Add check for max number of allowed characters

According to the crontab man pages, the maximum number of characters in
the command field is 998
https://manpages.debian.org/jessie/cron/crontab.5.en.html. This PR adds
a check to catch lines that are longer than 998. It updates the test
file as well. This change was requested in this issue
#22 and I have run into issues
with crontab failing because of lines being too long, so having the
linter catch this issue will be a big help.

chkcrontab_lib.py

@@ -83,6 +83,9 @@
 FILE_RE_WHITELIST = [re.compile(x) for x in
                      (r'\.in$', r'\.cron$', r'\.disabled$', r'^(\S+\.)?cron\.d$')]
 
+# Per https://manpages.debian.org/jessie/cron/crontab.5.en.html:
+# "The maximum permitted length for the command field is 998 characters."
+MAX_COMMAND_LENGTH = 998
 
 class FSM(object):
   """Finite State Machine.
@@ -738,6 +741,9 @@ def ValidateAndLog(self, log):
       log.LineWarn(log.MSG_BARE_PERCENT, 'A bare % is a line break in'
                    ' crontab and is commonly not intended.')
 
+    if len(self.command) > MAX_COMMAND_LENGTH:
+      log.LineError(log.MSG_COMMAND_LENGTH_ERROR, 'Command length is %d which is greater'
+                    ' than %d (max allowed characters)' % (len(self.command), MAX_COMMAND_LENGTH))
 
 class CronLineAt(CronLineTimeAction):
   """For cron lines specified with @ time specs."""
@@ -885,6 +891,7 @@ class LogCounter(object):
 
   _msg_kinds = set(('BARE_PERCENT',
                     'CHKCRONTAB_ERROR',
+                    'COMMAND_LENGTH_ERROR',
                     'FIELD_PARSE_ERROR',
                     'FIELD_VALUE_ERROR',
                     'INVALID_AT',

tests/test_crontab

@@ -69,3 +69,5 @@ OK_SPACE=" "
 @monthly root Good @ Command
 # FAIL 1 for bad time spec.
 @m0nthly root Bad @ Command
+# FAIL 1 for line too long
+0 21 * * wed root /bin/bash/myscript "999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999"