Fun with Windows paths.

I am currently attempting to implement a JavaScript library to handle file system paths in a portable manner.

Right now, I am having lots of fun with Windows paths and I wanted to share a few tidbits.

Under Windows, a path name can look like:

1. “\\?\drivename:” followed by backslash-separated components.
   Such paths can be either relative or absolute.
   In such paths, “.”, “..” and “/” are regular file names.
2. “\\.\drivename:” followed by backslash-separated components.
   Such paths can be either relative or absolute.
   In such paths, “.”, “..” and “/” are special names.
3. “\\?\UNC\servername” followed by backslash-separated components.
   Such paths can only be absolute.
   In such paths, “.”, “..” and “/” are regular file names.
4. “\\servername” followed by slash- or backslash- components.
   Such paths can only be absolute.
   In such paths, “.”, “..” and “/” are special names.
5. “drivename:” followed by slash- or backslash- components.
   Such paths can be either relative or absolute.
   In such paths, “.”, “..” and “/” are special names.
6. Just a series of slash- or backslash- components.
   Such paths can be either relative or absolute.
   In such paths, “.”, “..” and “/” are special names.

To simplify things further, depending on the version of Windows, a drive name can be:

• only one letter between A and Z;
• any sequence of letters between A an Z;
• something that looks like Volume{41AF5D4F-04CC-4D15-9389-734BD6F52A7E}.

Also

• if a path starts with “\\?\”, its length is limited to 32,767 chars;
• otherwise, its length is limited to 260 chars.

Also

• some names such as “LPT”, “COM”, etc. are reserved and cannot be used as file names;
• … unless your path starts with “\\”.

Also

• paths are case-insensitive;
• … except when they are case-sensitive because of the disk format;
• … except when they are case-sensitive because of something else.

Fortunately, the Windows APIs provides the following functions to simplify matters:

• PathCanonicalize (completely broken);
• GetFullPathName (broken);
• GetLongPathName (requires access permissions just to tell you if a path is well-formatted);
• UriCanonicalize (not sure what it does exactly, I haven’t tested it yet).

Of course, not all Windows API functions accept all schemes.

As you can imagine, I am having lots of fun.

Quick exercise given two paths A and B (either absolute or relative), how do you determine the path obtained by concatenating A and B?

If you are interested in following my progress, details are on bugzilla.