cutter: Add more specific error handling to upload backends

For youtube, know that 4xx's are safe even if finalizing was set.

For local, make all disk errors retryable since it doesn't matter.

cutter/cutter/upload_backends.py

@@ -17,8 +17,8 @@ class UploadError(Exception):
 	They should also indicate if the error is retryable without
 	manual intervention.
 	Examples of retryable errors:
-		Authorization errors (likely a bad config - let another node get it)
 		Short-term rate limits (try again in a few seconds)
+		Upload backends which are fully idempotent
 	Examples of unretryable errors:
 		Bad Request (indicates logic bug, or that the video is unacceptable in some way)
 		Long-term rate limits (trying again quickly is counterproductive, wait for operator)
@@ -144,9 +144,16 @@ class Youtube(UploadBackend):
 			},
 			json=json,
 		)
-		resp.raise_for_status()
+		if not resp.ok:
+			# Don't retry, because failed calls still count against our upload quota.
+			# The risk of repeated failed attempts blowing through our quota is too high.
+			raise UploadError("Youtube create video call failed with {resp.status_code}: {resp.content}".format(resp=resp))
 		upload_url = resp.headers['Location']
 		resp = self.client.request('POST', upload_url, data=data)
+		if 400 <= resp.status_code < 500:
+			# As above, don't retry. But with 4xx's we know the upload didn't go through.
+			# On a 5xx, we can't be sure (the server is in an unspecified state).
+			raise UploadError("Youtube video data upload failed with {status_code}: {resp.content}".format(resp=resp))
 		resp.raise_for_status()
 		id = resp.json()['id']
 		return id, 'https://youtu.be/{}'.format(id)
@@ -210,6 +217,7 @@ class Local(UploadBackend):
 		ext = 'ts' if self.encoding_settings is None else 'mp4'
 		filename = '{}-{}.{}'.format(safe_title, video_id, ext)
 		filepath = os.path.join(self.path, filename)
+		try:
 			if self.write_info:
 				with open(os.path.join(self.path, '{}-{}.json'.format(safe_title, video_id)), 'w') as f:
 					f.write(json.dumps({
@@ -220,6 +228,10 @@ class Local(UploadBackend):
 			with open(filepath, 'w') as f:
 				for chunk in data:
 					f.write(chunk)
+		except (OSError, IOError) as e:
+			# Because duplicate videos don't actually matter with this backend,
+			# we consider all disk errors retryable.
+			raise UploadError("{} while writing local file: {}".format(type(e).__name__, e), retryable=True)
 		if self.url_prefix is not None:
 			url = self.url_prefix + filename
 		else: