doc: fix stream async iterator sample

ronag · MylesBorins · commit d51de787d93e · 2020-01-16T01:39:07.000-05:00
The for await loop into writable loop could cause an unhandled exception in the case where we are waiting for data from the async iterable and this no `'error'` handler is registered on the writable. Fixes: #31222 PR-URL: #31252 Reviewed-By: Matteo Collina <matteo.collina@gmail.com> Reviewed-By: Rich Trott <rtrott@gmail.com> Reviewed-By: James M Snell <jasnell@gmail.com>
diff --git a/doc/api/stream.md b/doc/api/stream.md
@@ -2644,15 +2644,23 @@ const finished = util.promisify(stream.finished);
 
 const writable = fs.createWriteStream('./file');
 
-(async function() {
+async function pump(iterator, writable) {
 for await (const chunk of iterator) {
 // Handle backpressure on write().
- if (!writable.write(chunk))
+ if (!writable.write(chunk)) {
+ if (writable.destroyed) return;
 await once(writable, 'drain');
+ }
 }
 writable.end();
+}
+
+(async function() {
 // Ensure completion without errors.
- await finished(writable);
+ await Promise.all([
+ pump(iterator, writable),
+ finished(writable)
+ ]);
 })();
 ```
 

-Original file line number
+Diff line change
 constwritable=fs.createWriteStream('./file');
 -(asyncfunction() {
 +asyncfunctionpump(iterator, writable) {
 forawait (constchunkofiterator) {
 // Handle backpressure on write().
 -if (!writable.write(chunk))
 +if (!writable.write(chunk)) {
 +if (writable.destroyed) return;
 awaitonce(writable, 'drain');
 + }
+ }
 writable.end();
 +}
++
 +(asyncfunction() {
 // Ensure completion without errors.
 -awaitfinished(writable);
 +awaitPromise.all([
 +pump(iterator, writable),
 +finished(writable)
 + ]);
 })();
 ```