From 7c6bd4202da1d9b3b210c1527ded07579fba0dc6 Mon Sep 17 00:00:00 2001
From: "Peter F. Patel-Schneider" <pfpschneider@gmail.com>
Date: Tue, 21 Jan 2020 09:22:12 -0500
Subject: [PATCH] receiver: use dictionary for expected message length
 checking; ignore messages with unknown report ids

---
 lib/logitech_receiver/base.py | 45 +++++++++++++++++++----------------
 1 file changed, 25 insertions(+), 20 deletions(-)

diff --git a/lib/logitech_receiver/base.py b/lib/logitech_receiver/base.py
index 7d1162e8..29cfefca 100644
--- a/lib/logitech_receiver/base.py
+++ b/lib/logitech_receiver/base.py
@@ -44,6 +44,15 @@ _LONG_MESSAGE_SIZE = 20
 _MEDIUM_MESSAGE_SIZE = 15
 _MAX_READ_SIZE = 32
 
+# mapping from report_id to message length
+report_lengths = {
+	0x10: _SHORT_MESSAGE_SIZE,
+	0x11: _LONG_MESSAGE_SIZE,
+	0x20: _MEDIUM_MESSAGE_SIZE,
+	0x21: _MAX_READ_SIZE
+}
+
+
 """Default timeout on read (in seconds)."""
 DEFAULT_TIMEOUT = 4
 # the receiver itself should reply very fast, within 500ms
@@ -189,15 +198,16 @@ def read(handle, timeout=DEFAULT_TIMEOUT):
 		return reply[1:]
 
 
-# sanity checks on  message and report incorrect sizes when debugging
-def debug_message(data) :
+# sanity checks on  message report id and size
+def check_message(data) :
 	assert isinstance(data, bytes), (repr(data), type(data))
 	report_id = ord(data[:1])
-	assert ((report_id & 0xF0 == 0) or
-			(report_id == 0x10 and len(data) == _SHORT_MESSAGE_SIZE) or
-			(report_id == 0x11 and len(data) == _LONG_MESSAGE_SIZE) or
-			(report_id == 0x20 and len(data) == _MEDIUM_MESSAGE_SIZE)), \
-			"unexpected message size: report_id %02X message %s" % (report_id, _strhex(data))
+	if report_id in report_lengths:  # is this an HID++ or DJ message?
+		if report_lengths.get(report_id) == len(data):
+			return True
+		else:
+			_log.warn("unexpected message size: report_id %02X message %s" % (report_id, _strhex(data)))
+	return False
 
 
 def _read(handle, timeout):
@@ -218,13 +228,8 @@ def _read(handle, timeout):
 		close(handle)
 		raise NoReceiver(reason=reason)
 
-	if data:
-		debug_message(data)
+	if data and check_message(data): # ignore messages that fail check
 		report_id = ord(data[:1])
-		if report_id & 0xF0 == 0x00:
-			if _log.isEnabledFor(_DEBUG):
-				_log.debug("(%s) => r[%02X %s] ignoring unknown report", handle, report_id, _strhex(data[1:]))
-			return
 		devnumber = ord(data[1:2])
 
 		if _log.isEnabledFor(_DEBUG):
@@ -252,12 +257,12 @@ def _skip_incoming(handle, ihandle, notifications_hook):
 			raise NoReceiver(reason=reason)
 
 		if data:
-			debug_message(data)
-			report_id = ord(data[:1])
-			if notifications_hook and report_id & 0xF0:
-				n = make_notification(ord(data[1:2]), data[2:])
-				if n:
-					notifications_hook(n)
+			if check_message(data): # only process messages that pass check
+				report_id = ord(data[:1])
+				if notifications_hook:
+					n = make_notification(ord(data[1:2]), data[2:])
+					if n:
+						notifications_hook(n)
 		else:
 			# nothing in the input buffer, we're done
 			return
@@ -274,7 +279,7 @@ def make_notification(devnumber, data):
 
 	# regular keyboard key press reports and mouse movement reports are not notifications
 	# it would be better to check for report_id 0x20 but that information is not sent here
-	if ( len(data) == _MEDIUM_MESSAGE_SIZE-2  and  ( sub_id==0x02 or sub_id==0x01 ) ) :
+	if len(data) == _MEDIUM_MESSAGE_SIZE-2 and (sub_id==0x02 or sub_id==0x01):
 		return
 
 	address = ord(data[1:2])