Skip to content

Amend the GC warning in the README to clarify that consuming bodies is recommended but not required #4364

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
mcollina merged 1 commit into from
Jul 30, 2025
Merged

Amend the GC warning in the README to clarify that consuming bodies is recommended but not required #4364

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
20 changes: 11 additions & 9 deletions README.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -440,13 +440,14 @@ This behavior is intentional for server-side environments where CORS restriction
* https://fetch.spec.whatwg.org/#garbage-collection

The [Fetch Standard](https://fetch.spec.whatwg.org) allows users to skip consuming the response body by relying on
[garbage collection](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Memory_Management#garbage_collection) to release connection resources. Undici does not do the same. Therefore, it is important to always either consume or cancel the response body.
[garbage collection](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Memory_Management#garbage_collection) to release connection resources.

Garbage collection in Node is less aggressive and deterministic
(due to the lack of clear idle periods that browsers have through the rendering refresh rate)
which means that leaving the release of connection resources to the garbage collector can lead
to excessive connection usage, reduced performance (due to less connection re-use), and even
stalls or deadlocks when running out of connections.
Therefore, __it is important to always either consume or cancel the response body anyway__.

```js
// Do
Expand All @@ -459,7 +460,15 @@ for await (const chunk of body) {
const { headers } = await fetch(url);
```

The same applies for `request` too:
However, if you want to get only headers, it might be better to use `HEAD` request method. Usage of this method will obviate the need for consumption or cancelling of the response body. See [MDN - HTTP - HTTP request methods - HEAD](https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/HEAD) for more details.

```js
const headers = await fetch(url, { method: 'HEAD' })
.then(res => res.headers)
```

Note that consuming the response body is _mandatory_ for `request`:

```js
// Do
const { body, headers } = await request(url);
Expand All @@ -469,13 +478,6 @@ await res.body.dump(); // force consumption of body
const { headers } = await request(url);
```

However, if you want to get only headers, it might be better to use `HEAD` request method. Usage of this method will obviate the need for consumption or cancelling of the response body. See [MDN - HTTP - HTTP request methods - HEAD](https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/HEAD) for more details.

```js
const headers = await fetch(url, { method: 'HEAD' })
.then(res => res.headers)
```

#### Forbidden and Safelisted Header Names

* https://fetch.spec.whatwg.org/#cors-safelisted-response-header-name
Expand Down
Loading