Made metadata saving for gcode files more error resilient (hopefully that is)

src/octoprint/gcodefiles.py

@@ -70,6 +70,7 @@ class GcodeManager:
 		self._metadata = {}
 		self._metadataDirty = False
 		self._metadataFile = os.path.join(self._uploadFolder, "metadata.yaml")
+		self._metadataTempFile = os.path.join(self._uploadFolder, "metadata.yaml.tmp")
 		self._metadataFileAccessMutex = threading.Lock()
 
 		self._metadataAnalyzer = MetadataAnalyzer(getPathCallback=self.getAbsolutePath, loadedCallback=self._onMetadataAnalysisFinished)
@@ -111,7 +112,7 @@ class GcodeManager:
 		if gcode.extrusionAmount:
 			analysisResult["filament"] = "%.2fm" % (gcode.extrusionAmount / 1000)
 			if gcode.calculateVolumeCm3():
-				 analysisResult["filament"] += " / %.2fcm³" % gcode.calculateVolumeCm3()
+				analysisResult["filament"] += " / %.2fcm³" % gcode.calculateVolumeCm3()
 			dirty = True
 
 		if dirty:
@@ -134,9 +135,11 @@ class GcodeManager:
 			return
 
 		with self._metadataFileAccessMutex:
-			with open(self._metadataFile, "wb") as f:
+			with open(self._metadataTempFile, "wb") as f:
 				yaml.safe_dump(self._metadata, f, default_flow_style=False, indent="    ", allow_unicode=True)
 				self._metadataDirty = False
+			util.safeRename(self._metadataTempFile, self._metadataFile)
+
 		self._loadMetadata()
 		self._sendUpdateTrigger("gcodeFiles")
 
@@ -326,7 +329,7 @@ class GcodeManager:
 				if key == "prints":
 					val = self._metadata[filename][key]
 					formattedLast = None
-					if val["last"] is not None:
+					if "last" in val and val["last"] is not None:
 						formattedLast = {
 							"date": util.getFormattedDateTime(datetime.datetime.fromtimestamp(val["last"]["date"])),
 							"success": val["last"]["success"]

src/octoprint/util/__init__.py

@@ -7,6 +7,7 @@ import traceback
 import sys
 import time
 import re
+import tempfile
 
 from octoprint.settings import settings
 
@@ -139,3 +140,51 @@ def findCollisionfreeName(input, extension, existingFilenames):
 			power += 1
 
 	raise ValueError("Can't create a collision free filename")
+
+
+def safeRename(old, new):
+	"""
+	Safely renames a file.
+
+	On Windows this is achieved by first creating a backup file of the new file (if it
+	already exists), thus moving it, then renaming the old into the new file and finally removing the backup. If
+	anything goes wrong during those steps, the backup (if already there) will be renamed to its old name and thus
+	the operation hopefully result in a no-op.
+
+	On other operating systems the atomic os.rename function will be used instead.
+
+	@param old the path to the old file to be renamed
+	@param new the path to the new file to be created/replaced
+	"""
+
+	if sys.platform == "win32":
+		fh, backup = tempfile.mkstemp()
+		os.close(fh)
+
+		try:
+			if os.path.exists(new):
+				silentRemove(backup)
+				os.rename(new, backup)
+			os.rename(old, new)
+			os.remove(backup)
+		except OSError:
+			# if anything went wrong, try to rename the backup file to its original name
+			if os.path.exists(backup):
+				os.remove(new)
+			os.rename(backup, new)
+	else:
+		# on anything else than windows it's ooooh so much easier...
+		os.rename(old, new)
+
+
+def silentRemove(file):
+	"""
+	Silently removes a file. Does not raise an error if the file doesn't exist.
+
+	@param file the path of the file to be removed
+	"""
+
+	try:
+		os.remove(file)
+	except OSError:
+		pass