Session是什么？

Session 是面向连接的状态信息，是对 Http 无状态协议的补充。

Session 怎么工作？

Session 数据保留在服务端，而为了标识具体 Session 信息指向哪个连接，需要客户端传递向服务端发送一个连接标识，比如存在Cookies 中的session_id值（也可以通过URL的QueryString传递），服务端根据这个id 存取状态信息。

在服务端存储 Session，可以有很多种方案：

内存存储
数据库存储
分布式缓存存储

分布式Session

随着网站规模（访问量/复杂度/数据量）的扩容，针对单机的方案将成为性能的瓶颈，分布式应用在所难免。所以，有必要研究一下 Session 的分布式存储。

如前述， Session使用的标识其实是客户端传递的 session_id，在分布式方案中，一般会针对这个值进行哈希，以确定其在 hashing ring 的存储位置。

Session_id

在 Session 处理的事务中，最重要的环节莫过于客户端与服务端关于 session 标识的传递过程：

服务端查询客户端Cookies 中是否存在 session_id
1. 有session_id，是否过期？过期了需要重新生成；没有过期则延长过期
2. 没有 session_id，生成一个，并写入客户端的 Set-Cookie 的 Header，这样下一次客户端发起请求时，就会在 Request Header 的 Cookies带着这个session_id

比如我用 Express，那么我希望这个过程是自动完成的，不需要每次都去写 Response Header，那么我需要这么一个函数（摘自朴灵的《深入浅出Node.js》）：

var setHeader = function (req, res, next) {
    var writeHead = res.writeHead;
    res.writeHead = function () {
        var cookies = res.getHeader('Set-Cookie');
        cookies = cookies || [];
        console.log('writeHead, cookies: ' + cookies);
        var session = serialize('session_id', req.session.id);
        cookies = Array.isArray(cookies) ? cookies.concat(session) : 
                  [cookies, session];
        res.setHeader('Set-Cookie', cookies);
        return writeHead.apply(this, arguments);
    };

    next();
};

var setHeader = function (req, res, next) {

var writeHead = res.writeHead;

res.writeHead = function () {

var cookies = res.getHeader('Set-Cookie');

cookies = cookies || [];

console.log('writeHead, cookies: ' + cookies);

var session = serialize('session_id', req.session.id);

cookies = Array.isArray(cookies) ? cookies.concat(session) :

[cookies, session];

res.setHeader('Set-Cookie', cookies);

return writeHead.apply(this, arguments);

};

next();

};

这个函数替换了writeHead，在每次Response写Header时它都会得到执行机会，所以它是自动化的。这个req.session.id 是怎么得到的，稍候会有详细的代码示例。

Hashing Ring

hashing ring 就是一个分布式结点的回路（取值范围：0到2³²-1，在零点重合）：Session 应用场景中，它根据 session_id 的哈希值，按顺时针方向就近安排一个大于其值的结点进行存储。

实现这个回路的算法多种多样，比如一致性哈希。

我的哈希环实现（ hashringUtils.js：

var INT_MAX = 0x7FFFFFFF;

var node = function (nodeOpts) {
    nodeOpts = nodeOpts || {};
    if (nodeOpts.address) this.address = nodeOpts.address;
    if (nodeOpts.port) this.port = nodeOpts.port;
};
node.prototype.toString = function () {
    return this.address + ':' + this.port;
};

var ring = function (maxNodes, realNodes) {
    this.nodes = [];
    this.maxNodes = maxNodes;
    this.realNodes = realNodes;

    this.generate();
};
ring.compareNode = function (nodeA, nodeB) {
    return nodeA.address === nodeB.address &&
        nodeA.port === nodeB.port;
};
ring.hashCode = function (str) {
    if (typeof str !== 'string')
        str = str.toString();
    var hash = 1315423911, i, ch;
    for (i = str.length - 1; i >= 0; i--) {
        ch = str.charCodeAt(i);
        hash ^= ((hash << 5) + ch + (hash >> 2));
    }
    return  (hash & INT_MAX);
};
ring.prototype.generate = function () {
    var realLength = this.realNodes.length;
    this.nodes.splice(0); //clear all

    for (var i = 0; i < this.maxNodes; i++) {
        var realIndex = Math.floor(i / this.maxNodes * realLength);
        var realNode = this.realNodes[realIndex];
        var label = realNode.address + '#' + 
            (i - realIndex * Math.floor(this.maxNodes / realLength));
        var virtualNode = ring.hashCode(label);

        this.nodes.push({
            'hash': virtualNode,
            'label': label,
            'node': realNode
        });
    }

    this.nodes.sort(function(a, b){
        return a.hash - b.hash;
    });
};
ring.prototype.select = function (key) {
    if (typeof key === 'string')
        key = ring.hashCode(key);
    for(var i = 0, len = this.nodes.length; i<len; i++){
        var virtualNode = this.nodes[i];
        if(key <= virtualNode.hash) {
            console.log(virtualNode.label);
            return virtualNode.node;
        }
    }
    console.log(this.nodes[0].label);
    return this.nodes[0].node;
};
ring.prototype.add = function (node) {
    this.realNodes.push(node);

    this.generate();
};
ring.prototype.remove = function (node) {
    var realLength = this.realNodes.length;
    var idx = 0;
    for (var i = realLength; i--;) {
        var realNode = this.realNodes[i];
        if (ring.compareNode(realNode, node)) {
            this.realNodes.splice(i, 1);
            idx = i;
            break;
        }
    }
    this.generate();
};
ring.prototype.toString = function () {
    return JSON.stringify(this.nodes);
};

module.exports.node = node;
module.exports.ring = ring;

var INT_MAX = 0x7FFFFFFF;

var node = function (nodeOpts) {

nodeOpts = nodeOpts || {};

if (nodeOpts.address) this.address = nodeOpts.address;

if (nodeOpts.port) this.port = nodeOpts.port;

};

node.prototype.toString = function () {

return this.address + ':' + this.port;

};

var ring = function (maxNodes, realNodes) {

this.nodes = [];

this.maxNodes = maxNodes;

this.realNodes = realNodes;

this.generate();

};

ring.compareNode = function (nodeA, nodeB) {

return nodeA.address === nodeB.address &&

nodeA.port === nodeB.port;

};

ring.hashCode = function (str) {

if (typeof str !== 'string')

str = str.toString();

var hash = 1315423911, i, ch;

for (i = str.length - 1; i >= 0; i--) {

ch = str.charCodeAt(i);

hash ^= ((hash << 5) + ch + (hash >> 2));

}

return (hash & INT_MAX);

};

ring.prototype.generate = function () {

var realLength = this.realNodes.length;

this.nodes.splice(0); //clear all

for (var i = 0; i < this.maxNodes; i++) {

var realIndex = Math.floor(i / this.maxNodes * realLength);

var realNode = this.realNodes[realIndex];

var label = realNode.address + '#' +

(i - realIndex * Math.floor(this.maxNodes / realLength));

var virtualNode = ring.hashCode(label);

this.nodes.push({

'hash': virtualNode,

'label': label,

'node': realNode

});

}

this.nodes.sort(function(a, b){

return a.hash - b.hash;

});

};

ring.prototype.select = function (key) {

if (typeof key === 'string')

key = ring.hashCode(key);

for(var i = 0, len = this.nodes.length; i<len; i++){

var virtualNode = this.nodes[i];

if(key <= virtualNode.hash) {

console.log(virtualNode.label);

return virtualNode.node;

}

console.log(this.nodes[0].label);

return this.nodes[0].node;

};

ring.prototype.add = function (node) {

this.realNodes.push(node);

this.generate();

};

ring.prototype.remove = function (node) {

var realLength = this.realNodes.length;

var idx = 0;

for (var i = realLength; i--;) {

var realNode = this.realNodes[i];

if (ring.compareNode(realNode, node)) {

this.realNodes.splice(i, 1);

idx = i;

break;

}

this.generate();

};

ring.prototype.toString = function () {

return JSON.stringify(this.nodes);

};

module.exports.node = node;

module.exports.ring = ring;

配置

配置信息是需要根据环境而变化的，某些情况下它又是不能公开的（比如Session_id 加密用的私钥），所以需要一个类似的配置文件（ config.cfg：

{
    "session_key": "session_id",
    "SECRET": "myapp_moyerock",
    "nodes":
    [
       {"address": "127.0.0.1", "port": "6379"}
    ]
}

{

"session_key": "session_id",

"SECRET": "myapp_moyerock",

"nodes":

[

{"address": "127.0.0.1", "port": "6379"}

]

}

在Node 中序列化/反序列化JSON 是件令人愉悦的事，写个配置读取器也相当容易（configUtils.js：

var fs = require('fs');
var path = require('path');

var cfgFileName = 'config.cfg';
var cache = {};

module.exports.getConfigs = function () {
    if (!cache[cfgFileName]) {
        if (!process.env.cloudDriveConfig) {
            process.env.cloudDriveConfig = path.join(process.cwd(), cfgFileName);
        }
        if (fs.existsSync(process.env.cloudDriveConfig)) {
            var contents = fs.readFileSync(
                process.env.cloudDriveConfig, {encoding: 'utf-8'});
            cache[cfgFileName] = JSON.parse(contents);
        }
    }
    return cache[cfgFileName];
};

var fs = require('fs');

var path = require('path');

var cfgFileName = 'config.cfg';

var cache = {};

module.exports.getConfigs = function () {

if (!cache[cfgFileName]) {

if (!process.env.cloudDriveConfig) {

process.env.cloudDriveConfig = path.join(process.cwd(), cfgFileName);

}

if (fs.existsSync(process.env.cloudDriveConfig)) {

var contents = fs.readFileSync(

process.env.cloudDriveConfig, {encoding: 'utf-8'});

cache[cfgFileName] = JSON.parse(contents);

}

return cache[cfgFileName];

};

分布式Redis 操作

有了上述的基础设施，实现一个分布式 Redis 分配器就变得相当容易了。为演示，这里只简单提供几个操作 Hashes 的方法（redisMatrix.js：

var hashringUtils = require('../hashringUtils'),
    ring = hashringUtils.ring,
    node = hashringUtils.node;

var config = require('../configUtils');

var nodes = config.getConfigs().nodes;
for (var i = 0, len = nodes.length; i < len; i++) {
    var n = nodes[i];
    nodes[i] = new node({address: n.address, port: n.port});
}

var hashingRing = new ring(32, nodes);

module.exports = hashingRing;
module.exports.openClient = function (id) {
    var node = hashingRing.select(id);
    var client = require('redis').createClient(node.port, node.address);
    client.on('error', function (err) {
        console.log('error: ' + err);
    });
    return client;
};
module.exports.hgetRedis = function (id, key, callback) {
    var client = hashingRing.openClient(id);
    client.hget(id, key, function (err, reply) {
        if (err)
            console.log('hget error:' + err);
        client.quit();
        callback.call(null, err, reply);
    });
};
module.exports.hsetRedis = function (id, key, val, callback) {
    var client = hashingRing.openClient(id);
    client.hset(id, key, val, function (err, reply) {
        if (err)
            console.log('hset ' + key + 'error: ' + err);
        console.log('hset [' + key + ']:[' + val + '] reply is:' + reply);
        client.quit();

        callback.call(null, err, reply);
    });
};
module.exports.hdelRedis = function(id, key, callback){
    var client = hashingRing.openClient(id);
    client.hdel(id, key, function (err, reply) {
        if (err)
            console.log('hdel error:' + err);
        client.quit();
        callback.call(null, err, reply);
    });
};

var hashringUtils = require('../hashringUtils'),

ring = hashringUtils.ring,

node = hashringUtils.node;

var config = require('../configUtils');

var nodes = config.getConfigs().nodes;

for (var i = 0, len = nodes.length; i < len; i++) {

var n = nodes[i];

nodes[i] = new node({address: n.address, port: n.port});

}

var hashingRing = new ring(32, nodes);

module.exports = hashingRing;

module.exports.openClient = function (id) {

var node = hashingRing.select(id);

var client = require('redis').createClient(node.port, node.address);

client.on('error', function (err) {

console.log('error: ' + err);

});

return client;

};

module.exports.hgetRedis = function (id, key, callback) {

var client = hashingRing.openClient(id);

client.hget(id, key, function (err, reply) {

if (err)

console.log('hget error:' + err);

client.quit();

callback.call(null, err, reply);

});

};

module.exports.hsetRedis = function (id, key, val, callback) {

var client = hashingRing.openClient(id);

client.hset(id, key, val, function (err, reply) {

if (err)

console.log('hset ' + key + 'error: ' + err);

console.log('hset [' + key + ']:[' + val + '] reply is:' + reply);

client.quit();

callback.call(null, err, reply);

});

};

module.exports.hdelRedis = function(id, key, callback){

var client = hashingRing.openClient(id);

client.hdel(id, key, function (err, reply) {

if (err)

console.log('hdel error:' + err);

client.quit();

callback.call(null, err, reply);

});

};

分布式Session操作

session_id 的事务和分布式的Redis都有了，分布式的 Session 操作呼之欲出（sessionUtils.js：

var crypto = require('crypto');
var config = require('../config/configUtils');

var EXPIRES = 20 * 60 * 1000;
var redisMatrix = require('./redisMatrix');

var sign = function (val, secret) {
    return val + '.' + crypto
        .createHmac('sha1', secret)
        .update(val)
        .digest('base64')
        .replace(/[\/\+=]/g, '');
};
var generate = function () {
    var session = {};
    session.id = (new Date()).getTime() + Math.random().toString();
    session.id = sign(session.id, config.getConfigs().SECRET);
    session.expire = (new Date()).getTime() + EXPIRES;
    return session;
};
var serialize = function (name, val, opt) {
    var pairs = [name + '=' + encodeURIComponent(val)];
    opt = opt || {};

    if (opt.maxAge) pairs.push('Max-Age=' + opt.maxAge);
    if (opt.domain) pairs.push('Domain=' + opt.domain);
    if (opt.path) pairs.push('Path=' + opt.path);
    if (opt.expires) pairs.push('Expires=' + opt.expires);
    if (opt.httpOnly) pairs.push('HttpOnly');
    if (opt.secure) pairs.push('Secure');

    return pairs.join('; ');
};

var setHeader = function (req, res, next) {
    var writeHead = res.writeHead;
    res.writeHead = function () {
        var cookies = res.getHeader('Set-Cookie');
        cookies = cookies || [];
        console.log('writeHead, cookies: ' + cookies);
        var session = serialize(config.getConfigs().session_key, req.session.id);
        console.log('writeHead, session: ' + session);
        cookies = Array.isArray(cookies) ? cookies.concat(session) : [cookies, session];
        res.setHeader('Set-Cookie', cookies);
        return writeHead.apply(this, arguments);
    };

    next();
};

exports = module.exports = function session() {
    return function session(req, res, next) {
        var id = req.cookies[config.getConfigs().session_key];
        if (!id) {
            req.session = generate();
            id = req.session.id;
            var json = JSON.stringify(req.session);
            redisMatrix.hsetRedis(id, 'session', json,
                function () {
                    setHeader(req, res, next);
                });
        } else {
            console.log('session_id found: ' + id);
            redisMatrix.hgetRedis(id, 'session', function (err, reply) {
                var needChange = true;
                console.log('reply: ' + reply);
                if (reply) {
                    var session = JSON.parse(reply);
                    if (session.expire > (new Date()).getTime()) {
                        session.expire = (new Date()).getTime() + EXPIRES;
                        req.session = session;
                        needChange = false;
                        var json = JSON.stringify(req.session);
                        redisMatrix.hsetRedis(id, 'session', json,
                            function () {
                                setHeader(req, res, next);
                            });
                    }
                }

                if (needChange) {
                    req.session = generate();
                    id = req.session.id; // id need change
                    var json = JSON.stringify(req.session);
                    redisMatrix.hsetRedis(id, 'session', json,
                        function (err, reply) {
                            setHeader(req, res, next);
                        });
                }
            });
        }
    };
};

module.exports.set = function (req, name, val) {
    var id = req.cookies[config.getConfigs().session_key];
    if (id) {
        redisMatrix.hsetRedis(id, name, val, function (err, reply) {

        });
    }
};
/*
 get session by name
 @req request object
 @name session name
 @callback your callback
 */
module.exports.get = function (req, name, callback) {
    var id = req.cookies[config.getConfigs().session_key];
    if (id) {
        redisMatrix.hgetRedis(id, name, function (err, reply) {
            callback(err, reply);
        });
    } else {
        callback();
    }
};

module.exports.getById = function (id, name, callback) {
    if (id) {
        redisMatrix.hgetRedis(id, name, function (err, reply) {
            callback(err, reply);
        });
    } else {
        callback();
    }
};
module.exports.deleteById = function (id, name, callback) {
    if (id) {
        redisMatrix.hdelRedis(id, name, function (err, reply) {
            callback(err, reply);
        });
    } else {
        callback();
    }
};

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var crypto = require('crypto');

var config = require('../config/configUtils');

var EXPIRES = 20 * 60 * 1000;

var redisMatrix = require('./redisMatrix');

var sign = function (val, secret) {

return val + '.' + crypto

.createHmac('sha1', secret)

.update(val)

.digest('base64')

.replace(/[\/\+=]/g, '');

};

var generate = function () {

var session = {};

session.id = (new Date()).getTime() + Math.random().toString();

session.id = sign(session.id, config.getConfigs().SECRET);

session.expire = (new Date()).getTime() + EXPIRES;

return session;

};

var serialize = function (name, val, opt) {

var pairs = [name + '=' + encodeURIComponent(val)];

opt = opt || {};

if (opt.maxAge) pairs.push('Max-Age=' + opt.maxAge);

if (opt.domain) pairs.push('Domain=' + opt.domain);

if (opt.path) pairs.push('Path=' + opt.path);

if (opt.expires) pairs.push('Expires=' + opt.expires);

if (opt.httpOnly) pairs.push('HttpOnly');

if (opt.secure) pairs.push('Secure');

return pairs.join('; ');

};

var setHeader = function (req, res, next) {

var writeHead = res.writeHead;

res.writeHead = function () {

var cookies = res.getHeader('Set-Cookie');

cookies = cookies || [];

console.log('writeHead, cookies: ' + cookies);

var session = serialize(config.getConfigs().session_key, req.session.id);

console.log('writeHead, session: ' + session);

cookies = Array.isArray(cookies) ? cookies.concat(session) : [cookies, session];

res.setHeader('Set-Cookie', cookies);

return writeHead.apply(this, arguments);

};

next();

};

exports = module.exports = function session() {

return function session(req, res, next) {

var id = req.cookies[config.getConfigs().session_key];

if (!id) {

req.session = generate();

id = req.session.id;

var json = JSON.stringify(req.session);

redisMatrix.hsetRedis(id, 'session', json,

function () {

setHeader(req, res, next);

});

} else {

console.log('session_id found: ' + id);

redisMatrix.hgetRedis(id, 'session', function (err, reply) {

var needChange = true;

console.log('reply: ' + reply);

if (reply) {

var session = JSON.parse(reply);

if (session.expire > (new Date()).getTime()) {

session.expire = (new Date()).getTime() + EXPIRES;

req.session = session;

needChange = false;

var json = JSON.stringify(req.session);

redisMatrix.hsetRedis(id, 'session', json,

function () {

setHeader(req, res, next);

});

}

if (needChange) {

req.session = generate();

id = req.session.id; // id need change

var json = JSON.stringify(req.session);

redisMatrix.hsetRedis(id, 'session', json,

function (err, reply) {

setHeader(req, res, next);

});

}

});

}

};

module.exports.set = function (req, name, val) {

var id = req.cookies[config.getConfigs().session_key];

if (id) {

redisMatrix.hsetRedis(id, name, val, function (err, reply) {

});

}

};

get session by name

@req request object

@name session name

@callback your callback

module.exports.get = function (req, name, callback) {

var id = req.cookies[config.getConfigs().session_key];

if (id) {

redisMatrix.hgetRedis(id, name, function (err, reply) {

callback(err, reply);

});

} else {

callback();

}

};

module.exports.getById = function (id, name, callback) {

if (id) {

redisMatrix.hgetRedis(id, name, function (err, reply) {

callback(err, reply);

});

} else {

callback();

}

};

module.exports.deleteById = function (id, name, callback) {

if (id) {

redisMatrix.hdelRedis(id, name, function (err, reply) {

callback(err, reply);

});

} else {

callback();

}

};

结合 Express 应用

在 Express 中只需要简单的 use 就可以了（ app.js：

var session = require('../sessionUtils');
app.use(session());

1 2	var session = require('../sessionUtils'); app.use(session());

这个被引用的 session 模块暴露了一些操作 session 的方法，在需要时可以这样使用：

app.get('/user', function(req, res){
    var id = req.query.sid;
    session.getById(id, 'user', function(err, reply){
        if(reply){
               //Some thing TODO
        }
    });
    res.end('');
});

app.get('/user', function(req, res){

var id = req.query.sid;

session.getById(id, 'user', function(err, reply){

if(reply){

//Some thing TODO

}

});

res.end('');

});

小结

虽然本文提供的是基于 Express 的示例，但基于哈希算法和缓存设施的分布式思路，其实是放之四海而皆准的 🙂

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Mo Ye

A Conservative

Published

September 28, 2014

Mo Ye in Algorithm | September 28, 2014

Node + Redis 实现分布式Session方案

Session是什么？

Session 怎么工作？

分布式Session

Session_id

Hashing Ring

配置

分布式Redis 操作

分布式Session操作

结合 Express 应用

小结

Mo Ye

A Conservative

Published

September 28, 2014

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