javascript - Node/Express 路由不等待 Redis 服务器回调

Question

需要对下面的代码进行哪些具体更改，以便在对 Redis 客户端进行任何打开调用之前不发送 res.json(...) 命令.somecommand(..) 返回了吗？

下面的代码抛出与 client.hmset(uname, { ... } 试图在 res.json(...)< 之后设置响应 header 相关的错误 被调用。当我将 return res.json() 命令移动到 client.exists(uname, function(err, reply) { ... } 条件 block ，而不是它们在 block 内的当前位置，anonymous token 值被发送到客户端应用程序，而不是生成的 token value，表示Redis服务器的回调没有返回。

如何更改下面的代码，以便在返回 Redis 服务器回调之前，res.json( ... ) 命令无法运行？理想情况下，如果 Redis 服务器回调花费的时间太长，将有一些条件在发送错误消息之前等待一定时间。

通过在文件顶部添加以下两行，将 Redis 添加到包含以下所有代码的 routes.js 文件中:

var redis = require('redis');
var client = redis.createClient();

下面是在代码中对Redis服务器的各种调用:

client.exists(uname, function(err, reply) { ... }
client.hgetall(uname, function(err, object) { ... }
client.hmset(uname, { ... }
client.expire(uname, 10);

Node.js/Express.js API 路由的完整代码为:

app.get('/user**', function(req, res) {
    console.log("You Hit The User Route TOP");
    request({
        method: 'GET',
        url: authServer + '/uaa/user', 
        json: true, 
        auth: {
            user: null,
            password: null,
            sendImmediately: true,
            bearer: bearerToken 
        }
    }, function (error, response, body) {
        if(error){
          console.log('ERROR with user request.');
          return res.sendStatus(500);  
        }
        else {
            var uname = '';var jwtUser = 'empty';var jwtJSON = { "token" : "anonymous" }
            console.log(response.statusCode);
            if(body['name']){ 
                uname = body['name'];console.log('uname is: ');console.log(uname);
                if(uname.length > 0) {
                    scopesLocal = body['oauth2Request'].scope.toString();
                    client.exists(uname, function(err, reply) {//Check to see if a Redis key for the user already exists
                        if (reply === 1) {//a redis key DOES exist
                            console.log('\"'+uname+'\" exists');
                            client.hgetall(uname, function(err, object) {//retrieve all the values in the hash/object that we just set
                            if(object) {
                                if(object["jwt"]) { 
                                    console.log('object[\"jwt\"] is: ');console.log(object["jwt"]); 
                                    jwtJSON = { "token" : object["jwt"] };
                                    console.log('jwtJSON is: ');console.log(jwtJSON);
                                    return res.json(jwtJSON);
                                }
                            }
                        });
                        } else {//a redis key DOES NOT exist
                            console.log('\"'+uname+'\" doesn\'t exist');
                            jwtUser = generateJwt(uname, authoritiesLocal);
                            client.hmset(uname, {//store a hash/object
                                'AccessToken': body['details'].tokenValue,
                                'TokenType': body['details'].tokenType,
                                'Authenticated': body['authenticated'],
                                'Principal': body['principal'],
                                'Scopes': scopesLocal.toString(), 
                                'Authorities' : authoritiesLocal,
                                'jwt' : jwtUser
                            });
                            jwtJSON = { "token" : jwtUser };console.log('jwtJSON is: ');console.log(jwtJSON);
                            return res.json(jwtJSON);
                        }
                        client.expire(uname, 10);//set the key to expire in 10 seconds.  use this to manage session length
                    });//end of Redis conditional block
                    console.log('jwtJSON is: ');console.log(jwtJSON);
                } else { console.log('uname is empty!'); }
                return res.json(jwtJSON);
            }
        };
    });
    console.log("You Hit The User Route BOTTOM");
});

nodemon 终端中的错误信息是:

_http_outgoing.js:346
    throw new Error('Can\'t set headers after they are sent.');
    ^

Error: Can't set headers after they are sent.
    at ServerResponse.OutgoingMessage.setHeader (_http_outgoing.js:346:11)
    at ServerResponse.header (/home/user/nodejs_apps/oauth_seed_app/node_modules/express/lib/response.js:719:10)
    at ServerResponse.json (/home/user/nodejs_apps/oauth_seed_app/node_modules/express/lib/response.js:247:10)
    at Command.callback (/home/user/nodejs_apps/oauth_seed_app/app/routes.js:112:44)
    at normal_reply (/home/user/nodejs_apps/oauth_seed_app/node_modules/redis/index.js:714:21)
    at RedisClient.return_reply (/home/user/nodejs_apps/oauth_seed_app/node_modules/redis/index.js:816:9)
    at JavascriptRedisParser.Parser.returnReply (/home/user/nodejs_apps/oauth_seed_app/node_modules/redis/index.js:188:18)
    at JavascriptRedisParser.execute (/home/user/nodejs_apps/oauth_seed_app/node_modules/redis-parser/lib/parser.js:413:12)
    at Socket.<anonymous> (/home/user/nodejs_apps/oauth_seed_app/node_modules/redis/index.js:267:27)
    at emitOne (events.js:90:13)
    at Socket.emit (events.js:182:7)
    at readableAddChunk (_stream_readable.js:153:18)
    at Socket.Readable.push (_stream_readable.js:111:10)
    at TCP.onread (net.js:534:20)

我读了this posting关于具体的错误信息。我读了this other posting关于如何等待回调。我还读了this posting关于 Redis 对 Node.js 的回调但是我看不到如何将其他帖子的答案应用于上面代码中的 Redis 回调问题。

Answer 1

问题是 OP 中的 return res.json(jwtJSON); 命令没有被分离到离散的 if...else block 中。

解决方法是:

if(something) {
    //populate jwtJSON with a real JWT
    return res.json(jwtJSON);
} else {
    return res.json(jwtJSON);//this leaves the anonymous value
}  

对上面代码中的每个嵌套条件进行这种分离就解决了这个问题。