I'd been manually tracking the ADSL router stats for a while before I thought: "Why am I doing this copy and paste stuff when I could automate the whole process?".
The router (a Draytek Vigor) supported telnet command line access, so I needed the expect tool. I did try using netcat (as that is in FreeBSD base), but it killed the router telnet process, which took a reboot to resurrect).
The first attempt used expect and a couple of awk scripts tied together with a shell script. It worked, but all this scattered processing felt wrong. I wondered if I could do it all in python.
There is an expect analog for python - pexpect. Using this and standard python capabilities, the four files of expect, shell and awk scripts could be replaced by one python script. The source code is at the end of this article.
The ADSL line runs at 24Mb (I live opposite the exchange). Here's what the error rate looks like over a 10 day period.
Figure 1 - Uncorrected Download CRC errors - cumulative total
Figure 2 - Uncorrected Download CRC errors - # per hour
And here's the source code that produces the log file.
#!/usr/local/bin/python
#
# Extract and log ADSL router stats
#
# python adsl.py [-t n] [-l log_file] [-e email_address]
#
# Command arguments:
#
# -t n Set n as the threshold for the number of crc errors in a time
# period. Error counts above n will be notified via email.
# Default is 60.
# -l log_file Set pathname of log file. Default is
# /home/log/adsl-log.csv
# -e address Set email address to mail for errors in excess of threshold.
# Default is someone@example.com
import pexpect
import sys
import os
import time
import getopt
import re
def get_adsl_stats():
"Return Draytek Vigor adsl stats as a string, using pexpect."
child = pexpect.spawn("telnet gw")
child.expect("Account:")
child.sendline("admininstrator")
child.expect("Password: ")
child.sendline("redacted")
child.expect("> ")
child.sendline("show status")
child.expect("> ")
stats = child.before
child.sendline("exit")
return stats
def extract(field,text_block,now=time.localtime()):
"Return stringvalue for field in text_block (as presented by Draytek Vigor"
" report). Will also return values for field names date and time."
if field.lower() == "date":
return "%4d-%02d-%02d"%(now.tm_year,now.tm_mon,now.tm_mday)
elif field.lower() == "time":
return "%02d:%02d:%02d"%(now.tm_hour,now.tm_min,now.tm_sec)
else:
r = re.search(field+r"(\S*)",text_block)
if r:
return r.group(1)
return "(null)"
def last_line(filename):
"Returns last line of filename (a string)."
last = ""
if os.path.exists(filename):
for line in open(filename,"r").readlines():
last = line
return last
# list of fields to extract from adsl status
fields = ("Date", "Time", "System Uptime:", "Up Time:", "Uncorrected Blocks:",\
"UP Speed:", "Down Speed:", "SNR Margin:", "Loop Att.:", "State:")
# index for crc count field
crc_field = 4
# error report threshold (number of crc errors in reporting period)
threshold = 60
# log file path name
log_file = "/home/log/adsl-log.csv"
# default email address
email = "someone@example.com"
# read command line options (if any)
try:
opts,args = getopt.getopt(sys.argv[1:],'t:l:e:')
for o,v in opts:
if o == '-t':
threshold = int(v)
elif o == "-l":
log_file = v
elif o == "-e":
email = v
except getopt.GetoptError,e:
print >>sys.stderr,"%s: illegal argument: -%s" % (sys.argv[0],e.opt)
sys.exit(1)
# retrieve adsl stats from router and extract required reporting fields
t = get_adsl_stats()
record = list()
for f in fields:
record.append(extract(f,t))
# get previous log entry for crc count comparison
previous_log = last_line(log_file)
# calculate error count in last period
crc_now = int(record[crc_field])
prev_fields = previous_log.split(",")
# handle case when no previous log entry exists
if len(prev_fields) > crc_field and prev_fields[crc_field].isdigit():
crc_prev = int(prev_fields[crc_field])
crc_cnt = crc_now-crc_prev
if crc_cnt < 0: crc_cnt = crc_now # assume line reset
else:
crc_cnt = 0
# add crc count in last period to record data and write to log file
record.append(crc_cnt)
l = open(log_file,"a")
for f in record:
l.write("%s,"%(f,))
l.write("\n")
l.close()
# check if error report needs to be mailed
if crc_cnt > threshold:
subject = "'ADSL Error Rate Alert: %d errors reported.'"%(crc_cnt,)
# use echo to suppress null body message from mail
os.system("echo ''|/usr/bin/mail -s "+subject+" "+email)
