HTTP

SSL/TLS

1xx Informational

HTTP/1.0 don't have any 1xx status codes, server MUST NOT send a 1xx response to an HTTP/1.0 client

100 - Continue

• When the request contains an Expect header field that includes a 100-continue expectation,
  the 100 response indicates that the server wishes to receive the request content

2xx ok

200 Ok

204 No Content

• Successfull result of a PUT and DELETE method
• Save and Continue editing functionality
• Cacheable by Default, provided an ETag is included in response
• Can be used as a response to cors-preflight fetch but, firefox seemed to have issue around 2020, so use 200

3xx Redirection Messages

301 - Moved Permanently, 308 - Permanent Redirect

• browser redirects to the new URL and search engines update their links to the resource.
• Use 301 code only as a response for GET and HEAD methods.
• Use the 308 code for POST methods, as method change is explicity prohibited

302 - Found, 307 - Temporary Redirect

• browser redirects to this page but search engines don't update their links to the resource (in 'SEO-speak', it is said that the 'link-juice' is not sent to the new URL)
• Use 302 code only as a response for GET and HEAD methods.
• 307 guarantees that the method and the body will not be changed when the redirected request is made

303 - See other

• you want the method used to be changed to GET.
• This is useful when you want to give a response to a PUT method that is not the uploaded resource but a confirmation message such as: 'you successfully uploaded XYZ'

4xx Client Error Responses

401 Unauthorized

• client request not completed because it lacks valid authentication credentials for the requested resource.
• user authentication can allow access to the resource.

403 Forbidden

• server understands the request but refuses to authorize it
• user authentication will not allow access to the resource.

405 Method Not Allowed

• target resource doesn't allow the method in request-line
• origin server must generate an Allow header field in a 405 response containing the methods supported by the targe resource
• this response is hueristic cacheable, unless have some caching mechansims using Cache-Control header

Allow: GET, POST, HEAD

406 Not Acceptable

If the Accept header does not specify any known media types, the web server could generate an HTTP 406 (Not Acceptable) response message or return a message with a default media type.

415 Unsupported Media Type

• Server refuses to accept the request because the payload format is in an unsupported format
• Format problem due to 'Content-Type' or 'Content-Encoding'. or application inspecting the data directly