AWS Lambda提前结束(没有任何显式返回或回调)

Question

我在使用一些node.js代码时遇到了一些问题,我将其放入AWS Lambda.我需要做几个异步调用,虽然第一个是我期望的行为,但lambda函数在第二个调用完成之前终止.

返回值为null,这让我认为lambda正在触及它的隐式回调,但是我认为它不应该这样做,而有一个尚未解决的承诺.

码:

exports.handle = async function(event, context) {
  var AWS = require("aws-sdk");

  AWS.config.update({
    region: "eu-west-1",
    endpoint: "dynamodb.eu-west-1.amazonaws.com"
  });

  var docClient = new AWS.DynamoDB.DocumentClient();
  console.log("Scanning Catalogue...");

  var params = {
    TableName : "Catalogue"
  };

  await docClient.scan(params).promise().then(function (data) {
    console.log("Scan succeeded.");
    data.Items.forEach(function (item) {
      //console.log(item.url);
      checkIfUpdateRequired(item);
    })
  })
}

async function checkIfUpdateRequired (catalogueItem) {
  var request = require("request-promise");
  console.log("Getting " + catalogueItem.url);

  await request(catalogueItem.url).then(function(response) {
    console.log(response.statusCode);
    console.log(response.headers['content-type']);
  });

}

日志输出:

START RequestId: 634a55b7-6258-11e8-9f18-6b300c3b5de1 Version: $LATEST
2018-05-28T09:20:44.425Z    634a55b7-6258-11e8-9f18-6b300c3b5de1    Scanning Catalogue...
2018-05-28T09:20:45.446Z    634a55b7-6258-11e8-9f18-6b300c3b5de1    Scan succeeded.
2018-05-28T09:20:47.967Z    634a55b7-6258-11e8-9f18-6b300c3b5de1    Getting https://raw.githubusercontent.com/BSData/wh40k/master/Aeldari%20-%20Craftworlds.cat
2018-05-28T09:20:48.028Z    634a55b7-6258-11e8-9f18-6b300c3b5de1    Getting https://raw.githubusercontent.com/BSData/wh40k/master/Imperium%20-%20Adeptus%20Custodes.cat
END RequestId: 634a55b7-6258-11e8-9f18-6b300c3b5de1
REPORT RequestId: 634a55b7-6258-11e8-9f18-6b300c3b5de1  Duration: 7882.68 ms    Billed Duration: 7900 ms    Memory Size: 128 MB Max Memory Used: 49 MB

所以日志告诉我调用checkIfUpdateRequired(),但lambda在完成promise之前结束(报告成功,结果值为null).我没有对处理程序进行任何手动返回或回调,这似乎是与lambda结束'早期'相关的问题的标准.

我的智慧结束了,任何人都可以提出任何建议吗？

Answer 1

你不是在等待承诺checkIfUpdateRequired完成；而是在等待。docClient.scan原始代码中的所有内容都是同步的。用于Promise.all等待所有承诺完成：

await docClient.scan(params).promise().then(function (data) {
  console.log("Scan succeeded.");
  return Promise.all(data.Items.map(checkIfUpdateRequired));
});

请注意，如果您使用的是await，那么如果您习惯使用它而不是.then. 例如，您可以重构为：

const data = await docClient.scan(params).promise();
return Promise.all(data.Items.map(checkIfUpdateRequired));

和

async function checkIfUpdateRequired (catalogueItem) {
  // actually, better to only require once, rather than on every function call
  const request = require("request-promise");
  console.log("Getting " + catalogueItem.url);
  const response = await request(catalogueItem.url)
  console.log(response.statusCode);
  console.log(response.headers['content-type']);
}