1.首先需要在公众号的开发者中心启用服务器配置

exports.wechat = function (req, res) {
    
    var echostr, nonce, signature, timestamp;
    signature = req.query.signature;
    timestamp = req.query.timestamp;
    nonce = req.query.nonce;
    echostr = req.query.echostr;
    if(check(timestamp,nonce,signature,"weixin")){
        return res.send(echostr);
    }else{
        return res.end();
    }
};

function check(timestamp, nonce, signature ,token) {
    var currSign, tmp;
    tmp = [token, timestamp, nonce].sort().join("");
    currSign = crypto.createHash("sha1").update(tmp).digest("hex");
    return currSign === signature;
};

2.如果有用户发送消息给公众号，微信服务器就会发送一个post请求到服务器配置里的URL,只要接收post过来的xml内容再以xml格式返回就可以实现消息的接收和回复

exports.wechatdo = function (req, res) {
    var _da;
    req.on("data",function(data){
        /*微信服务器传过来的是xml格式的，是buffer类型，因为js本身只有字符串数据类型，所以需要通过toString把xml转换为字符串*/
        _da = data.toString("utf-8");

    });
    req.on("end",function(){
        //console.log("end");
        var ToUserName = getXMLNodeValue('ToUserName',_da);
        var FromUserName = getXMLNodeValue('FromUserName',_da);
        var CreateTime = getXMLNodeValue('CreateTime',_da);
        var MsgType = getXMLNodeValue('MsgType',_da);
        var Content = getXMLNodeValue('Content',_da);
        var MsgId = getXMLNodeValue('MsgId',_da);
        console.log(ToUserName);
        console.log(FromUserName);
        console.log(CreateTime);
        console.log(MsgType);
        console.log(Content);
        console.log(MsgId);
        var xml = '<xml><ToUserName>'+FromUserName+'</ToUserName><FromUserName>'+ToUserName+'</FromUserName><CreateTime>'+CreateTime+'</CreateTime><MsgType>'+MsgType+'</MsgType><Content>'+Content+'</Content></xml>';
        res.send(xml);
    });
};

function getXMLNodeValue(node_name,xml){
    var tmp = xml.split("<"+node_name+">");
    var _tmp = tmp[1].split("</"+node_name+">");
    return _tmp[0];
}