[core] input: add logging for input events

to debug input event issues (which seem to become more frequent), add
some input event logging.

see #336

bumblebee/input.py

@@ -5,9 +5,12 @@ import json
 import uuid
 import time
 import select
+import logging
 import threading
 import bumblebee.util
 
+log = logging.getLogger(__name__)
+
 LEFT_MOUSE = 1
 MIDDLE_MOUSE = 2
 RIGHT_MOUSE = 3
@@ -24,6 +27,7 @@ def read_input(inp):
     """Read i3bar input and execute callbacks"""
     epoll = select.epoll()
     epoll.register(sys.stdin.fileno(), select.EPOLLIN)
+    log.debug("starting click event processing")
     while inp.running:
         if is_terminated():
             return
@@ -36,14 +40,18 @@ def read_input(inp):
             line = "["
             while line.startswith("["):
                 line = sys.stdin.readline().strip(",").strip()
+                log.debug("new event: {}".format(line))
             inp.has_event = True
             try:
                 event = json.loads(line)
                 if "instance" in event:
                     inp.callback(event)
                     inp.redraw()
-            except ValueError:
-                pass
+                else:
+                    log.debug("field 'instance' missing in input, not processing the event")
+            except ValueError as e:
+                log.debug("failed to parse event: {}".format(e))
+    log.debug("exiting click event processing")
     epoll.unregister(sys.stdin.fileno())
     epoll.close()
     inp.has_event = True