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问将AWS Lambda函数转换为使用承诺？
EN

Stack Overflow用户

提问于 2016-11-06 01:22:13

回答 5查看 17.4K关注 0票数 8

我正在编写一个简单的HTTP 'ping‘函数，该函数正在使用AWS定期执行。它使用四个异步函数: http.get、S3.getObject、S3.putObject和nodemailer.sendMail。每个模块似乎都有一个稍微不同的回调模型。

在阅读了有关承诺的文章之后，我花了太多的时间试图将下面的代码转换为使用Q承诺，结果失败了。

对于我自己的教育，以及其他人的教育，我希望有人能帮我把这个转变成使用承诺(不一定是Q)：

'use strict';

var http = require('http');
var nodemailer = require('nodemailer');
var AWS = require('aws-sdk');
var s3 = new AWS.S3( { params: { Bucket: 'my-bucket' } } );

exports.handler = (event, context, callback) => {
  var lastStatus;

  var options = {
    host: event.server.host,
    port: event.server.port ? event.server.port : 80,
    path: event.server.path ? event.server.path : '',
    method: event.server.method ? event.server.method : 'HEAD',
    timeout: 5000
  };
  var transporter = nodemailer.createTransport({
    host: event.mail.host,
    port: event.mail.port ? event.mail.port : 587,
    auth: {
      user: event.mail.user,
      pass: event.mail.pass
    }
  });

  var d = new Date();
  var UTCstring = d.toUTCString();

  // email templates 
  var downMail = {
    from: event.mail.from,
    to: event.mail.to,
    subject: 'Lambda DOWN alert: SITE (' + event.server.host + ') is DOWN',
    text: 'LambdaAlert DOWN:\r\nSITE (' + event.server.host + ') is DOWN as at ' + UTCstring + '.'
  };
  var upMail = {
    from: event.mail.from,
    to: event.mail.to,
    subject: 'Lambda UP alert: SITE (' + event.server.host + ') is UP',
    text: 'LambdaAlert UP:\r\nSITE (' + event.server.host + ') is UP as at ' + UTCstring + '.'
  };

  // Run async chain to ensure that S3 calls execute in proper order
  s3.getObject( { Key: 'lastPingStatus' }, (err, data) => {
    // get last status from S3
    if (err) { lastStatus = "UP"; } else {
      lastStatus = data.Body.toString();
      console.log("Last observed status: " + lastStatus);
    }
    http_request(options, lastStatus);
  });

  function http_request(requestOptions, lastStatus) {
    var req = http.request(requestOptions, function(res) {
      if (res.statusCode == 200) {
        if (lastStatus == "DOWN") {
          console.log('Email up notice sending...');
          transporter.sendMail(upMail, function(error, info) {
            if (error) {
              console.log("ERROR: " + error);
              callback(null, "ERROR: " + error);
            } else {
              console.log('No further details available.');
              callback(null, 'Up message sent');
            }
          });
        }
        s3.putObject({ Key: 'lastPingStatus', Body: 'UP', ContentType: 'text/plain' }, (error, data) => { console.log("Saved last state as UP"); });
        callback(null, 'Website is OK.');
      }
    });
    req.on('error', function(e) {
      if (lastStatus == "UP") {
        console.log('Email down notice sending...');
        transporter.sendMail(downMail, function(error, info) {
          if (error) {
            console.log("ERROR: " + error);
            callback(null, "ERROR: " + error);
          } else {
            console.log('No further details available.');
            callback(null, 'Down message sent');
          }
        });
        s3.putObject({ Key: 'lastPingStatus', Body: 'DOWN', ContentType: 'text/plain' }, (error, data) => { console.log("Saved last state as DOWN"); });
        callback(null, 'Website is DOWN.');
      }
    });
    req.end();
  }
};

编辑：第一次尝试使用承诺编写：

'use strict';

var http = require('http');
var nodemailer = require('nodemailer');
var AWS = require('aws-sdk');
var s3 = new AWS.S3( { params: { Bucket: 'lambda-key-storage' } } );

exports.handler = (event, context, callback) => {
  var lastStatus;

  var options = {
    host: event.server.host,
    port: event.server.port ? event.server.port : 80,
    path: event.server.path ? event.server.path : '',
    method: event.server.method ? event.server.method : 'HEAD',
    timeout: 5000
  };
  var transporter = nodemailer.createTransport({
    host: event.mail.host,
    port: event.mail.port ? event.mail.port : 587,
    auth: {
      user: event.mail.user,
      pass: event.mail.pass
    }
  });

  var d = new Date();
  var UTCstring = d.toUTCString();

  // email templates 
  var downMail = {
    from: event.mail.from,
    to: event.mail.to,
    subject: 'Lambda DOWN alert: SITE (' + event.server.host + ') is DOWN',
    text: 'LambdaAlert DOWN:\r\nSITE (' + event.server.host + ') is DOWN as at ' + UTCstring + '.'
  };
  var upMail = {
    from: event.mail.from,
    to: event.mail.to,
    subject: 'Lambda UP alert: SITE (' + event.server.host + ') is UP',
    text: 'LambdaAlert UP:\r\nSITE (' + event.server.host + ') is UP as at ' + UTCstring + '.'
  };

  var myProm = new Promise(function(resolve, reject) {
    console.log("called 1");
    s3.getObject( { Key: 'lastPingStatus' }, (err, data) => {
      // get last status from S3
      if (err) { 
        resolve("UP"); 
      } else {
        resolve(data.Body.toString());
      }
    });
  })
  .then(function(lastStatus) {
    console.log("called 2");
    console.log("Last observed status: " + lastStatus);
    var req = http.request(options, function(res) {
      resolve(res.statusCode);
    });
    req.on('error', function(e) {
      reject(e);
    });
    req.end();
    return "??";
  })
  .then(function(statusCode) {
    console.log("called 3");
    if (statusCode == 200) {
      if (lastStatus == "DOWN") {
        console.log('Email up notice sending...');
        resolve("upTrigger");
      } else {
        resolve("upNoTrigger");
      }
      s3.putObject({ Key: 'lastPingStatus', Body: 'UP', ContentType: 'text/plain' }, (err, data) => { console.log("Saved last state as UP"); });
      callback(null, 'Website is OK.');
    }
  })
  .catch(function(err){
    console.log("called 3 - error");
    // Send mail notifying of error
    if (lastStatus == "UP") {
      console.log('Email down notice sending...');
      resolve("downTrigger");
      s3.putObject({ Key: 'lastPingStatus', Body: 'DOWN', ContentType: 'text/plain' }, (error, data) => { console.log("Saved last state as DOWN"); });
      callback(null, 'Website is DOWN.');
      return("downTrigger");
    } else {
      return "downNoTrigger";
    }
  })
  .then(function(trigger) {
    console.log("called 4");
    if (trigger == "upTrigger") {
      transporter.sendMail(upMail, (error, info) => {
        if (error) {
          console.log("ERROR: " + error);
          callback(null, "ERROR: " + error);
        } else {
          console.log('Up message sent.');
          callback(null, 'Up message sent');
        }
      });
    } else if (trigger == "downTrigger") {
      transporter.sendMail(downMail, (error, info) => {
        if (error) {
          console.log("ERROR: " + error);
          callback(null, "ERROR: " + error);
        } else {
          console.log('Down message sent.');
          callback(null, 'Down message sent');
        }
      });
    }
    console.log("Outcome of ping was: ", trigger);
  });
};

这不太管用。结果日志如下：

called 1
called 2
Last observed status: UP
called 3
called 4
Outcome of ping was:  undefined
ReferenceError: resolve is not defined

promise

aws-lambda

node.js

amazon-s3

回答 5

Stack Overflow用户

发布于 2016-11-06 04:11:42

将典型的异步函数转换为承诺是非常直接的。我宁愿尝试演示如何转换它，也不愿编写代码，因为您没有从中学到任何东西。

通常，对于节点，您将得到类似于以下内容的内容：

  doSomethingAsync(callback);

    function doSomethingAsync(callback){
        var err, result;
        // Do some work
        ... 

        callback(err, result);
    }
    function callback(err, result){
        if(err){
            // Handle error
        } else{
            // Success so do something with result
        }
    }

包装异步函数的承诺通常如下所示：

var myProm = new Promise(function(resolve, reject){
     doSomethingAsync(function(err, result){       
        if(err){
            reject(err);
        } else{
            resolve(result)
        } 
     });
})
.then(function(result){
  // Success so do something with result
  console.log("Success:", result)
})
.catch(function(err){
 // Handle error
  console.log("Error: ", err);
})
.then(function(result){
   // Where's my result? - result == undefined as we didn't return anything up the chain
  console.log("I always execute but result is gone", result)
})

要将结果向下传递给我们的“始终那么”方法，我们需要返回一个承诺或一个值：

var myProm = new Promise(function(resolve, reject){
         doSomethingAsync(function(err, result){       
            if(err){
                reject(err);
            } else{
                resolve(result)
            } 
         });
    })
    .then(function(result){
      // Success so do something with result
      console.log("Success:", result)
      return result;
    })
    .catch(function(err){
     // Handle error
      console.log("Error: ", err);
      return err;
    })
    .then(function(result){
      // The err/result now gets passed down the chain :)
      console.log("Oh there it is", result)
    })

我认为使用上述模式应该能够满足代码示例中大多数异步方法和事件的需要，如果有任何特定的方法和事件给您带来麻烦，请给出一个注释，我将尝试介绍这些具体的示例。

这里有一个尝试，把它转换成承诺--我很累了，所以为任何混乱或错误道歉--还有很多清理工作可以做。

本质上，我所做的就是尝试将代码分解为任务，并将这些任务包装成一个承诺。这样，我们就可以根据需要解决/拒绝并锁定它们。

'use strict';

var http = require('http');
var nodemailer = require('nodemailer');
var AWS = require('aws-sdk');
var s3 = new AWS.S3( { params: { Bucket: 'my-bucket' } } );

exports.handler = function (event, context, callback) {
    var lastStatus;

    var options = {
        host: event.server.host,
        port: event.server.port ? event.server.port : 80,
        path: event.server.path ? event.server.path : '',
        method: event.server.method ? event.server.method : 'HEAD',
        timeout: 5000
    };
    var transporter = nodemailer.createTransport({
        host: event.mail.host,
        port: event.mail.port ? event.mail.port : 587,
        auth: {
            user: event.mail.user,
            pass: event.mail.pass
        }
    });

    var d = new Date();
    var UTCstring = d.toUTCString();

    // email templates
    var downMail = {
        from: event.mail.from,
        to: event.mail.to,
        subject: 'Lambda DOWN alert: SITE (' + event.server.host + ') is DOWN',
        text: 'LambdaAlert DOWN:\r\nSITE (' + event.server.host + ') is DOWN as at ' + UTCstring + '.'
    };
    var upMail = {
        from: event.mail.from,
        to: event.mail.to,
        subject: 'Lambda UP alert: SITE (' + event.server.host + ') is UP',
        text: 'LambdaAlert UP:\r\nSITE (' + event.server.host + ') is UP as at ' + UTCstring + '.'
    };

    // Run async chain to ensure that S3 calls execute in proper order

    function getLastPingStatus(){
        return new Promise(function(resolve, reject){
            s3.getObject( { Key: 'lastPingStatus' }, function(err, data) {
                // get last status from S3
                if (err) {
                    lastStatus = "UP";
                    reject(lastStatus)
                } else {
                    lastStatus = data.Body.toString();
                    resolve(lastStatus);
                    console.log("Last observed status: " + lastStatus);
                }
            });
        })
    }
    getLastPingStatus()
        .then(httpRequest)
        .catch(httpRequest); // Otherwise a reject will throw an error

    function sendMail(mail, status){ // status = "up" or "down" -
        return new Promise(function(resolve, reject){
            transporter.sendMail(mail, function(error, info) {
                if (error) {
                    console.log("ERROR: " + error);
                    reject(null, "ERROR: " + error);
                } else {
                    console.log('No further details available.');
                    resolve(null, status + ' message sent');
                }
            });
        });
    }

    function saveStatus(up) {
        return new Promise(function (resolve, reject) {
            var saveOptions,
                message;
            // I didn't bother refactoring these as promises at they do the same thing regardless of outcome
            if(up){
                saveOptions = [{ Key: 'lastPingStatus', Body: 'UP', ContentType: 'text/plain' }, function(error, data) { console.log("Saved last state as UP"); }];
                message = 'Website is OK.';
            } else{
                saveOptions = [{ Key: 'lastPingStatus', Body: 'DOWN', ContentType: 'text/plain' }, function(error, data)  { console.log("Saved last state as DOWN"); }];
                message = 'Website is DOWN.';
            }
            s3.putObject.apply(this, saveOptions);
            callback(null, message);
        });
    }

    function httpRequest(lastStatus) {
        var requestOptions = options;
        return new Promise (function (resolve, reject){
            var req = http.request(requestOptions, function(res) {
                if (res.statusCode == 200) {
                    if (lastStatus == "DOWN") {
                        console.log('Email up notice sending...');
                        sendMail(upMail, "Up")
                            .then(resolve, reject) 
                            .then(saveStatus(true))
                            .then(callback)
                    }
                }
            });
            req.on('error', function(e) {
                if (lastStatus == "UP") {
                    console.log('Email down notice sending...');
                    sendmail(downMail, "Down")
                        .then(resolve, reject)
                        .then(saveStatus(false))
                        .then(callback)
                }
            });
            req.end();

        });

    }
};

票数 11

Stack Overflow用户

发布于 2018-04-27 06:15:25

AWS支持所有服务的本机承诺。有些需要额外的参数才能正确返回，比如Lambda.invoke()。

从本质上说

s3.putObject({ Key: 'key', Bucket: 'bucket' }).promise()
    .then(data => {
        // this is the same as the data callback parameter
    })
    .catch(error => {
        // handle your error
    })

或者，您可以使用async/await

const file = await s3.getObject(params).promise()
// do things with the result

要快速访问实际文件(而不是元数据)：

const file = JSON.parse(await s3.getObject(params).promise().then(res => res.Body));

https://docs.aws.amazon.com/sdk-for-javascript/v2/developer-guide/using-promises.html

票数 7

Stack Overflow用户

发布于 2016-11-06 12:57:56

为了"promisify“回调函数，imho，最简单、更简洁的方法是使用蓝鸟。您只是不想为了简化代码而编写胶水代码，这是适得其反的(而且容易出错)。

来自文档：

var Promise = require("bluebird");
var readFile = Promise.promisify(require("fs").readFile);

readFile("myfile.js", "utf8").then(function(contents) {
    return eval(contents);
}).then(function(result) {
    console.log("The result of evaluating myfile.js", result);
}).catch(SyntaxError, function(e) {
    console.log("File had syntax error", e);
//Catch any other error
}).catch(function(e) {
    console.log("Error reading file", e);
});

票数 5

页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持

原文链接：

https://stackoverflow.com/questions/40445087

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