[1] How to send a custom http status code? - Kohana Forums (2017-06-10 16:14:44 +09:00) http://forum.kohanaframework.org/discussion/9478/how-to-send-a-custom-http-status-code/p1

[2] java - Is it possible to return HttpStatus status which is not from HttpStatus enum in Spring MVC - Stack Overflow (2017-06-10 16:15:08 +09:00) https://stackoverflow.com/questions/42919826/is-it-possible-to-return-httpstatus-status-which-is-not-from-httpstatus-enum-in/42920039

[3] Daniel E. Renferさんのツイート: "The HTTP status code 555 should be reserved for errors related to the server only existing in a movie or tv show." (2017-06-10 16:12:00 +09:00) https://twitter.com/duck1123/status/228321909824176128

[4] Setting the HTTP response status title, "555 - Dropbox had an error" - MuleSoft (2017-06-10 16:15:37 +09:00) https://forums.mulesoft.com/questions/57701/setting-the-http-response-status-title-555-dropbox.html

[5]

Bitbucket API (2017-06-10 16:16:37 +09:00) https://developer.atlassian.com/bitbucket/api/2/reference/resource/repositories/%7Busername%7D/%7Brepo_slug%7D/patch/%7Bspec%7D

555
If the diff was too large and timed out.
Since this endpoint does not employ any form of pagination, but instead returns the diff as a single document, it can run into trouble on very large diffs. If Bitbucket times out in cases like these, a 555 status code is returned.