JSONDecodeError when closing notebook

[jmarcedwards]

Description

What steps will reproduce the problem?

I am new to Spyder & the Jupyter plugin. I was just trying to close a notebook, and this error window popped up.

Traceback

  File "/Users/marcedw/opt/anaconda3/lib/python3.7/site-packages/spyder_notebook/widgets/notebooktabwidget.py", line 214, in close_client
    client.shutdown_kernel()
  File "/Users/marcedw/opt/anaconda3/lib/python3.7/site-packages/spyder_notebook/widgets/client.py", line 312, in shutdown_kernel
    kernel_id = self.get_kernel_id()
  File "/Users/marcedw/opt/anaconda3/lib/python3.7/site-packages/spyder_notebook/widgets/client.py", line 291, in get_kernel_id
    sessions = json.loads(sessions_response.content.decode())
  File "/Users/marcedw/opt/anaconda3/lib/python3.7/json/__init__.py", line 348, in loads
    return _default_decoder.decode(s)
  File "/Users/marcedw/opt/anaconda3/lib/python3.7/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/Users/marcedw/opt/anaconda3/lib/python3.7/json/decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

Versions

• Spyder version: 4.1.4
• Python version: 3.7.6
• Qt version: 5.12.9
• PyQt5 version: 5.12.3
• Operating System: Darwin 19.6.0

Dependencies

# Mandatory:
applaunchservices >=0.1.7      :  0.2.1 (OK)
atomicwrites >=1.2.0           :  1.4.0 (OK)
chardet >=2.0.0                :  3.0.4 (OK)
cloudpickle >=0.5.0            :  1.5.0 (OK)
diff_match_patch >=20181111    :  20200713 (OK)
intervaltree                   :  None (OK)
IPython >=4.0                  :  7.17.0 (OK)
jedi =0.17.1                   :  None (OK)
nbconvert >=4.0                :  5.6.1 (OK)
numpydoc >=0.6.0               :  1.1.0 (OK)
parso =0.7.0                   :  0.7.0 (OK)
pexpect >=4.4.0                :  4.8.0 (OK)
pickleshare >=0.4              :  0.7.5 (OK)
psutil >=5.3                   :  5.7.2 (OK)
pygments >=2.0                 :  2.6.1 (OK)
pylint >=1.0                   :  2.6.0 (OK)
pyls >=0.34.0;<1.0.0           :  0.34.1 (OK)
qdarkstyle >=2.8               :  2.8.1 (OK)
qtawesome >=0.5.7              :  0.7.2 (OK)
qtconsole >=4.6.0              :  4.7.6 (OK)
qtpy >=1.5.0                   :  1.9.0 (OK)
rtree >=0.8.3                  :  0.9.4 (OK)
sphinx >=0.6.6                 :  3.2.1 (OK)
spyder_kernels >=1.9.2;<1.10.0 :  1.9.3 (OK)
watchdog                       :  None (OK)
zmq >=17                       :  19.0.1 (OK)

# Optional:
cython >=0.21                  :  0.29.21 (OK)
matplotlib >=2.0.0             :  3.1.3 (OK)
numpy >=1.7                    :  1.18.1 (OK)
pandas >=0.13.1                :  1.1.1 (OK)
scipy >=0.17.0                 :  1.5.2 (OK)
sympy >=0.7.3                  :  1.6.2 (OK)

# Spyder plugins:
spyder_notebook                :  0.3.0 (OK)

[juanis2112]

Hi @jmarcedwards thanks for reporting this. @jitseniesen can you please take a look at this?

[major-s]

I experience the same JSON error running Spyder on Window 10, only the last line differs:
raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 2 column 1 (char 1)

[jitseniesen]

I think Spyder can ignore this error, but I want to consider it a bit more because I don't understand exactly what is happening.

[jitseniesen]

It looks like there is a bug in the code introduced in PR #232, in that the plugin tries to decode the server response before checking the response status. It's plausible that if the response status indicates an error, the response itself is incorrect or incomplete or empty, and that would explain the error message. I will fix this and hopefully that will resolve the issue.