support file-as-volume (#696);

a volume can be a single file instead of a folder,
but a misleading warning indicated otherwise

README.md

@@ -572,6 +572,8 @@ for example `-v /mnt::r -v /var/empty:web/certs:r` mounts the server folder `/mn
 
 the example config file right above this section may explain this better; the first volume `/` is mapped to `/srv` which means http://127.0.0.1:3923/music would try to read `/srv/music` on the server filesystem, but since there's another volume at `/music` mapped to `/mnt/music` then it'll go to `/mnt/music` instead
 
+> ℹ️ this also works for single files, because files can also be volumes
+
 
 ## dotfiles
 

copyparty/up2k.py

@@ -926,6 +926,12 @@ class Up2k(object):
         with self.mutex, self.reg_mutex:
             # only need to protect register_vpath but all in one go feels right
             for vol in vols:
+                if bos.path.isfile(vol.realpath):
+                    self.volstate[vol.vpath] = "online (just-a-file)"
+                    t = "NOTE: volume [/%s] is a file, not a folder"
+                    self.log(t % (vol.vpath,))
+                    continue
+
                 try:
                     # mkdir gonna happen at snap anyways;
                     bos.makedirs(vol.realpath, vf=vol.flags)