http-header-list/index.js

Parser and logic functions for HTTP header lists

/** @typedef {object} HeaderValue
 *
 * @property {string} value Option value
 * @property {number} weight Weight of option
 * @property {{[key: string]: string}} parameters Option parameters
 */

/** @constructor
 * Create a parse header object that contains the parsed header
 *
 * @param {string} header Header value to parse
 */
export function HeaderList(header) {
	if (typeof header !== 'string') {
		throw new Error('headerValue should be a string');
	}

	/**
	 * The original header value
	 */
	this.header = header;
	/** @type {HeaderValue[]}
	 * The parsed and sorted list of header values. The header values are
	 * sorted in descending order by the weight factor, q. If a header value
	 * does not have a weight factor, it will default to 1
	 */
	this.list;

	if (!header) {
		this.list = [];
		return;
	}

	const headerParts = header.split(/ *, */);
	const headerOptions = [];

	for (let i = 0; i < headerParts.length; i++) {
		const parts = headerParts[i].split(/ *; */);

		const option = {
			value: parts.shift(),
			weight: 1,
			parameters: {}
		};

		for (let j = 0; j < parts.length; j++) {
			const parameters = parts[j].split(/ *= */);

			if (parameters[0] === 'q') {
				const weight = Number(parameters[1]);

				if (!isNaN(weight)) {
					option.weight = weight;
				}
			} else {
				option.parameters[parameters[0]] = parameters[1];
			}
		}

		headerOptions.push(option);
	}

	headerOptions.sort((a, b) => {
		if (a.weight < b.weight) {
			return 1;
		}

		if (a.weight > b.weight) {
			return -1;
		}

		return 0;
	});

	this.list = headerOptions;
}

/**
 * Find the first matching value that matches one of the values in the
 * given array
 *
 * @param {string[]} possibleValues Possible values to match against
 */
HeaderList.prototype.firstMatch = function firstMatch(possibleValues) {
	for (let i = 0; i < this.list.length; i++) {
		if (possibleValues.indexOf(this.list[i].value) !== -1) {
			return this.list[i];
		}
	}
};

/**
 * Parse the given header and find the first matching value
 *
 * @param {string} header Header value to parse
 * @param {string[]} possibleValues Possible values to match on
 *
 * @returns {HeaderValue} The first matching header value
 */
export const firstHeaderMatch = (header, possibleValues) => {
	if (!header) {
		return null;
	}

	const list = new HeaderList(header);

	return list.firstMatch(possibleValues);
};