Expect and waitfor error with ValueError

[sjstewart]

I'm trying to connect to a telnet server that has a Linux system connected to it, issue a newline character, and use either waitfor or expect (something using regular expressions) to match and get the output. I am able to get this to work consistently using read_until:

tn.read_until(b'#', 5)
''
tn.read_until(b'#', 5)
'# hithere\r\nroot@localhost:~# '

However, expect gives me this "negative seek position" error:

tn.expect(['#'], 1)
Traceback (most recent call last):
File "", line 1, in
File "/u/stewarts/.local/lib/python3.7/site-packages/Exscript/protocols/telnetlib.py", line 752, in expect
return self._waitfor(relist, timeout, True, cleanup=cleanup)
File "/u/stewarts/.local/lib/python3.7/site-packages/Exscript/protocols/telnetlib.py", line 691, in _waitfor
self.cookedq.seek(qlen - search_window_size)
ValueError: Negative seek position -150

After seeing telnetlib is deprecated I was looking for a drop in replacement and this seemed the closest.

Edit: I think this is using exscript 2.6.28 and it is on Debian 10 with python 3.7.3

[knipknap]

Can you try if the problem also exists in Version a48030c?

[sjstewart]

It looks like the version I'm using does have that change to collections.py.

[knipknap]

Every version since does ;-), but the question was whether you have the same problem with the version from this particular commit. Because there were some changes after that that may have caused the problem.

[sjstewart]

Ahhh, gotcha. I checked out the code as of that commit and gave it another try, it looks like it happens the same:

tn.write(b'# testing\n')
tn.expect(['#'],1)
Traceback (most recent call last):
File "", line 1, in
File "/u/stewarts/.local/lib/python3.7/site-packages/Exscript/protocols/telnetlib.py", line 705, in expect
return self._waitfor(relist, timeout, True, cleanup=cleanup)
File "/u/stewarts/.local/lib/python3.7/site-packages/Exscript/protocols/telnetlib.py", line 644, in _waitfor
self.cookedq.seek(qlen - search_window_size)
ValueError: Negative seek position -150
tn.waitfor(['#'],1)
Traceback (most recent call last):
File "", line 1, in
File "/u/stewarts/.local/lib/python3.7/site-packages/Exscript/protocols/telnetlib.py", line 698, in waitfor
return self._waitfor(relist, timeout, False, cleanup)
File "/u/stewarts/.local/lib/python3.7/site-packages/Exscript/protocols/telnetlib.py", line 644, in _waitfor
self.cookedq.seek(qlen - search_window_size)
ValueError: Negative seek position -150