File URLs in NSURL

[Fred Kiefer]

While playing around with thumbnails (thanks to Charles Philip Chan for 
the link!) I came up with the following code:

  file = @"~/GNUstep/Images/TextSystem1.png";
  absolute = [file stringByStandardizingPath];
  NSLog(@"file: %@, absolute: %@", file, absolute);
  absolute = [[NSURL fileURLWithPath: absolute] relativeString];
  digest = [[[[absolute dataUsingEncoding: NSASCIIStringEncoding]
                 md5Digest] hexadecimalRepresentation] lowercaseString];

  NSLog(@"file: %@, absolute: %@, digest %@", file, absolute, digest);
  file = [[[@"~" stringByAppendingPathComponent: @".thumbnails"]
              stringByAppendingPathComponent: @"normal"]
             stringByAppendingPathComponent:
                 [digest stringByAppendingPathExtension: @"png"]];

  image = [[NSImage alloc] initByReferencingFile: file];

But this does not give the correct result. According to the 
specification the URL file name "absolute" should be something like
file:///home/fred/GNUstep/Images/TextSystem1.png

but in GNUStep I do get:
file:/home/fred/GNUstep/Images/TextSystem1.png

When using absoluteString instead of relativeString I get:
file://localhost/home/fred/GNUstep/Images/TextSystem1.png

Again this will result in a different MD5 digest than the one expected 
by the thumbnail standard, so we wont find the correct file. The 
question now is, if there is another method to get the required string 
or if this is a bug in GNUstep, which we should correct.

Cheers
Fred