"No JSON object could be decoded" backtrace on tahoe mv

[np]

The following command:

tahoe mv tahoe:'do not exists' baz

Yields:

Traceback (most recent call last):
  File "/home/ertai/w/a/tahoe/support/bin/tahoe", line 8, in <module>
    load_entry_point('allmydata-tahoe==1.6.1-r4442', 'console_scripts', 'tahoe')()
  File "/home/ertai/w/a/tahoe/src/allmydata/scripts/runner.py", line 102, in run
    rc = runner(sys.argv[1:])
  File "/home/ertai/w/a/tahoe/src/allmydata/scripts/runner.py", line 89, in runner
    rc = cli.dispatch[command](so)
  File "/home/ertai/w/a/tahoe/src/allmydata/scripts/cli.py", line 500, in mv
    rc = tahoe_mv.mv(options, mode="move")
  File "/home/ertai/w/a/tahoe/src/allmydata/scripts/tahoe_mv.py", line 32, in mv
    nodetype, attrs = simplejson.loads(data)
  File "/home/ertai/w/a/tahoe/support/lib/python2.6/site-packages/simplejson-2.1.1-py2.6-linux-x86_64.egg/simplejson/__init__.py", line 384, in loads
    return _default_decoder.decode(s)
  File "/home/ertai/w/a/tahoe/support/lib/python2.6/site-packages/simplejson-2.1.1-py2.6-linux-x86_64.egg/simplejson/decoder.py", line 402, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/home/ertai/w/a/tahoe/support/lib/python2.6/site-packages/simplejson-2.1.1-py2.6-linux-x86_64.egg/simplejson/decoder.py", line 420, in raw_decode
    raise JSONDecodeError("No JSON object could be decoded", s, idx)
simplejson.decoder.JSONDecodeError: No JSON object could be decoded: line 1 column 0 (char 0)

[davidsarah]

Special case of #1048.

[davidsarah]

With trunk, I get:

$ bin/tahoe mv tahoe:'do not exists' baz
Error: 404 Not Found
No such child: do not exists

Can anyone reproduce the error in the description?

TODO: confirm that this is fixed by:

• looking at what was wrong with the JSON returned by a 1.6.1 gateway, and checking that a more recent gateway returns correct JSON;
• possibly adding a unit test.