Open URLs

Open URLs

[vlc]

Hi *,

I am looking for a way to open URLs (like "file:///home/vlc/file") as
files - as you would do with "Open (Handle, In_File, "/home/vlc/
file")".

I could surely just remove the heading "file://", but this would still
leave me with the problem of special characters like "file:///home/vlc/
name%20with%20spaces".

Does anybody know of a way to translate URLs to paths?

Thanks a lot in advance!

Re: Open URLs

[Gautier write-only]

> I am looking for a way to open URLs (like "file:///home/vlc/file") as
> files - as you would do with "Open (Handle, In_File, "/home/vlc/
> file")".
>
> I could surely just remove the heading "file://", but this would still
> leave me with the problem of special characters like "file:///home/vlc/
> name%20with%20spaces".
>
> Does anybody know of a way to translate URLs to paths?

What about doing successive string replacements:
"file://" -> ""
"%20" -> " "
etc.
?
Probably you need to make a "Replace_all" function using
Ada.Strings.Fixed's routines (unless it's already there), then it
should be straightforward.
______________________________________________________________
Gautier's Ada programming -- http://gautiersblog.blogspot.com/

Re: Open URLs

[Pascal Obry]

Le 03/01/2010 19:17, vlc a �crit :
> Does anybody know of a way to translate URLs to paths?
>
> Thanks a lot in advance!

Not directly. After removing the file:// prefix, you can use AWS.URL.Decode.

Pascal.

-- 

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Re: Open URLs

[vlc]

On Jan 3, 7:36 pm, Pascal Obry <pas...@obry.net> wrote:
>
> Not directly. After removing the file:// prefix, you can use AWS.URL.Decode.
>
> Pascal.

Thanks. This looks quite promising!

Re: Open URLs

[Dmitry A. Kazakov]

On Sun, 3 Jan 2010 10:17:58 -0800 (PST), vlc wrote:

> I am looking for a way to open URLs (like "file:///home/vlc/file") as
> files - as you would do with "Open (Handle, In_File, "/home/vlc/
> file")".
> 
> I could surely just remove the heading "file://", but this would still
> leave me with the problem of special characters like "file:///home/vlc/
> name%20with%20spaces".

The third / is a delimiter, theoretically there could be something between
file:// and /. The path might be followed by queries and fragments, see
here:

   http://en.wikipedia.org/wiki/URI_scheme#Generic_syntax
 
> Does anybody know of a way to translate URLs to paths?

You just parse it. What is the problem, except that the number of URI
schemes is huge.

Regarding replacing %20 with SP, I am not sure if this has to be done. You
have to dig the documents (RFC) to verify if %<number> is indeed a defined
escape sequence, if there are any in the URI, I do not remember. Otherwise
it is a part of the file name to be passed further as is.

In any case, when you write a parser, you could make it recognize escape
sequences, delimiters etc as it moves the cursor left to right. Something
like:

   Pointer := URI'First;
   ... -- Get scheme, advance pointer
   case Scheme is
      when File_Schema =>
         declare
            Path : Unbounded_String;
            Code_Point : Integer;
         begin
            loop
               if URI (Pointer) = '%' then
                  Get (URI, Pointer, Code_Point);
                  Append (Path, Character'Val (Code_Point));         
               elsif Is_In (Delimiters, URI (Pointer)) then
                  exit;
               else
                  Append (Path, URI (Pointer));
                  Pointer := Pointer + 1;
               end if;
               exit when Pointer > URI'Last;
            end loop;
            ...
etc

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de

Re: Open URLs

[David Thompson]

On Sun, 3 Jan 2010 21:05:46 +0100, "Dmitry A. Kazakov"
<mailbox@dmitry-kazakov.de> wrote:

> On Sun, 3 Jan 2010 10:17:58 -0800 (PST), vlc wrote:
> 
> > I am looking for a way to open URLs (like "file:///home/vlc/file") as
> > files - as you would do with "Open (Handle, In_File, "/home/vlc/
> > file")".
> > 
> > I could surely just remove the heading "file://", but this would still
> > leave me with the problem of special characters like "file:///home/vlc/
> > name%20with%20spaces".
> 
> The third / is a delimiter, theoretically there could be something between
> file:// and /. The path might be followed by queries and fragments, see
> here:
> 
>    http://en.wikipedia.org/wiki/URI_scheme#Generic_syntax
>  
Although one can just say queries aren't supported for resources that
are actually files, since they don't make sense. (Although they might
for something like a cryptographic FS where you must supply a password
-- but then whether you should allow a password to be supplied by a
potentially untrusted path is another issue.)

Fragments are supposed to be implemented by the user agent (for the
web, normally a browser); it's not clear to me whether the OP does or
anyone else would want this below or above the proposed API.

> > Does anybody know of a way to translate URLs to paths?
> 
> You just parse it. What is the problem, except that the number of URI
> schemes is huge.
> 
Nontrivial but I wouldn't say huge -- and the number that make sense
for files is pretty small. And the OP apparently only needs one.

> Regarding replacing %20 with SP, I am not sure if this has to be done. You
> have to dig the documents (RFC) to verify if %<number> is indeed a defined
> escape sequence, if there are any in the URI, I do not remember. Otherwise
> it is a part of the file name to be passed further as is.
> 
Yes % two-hex is in STD66=RFC3986 2, and %20=SP is even the example.

Of course if there are codepoints not allowed in a pathname, like NUL
on Unix, you can't support the corresponding escape %00 in a URI. 
And you need to decide some things like whether %2F is treated as a
branch-character / which is similarly unsupportable, or as a branch
delimiter in violation of the nominal URI semantics.

<snip code>