issue about pexpect logfile_read - python-2.x

Question

use pexpect SSH connections to run cmds on remote server, the command can be executed, but the results displayed on the terminal are not as expected, code like this（At first there was no time.sleep, it was added for debugging）
import logging
import time
from pexpectUtility import Session
logger = logging.getLogger(__name__)
def test_create_and_show():
cliPrompt = 'dev-r0'
hostPrompt = 'admin#dev-r0'
aa = Session()
aa.connect("admin","password", "10.10.0.10")
time.sleep(2)
aa.child.sendline("sonic-cli")
aa.child.expect(cliPrompt, 3)
tTime = 0
time.sleep(tTime)
aa.child.sendline("configure terminal")
aa.child.expect(cliPrompt, 3)
time.sleep(tTime)
aa.child.sendline("end")
aa.child.expect(cliPrompt, 3)
time.sleep(tTime)
aa.child.sendline("exit")
aa.child.expect(hostPrompt, 3)
aa.disconnect()
the pexpectUtility.py
import sys
import logging as log
if sys.platform == 'win32':
import WExpect as pexpect
spawn_class = pexpect.spawn_windows
else:
import pexpect
spawn_class = pexpect.spawn
class MutliIO:
def __init__(self, *fds):
self.fds = fds
def write(self, data):
for fd in self.fds:
fd.write(data)
def flush(self):
for fd in self.fds:
fd.flush()
class Session(spawn_class):
def __init__(self):
self.child = None
def connect(self, username, password, serverIp, protocol='ssh'):
self.protocol = protocol
self.username = username
self.password = password
self.serverIp = serverIp
if protocol == 'ssh':
cmd = "ssh -x -o StrictHostKeyChecking=no -l %s " % self.username
else:
cmd = "telnet "
cmd = cmd + serverIp
log.info('Connecting to Dut: %s\n' %(cmd))
expect_list = ['ogin: $', '[P|p]assword:', '\[confirm\] $',
'\[confirm yes/no\]:', '\[yes/no\]:', '\(yes/no\)\?',
'\[y/n\]:', '--More--', 'ONIE:/ #',
pexpect.TIMEOUT, pexpect.EOF]
self.child = spawn_class(cmd)
logfile = open('pexpect.log', 'w')
self.child.logfile_read = MutliIO(sys.stdout)
# self.child.logfile_read = MutliIO(sys.stdout, logfile)
# self.child.logfile_read = MutliIO(logfile)
try:
re = self.child.expect(expect_list, 10)
log.debug("expect pwd: {}".format(re))
except Exception as err:
log.error('%s' %err)
raise
# login
try:
self.child.sendline(self.password)
except Exception as err:
raise RuntimeError("login failed!", err)
def disconnect(self):
self.child.sendline("exit")
self.child.expect(pexpect.EOF)
self.child.close()
if self.child.logfile_read != None:
self.child.logfile_read = None
Executed commands are repeated displayed, just like batch input. log is as follows:
admin#dev-r0:~$ sonic-cli
configure terminal
configure terminal
end
exit
dev-r0# configure terminal
dev-r0(config)# end
dev-r0# exit
admin#dev-r0:~$ exit
logout
Connection to 10.10.0.10 closed.
When I set tTime to 5 (each command interval is 5 seconds) the log is as expected，I think this is not a good solution，I also want to know the root cause
admin#dev-r0:~$ sonic-cli
dev-r0# configure terminal
dev-r0(config)# end
dev-r0# exit
admin#dev-r0:~$ exit
logout
Connection to 10.10.0.10 closed.
When I directly use expect to implement the above operation, there is no need to wait for 5 seconds between commands, and the log displayed by the terminal is normal.
why pexpect has this issue? how to solve this？ Thanks in advance

Answer 1

This is not the whole answer, but a first point to fix. After the
sendline("sonic-cli") the first expect() is going to return
immediately, as it will match the prompt admin#dev-r0:~$ which is already
there waiting, before the sonic-cli command arrives. This means the next
command configure terminal is sent immediately after sonic-cli.
You should enhance the connect() routine to expect the admin#dev-r0:~$
prompt before returning, or use this expect instead of the sleep(2) which
should not be necessary.

Answer 2

Referring to the sample code of pexpect on the Internet, I found that the root cause is a code problem: missing a expect() after sendline()
The changes are as follows:
# login
try:
self.child.sendline(self.password)
HOST_PROMPT = '\$' # remote server prompt
re = self.child.expect(HOST_PROMPT)
except Exception as err:
raise RuntimeError("login failed!", err)