W3C home > Mailing lists > Public > uri@w3.org > January 2006

Re: path-abempty in URI

From: Tom Petch <nwnetworks@dial.pipex.com>
Date: Sat, 7 Jan 2006 21:20:45 +0100
Message-ID: <019101c613c8$239397e0$0601a8c0@pc6>
To: <uri@w3.org>, "Frank Ellermann" <nobody@xyzzy.claranet.de>

----- Original Message -----
From: "Frank Ellermann" <nobody@xyzzy.claranet.de>
To: <uri@w3.org>
Sent: Saturday, January 07, 2006 7:42 PM
Subject: Re: path-abempty in URI
>
> Tom Petch wrote:
>
> > My understanding from reading the text is that <path-abempty>
> > exists to ensure that there is always an authority between
> > the // that comes after scheme: and before the // that may
> > start a path
>
> The "//" after the scheme ":" is only used in conjunction with
> hier-part = "//" authority path-abempty
>
> You can also have a scheme ":" with path-absolute, path-empty,
> and path-rootless, and in these three cases there's no "//"
> after the scheme ":".
>
> 1 - path-empty is 0<pchar>, no slashes in sight, next stop "?".
> 2 - path-absolute is "/" segment-nz etc., segment-nz is 1*pchar
>     So here you have precisely one slash after the scheme ":".
> 3 - path-rootless starts with segment-nz, no "/" after the ":"
>
> That leaves "//" authority path-abempty to get an interesting
> number of slashes after the scheme ":".
>
> Ignoring optional parts <authority> is at least a <host>, and
> <host> is IP-literal / IPv4addrss / reg-name.  I'm positive
> that the former are never empty, but <reg-name> can be empty.
>
> path-abempty is zero or more "/" segment, and segment is zero
> or more pchar.  So you can have file:///etc (three slashes),
> and in theory also more slashes if the segments are "empty".
>
> In practice file: is the only URI scheme I know that allows an
> empty reg-name (in that case instead of localhost), are there
> any other schemes with a similar "feature" ?
>
> >      scheme:////SERVERA/////////////////////////?abnf=ok
> > where the path is //SERVERA///... is allowed.  Comments?
>
> Yes, you're right.  I didn't know that, thanks for info, bye
>
It was not so much a question of allowing an empty reg-name, as of requiring an
authority to be present, to be of at least one character.  I wanted to check
that my reading of the ABNF for authority in URI was correct, and you say it is.
In which case, importing the rules from URI is not of itself enough, some
additional textual comment is needed so that
    scheme://///////////
while conforming to the ABNF, is not regarded as valid.

Of course it is possible to write ABNF to achieve (almost) anything, but
sometimes I see it as better to get there by adding a comment:-)

Tom Petch
Received on Saturday, 7 January 2006 21:26:24 UTC

This archive was generated by hypermail 2.3.1 : Tuesday, 6 January 2015 21:25:09 UTC