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editing: README.md

# on-finished

[![NPM Version][npm-version-image]][npm-url]
[![NPM Downloads][npm-downloads-image]][npm-url]
[![Node.js Version][node-image]][node-url]
[![Build Status][ci-image]][ci-url]
[![Coverage Status][coveralls-image]][coveralls-url]

Execute a callback when a HTTP request closes, finishes, or errors.

## Install

This is a [Node.js](https://nodejs.org/en/) module available through the
[npm registry](https://www.npmjs.com/). Installation is done using the
[`npm install` command](https://docs.npmjs.com/getting-started/installing-npm-packages-locally):

```sh
$ npm install on-finished
```

## API

```js
var onFinished = require('on-finished')
```

### onFinished(res, listener)

Attach a listener to listen for the response to finish. The listener will
be invoked only once when the response finished. If the response finished
to an error, the first argument will contain the error. If the response
has already finished, the listener will be invoked.

Listening to the end of a response would be used to close things associated
with the response, like open files.

Listener is invoked as `listener(err, res)`.

```js
onFinished(res, function (err, res) {
  // clean up open fds, etc.
  // err contains the error if request error'd
})
```

### onFinished(req, listener)

Attach a listener to listen for the request to finish. The listener will
be invoked only once when the request finished. If the request finished
to an error, the first argument will contain the error. If the request
has already finished, the listener will be invoked.

Listening to the end of a request would be used to know when to continue
after reading the data.

Listener is invoked as `listener(err, req)`.

```js
var data = ''

req.setEncoding('utf8')
req.on('data', function (str) {
  data += str
})

onFinished(req, function (err, req) {
  // data is read unless there is err
})
```

### onFinished.isFinished(res)

Determine if `res` is already finished. This would be useful to check and
not even start certain operations if the response has already finished.

### onFinished.isFinished(req)

Determine if `req` is already finished. This would be useful to check and
not even start certain operations if the request has already finished.

## Special Node.js requests

### HTTP CONNECT method

The meaning of the `CONNECT` method from RFC 7231, section 4.3.6:

> The CONNECT method requests that the recipient establish a tunnel to
> the destination origin server identified by the request-target and,
> if successful, thereafter restrict its behavior to blind forwarding
> of packets, in both directions, until the tunnel is closed.  Tunnels
> are commonly used to create an end-to-end virtual connection, through
> one or more proxies, which can then be secured using TLS (Transport
> Layer Security, [RFC5246]).

In Node.js, these request objects come from the `'connect'` event on
the HTTP server.

When this module is used on a HTTP `CONNECT` request, the request is
considered "finished" immediately, **due to limitations in the Node.js
interface**. This means if the `CONNECT` request contains a request entity,
the request will be considered "finished" even before it has been read.

There is no such thing as a response object to a `CONNECT` request in
Node.js, so there is no support for one.

### HTTP Upgrade request

The meaning of the `Upgrade` header from RFC 7230, section 6.1:

> The "Upgrade" header field is intended to provide a simple mechanism
> for transitioning from HTTP/1.1 to some other protocol on the same
> connection.

In Node.js, these request objects come from the `'upgrade'` event on
the HTTP server.

When this module is used on a HTTP request with an `Upgrade` header, the
request is considered "finished" immediately, **due to limitations in the
Node.js interface**. This means if the `Upgrade` request contains a request
entity, the request will be considered "finished" even before it has been
read.

There is no such thing as a response object to a `Upgrade` request in
Node.js, so there is no support for one.

## Example

The following code ensures that file descriptors are always closed
once the response finishes.

```js
var destroy = require('destroy')
var fs = require('fs')
var http = require('http')
var onFinished = require('on-finished')

http.createServer(function onRequest (req, res) {
  var stream = fs.createReadStream('package.json')
  stream.pipe(res)
  onFinished(res, function () {
    destroy(stream)
  })
})
```

## License

[MIT](LICENSE)

[ci-image]: https://badgen.net/github/checks/jshttp/on-finished/master?label=ci
[ci-url]: https://github.com/jshttp/on-finished/actions/workflows/ci.yml
[coveralls-image]: https://badgen.net/coveralls/c/github/jshttp/on-finished/master
[coveralls-url]: https://coveralls.io/r/jshttp/on-finished?branch=master
[node-image]: https://badgen.net/npm/node/on-finished
[node-url]: https://nodejs.org/en/download
[npm-downloads-image]: https://badgen.net/npm/dm/on-finished
[npm-url]: https://npmjs.org/package/on-finished
[npm-version-image]: https://badgen.net/npm/v/on-finished

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