDT