AssertionError on DELETE when child links point to yourself

[zooko]

USSJoin accidentally made a directory with all of its child links pointing to itself:

[
 "dirnode",
 {
  "rw_uri": "URI:DIR2:qtotg7dsasgg367iigdmloryjy:3iblclsl5vvuguthfgyu6r5r6fqz2eakolo5zf5dd4so7uwyqsua",
  "verify_uri":
"URI:DIR2-Verifier:7adhej5azpcfstqm7hozdplqyy:3iblclsl5vvuguthfgyu6r5r6fqz2eakolo5zf5dd4so7uwyqsua",
  "ro_uri": "URI:DIR2-RO:gnc3ftwpfi2s63fmupirayl7b4:3iblclsl5vvuguthfgyu6r5r6fqz2eakolo5zf5dd4so7uwyqsua",
  "children": {
   "1": [
    "dirnode",
    {
     "mutable": true,
     "verify_uri":
"URI:DIR2-Verifier:7adhej5azpcfstqm7hozdplqyy:3iblclsl5vvuguthfgyu6r5r6fqz2eakolo5zf5dd4so7uwyqsua",
     "ro_uri": "URI:DIR2-RO:gnc3ftwpfi2s63fmupirayl7b4:3iblclsl5vvuguthfgyu6r5r6fqz2eakolo5zf5dd4so7uwyqsua",
     "rw_uri": "URI:DIR2:qtotg7dsasgg367iigdmloryjy:3iblclsl5vvuguthfgyu6r5r6fqz2eakolo5zf5dd4so7uwyqsua",
...

At some point he got an AssertionError, attached in HTML format.

[zooko]

From the stack trace it looks like USSJoin was attempting to delete one of the child links when it goes this assertion failure.

[davidsarah]

Making such a directory isn't a problem in itself; this definitely looks like a bug in the webapi handling of DELETE.

[davidsarah]

The assertion that failed is assert self.parentnode and self.name in DirectoryNodeHandler's render_DELETE method​, i.e. either self.parentnode or self.name is falsy. Those fields are only set in the constructor, which is only called from make_handler_for​, so we're looking for a call to make_handler_for with a missing or falsy parentnode or name argument. But there are quite a few calls to that, and the necessary context isn't on the reported stack trace.

I can see how you might get this error by trying to DELETE .../uri/URI:..., I think -- are we sure that USSJoin didn't attempt to do that?

The testgrid is down atm; I'll try some tests of this when it comes back up.