PATCH requests allow you to perform partial updates on many of our REST APIs and in most cases can save bandwidth.
PATCH
If you have ever tried to do a PATCH request on an App Engine application, you probably realized that it is not possible and that the list of HTTP Methods allowed is whitelisted to the following methods only: GET, POST, HEAD, PUT and DELETE. Trying to perform a PATCH request raises the following Exception:
GET
POST
HEAD
PUT
DELETE
java.net.ProtocolException: PATCH is not one of the supported http methods: [GET, POST, HEAD, PUT, DELETE]
There is a workaround to this. Most of our APIs support the X-HTTP-Method-Override header. This header can be used in a POST request to “fake” other HTTP methods. Simply set the value of the X-HTTP-Method-Override header to the HTTP method you would like to actually perform.
X-HTTP-Method-Override
For example, to make a PATCH request to the Google Tasks API to update only the Notes field of a particular task you could use the following HTTP request:
Notes
POST /tasks/v1/lists/@default/tasks/TASK_ID HTTP/1.1 Host: www.googleapis.com X-HTTP-Method-Override: PATCH Authorization: Bearer Content-Type: application/json Content-Length: 31 {“Notes” : “Patch is working!”}
Which would be equivalent to this HTTP Request, which is not supported on App Engine:
PATCH /tasks/v1/lists/@default/tasks/TASK_ID HTTP/1.1 Host: www.googleapis.com Authorization: Bearer Content-Type: application/json Content-Length: 31 {“Notes” : “Patch is working!”}
For instance, in an App Engine Java environment you could construct and execute this request this way:
URL url = new URL("https://www.googleapis.com/tasks/v1/" + "lists/@default/tasks/" + TASK_ID); HTTPRequest request = new HTTPRequest(url, HTTPMethod.POST); request.addHeader(new HTTPHeader("X-HTTP-Method-Override", "PATCH")); request.addHeader(new HTTPHeader("Authorization", "Bearer " + ACCESS_TOKEN)); request.setPayload("{\"Notes\" : \"Patch is working!\"}".getBytes()); URLFetchService fetchService = URLFetchServiceFactory.getURLFetchService(); HTTPResponse response = fetchService.fetch(request);
This trick can also be used if your application server is behind a firewall, behind a proxy server or in any other environment where HTTP methods other than POST might not be allowed. In that case you could use the X-HTTP-Method-Override header the same way to workaround these limitations.
You may also use our Google APIs Client library for Java or our Google APIs Client library for Python, both of which have support for PATCH requests and use the X-HTTP-Method-Override header when appropriate.
