图片列表大概有1万个图片地址，
使用nodejs下载的时候，莫名其妙就会出现错误。

基本代码如下：

var downloadImage2 = function (src) {
          var iArr = src.split("/");
        var imageName = iArr[iArr.length - 1];
        //console.log("Download begin: " + imageSrc);

        var download = function(uri, filename, callback) {
            request.head(uri, function(err, res, body) {
                // console.log('content-type:', res.headers['content-type']);
                // console.log('content-length:', res.headers['content-length']);
if (uri) {request(uri).pipe(fs.createWriteStream(filename)).on('close', callback);}
                
            });
        };

        download(src, "./images/" + imageName, function() {
            console.log('done: ' + index++);

        });
    
}

出现的错误也有点莫名其妙，有时候是：

events.js:160
      throw er; // Unhandled 'error' event
      ^

Error: Invalid URI "undefined"
    at Request.init (/Users//dirread/node_modules/request/request.js:275:31)
    at new Request (/Users/dirread/node_modules/request/request.js:129:8)
    at request (/Users/dirread/node_modules/request/index.js:55:10)
    at Request._callback (/Users//down.js:21:11)
    at self.callback (/Users//dirread/node_modules/request/request.js:187:22)
    at emitOne (events.js:96:13)
    at Request.emit (events.js:188:7)