var net = require('net');

var local_port = 8893;

//在本地创建一个server监听本地local_port端口

net.createServer(function (client)

{

    //首先监听浏览器的数据发送事件，直到收到的数据包含完整的http请求头

    var buffer = new Buffer(0);

    client.on('data',function(data)

    {

        buffer = buffer_add(buffer,data);

        if (buffer_find_body(buffer) == -1) return;

        var req = parse_request(buffer);

        if (req === false) return;

        client.removeAllListeners('data');

        relay_connection(req);

    });

    //从http请求头部取得请求信息后，继续监听浏览器发送数据，同时连接目标服务器，并把目标服务器的数据传给浏览器

    function relay_connection(req)

    {

        console.log(req.method+' '+req.host+':'+req.port);

        //如果请求不是CONNECT方法（GET, POST），那么替换掉头部的一些东西

        if (req.method != 'CONNECT')

        {

            //先从buffer中取出头部

            var _body_pos = buffer_find_body(buffer);

            if (_body_pos < 0) _body_pos = buffer.length;

            var header = buffer.slice(0,_body_pos).toString('utf8');

            //替换connection头

            header = header.replace(/(proxy\-)?connection\:.+\r\n/ig,'')

                    .replace(/Keep\-Alive\:.+\r\n/i,'')

                    .replace("\r\n",'\r\nConnection: close\r\n');

            //替换网址格式(去掉域名部分)

            if (req.httpVersion == '1.1')

            {

                var url = req.path.replace(/http\:\/\/[^\/]+/,'');

                if (url.path != url) header = header.replace(req.path,url);

            }

            buffer = buffer_add(new Buffer(header,'utf8'),buffer.slice(_body_pos));

        }

        //建立到目标服务器的连接

        var server = net.createConnection(req.port,req.host);

        //交换服务器与浏览器的数据

        client.on("data", function(data){ server.write(data); });

        server.on("data", function(data){ client.write(data); });

        if (req.method == 'CONNECT')

            client.write(new Buffer("HTTP/1.1 200 Connection established\r\nConnection: close\r\n\r\n"));

        else

            server.write(buffer);

    }

}).listen(local_port);

console.log('Proxy server running at localhost:'+local_port);

//处理各种错误

process.on('uncaughtException', function(err)

{

    console.log("\nError!!!!");

    console.log(err);

});

/**

* 从请求头部取得请求详细信息

* 如果是 CONNECT 方法，那么会返回 { method,host,port,httpVersion}

* 如果是 GET/POST 方法，那么返回 { metod,host,port,path,httpVersion}

*/

function parse_request(buffer)

{

    var s = buffer.toString('utf8');

    var method = s.split('\n')[0].match(/^([A-Z]+)\s/)[1];

    if (method == 'CONNECT')

    {

        var arr = s.match(/^([A-Z]+)\s([^\:\s]+)\:(\d+)\sHTTP\/(\d\.\d)/);

        if (arr && arr[1] && arr[2] && arr[3] && arr[4])

            return { method: arr[1], host:arr[2], port:arr[3],httpVersion:arr[4] };

    }

    else

    {

        var arr = s.match(/^([A-Z]+)\s([^\s]+)\sHTTP\/(\d\.\d)/);

        if (arr && arr[1] && arr[2] && arr[3])

        {

            var host = s.match(/Host\:\s+([^\n\s\r]+)/)[1];

            if (host)

            {

                var _p = host.split(':',2);

                return { method: arr[1], host:_p[0], port:_p[1]?_p[1]:80, path: arr[2],httpVersion:arr[3] };

            }

        }

    }

    return false;

}

/**

* 两个buffer对象加起来

*/

function buffer_add(buf1,buf2)

{

    var re = new Buffer(buf1.length + buf2.length);

    buf1.copy(re);

    buf2.copy(re,buf1.length);

    return re;

}

/**

* 从缓存中找到头部结束标记("\r\n\r\n")的位置

*/

function buffer_find_body(b)

{

    for(var i=0,len=b.length-3;i<len;i++)

    {

        if (b[i] == 0x0d && b[i+1] == 0x0a && b[i+2] == 0x0d && b[i+3] == 0x0a)

        {

            return i+4;

        }

    }

    return -1;

}