Make hgweb.staticfile() more secure and portable.

Without this, files in directories next to the static directory starting
with 'static' could be retrieved, e.g. with '../static.private/foo'.
Additionally staticfile now generates platform specific pathnames from
the /-separated paths given in the URL.
Illegal file names (e.g. containing %00) now yield a sane error message.

mercurial/hgweb.py

@@ -73,31 +73,28 b' def get_mtime(repo_path):'
         return os.stat(hg_path).st_mtime
 
 def staticfile(directory, fname):
-    fname = os.path.realpath(os.path.join(directory, fname))
+    """return a file inside directory with guessed content-type header
+
+    fname always uses '/' as directory separator and isn't allowed to
+    contain unusual path components.
+    Content-type is guessed using the mimetypes module.
+    Return an empty string if fname is illegal or file not found.
 
+    """
+    parts = fname.split('/')
+    path = directory
+    for part in parts:
+        if (part in ('', os.curdir, os.pardir) or
+            os.sep in part or os.altsep is not None and os.altsep in part):
+            return ""
+        path = os.path.join(path, part)
     try:
-        # the static dir should be a substring in the real
-        # file path, if it is not, we have something strange
-        # going on => security breach attempt?
-        #
-        # This will either:
-        #   1) find the `static' path at index 0  =  success
-        #   2) find the `static' path at other index  =  error
-        #   3) not find the `static' path  =  ValueError generated
-        if fname.index(directory) != 0:
-            # generate ValueError manually
-            raise ValueError()
-
-        os.stat(fname)
-
-        ct = mimetypes.guess_type(fname)[0] or "text/plain"
-        return "Content-type: %s\n\n%s" % (ct, file(fname).read())
-    except ValueError:
-        # security breach attempt
+        os.stat(path)
+        ct = mimetypes.guess_type(path)[0] or "text/plain"
+        return "Content-type: %s\n\n%s" % (ct, file(path).read())
+    except (TypeError, OSError):
+        # illegal fname or unreadable file
         return ""
-    except OSError, e:
-        if e.errno == errno.ENOENT:
-            return ""
 
 class hgrequest(object):
     def __init__(self, inp=None, out=None, env=None):