Allow dispatching of messages with no target address information

Background: Some service plugins, like `apprise-json` or
`apprise-discord`, don't need/accept any additional information about
single or multiple recipients at all.

So, this patch makes the machinery accept items without any attached
or resolved recipient information, i.e. without `target` and `addrs`
attributes.

Author: amotl

CHANGES.rst

@@ -6,6 +6,11 @@ mqttwarn changelog
 in progress
 ===========
 
+- Allow dispatching of messages with no target address information.
+  This helps for service plugins like Apprise to make the configuration
+  snippet more compact. Now, service configurations can omit the ``targets``
+  option altogether.
+
 
 2021-10-17 0.27.0
 =================

HANDBOOK.md

@@ -543,10 +543,6 @@ targets  = {
 [config:apprise-json]
 module   = 'apprise'
 baseuri  = 'json://localhost:1234/mqtthook'
-; Surrogate for satisfying machinery. 
-targets  = {
-    'n/a' : [''],
-    }
 
 [apprise-test]
 topic    = apprise/#

mqttwarn/context.py

@@ -102,17 +102,12 @@ def get_service_config(self, service):
         return dict(config)
 
     def get_service_targets(self, service):
+        # Be more graceful with jobs w/o any target address information (2021-10-18 [amo]).
         try:
-            targets = self.config.getdict('config:' + service, 'targets')
-            if type(targets) != dict:
-                logger.error("No targets for service `%s'" % service)
+            targets = self.config.getdict('config:' + service, 'targets') or [None]
+            return targets
         except:
-            logger.error("No targets for service `%s'" % service)
-
-        if targets is None:
-            return {}
-
-        return dict(targets)
+            logger.exception("Unable to access targets for service `%s'" % service)
 
 
 @attr.s

mqttwarn/core.py

@@ -454,12 +454,18 @@ def processor(worker_id=None):
             q_in.task_done()
             continue
 
+        # Be more graceful with jobs w/o any target address information (2021-10-18 [amo]).
+        if target is None:
+            addrs = []
+        else:
+            addrs = service_targets[target]
+
         item = {
             'service'       : service,
             'section'       : section,
             'target'        : target,
             'config'        : service_config,
-            'addrs'         : service_targets[target],
+            'addrs'         : addrs,
             'topic'         : topic,
             'payload'       : job.payload,
             'data'          : None,

mqttwarn/model.py

@@ -1,6 +1,6 @@
 # -*- coding: utf-8 -*-
 # (c) 2021 The mqttwarn developers
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from typing import Dict, List, Union
 
 
@@ -13,7 +13,7 @@ class ProcessorItem:
     service: str = None
     target: str = None
     config: Dict = None
-    addrs: List[str] = None
+    addrs: List[str] = field(default_factory=list)
     priority: int = None
     topic: str = None
     title: str = None