Handle Repetier resend repetitions

Repetier might resend the same resend request to make sure it arrives.
This commit makes OctoPrint not react to such a repeated request and
instead ignore up to a configurable amount of repeated requests for
the same (current) line.

src/octoprint/settings.py

@@ -86,7 +86,9 @@ default_settings = {
 		"additionalBaudrates": [],
 		"longRunningCommands": ["G4", "G28", "G29", "G30", "G32", "M400", "M226"],
 		"checksumRequiringCommands": ["M110"],
-		"helloCommand": "M110 N0"
+		"helloCommand": "M110 N0",
+		"ignoreIdenticalResends": False,
+		"identicalResendsCountdown": 7
 	},
 	"server": {
 		"host": "0.0.0.0",

src/octoprint/util/comm.py

@@ -249,6 +249,8 @@ class MachineCom(object):
 		self._lastResendNumber = None
 		self._currentResendCount = 0
 		self._resendSwallowNextOk = False
+		self._resendSwallowRepetitions = settings().getBoolean(["serial", "ignoreIdenticalResends"])
+		self._resendSwallowRepetitionsCounter = 0
 		self._checksum_requiring_commands = settings().get(["serial", "checksumRequiringCommands"])
 
 		self._clear_to_send = CountedEvent(max=10, name="comm.clear_to_send")
@@ -1484,9 +1486,18 @@ class MachineCom(object):
 				self._currentResendCount += 1
 				return
 
+			# If we ignore resend repetitions (Repetier firmware...), check if we
+			# need to do this now. If the same line number has been requested we
+			# already saw and resent, we'll ignore it up to <counter> times.
+			if self._resendSwallowRepetitions and lineToResend == self._lastResendNumber and self._resendSwallowRepetitionsCounter > 0:
+				self._logger.debug("Ignoring resend request for line %d, that is probably a repetition sent by the firmware to ensure it arrives, not a real request" % lineToResend)
+				self._resendSwallowRepetitionsCounter -= 1
+				return
+
 			self._resendDelta = resendDelta
 			self._lastResendNumber = lineToResend
 			self._currentResendCount = 0
+			self._resendSwallowRepetitionsCounter = settings().getInt(["serial", "identicalResendsCountdown"])
 
 			if self._resendDelta > len(self._lastLines) or len(self._lastLines) == 0 or self._resendDelta < 0:
 				self._errorValue = "Printer requested line %d but no sufficient history is available, can't resend" % lineToResend