用Node.js起一个小的web server

用Node.js起一个小的web server算是Node.js的基本操作了，老本行，下面的例子是启动一个小的server，可以然后可以进行文件传输。

let http = require('http'),
    fs = require('fs');

http.createServer(function (request, response){
    if (request.url === '/') {
        response.writeHead(200, {"Content-Type":"text/plain"});
        response.end("Hello, it's ready for downloading...");
        return; 
    }

    let file = request.url.substring(1, request.url.length);

    console.log(new Date().toISOString() + "\t" + file); 

    fs.exists(file, function(exists){
        if (exists) {
            response.writeHead(200, {
            "Content-Type": "application/octet-stream",
            "Content-Disposition": "attachment; filename=" + file});
            fs.createReadStream(file).pipe(response);
        } else {
            response.writeHead(400, {"Content-Type": "text/plain"});
            response.end("ERROR: File does not exist - " + file);
        }
    });
}).listen(8877);

console.log('Running on 8877...');