diff options
author | Chetan Karande <kchetan.tech@gmail.com> | 2019-09-03 20:34:36 +0300 |
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committer | Michaƫl Zasso <targos@protonmail.com> | 2019-09-20 10:36:18 +0300 |
commit | 32bb58ba9cff3f1f27e3275625b9a45864d94e7c (patch) | |
tree | 10e492c77af5a589a0335491a0cc39da2d7ae4fb /doc/api | |
parent | 735ef8b235a186a476f4b3bfa6c172b680bb24d6 (diff) |
doc: fix unsafe writable stream code example
Update writable stream code example using async iterator to use safer
`finished()` method instead of a `finish` event to avoid uncaught
exceptions
Fixes: https://github.com/nodejs/node/issues/29397
PR-URL: https://github.com/nodejs/node/pull/29425
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Diffstat (limited to 'doc/api')
-rw-r--r-- | doc/api/stream.md | 32 |
1 files changed, 26 insertions, 6 deletions
diff --git a/doc/api/stream.md b/doc/api/stream.md index 064b23d78fa..7fc4dd4452e 100644 --- a/doc/api/stream.md +++ b/doc/api/stream.md @@ -2556,6 +2556,7 @@ it is important to ensure the correct handling of backpressure and errors. ```js const { once } = require('events'); +const finished = util.promisify(stream.finished); const writable = fs.createWriteStream('./file'); @@ -2567,18 +2568,24 @@ const writable = fs.createWriteStream('./file'); } writable.end(); // Ensure completion without errors. - await once(writable, 'finish'); + await finished(writable); })(); ``` -In the above, errors on the write stream would be caught and thrown by the two -`once()` listeners, since `once()` will also handle `'error'` events. +In the above, errors on `write()` would be caught and thrown by the +`once()` listener for the `'drain'` event, since `once()` will also handle the +`'error'` event. To ensure completion of the write stream without errors, +it is safer to use the `finished()` method as above, instead of using the +`once()` listener for the `'finish'` event. Under certain cases, an `'error'` +event could be emitted by the writable stream after `'finish'` and as `once()` +will release the `'error'` handler on handling the `'finish'` event, it could +result in an unhandled error. -Alternatively the readable stream could be wrapped with `Readable.from()` and +Alternatively, the readable stream could be wrapped with `Readable.from()` and then piped via `.pipe()`: ```js -const { once } = require('events'); +const finished = util.promisify(stream.finished); const writable = fs.createWriteStream('./file'); @@ -2586,7 +2593,20 @@ const writable = fs.createWriteStream('./file'); const readable = Readable.from(iterator); readable.pipe(writable); // Ensure completion without errors. - await once(writable, 'finish'); + await finished(writable); +})(); +``` + +Or, using `stream.pipeline()` to pipe streams: + +```js +const pipeline = util.promisify(stream.pipeline); + +const writable = fs.createWriteStream('./file'); + +(async function() { + const readable = Readable.from(iterator); + await pipeline(readable, writable); })(); ``` |