What is the WordPress REST API `rest_pre_serve_request` action and how does it enable custom response handling?

Question

WordPress Expert — Hard

What is the WordPress REST API `rest_pre_serve_request` action and how does it enable custom response handling?

Accepted Answer

The WordPress REST API `rest_pre_serve_request` action fires after the response is prepared but before it is sent. Returning true from a callback indicates that the response has been manually served, preventing WordPress from sending its own response. This allows for custom serialization formats, streaming responses, or adding custom response headers not supported by WP_REST_Response.