main.js

(function() {

const HT = '\t';
const SP = ' ';
const CR = '\r';
const NF = '\n';

const SPACES = [SP, HT, CR, NF];

const SEPARATORS = [
    '(', ')', '<', '>', '@', 
    ',', ';', ':', '\\', '"',
    '/', '[', ']', '?', '=',
    '{', '}', SP, HT
];

function skipSpaces(value, pos) {
    while (pos < value.length && SPACES.indexOf(value.charAt(pos)) >= 0) pos++;

    return pos;
}

function readToken(value, pos) {
    var start = pos;
    while (pos < value.length && SEPARATORS.indexOf(value.charAt(pos)) == -1) {
        pos++;
    }
    
    return value.substring(start, pos);
}

function readQuotedString(value, pos) {
    var ch;
    var start = pos;
    
    pos++;
    while (pos < value.length) {
        ch = value.charAt(pos);
        if (ch === '"') break;
        if (ch === '\\') pos++;
        pos++;
    }
    
    return value.substring(start, pos + 1);
}

function decodeQuotedString(value) { 
    value = value.substr(1, value.length - 2);
    var start = 0, p;
    var result = '';
    
    while((p = value.indexOf('\\', start)) != -1) {
        result += value.substring(start, p);
        start = p + 2;
    }
    
    result += value.substring(start);
    
    return result;
}

function readLinkParam(value, pos, link) {
    var pname = readToken(value, pos);
    pos = skipSpaces(value, pos + pname.length);
    if (value.charAt(pos) !== '=')
        throw new Error('Unexpected token: ' + pos);

    pos++;
    
    var isQuotedString = value.charAt(pos) === '"';
    var pvalue;
    if (isQuotedString) {
        pvalue = readQuotedString(value, pos);
        pos += pvalue.length;
        pvalue = decodeQuotedString(pvalue);
        
    } else {
        pvalue = readToken(value, pos);
        pos += pvalue.length;
        
        if (pname == 'type') {
            if (value.charAt(pos) !== '/')
                throw new Error('Unexpected token: ' + pos);
            pos++;
            var subtype = readToken(value, pos);
            pos += subtype.length;
            pvalue += '/' + subtype;
        }
    }
    link[pname] = pvalue;
    
    return pos;
}

function readLink(value, pos, link) {
    if (value.charAt(pos) !== '<')
        throw new Error('Unexpected token: ' + pos);
    
    var p = value.indexOf('>', pos);
    if (p === -1) throw new Error('Unexpected token: ' + pos);

    link.href = value.substring(pos + 1, p);
    pos = skipSpaces(value, p + 1);
    
    while(pos < value.length && value.charAt(pos) === ';') {
        pos = skipSpaces(value, pos + 1);
        pos = readLinkParam(value, pos, link);
        pos = skipSpaces(value, pos);
    }
    
    return pos;
}

var httpLink = {};

/**
 * Parse the given string.
 * @param {String} value string as defined in http://www.w3.org/wiki/LinkHeader
 * @return {Array} array of link objects
 * @example '<http://example.com/TheBook/chapter2>; rel="previous"' -> [{href: 'http://example.com/TheBook/chapter2', rel: 'previous'}]
 */
httpLink.parse = function(value) {
    var pos = 0;
    
    var links = [];
    var link;
    
    while (pos < value.length && (pos === 0 || value.charAt(pos) === ',' && pos++)) {
        link = {};
        pos = skipSpaces(value, pos);
        pos = readLink(value, pos, link);
        links.push(link);
        pos = skipSpaces(value, pos);
    }
    
    if (pos < value.length)
        throw new Error('Unexpected token: ' + pos);
    
    return links;
};

httpLink.stringify = function(array) {
    return array.map(function(obj) {
        var href = obj.href;
        var attr = Object.keys(obj).filter(function(key) {
            return key !== 'href';
        }).map(function(key) {
            return key + '=' + JSON.stringify(obj[key]);
        });

        return ['<' + obj.href + '>'].concat(attr).join('; ');
    }).join(', ');
}

if (typeof define === 'function' && define.amd) { // RequireJS AMD
    define('http-link', [], function () {
        return httpLink;
    });
    
} else if (typeof module === 'object' && module.exports) { // NodeJS, CommonJS
    module.exports = httpLink;

} else { // browser <script>
    this.httpLink = httpLink;
}

})();