fix: send error.statusCode when available if the reply.statusCode is …

…200 or undefined

lib/hooks.js

@@ -32,8 +32,16 @@ exports.onResponseSize = function (request, reply, payload, next) {
 };
 
 exports.onError = function (request, reply, error, done) {
+    let code = undefined;
     /* istanbul ignore next */
-    const code = reply.statusCode < 400 ? 500 : reply.statusCode;
+    if (!reply.statusCode || reply.statusCode === 200) {
+        // reply has 200 statusCode by default with fastify 4 so we need to check and retrieve the status code of the Error object.
+        // @see https://github.com/fastify/fastify/issues/4501
+        code = error.statusCode || error.status || 500;
+    } else {
+        code = reply.statusCode < 400 ? 500 : reply.statusCode;
+    }
+
     request.sendCounterMetric(`errors.${code}`);
     done();
 };