Downldr

A simple downloader which prevents writing invalid files:

• Will throw an error in case of non 2xx status code
• Allows file type filtering

Install

npm install downldr

API

downldr(input, [options])

Returns a PassThrough stream with some extra events.

• complete: When the target or returned stream is fully written.
• type: Triggered when the file type is available & filter function is not passed or returned true.
• abort: When the request is aborted.

input

Type: string / object (request options)

You can pass either an URL or an object that will be passed directly to request.

options (optional)

• ignoreStatus - If true it will ignore non 2xx status code, defaults to false

• target - Takes a function or a Writable Stream. When passed the response will be piped into this stream. If it's a function the file will be passed extension if available & must return a Writable Stream. The function will only be executed once the download is valid: 2xx status code & wasn't filtered by the filter function.

• filter - which takes a function that should return false value if the download should be aborted.

This function will be triggered with the first chunk, and uses file-type to detect the file type.

function filter(type, chunk, statusCode) {
    // - type.mime may be null if `file-type` fails to detect the type
    // - type.contentType will always contain the response Conten-Type header
    // 		but the Content-Type header is not always 
    // 		accurate; A video with png extension
	return type.mime === 'image/jpeg'; // Only accepts jpeg
}

If the file type is not in this list type.mime will be undefined, but you can do the checks either using type.contentType or the first chunk

Note: type.mime may also be undefined for: docx/pptx/xlsx

The exception is detection of docx, pptx, and xlsx which potentially requires reading the whole file.

const downldr = require('downldr');

downldr('https://example.com/video.mp4')
	.on('error', console.error)
	.pipe(fs.createWriteStream('/tmp/video.mp4'))

downldr().abort()

This method will abort the current download. It uses request.abort()

const downldr = require('downldr');

const req = downldr('https://example.com/video.mp4')
	.on('error', console.error)
	.on('abort', () => console.log('Aborted!'));

req.abort();

.promise(input, options)

A convenient Promise wrapper around downldr.

options.target is required, since .pipe isn't available.

await downldr.promise('https://example.com/image', {
	filter: type => type && type.mime.startsWith('image/'),
	target: (ext) => fs.createWriteStream(`out.${ext}`)
});

Will resolve once target is fully written, and reject if an error occurs.

Examples

File type filter

const downldr = require('downldr');

downldr('https://example.com/image.jpg', {
	filter: (type, chunk, statusCode) => {
		// or check the first chunk or the statusCode
		return type.mime && type.mime.startsWith('image/');			
	}
})
.on('error', console.error)
.pipe(fs.createWriteStream('/tmp/image.jpg'))

Create stream on success

When saving the file to disk, a common practice is:

read
	.pipe(fs.createWriteStream('/tmp/file.txt');

But if the Readable stream fails, we end up with an empty file. To avoid that downldr can take a target option (function) which will be executed only when it's time to actually write to the stream.

downldr('https://example.com/image', {
	filter: type => type.mime == 'image/png',
	target: (ext) => fs.createWriteStream(`out.${ext}`)
})
.on('error', console.error)
.on('complete', () => console.log('done!'));

Set request Content-Type

const downldr = require('downldr');

app.get('/download/:image', (req, res) => {
	downldr(`http://example.com/${req.params.image}`, {
		filter: ({ mime = '' }) => {
		    // type.mime may be undefined for some files
		    // so we default it to = '' to safely use .startsWith
			return mime.startsWith('image/');			
		}
	})
	// 'type' is only triggered once filter returned true
	.on('type', type => res.set('Content-Type', type.mime))
	.on('error', err => {
		res.status(404)
			.send('Image not found')
	})
	.pipe(res); // Nothing will be piped if 'error' is triggered
});

License

ISC