挂起等待 s3.listObjects

Question

我有一个事件会触发 lambda 代码，该代码会尝试列出一个存储桶中的所有对象，然后将它们复制到另一个存储桶。

通过事件调用处理程序的代码

const cfnHandlerWrapper = async (event, handler) => {
    let resultPromise;
    try {
        handler(event).then(function() {
            console.log(`Successfully copied over all artifacts`);
            resultPromise = sendSuccess(event);
        }).catch(function(error) {
            console.log(`Failed copying over all artifacts: ${error}`);
            throw error;
        });
    } catch (e) {
        console.log('ERROR RUNNING HANDLER:');
        console.log(e);
        resultPromise = sendFailure(e.message || 'Something went wrong', event);
    }
    return resultPromise;
};

处理复制的代码

const copyHandler = async (event) => {
    console.log('Running Agent artifacts copy handler');

    const {RequestType, ResourceProperties} = event;
    const {DestBucket, SrcBucket, AdditionalArtifactsPath} = ResourceProperties;

    if (RequestType === 'Create' || RequestType === 'Update') {
        const srcLocation = [SrcBucket, AdditionalArtifactsPath].join('/');
        const batsAdditionalArtifactsParams = {
            Bucket: SrcBucket,
            Delimiter: '',
            Prefix: `${AdditionalArtifactsPath}/`
        };

        let copyPromises = [];
        console.log("about to await s3.listObjects()...");

        let listObjectsResult;
        try {
            listObjectsResult = await s3.listObjects(batsAdditionalArtifactsParams).promise();
        } catch(err) {
            console.log(`Failed to list objects for ${srcLocation}, err: ${err}`);
            throw err;
        }
        console.log(`finished waiting for listObjects. listObjectsResult: ${listObjectsResult}`);
        console.log(`Successfully listed objects in ${srcLocation}. Attempting to copy all artifacts to ${DestBucket}`);
        listObjectsResult.Contents.forEach((object) => {
            console.log(`parsing object ${object}`);
            let keyParts = object.Key.split('/');
            let fileKey = keyParts.pop();
            let destKey = fileKey.includes(agentBootstrapScript) ? `${agentBootstrapScriptsFolder}/${agentBootstrapScript}` : fileKey; // Adhere to bootstrap folder structure
            let copyParams = {
                Bucket: DestBucket,
                CopySource: `${srcLocation}/${fileKey}`,
                Key: destKey
            };
            console.log("pushing copy promise");
            copyPromises.push(s3.copyObject(copyParams).promise()
                .then(function(data) {
                    console.log(`Successfully copied ${fileKey} from ${srcLocation} to ${DestBucket}! data=${data}`);
                }).catch(function(err) {
                console.log(`Encountered error while copying ${fileKey} from ${srcLocation} to ${DestBucket}, error: ${err}`);
            }));
        });
        console.log("about to await Promise.all()....");
        await Promise.all(copyPromises);
    } else {
        console.log(`Received event type ${RequestType}, not copying anything`);
    }

    console.log("returning Promise.resolve()");
    return Promise.resolve();
};

这段代码只输出日志信息 about to await s3.listObjects()...，所以看起来它卡在了等待中：

listObjectsResult = await s3.listObjects(batsAdditionalArtifactsParams).promise();

我想要做的就是等待列出所有对象，承诺复制这些对象，然后使用 Promise.all 等待所有这些复制完成，然后再从此处理程序返回。我在 await 周围放了一个 try/catch ，但它看起来就像永远卡在等待中一样。关于此的任何提示，甚至如何调试这种情况？

Answer 1

你的代码很混乱。您将 async/await 与 Promise.then 混合在一起。通常你会选择一种方式，但绝不会同时选择两种方式。

通过查看您的代码，我猜测 sendResult returns 一个 Promise，因为您将其结果分配给了一个名为 resultPromise 的对象但你永远不会等待它。

copyHandler 也是 returns 一个 Promise，但你不等待它（你正在链接 then 调用）但是当它到达 return resultPromise 时，promise 还没有已解决。

对我来说，问题出在您的 cfnHandlerWrapper 函数上。我会更改您发布到的代码：

const cfnHandlerWrapper = async (event, handler) => {
    try {
        await copyHandler(event)
        console.log(`Successfully copied over all artifacts`);
        return await sendSuccess(event);
    } catch (e) {
        console.log('ERROR RUNNING HANDLER:');
        console.log(e);
        return await sendFailure(e.message || 'Something went wrong', event);
    }
};

现在，在您的 forEach 上，您还有另一个问题，因为其中的代码包含也会运行异步的承诺，所以当您调用 await Promise.all(copyPromises);、copyPromises 尚未填充您期望的所有承诺（可能会填充 none）。

我会改用 for of（下面只有相关代码）：

for (const object of listObjectsResult.Contents) {
    console.log(`parsing object ${object}`);
    let keyParts = object.Key.split('/');
    let fileKey = keyParts.pop();
    let destKey = fileKey.includes(agentBootstrapScript) ? `${agentBootstrapScriptsFolder}/${agentBootstrapScript}` : fileKey; // Adhere to bootstrap folder structure
    let copyParams = {
        Bucket: DestBucket,
        CopySource: `${srcLocation}/${fileKey}`,
        Key: destKey
    };
    console.log("pushing copy promise");
    copyPromises.push(s3.copyObject(copyParams).promise())
}
console.log("about to await Promise.all()....");
await Promise.all(copyPromises)

如果不对这段代码进行测试，很难判断它是否有效，但我不明白为什么它会失败。不管怎样，试着把你的组件分解成更小的部分，看看它到底在哪里失败了。不过，我把我所有的钱都赌在你对待承诺的方式上。

挂起等待 s3.listObjects

Hangs on await s3.listObjects

javascript

node.js

aws-lambda

aws-sdk-nodejs