Re: partial URLs ?

BearHeart/Bill Weinman (
Wed, 20 Dec 1995 20:36:46 -0600

Hi, Kids,

I wouldn't bother with this, except that since I sent the
message that got this thread rolling I've seen over 150 messages
in about 24 hrs. (I don't know the exact number, but it was over
100 when I cleaned up this afternoon.) Most of them are duplicates
or triplicates of the same message. (And not all are on this

Part of the reason for that is that the thread is now being
echoed to two lists that I subscribe to--but about a third of the
traffic is because of the practice of replying to several individuals
(invariably one of them is me) as well as to the lists.

Could we try to bring the distribution of this thread back down to
just the lists? It would help my frazzled nerves a bit.

<now back to our regularly-scheduled argument>

John Franks Wrote:
>As I recall the draft RFC for URL's specifies that certain characters
>(like space) are forbidden, certain (like '?') have special meaning
>and otherwise the "path" part of a URL is an opaque string (which, in
>particular, may have nothing to do with a path). Neither '/' nor '.'
>are forbidden or have special meaning. They do have special meaning
>*for some implementations* and no special meaning for others.
>Likewise the colon may have special meaning for some implementations
>and not for others.

I think you're right that there is nothing about the "../"
string that's in violation of URL-law. But then, I don't think
a URL is a very exact science anyway <g>.

>It would, of course, be quite reasonable for the HTTP spec to have
>a UNIX-centric warning to implementors that they should make this
>string illegal for their implementation (or risk the consequences).

Yes, "/../" is a unixism, but the path part of a URL is inherently
platform specific. I see URLs with "\" in them for DOS-type hosts, and
"\..\" is just as much of a problem--maybe more because of the lack
of permissions-bits in most DOSish OSs. The code I've seen that 403s
these things checks for the ".." and that seems to be a pretty
universal string for "go up a level in the file system", or do you
know of an OS with more than 3 servers on the net that doesn't work
that way?

(side note: MS has implemented "..." and "...." in Win95 for
referencing up two- and three- levels respectively. I don't know about
NT, but if it's not in there now it soon will be. A check for ".."
would obviously catch this as well.)

My bottom line here is that ".." in a path ought to be illegal
in HTTP, perhaps with a notation to that effect in HTML.

* BearHeart / Bill Weinman
* * * *
* Author of The CGI Book: * *
* Trust everyone, but brand your cattle.