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Mimic a Node.js HTTP response stream

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'use strict';

// We define these manually to ensure they're always copied
// even if they would move up the prototype chain
// https://nodejs.org/api/http.html#http_class_http_incomingmessage
const knownProperties = [
	'aborted',
	'complete',
	'headers',
	'httpVersion',
	'httpVersionMinor',
	'httpVersionMajor',
	'method',
	'rawHeaders',
	'rawTrailers',
	'setTimeout',
	'socket',
	'statusCode',
	'statusMessage',
	'trailers',
	'url'
];

module.exports = (fromStream, toStream) => {
	if (toStream._readableState.autoDestroy) {
		throw new Error('The second stream must have the `autoDestroy` option set to `false`');
	}

	const fromProperties = new Set(Object.keys(fromStream).concat(knownProperties));

	const properties = {};

	for (const property of fromProperties) {
		// Don't overwrite existing properties.
		if (property in toStream) {
			continue;
		}

		properties[property] = {
			get() {
				const value = fromStream[property];
				const isFunction = typeof value === 'function';

				return isFunction ? value.bind(fromStream) : value;
			},
			set(value) {
				fromStream[property] = value;
			},
			enumerable: true,
			configurable: false
		};
	}

	Object.defineProperties(toStream, properties);

	fromStream.once('aborted', () => {
		toStream.destroy();

		toStream.emit('aborted');
	});

	fromStream.once('close', () => {
		if (fromStream.complete) {
			if (toStream.readable) {
				toStream.once('end', () => {
					toStream.emit('close');
				});
			} else {
				toStream.emit('close');
			}
		} else {
			toStream.emit('close');
		}
	});

	return toStream;
};