How to Make a PATCH HTTP Callout in Apex?

Question:

How can I make a PATCH HTTP callout from Apex? I discovered that the HttpRequest class in Apex does not directly support the PATCH method. When attempting to send a PATCH request, I receive a System.CalloutException: Invalid HTTP method: PATCH.

This is problematic because I need to call out to a third-party service, and the workaround available for Salesforce REST API requests (using RestRequest) is not applicable.

What approaches or workarounds can I use to send a PATCH request from Salesforce? Using external tools or avoiding Apex is not an option.

Answer:

While Apex does not natively support the PATCH method in the HttpRequest class, a common workaround is to use the X-HTTP-Method-Override header. Many servers, including those of third-party APIs, accept this header to indicate the desired HTTP method. You can set the request method to POST and include this header to specify PATCH.

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Here is an example:

String eventId = 'abcdefghijklmnop';
String user = 'user@gmail.com';
user = EncodingUtil.urlEncode(user, 'UTF-8');

Http h = new Http();
HttpRequest req = new HttpRequest();
req.setEndpoint(
    'https://www.googleapis.com/calendar/v3/calendars/' + user + '/events/' + eventId
);
req.setBody('{ "Description" : "test description" }');
req.setHeader('Authorization', 'Bearer ' + authToken);
req.setHeader('Content-Type', 'application/json');
req.setHeader('X-HTTP-Method-Override', 'PATCH');
req.setMethod('POST');
HttpResponse res = h.send(req);

In this example, the following steps are taken:

1. The X-HTTP-Method-Override header is set to PATCH.
2. The HTTP method is set to POST, which Salesforce supports.
3. The server interprets the header and processes the request as a PATCH.

If the third-party API does not support X-HTTP-Method-Override, an alternative approach is to use middleware or an external service to handle the PATCH request. The middleware can accept a POST request from Salesforce and then perform the PATCH request to the target service. However, this requires additional infrastructure and may not always be viable.

This workaround ensures compatibility with servers that honor the X-HTTP-Method-Override header, allowing you to perform PATCH operations from Salesforce.

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