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chore(docs): add request() example for conditionally reading the body #3743

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merged 3 commits into from
Oct 26, 2024
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chore(docs): add request() example for conditionally reading the body #3743

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c647f36
chore(docs): add request() example for conditionally reading the body
styfle Oct 16, 2024
0cfd421
Update docs/docs/api/Dispatcher.md
Uzlopak Oct 17, 2024
39965c7
Update docs/docs/api/Dispatcher.md
mcollina Oct 25, 2024
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24 changes: 24 additions & 0 deletions docs/docs/api/Dispatcher.md
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Original file line number Diff line number Diff line change
Expand Up @@ -527,6 +527,7 @@ try {
console.log('headers', headers)
body.setEncoding('utf8')
body.on('data', console.log)
body.on('error', console.error)
body.on('end', () => {
console.log('trailers', trailers)
})
Expand Down Expand Up @@ -630,6 +631,29 @@ try {
}
```

#### Example 3 - Conditionally reading the body

Remember to fully consume the body even in the case when it is not read.

```js
const { body, statusCode } = await client.request({
path: '/',
method: 'GET'
})

body.on('error', console.error) // prevent process from crashing on error

if (statusCode === 200) {
const buffer = await body.arrayBuffer()
return buffer
}

for await (const _chunk of body) {
// force consumption of body to avoid memory leak
}
return null
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```
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Suggested change
```js
const { body, statusCode } = await client.request({
path: '/',
method: 'GET'
})
body.on('error', console.error) // prevent process from crashing on error
if (statusCode === 200) {
const buffer = await body.arrayBuffer()
return buffer
}
for await (const _chunk of body) {
// force consumption of body to avoid memory leak
}
return null
```
```js
const { body, statusCode } = await client.request({
path: '/',
method: 'GET'
})
if (statusCode === 200) {
return await body.arrayBuffer()
}
await body.dump()
return null

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@ronag @mcollina I think its important to keep the body.on('error', console.error) handler because any code added between the client.request() and the await body calls could throw and then it would be uncatchable.

Since this example is about conditional code, I think its best practice to keep it in there to avoid this footgun.

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Furthermore, I don't think await body.dump() is sufficient.

It says it defaults to 131072 but what if the body is larger than that?

undici/lib/api/readable.js

Line 254 in 8e025d1

* @param {number} [opts.limit = 131072] Number of bytes to read.

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Friendly ping @mcollina @ronag

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@styfle styfle Oct 30, 2024 •
edited
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@mcollina @ronag I created PR #3788

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handler because any code added between the client.request() and the await body calls could throw and then it would be uncatchable.

That would be incorrect code anyway...

It says it defaults to 131072 but what if the body is larger than that?

It will close the connection if the body is larger.


### `Dispatcher.stream(options, factory[, callback])`

A faster version of `Dispatcher.request`. This method expects the second argument `factory` to return a [`stream.Writable`](https://nodejs.org/api/stream.html#stream_class_stream_writable) stream which the response will be written to. This improves performance by avoiding creating an intermediate [`stream.Readable`](https://nodejs.org/api/stream.html#stream_readable_streams) stream when the user expects to directly pipe the response body to a [`stream.Writable`](https://nodejs.org/api/stream.html#stream_class_stream_writable) stream.
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