Source

File: wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php

public function update_item( $request ) {
		$valid_check = $this->get_post( $request['id'] );
		if ( is_wp_error( $valid_check ) ) {
			return $valid_check;
		}

		$post = $this->prepare_item_for_database( $request );

		if ( is_wp_error( $post ) ) {
			return $post;
		}

		// Convert the post object to an array, otherwise wp_update_post() will expect non-escaped input.
		$post_id = wp_update_post( wp_slash( (array) $post ), true );

		if ( is_wp_error( $post_id ) ) {
			if ( 'db_update_error' === $post_id->get_error_code() ) {
				$post_id->add_data( array( 'status' => 500 ) );
			} else {
				$post_id->add_data( array( 'status' => 400 ) );
			}
			return $post_id;
		}

		$post = get_post( $post_id );

		/** This action is documented in wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php */
		do_action( "rest_insert_{$this->post_type}", $post, $request, false );

		$schema = $this->get_item_schema();

		if ( ! empty( $schema['properties']['format'] ) && ! empty( $request['format'] ) ) {
			set_post_format( $post, $request['format'] );
		}

		if ( ! empty( $schema['properties']['featured_media'] ) && isset( $request['featured_media'] ) ) {
			$this->handle_featured_media( $request['featured_media'], $post_id );
		}

		if ( ! empty( $schema['properties']['sticky'] ) && isset( $request['sticky'] ) ) {
			if ( ! empty( $request['sticky'] ) ) {
				stick_post( $post_id );
			} else {
				unstick_post( $post_id );
			}
		}

		if ( ! empty( $schema['properties']['template'] ) && isset( $request['template'] ) ) {
			$this->handle_template( $request['template'], $post->ID );
		}

		$terms_update = $this->handle_terms( $post->ID, $request );

		if ( is_wp_error( $terms_update ) ) {
			return $terms_update;
		}

		if ( ! empty( $schema['properties']['meta'] ) && isset( $request['meta'] ) ) {
			$meta_update = $this->meta->update_value( $request['meta'], $post->ID );

			if ( is_wp_error( $meta_update ) ) {
				return $meta_update;
			}
		}

		$post          = get_post( $post_id );
		$fields_update = $this->update_additional_fields_for_object( $post, $request );

		if ( is_wp_error( $fields_update ) ) {
			return $fields_update;
		}

		$request->set_param( 'context', 'edit' );

		// Filter is fired in WP_REST_Attachments_Controller subclass.
		if ( 'attachment' === $this->post_type ) {
			$response = $this->prepare_item_for_response( $post, $request );
			return rest_ensure_response( $response );
		}

		/** This action is documented in wp-includes/rest-api/endpoints/class-wp-rest-posts-controller.php */
		do_action( "rest_after_insert_{$this->post_type}", $post, $request, false );

		$response = $this->prepare_item_for_response( $post, $request );

		return rest_ensure_response( $response );
	}