Updating parts of a resource on the server

PATCH Method

Preliminaries

This note provides supplementary information about the server's implementation of the standard HTTP PATCH method, used to replace portions of a resource.

The PATCH method is used by interactive AJAX calls to request the server to update portions of an existing resource.

A software developer must write a custom module with a handler to carry out the request (presumably via some type of server database), and the webmaster must configure a dynamic route with *methods=PATCH which references that module.

Request/response handlers

The server's request/response cycle for PATCH requests is fulfilled using this sequence of handlers:

	Request Handler	Optional	Configurable
1	Server Name Indication	no	no
2	Hosts	no	yes
3	IP Access	yes	yes
4	Resource Masks	yes	yes
5	Raw Path	no	no
6	Cookies	no	no
7	Forbidden	yes	yes
8	Cross Origin	yes	yes
9	RBAC	yes	yes
10	Content Length	no	no
11	Content Decoding	no	no
12	WWW Form Data	no	no
13	Multipart Form Data	no	no
	Dynamic Handler	Optional	Configurable
14	Router	yes	yes
	Response Handler	Optional	Configurable
15	Content Length	no	no
16	Status Codes	no	yes

Status codes

Successful responses are finalized by the dynamic module with any of these status codes:

200 "OK" when the response contains a payload and these response headers: content-type, content-length and optionally content-encoding.
204 "No Content" when the response has no payload.
207 "Multi Status" with a payload that has individual status codes for each part of the multipart request.
303 "See Other" when the processing is successful and the browser should issue a follow-on GET request to the URI declared in the response's location header.
307 "Temporary Redirect" when the processing is successful and the browser should issue a follow-on PATCH request to the URI declared in the response's location header.

Content length

PATCH requests must contain a content-length header. If not present, the request will fail with a status code of 411 and an information header of rw-content-length-missing.

The maximum size of a file to be uploaded is limited by the server to the size configured in restrictions/content-length-limit. If the file is too large, the request will fail with a status code of 413 and an information header of rw-content-length-limit.

Content encoding

PATCH requests may be uploaded in compressed form if the request includes an acceptable content-encoding header with a value of 'br', 'gzip' or 'deflate'. The uploaded request body will be decompressed and made available to plugin work orders in uncompressed form.

The request will fail with status code 406 if the Content Encoding module is not enabled or if the encoding value is not acceptable. An rw-content-decoding information header is added to this type of unsuccessful response.