node-filter.js

/**
 * 过滤掉不能下载的节点
 */

module.exports = NodeFilter;

/*
 nodesArray: {uri: string type: string capacity: number}
 cb: function
 range: {start: number end: number}
 */

var debug = require('debug')('pear:node-filter');

function NodeFilter(nodesArray, cb, range) {

    // cb(nodesArray, 0);
    var doneCount = 0;
    var usefulNodes = [];
    var fileLength = 0;
    if (!range) {
        range = {
            start: 0,
            end: nodesArray.length
        }
    } else if (range.end > nodesArray.length) {
        range.end = nodesArray.length;
    }

    //计时
    var timeStart = performance.now();

    for (var i=range.start;i<range.end;++i) {

        try {
            connectTest(nodesArray[i]);
        } catch (e) {
            // debug(nodesArray[i].uri + ':' + JSON.stringify(e))
        }
    }

    function connectTest(node) {

        var xhr = new XMLHttpRequest;
        xhr.timeout = 1500;
        xhr.open('head', node.uri);
        xhr.onload = function () {
            doneCount ++;
            node.time = performance.now() - timeStart;
            // console.warn(`node.time ${node.time}`);
            if (this.status >= 200 && this.status<300) {
                usefulNodes.push(node);
                fileLength = xhr.getResponseHeader('content-length');
            }
            chenkDone();
        };
        xhr.ontimeout = function() {
            doneCount ++;
            debug(node.uri + ' timeout');
            chenkDone();
        };
        xhr.onerror = function() {
            doneCount ++;
            chenkDone();
        };
        xhr.send();

    };

    function chenkDone() {

        // if (doneCount === nodesArray.length) {
        //     cb(usefulNodes, fileLength);
        // }

        if (doneCount === (range.end-range.start)) {

            //根据capacity对节点进行排序
            // usefulNodes.sort(function (a, b) {          //按能力值从大到小排序
            //     return b.capacity - a.capacity;
            // });

            //根据响应时间排序
            usefulNodes.sort(function (a, b) {          //按响应时间从小到大排序
                return a.time - b.time;
            });

            for(var i = 0; i < usefulNodes.length; i++) {
                debug('node ' + i + ' capacity ' + usefulNodes[i].capacity);
            }
            debug('length: ' + usefulNodes.filter(function (node) {
                    return node.capacity >= 5;
                }).length);

            cb(usefulNodes, fileLength);
        }
    }

};