Loss of system date information can cause itsdangerous crash.

[jifanchn]

Flask and itsdangerous crash in an embedded system.

Traceback (most recent call last):
  File "/opt/local/lib/python3.5/site-packages/Flask-0.12.1-py3.5.egg/flask/app.py", line 1982, in wsgi_app
	response = self.full_dispatch_request()
  File "/opt/local/lib/python3.5/site-packages/Flask-0.12.1-py3.5.egg/flask/app.py", line 1615, in full_dispatch_request
	return self.finalize_request(rv)
  File "/opt/local/lib/python3.5/site-packages/Flask-0.12.1-py3.5.egg/flask/app.py", line 1632, in finalize_request
	response = self.process_response(response)
  File "/opt/local/lib/python3.5/site-packages/Flask-0.12.1-py3.5.egg/flask/app.py", line 1858, in process_response
	self.save_session(ctx.session, response)
  File "/opt/local/lib/python3.5/site-packages/Flask-0.12.1-py3.5.egg/flask/app.py", line 924, in save_session
	return self.session_interface.save_session(self, session, response)
  File "/opt/local/lib/python3.5/site-packages/Flask-0.12.1-py3.5.egg/flask/sessions.py", line 363, in save_session
	val = self.get_signing_serializer(app).dumps(dict(session))
  File "/opt/local/lib/python3.5/site-packages/itsdangerous-0.24-py3.5.egg/itsdangerous.py", line 566, in dumps
	rv = self.make_signer(salt).sign(payload)
  File "/opt/local/lib/python3.5/site-packages/itsdangerous-0.24-py3.5.egg/itsdangerous.py", line 409, in sign
	timestamp = base64_encode(int_to_bytes(self.get_timestamp()))
  File "/opt/local/lib/python3.5/site-packages/itsdangerous-0.24-py3.5.egg/itsdangerous.py", line 220, in int_to_bytes
	assert num >= 0
AssertionError

I think this is because date is lost in this system

date
zynq> date
Fri Aug 14 19:25:11 UTC 2009

which causes

def get_timestamp(self):
    """Returns the current timestamp.  This implementation returns the
    seconds since 1/1/2011.  The function must return an integer.
    """
    return int(time.time() - EPOCH)

returns some wrong information (time < 0) and

def int_to_bytes(num):
    assert num >= 0
    rv = []
    while num:
        rv.append(int_to_byte(num & 0xff))
        num >>= 8
    return b''.join(reversed(rv))

assert num >= 0 (which is < 0) failed.

After doing,

zynq> date -s "2018-08-21 15:15:00"
Tue Aug 21 15:15:00 UTC 2018

everything works.

[untitaker]

We can provide a nicer error message but it'sdangerous should still throw an exception

[jifanchn]

thanks, it's much better.

[davidism]

Fixed in #46, which removes the epoch adjustment.