如何重复请求,直到一个成功而没有在节点中阻塞？

Question

我有一个带参数和回调的函数.它应该向远程API发出请求并根据参数获取一些信息.当它获得信息时,它需要将其发送到回调.现在,远程API有时无法提供.我需要我的功能继续尝试,直到它设法做到这一点然后用正确的数据调用回调.

目前,我在函数内部有以下代码,但我认为像while(!done); 是不正确的节点代码.

var history = {};
while (true) {
    var done = false;
    var retry = true;
    var req = https.request(options, function(res) {
        var acc = "";
        res.on("data", function(msg) {
            acc += msg.toString("utf-8");
        });
        res.on("end", function() {
            done = true;
            history = JSON.parse(acc);
            if (history.success) {
                retry = false;
            }
        });
    });
    req.end();
    while (!done);
    if (!retry) break;
}
callback(history);

我该怎么做正确的方法？

Answer 1

没有必要重新发明轮子......在这种情况下,您可以使用流行的异步实用程序库,"重试"方法.

// try calling apiMethod 3 times
async.retry(3, apiMethod, function(err, result) {
    // do something with the result
});

// try calling apiMethod 3 times, waiting 200 ms between each retry
async.retry({times: 3, interval: 200}, apiMethod, function(err, result) {
    // do something with the result
});

async GitHub页面

async.retry docs

Answer 2

绝对不是要走的路 - 而(完成); 将进入一个硬循环并占用你所有的CPU.

相反,你可以做这样的事情(未经测试,你可能想要实现某种退避):

function tryUntilSuccess(options, callback) {
    var req = https.request(options, function(res) {
        var acc = "";
        res.on("data", function(msg) {
            acc += msg.toString("utf-8");
        });
        res.on("end", function() {
            var history = JSON.parse(acc);  //<== Protect this if you may not get JSON back
            if (history.success) {
                callback(null, history);
            } else {
                tryUntilSuccess(options, callback);
            }
        });
    });
    req.end();

    req.on('error', function(e) {
        // Decide what to do here
        // if error is recoverable
        //     tryUntilSuccess(options, callback);
        // else
        //     callback(e);
    });
}

// Use the standard callback pattern of err in first param, success in second
tryUntilSuccess(options, function(err, resp) {
    // Your code here...
});

Answer 3

我发现Dmitry使用异步实用程序库的答案非常有用,也是最好的答案.

这个答案将他的例子扩展到定义apiMethod函数的工作版本并向其传递一个参数.我打算将代码添加为注释,但单独的答案更清晰.

const async = require('async');

const apiMethod = function(uri, callback) {
  try {
    // Call your api here (or whatever thing you want to do) and assign to result.
    const result = ...
    callback(null, result);
  } catch (err) {
    callback(err);
  }
};

const uri = 'http://www.test.com/api';

async.retry(
    { times: 5, interval: 200 },
    function (callback) { return apiMethod(uri, callback) },
    function(err, result) {
      if (err) {
        throw err; // Error still thrown after retrying N times, so rethrow.
      }
  });

重试文档:https://caolan.github.io/async/docs.html#retry

注意,在任务中调用apiMethod(uri,callback)的替代方法是使用async.apply:

async.retry(
        {times: 5, interval: 200},
        async.apply(task, dir),
        function(err, result) {
          if (err) {
            throw err; // Error still thrown after retrying N times, so rethrow.
          }
      });

我希望这为某人提供了一个很好的复制/粘贴锅炉板解决方案.

Answer 4

这是你想要做的吗？

var history = {};

function sendRequest(options, callback) {
    var req = https.request(options, function (res) {
        var acc = "";
        res.on("data", function (msg) {
            acc += msg.toString("utf-8");
        });
        res.on("end", function () {
            history = JSON.parse(acc);
            if (history.success) {
                callback(history);
            }
            else {
                sendRequest(options, callback);
            }
        });
    });
    req.end();
}

sendRequest(options, callback);