[feat] stored context for requests so that if there's an error, the stack will be helpful

Makefile

@@ -16,3 +16,6 @@ clean:
 
 bundle:
 	deno bundle --log-level info --unstable src/mod.ts ./nats.js
+
+fmt:
+	deno fmt src/ doc/ bin/ nats-base-client/ examples/ tests/

nats-base-client/nats.ts

@@ -154,17 +154,24 @@ export class NatsConnectionImpl implements NatsConnection {
         ? opts.reply
         : createInbox(this.options.inboxPrefix);
       const d = deferred<Msg>();
+      const errCtx = new Error();
       this.subscribe(
         inbox,
         {
           max: 1,
           timeout: opts.timeout,
           callback: (err, msg) => {
             if (err) {
+              // timeouts from `timeout()` will have the proper stack
+              if (err.code !== ErrorCode.Timeout) {
+                err.stack += `\n\n${errCtx.stack}`;
+              }
               d.reject(err);
             } else {
               err = isRequestError(msg);
               if (err) {
+                // if we failed here, help the developer by showing what failed
+                err.stack += `\n\n${errCtx.stack}`;
                 d.reject(err);
               } else {
                 d.resolve(msg);

nats-base-client/request.ts

@@ -23,6 +23,7 @@ export class Request {
   received: number;
   deferred: Deferred<Msg>;
   timer: Timeout<Msg>;
+  ctx: Error;
   private mux: MuxSubscription;
 
   constructor(
@@ -35,13 +36,15 @@ export class Request {
     this.token = nuid.next();
     extend(this, opts);
     this.timer = timeout<Msg>(opts.timeout);
+    this.ctx = new Error();
   }
 
   resolver(err: Error | null, msg: Msg): void {
     if (this.timer) {
       this.timer.cancel();
     }
     if (err) {
+      err.stack += `\n\n${this.ctx.stack}`;
       this.deferred.reject(err);
     } else {
       this.deferred.resolve(msg);

tests/timeout_test.ts

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2021 The NATS Authors
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+import {
+  assertStringIncludes,
+  fail,
+} from "https://deno.land/std@0.95.0/testing/asserts.ts";
+import { connect } from "../src/connect.ts";
+import { createInbox, Empty } from "../nats-base-client/mod.ts";
+
+Deno.test("timeout - request noMux stack is useful", async () => {
+  const nc = await connect({ servers: "demo.nats.io" });
+  const subj = createInbox();
+  try {
+    await nc.request(subj, Empty, { noMux: true, timeout: 250 });
+    fail("request should have failed!");
+  } catch (err) {
+    assertStringIncludes(err.stack, "timeout_test");
+  }
+  await nc.close();
+});
+
+Deno.test("timeout - request stack is useful", async () => {
+  const nc = await connect({ servers: "demo.nats.io" });
+  const subj = createInbox();
+  try {
+    await nc.request(subj, Empty, { timeout: 250 });
+    fail("request should have failed!");
+  } catch (err) {
+    assertStringIncludes(err.stack, "timeout_test");
+    console.log(err.stack);
+  }
+  await nc.close();
+});