Fix crash on startup thanks to invalid default profile & auto connect

See OctoPrint#1942

This does NOT fix the root cause of `_default.profile` becoming an
empty file (apparently during migration from config.yaml?), however
since this particular situation was impossible to reproduce so far this
workaround for the consequences will have to suffice for now since we
want a hotfix as fast as possible for 1.3.3.

src/octoprint/printer/profile.py

@@ -215,33 +215,55 @@ def _migrate_old_default_profile(self):
 		if self.exists("_default"):
 			return
 
+		if not isinstance(default_overrides, dict):
+			self._logger.warn("Existing default profile from settings is not a valid profile, refusing to migrate: {!r}".format(default_overrides))
+			return
+
 		default_overrides["id"] = "_default"
 		self.save(default_overrides)
 
 		settings().set(["printerProfiles", "defaultProfile"], None)
 		settings().save()
 
+		self._logger.info("Migrated default printer profile from settings to _default.profile: {!r}".format(default_overrides))
+
 	def _verify_default_available(self):
 		default_id = settings().get(["printerProfile", "default"])
 		if default_id is None:
 			default_id = "_default"
 
 		if not self.exists(default_id):
 			if not self.exists("_default"):
-				self._logger.error("Selected default profile {} and _default do not exist, creating _default again and setting it as default".format(default_id))
+				if default_id == "_default":
+					self._logger.error("Profile _default does not exist, creating _default again and setting it as default")
+				else:
+					self._logger.error("Selected default profile {} and _default do not exist, creating _default again and setting it as default".format(default_id))
 				self.save(self.__class__.default, allow_overwrite=True, make_default=True)
 			else:
 				self._logger.error("Selected default profile {} does not exists, resetting to _default".format(default_id))
 				settings().set(["printerProfiles", "default"], "_default")
 				settings().save()
+			default_id = "_default"
+
+		profile = self.get(default_id)
+		if profile is None:
+			self._logger.error("Selected default profile {} is invalid, resetting to default values".format(default_id))
+			profile = copy.deepcopy(self.__class__.default)
+			profile["id"] = default_id
+			self.save(self.__class__.default, allow_overwrite=True, make_default=True)
 
 	def select(self, identifier):
 		if identifier is None or not self.exists(identifier):
 			self._current = self.get_default()
 			return False
 		else:
 			self._current = self.get(identifier)
-			return True
+			if self._current is None:
+				self._logger.error("Profile {} is invalid, cannot select, falling back to default".format(identifier))
+				self._current = self.get_default()
+				return False
+			else:
+				return True
 
 	def deselect(self):
 		self._current = None
@@ -310,6 +332,8 @@ def get_default(self):
 			profile = self.get(default)
 			if profile is not None:
 				return profile
+			else:
+				self._logger.warn("Default profile {} is invalid, falling back to built-in defaults".format(default))
 
 		return copy.deepcopy(self.__class__.default)
 
@@ -344,6 +368,7 @@ def _load_all(self):
 			try:
 				profile = self._load_from_path(path)
 			except InvalidProfileError:
+				self._logger.warn("Profile {} is invalid, skipping".format(identifier))
 				continue
 
 			if profile is None:
@@ -373,6 +398,9 @@ def _load_from_path(self, path):
 		with open(path) as f:
 			profile = yaml.safe_load(f)
 
+		if profile is None or not isinstance(profile, dict):
+			raise InvalidProfileError("Profile is None or not a dictionary")
+
 		if self._migrate_profile(profile):
 			try:
 				self._save_to_path(path, profile, allow_overwrite=True)

src/octoprint/server/__init__.py

@@ -475,11 +475,14 @@ def joined_dict(*dicts):
 
 		# auto connect
 		if self._settings.getBoolean(["serial", "autoconnect"]):
-			(port, baudrate) = self._settings.get(["serial", "port"]), self._settings.getInt(["serial", "baudrate"])
-			printer_profile = printerProfileManager.get_default()
-			connectionOptions = printer.__class__.get_connection_options()
-			if port in connectionOptions["ports"]:
-				printer.connect(port=port, baudrate=baudrate, profile=printer_profile["id"] if "id" in printer_profile else "_default")
+			try:
+				(port, baudrate) = self._settings.get(["serial", "port"]), self._settings.getInt(["serial", "baudrate"])
+				printer_profile = printerProfileManager.get_default()
+				connectionOptions = printer.__class__.get_connection_options()
+				if port in connectionOptions["ports"]:
+						printer.connect(port=port, baudrate=baudrate, profile=printer_profile["id"] if "id" in printer_profile else "_default")
+			except:
+				self._logger.exception("Something went wrong while attempting to automatically connect to the printer")
 
 		# start up watchdogs
 		if self._settings.getBoolean(["feature", "pollWatched"]):