fix(cli): CLI timeout fetching notices prints "unreachable" branch er…

…ror message (#20308)

fixes #20069

Problem: the [error message](https://github.com/aws/aws-cdk/blob/fd306ee05cfa7ebaa8d997007500d89d62868897/packages/aws-cdk/lib/notices.ts#L148-L154) should not be displayed. It was part of a backup timer acting as a fail-safe.

Additionally, the timer from `setTimeout()` is not cleared. the issue is being addressed by invoking `unref()`.

Overall, the behavior is correct: the request is being terminated, but the error message prompted the users encountering it to open an issue.



----

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### Adding new Unconventional Dependencies:

* [ ] This PR adds new unconventional dependencies following the process described [here](https://github.com/aws/aws-cdk/blob/master/CONTRIBUTING.md/#adding-new-unconventional-dependencies)

### New Features

* [ ] Have you added the new feature to an [integration test](https://github.com/aws/aws-cdk/blob/master/INTEGRATION_TESTS.md)?
	* [ ] Did you use `yarn integ` to deploy the infrastructure and generate the snapshot (i.e. `yarn integ` without `--dry-run`)?

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/aws-cdk/lib/notices.ts

@@ -1,3 +1,4 @@
+import { ClientRequest } from 'http';
 import * as https from 'https';
 import * as path from 'path';
 import * as fs from 'fs-extra';
@@ -108,9 +109,18 @@ export class WebsiteNoticeDataSource implements NoticeDataSource {
   fetch(): Promise<Notice[]> {
     const timeout = 3000;
     return new Promise((resolve, reject) => {
+      let req: ClientRequest | undefined;
+
+      let timer = setTimeout(() => {
+        if (req) {
+          req.destroy(new Error('Request timed out'));
+        }
+      }, timeout);
+
+      timer.unref();
+
       try {
-        const req = https.get('https://cli.cdk.dev-tools.aws.dev/notices.json',
-          { timeout },
+        req = https.get('https://cli.cdk.dev-tools.aws.dev/notices.json',
           res => {
             if (res.statusCode === 200) {
               res.setEncoding('utf8');
@@ -138,20 +148,6 @@ export class WebsiteNoticeDataSource implements NoticeDataSource {
             }
           });
         req.on('error', reject);
-        req.on('timeout', () => {
-          // The 'timeout' event doesn't stop anything by itself, it just
-          // notifies that it has been long time since we saw bytes.
-          // In our case, we want to give up.
-          req.destroy(new Error('Request timed out'));
-        });
-
-        // It's not like I don't *trust* the 'timeout' event... but I don't trust it.
-        // Add a backup timer that will destroy the request after all.
-        // (This is at least necessary to make the tests pass, but that's probably because of 'nock'.
-        // It's not clear whether users will hit this).
-        setTimeout(() => {
-          req.destroy(new Error('Request timed out. You should never see this message; if you do, please let us know at https://github.com/aws/aws-cdk/issues'));
-        }, timeout + 200);
       } catch (e) {
         reject(new Error(`HTTPS 'get' call threw an error: ${e.message}`));
       }