Improve Post Stats cache handling for invalid or error data

projects/packages/stats/changelog/update-blog_stats_debug

@@ -0,0 +1,4 @@
+Significance: patch
+Type: changed
+
+Improve Post Stats cache handling for invalid or error data

projects/packages/stats/src/class-wpcom-stats.php

@@ -508,15 +508,15 @@ protected function fetch_post_stats( $args, $post_id ) {
 				|| empty( $data )
 				|| is_wp_error( $data )
 			) {
-				return $data;
+				return $this->refresh_post_stats_cache( $endpoint, $args, $post_id, $meta_name );
 			}
 
 			$time  = key( $data );
 			$views = $data[ $time ] ?? null;
 
 			// Bail if data is malformed.
 			if ( ! is_numeric( $time ) || ! is_array( $views ) ) {
-				return $data;
+				return $this->refresh_post_stats_cache( $endpoint, $args, $post_id, $meta_name );
 			}
 
 			/** This filter is already documented in projects/packages/stats/src/class-wpcom-stats.php */
@@ -530,8 +530,26 @@ protected function fetch_post_stats( $args, $post_id ) {
 			}
 		}
 
+		return $this->refresh_post_stats_cache( $endpoint, $args, $post_id, $meta_name );
+	}
+
+	/**
+	 * Force fetch stats from WPCOM, and update cache if needed.
+	 *
+	 * @param string $endpoint The stats endpoint.
+	 * @param array  $args The query arguments.
+	 * @param int    $post_id The post ID.
+	 * @param string $meta_name The meta name.
+	 *
+	 * @return array|WP_Error
+	 */
+	protected function refresh_post_stats_cache( $endpoint, $args, $post_id, $meta_name ) {
 		$wpcom_stats = $this->fetch_remote_stats( $endpoint, $args );
-		update_post_meta( $post_id, $meta_name, array( time() => $wpcom_stats ) );
+
+		// Don't write error or empty results to cache.
+		if ( ! is_wp_error( $wpcom_stats ) && ! empty( $wpcom_stats ) ) {
+			update_post_meta( $post_id, $meta_name, array( time() => $wpcom_stats ) );
+		}
 
 		return $wpcom_stats;
 	}