diff --git a/src/octoprint/util/__init__.py b/src/octoprint/util/__init__.py
index 3f5af26b..0c5e66d2 100644
--- a/src/octoprint/util/__init__.py
+++ b/src/octoprint/util/__init__.py
@@ -8,6 +8,7 @@ import sys
 import time
 import re
 import tempfile
+from flask import make_response
 
 from octoprint.settings import settings
 
@@ -188,3 +189,38 @@ def silentRemove(file):
 		os.remove(file)
 	except OSError:
 		pass
+
+
+def sanitizeAscii(line):
+	return unicode(line, 'ascii', 'replace').encode('ascii', 'replace').rstrip()
+
+
+def filterNonAscii(line):
+	"""
+	Returns True if the line contains non-ascii characters, false otherwise
+
+	@param line the line to test
+	"""
+
+	try:
+		unicode(line, 'ascii').encode('ascii')
+		return False
+	except ValueError:
+		return True
+
+
+def getJsonCommandFromRequest(request, valid_commands):
+	if not "application/json" in request.headers["Content-Type"]:
+		return None, None, make_response("Expected content-type JSON", 400)
+
+	data = request.json
+	if not "command" in data.keys() or not data["command"] in valid_commands.keys():
+		return None, None, make_response("Expected valid command", 400)
+
+	command = data["command"]
+	for parameter in valid_commands[command]:
+		if not parameter in data:
+			return None, None, make_response("Mandatory parameter %s missing for command %s" % (parameter, command), 400)
+
+	return command, data, None
+
diff --git a/src/octoprint/util/comm.py b/src/octoprint/util/comm.py
index 924fef29..57599ed6 100644
--- a/src/octoprint/util/comm.py
+++ b/src/octoprint/util/comm.py
@@ -20,7 +20,7 @@ from octoprint.util.avr_isp import ispBase
 from octoprint.settings import settings
 from octoprint.events import eventManager
 from octoprint.gcodefiles import isGcodeFileName
-from octoprint.util import getExceptionString, getNewTimeout
+from octoprint.util import getExceptionString, getNewTimeout, sanitizeAscii, filterNonAscii
 from octoprint.util.virtual import VirtualPrinter
 
 try:
@@ -513,7 +513,11 @@ class MachineCom(object):
 				##~~ SD file list
 				# if we are currently receiving an sd file list, each line is just a filename, so just read it and abort processing
 				if self._sdFileList and isGcodeFileName(line.strip().lower()) and not 'End file list' in line:
-					self._sdFiles.append(line.strip().lower())
+					filename = line.strip().lower()
+					if filterNonAscii(filename):
+						self._logger.warn("Got a file from printer's SD that has a non-ascii filename (%s), that shouldn't happen according to the protocol" % filename)
+					else:
+						self._sdFiles.append(filename)
 					continue
 
 				##~~ Temperature processing
@@ -826,7 +830,7 @@ class MachineCom(object):
 		if ret == '':
 			#self._log("Recv: TIMEOUT")
 			return ''
-		self._log("Recv: %s" % (unicode(ret, 'ascii', 'replace').encode('ascii', 'replace').rstrip()))
+		self._log("Recv: %s" % sanitizeAscii(ret))
 		return ret
 
 	def _sendNext(self):
@@ -1202,4 +1206,4 @@ class PrintingGcodeFileInformation(PrintingFileInformation):
 
 class StreamingGcodeFileInformation(PrintingGcodeFileInformation):
 	def __init__(self, filename):
-		PrintingGcodeFileInformation.__init__(self, filename, None)
\ No newline at end of file
+		PrintingGcodeFileInformation.__init__(self, filename, None)