Make config set options inside the lib module

Instead of depending on config.py defining several magic variables,
move the default configuration in the config instance at the root of
the lib module, and make config.py override them as needed.

config.py

 from lib.checks import *
+from lib import config
 
 
 # This is the base granularity (in seconds) for polling
 # Each check may then individually be configured to run every N * tick
-base_tick = 60
+config.base_tick = 60
 
 # Email addresses to send to when an alert is triggered
-emails = ['john@localhost']
+config.emails.to.append('john@localhost')
 
 # Subject template for state change email notifications
 # available substitutions:
 #   - state ("Problem" or "OK")
 #   - check (check's name, like "CheckDNSRec6")
 #   - dest  (the target of the check ie. an IP or a Host's 'name' parameter)
-subject_tpl = "[ARN] {state}: {check} on {dest}"
+config.emails.subject_tpl = "[ARN] {state}: {check} on {dest}"
 
 
 mail     = Host(ipv4='127.0.0.1', ipv6='::1', name='LXC mail')
@@ -21,11 +22,10 @@ web      = Host(ipv4='127.0.0.0', ipv6='::42', name='Bad IPs')
 alsace   = Host(ipv4='127.0.0.1', ipv6='::1')
 recursif = Host(ipv4='89.234.141.66', ipv6='2a00:5881:8100:1000::31', name='DNS récursif')
 
-checks = Checks()
-checks.add(CheckDNSZone, ["arn-fai.net", "netlib.re"], ip_version=4)
-checks.add(CheckPing4, [mail, web], retry=2)
-checks.add(CheckPing6, [mail, web], retry=2)
-checks.add(CheckDNSRec4, [recursif])
-checks.add(CheckDNSRec6, [recursif])
-# checks.add(CheckSMTP4, [mail, alsace])
-# checks.add(CheckSMTP6, [mail, alsace])
+config.checks.add(CheckDNSZone, ["arn-fai.net", "netlib.re"], ip_version=4)
+config.checks.add(CheckPing4, [mail, web], retry=2)
+config.checks.add(CheckPing6, [mail, web], retry=2)
+config.checks.add(CheckDNSRec4, [recursif])
+config.checks.add(CheckDNSRec6, [recursif])
+# config.checks.add(CheckSMTP4, [mail, alsace])
+# config.checks.add(CheckSMTP6, [mail, alsace])

lib/__init__.py

+from .attrtree import AttrTree
+from .checks import Checks
+
+
+config = AttrTree()
+
+# the list of checks
+config.install_attr('checks', Checks())
+
+# This is the base granularity (in seconds) for polling
+# Each check may then individually be configured to run every N * tick
+config.install_attr('base_tick', 60)
+
+# Email addresses to send to when an alert is triggered
+config.install_attr('emails.to', [])
+
+# Subject template for state change email notifications
+# available substitutions:
+#   - state ("Problem" or "OK")
+#   - check (check's name, like "CheckDNSRec6")
+#   - dest  (the target of the check ie. an IP or a Host's 'name' parameter)
+config.install_attr('emails.subject_tpl', '[DOMAIN] {state}: {check} on {dest}')

lib/attrtree.py

+class AttrTree(object):
+    """ A class holding attributes/items, but not allowing to create
+    new ones implicitely.  Use .install_attr() instead. """
+
+    def __init__(self):
+        object.__setattr__(self, '_attrs', {})
+
+    def install_attr(self, key, default):
+        if key in self._attrs:
+            raise KeyError('Key "%s" already exists' % key)
+        stems = key.split('.', 2)
+        if len(stems) < 2:
+            self._attrs[key] = default
+        elif stems[0] in self._attrs:
+            self._attrs[stems[0]].install_attr(stems[1], default)
+        else:
+            sub = AttrTree()
+            sub.install_attr(stems[1], default)
+            self._attrs[stems[0]] = sub
+
+    def __getitem__(self, key):
+        return self._attrs[key]
+
+    def __setitem__(self, key, value):
+        if not key in self._attrs:
+            raise KeyError('Key "%s" does not exist' % key)
+        elif isinstance(self._attrs[key], AttrTree):
+            raise KeyError('Key "%s" is not settable' % key)
+        self._attrs[key] = value
+
+    def __getattr__(self, key):
+        return self[key]
+
+    def __setattr__(self, key, value):
+        self[key] = value

lib/mails.py

@@ -10,11 +10,11 @@ import email.charset
 email.charset.add_charset('utf-8', email.charset.QP, email.charset.QP, 'utf-8')
 
 def send_email_for_check(check):
-    from config import emails, subject_tpl
+    from . import config
     addr_from  = "Picomon <picomon@%s>" % socket.getfqdn()
 
     # ensure we do not traceback with unknown substitutions
-    subject = subject_tpl.format_map(
+    subject = config.emails.subject_tpl.format_map(
               defaultdict(lambda: "<no substitution>",
                           state='OK' if check.ok else 'Problem',
                           check=check.__class__.__name__,
@@ -30,12 +30,12 @@ def send_email_for_check(check):
     msg = MIMEText(msg_text.encode('utf-8').decode('latin1'), 'plain', 'utf-8')
     msg['Subject'] = subject
     msg['From']    = addr_from
-    msg['To']      = ", ".join(emails)
+    msg['To']      = ", ".join(config.emails.to)
 
     try:
         server = smtplib.SMTP('localhost')
         # server.set_debuglevel(1)
-        server.sendmail(addr_from, emails, msg.as_string())
+        server.sendmail(addr_from, config.emails.to, msg.as_string())
         server.quit()
     except Exception as e:
         print("Couldn't send email: %s" % str(e), file=stderr)

picomon.py

 import concurrent.futures
-from config import *
 import signal
 import argparse
 from time import sleep
+import config as user_config
+from lib import config
 
 
 def usr1_handler(signum, frame):
     print ("""Signal SIGUSR1 caught, printing state of checks.
 
     Checks in error:""")
-    for check in checks:
+    for check in config.checks:
         if not check.ok:
             print ('-+' * 40)
             print ("Check %s is in error state:\n\t%s" % (check,
@@ -17,7 +18,7 @@ def usr1_handler(signum, frame):
     print ('-+' * 40, """
 
     Other checks (usually OK but may be in retry mode):""")
-    for check in checks:
+    for check in config.checks:
         if check.ok:
             print ("Check %s is %s" % (check,
                    "OK" if check.retry_count == 0 else "retrying"))
@@ -41,7 +42,7 @@ if __name__ == '__main__':
 
         if args.one:
             futures = []
-            for check in checks:
+            for check in config.checks:
                 futures.append(executor.submit(runner, check))
 
             for future in concurrent.futures.as_completed(futures):
@@ -54,6 +55,6 @@ if __name__ == '__main__':
         else:
             # This will drift slowly as it takes (base_tick + espilon) seconds
             while True:
-                for check in checks:
+                for check in config.checks:
                     executor.submit(check.run())
-                sleep(base_tick)
+                sleep(config.base_tick)