使用Express / Node.js和Angular处理取消的请求 [英] Handling cancelled request with Express/Node.js and Angular

问题描述

当客户端/浏览器取消挂起的HTTP请求时，Node Express继续处理请求。对于密集的请求，CPU仍然在忙于不必要的请求。

有没有办法要求Node.js / Express杀死/停止这些待处理的请求请求被取消？

由于AngularJS 1.5 HTTP请求很容易 $ cancelRequest（） $ $ http 的ngResource / service / $ resource =noreferrer $ c> / $ resource 对象。

当公开API方法时，可能会发生这种取消，完成或搜索字段：在字段中输入要自动完成或提前输入时，先前的请求可以被取消。

全局 server.timeout 不能解决问题：1）它是所有暴露的API方法的全局设置的先验2）取消的请求中正在进行的处理不会被终止。

解决方案

注入 req 对象与侦听器一起发送 .on（）。

收听关闭事件允许在客户端关闭连接时处理（请求由Angular取消，或者例如用户关闭查询选项卡） / p>

这里有两个简单的例子，如何使用关闭事件来停止请求处理。

示例1：可取消同步块

  var clientCancelledRequest ='clientCancelledRequest'; 
 
 function cancellableAPIMethodA（req，res，next）{
 var cancelRequest = false; 
 
 req.on（'close'，function（err）{
 cancelRequest = true; 
}）; 
 
 var superLargeArray = [/ * ... * /]; 
 
 try {
 // Long processing loop 
 superLargeArray.forEach（function（item）{
 if（cancelRequest）{
 throw {type：clientCancelledRequest }; 
} 
 / *处理项目* / 
}）; 
 
 //在客户端取消请求之前完成的作业，将结果发送给客户端
 res.send（/ * results * /）; 
} catch（e）{
 //重新抛出（或调用next（e））非取消异常
 if（e.type！== clientCancelledRequest）{
扔e 
} 
} 
 
 //在客户端取消请求之前完成的作业，将结果发送给客户
 res.send（/ * results * /）; 
} 
  

示例2：具有承诺的可取消异步块（类似于减少）

  function cancellableAPIMethodA（req，res，next）{
 var cancelRequest = false; 
 
 req.on（'close'，function（err）{
 cancelRequest = true; 
}）; 
 
 var superLargeArray = [/ * ... * /]; 
 
 var promise = Q.when（）; 
 superLargeArray.forEach（function（item）{
 promise = promise.then（function（）{
 if（cancelRequest）{
 throw {type：clientCancelledRequest}; 
} 
 / *工作项目* / 
}）; 
}）; 
 
 promise.then（function（）{
 //在客户端取消请求之前完成的作业，将结果发送给客户
 res.send（/ * results * /）; 
}）
 .catch（function（err）{
 //重新抛出（或调用next（err））对非取消异常
 if（err.type！= = clientCancelledRequest）{
 throw err; 
} 
}）
 .done（）; 
} 
  

When a pending HTTP request is cancelled by a client/browser it seems that Node with Express continues to process the request. For intensive requests, the CPU is still being kept busy with unnecessary requests.

Is there a way to ask Node.js/Express to kill/stop these pending requests that are requested to be cancelled?

It becomes particularly useful given that since AngularJS 1.5 HTTP request are easily cancellable by calling $cancelRequest() on $http/$resource objects.

Such cancellations could occur when exposing an API method providing results for auto-completion or search fields: when typing in the field to be autocompleted or type-aheaded, previous request(s) can be cancelled.

A global server.timeout does not solve the problem: 1) it is a priori a global setting for all exposed API methods 2) ongoing processing in the canceled request is not killed.

解决方案

Injected reqobject is shipped with listeners .on().

Listening to close event allows to handle when client close the connection (request cancelled by Angular or, e.g., user closed the querying tab).

Here are 2 simple examples how to use the closeevent to stop request processing.

Example 1: Cancellable synchronous block

var clientCancelledRequest = 'clientCancelledRequest';

function cancellableAPIMethodA(req, res, next) {
    var cancelRequest = false;

    req.on('close', function (err){
       cancelRequest = true;
    });

    var superLargeArray = [/* ... */];

    try {
        // Long processing loop
        superLargeArray.forEach(function (item) {
                if (cancelRequest) {
                    throw {type: clientCancelledRequest};
                }
                /* Work on item */
        });

        // Job done before client cancelled the request, send result to client
        res.send(/* results */);
    } catch (e) {
        // Re-throw (or call next(e)) on non-cancellation exception
        if (e.type !== clientCancelledRequest) {
            throw e;
        }
    }

    // Job done before client cancelled the request, send result to client
    res.send(/* results */);
}

Example 2: Cancellable asynchronous block with promises (analog to a reduce)

function cancellableAPIMethodA(req, res, next) {
    var cancelRequest = false;

    req.on('close', function (err){
       cancelRequest = true;
    });

    var superLargeArray = [/* ... */];

    var promise = Q.when();
    superLargeArray.forEach(function (item) {
            promise = promise.then(function() {
                if (cancelRequest) {
                    throw {type: clientCancelledRequest};
                } 
                /* Work on item */ 
            });
    });

    promise.then(function() {
        // Job done before client cancelled the request, send result to client
        res.send(/* results */);
    })
    .catch(function(err) {
        // Re-throw (or call next(err)) on non-cancellation exception
        if (err.type !== clientCancelledRequest) {
            throw err;
        }
    })
    .done();
}

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