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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Open URLs
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Date: Sun, 3 Jan 2010 21:05:46 +0100
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Date: 2010-01-03T21:05:47+01:00
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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