如何从 Lambda function 访问 S3 object？

Question

I am attempting to access a text file stored in an AWS S3 bucket. At present, it contains only the word "Test".

At first, I thought I was having problems with fs.readfile, but now I've discovered that the problem is more fundamental. I cannot access the file at all. AWS from Node.js does not appear to be able to see the file at all.

I am using the following Lambda function:

const aws = require('aws-sdk');
const s3 = new aws.S3({ apiVersion: '2006-03-01' });

    exports.handler = async (event, context, callback) => { 
    // Get the object from the event and show its content type
    const bucket = event.Records[0].s3.bucket.name;
    const key = event.Records[0].s3.object.key; // decodeURIComponent(event.Records[0].s3.object.key.replace(/\+/g, ' '));
    console.log('Bucket = ' + bucket);
    console.log('key = ' + key);

    var params = {Bucket: bucket, Key: key};
    console.log('Checking file existence');
    console.log(params);
    console.log('Calling s3.getObject');
    s3.getObject(params, function(err, data) { 
        console.log('S3.getObject called');
        console.log('err = ' + err);
        if (err) {
            console.log(err, err.stack); // an error occurred
            callback(err);
        } else {
            console.log(data);           // successful response
            callback(null, null);
        }
        console.log('Leaving s3.getObject');
    });
};

The testbed function contains the following code:

{
  "Records": [
    {
      "eventVersion": "2.0",
      "eventSource": "aws:s3",
      "awsRegion": "us-east-1",
      "eventTime": "1970-01-01T00:00:00.000Z",
      "eventName": "ObjectCreated:Put",
      "userIdentity": {
        "principalId": "EXAMPLE"
      },
      "requestParameters": {
        "sourceIPAddress": "127.0.0.1"
      },
      "responseElements": {
        "x-amz-request-id": "EXAMPLE123456789",
        "x-amz-id-2": "EXAMPLE123/5678abcdefghijklambdaisawesome/mnopqrstuvwxyzABCDEFGH"
      },
      "s3": {
        "s3SchemaVersion": "1.0",
        "configurationId": "testConfigRule",
        "bucket": {
          "name": "wgtiplists",
          "ownerIdentity": {
            "principalId": "EXAMPLE"
          },
          "arn": "arn:aws:s3:::wgtiplists"
        },
        "object": {
          "key": "tiplist.txt",
          "size": 1024,
          "eTag": "0123456789abcdef0123456789abcdef",
          "sequencer": "0A1B2C3D4E5F678901"
        }
      }
    }
  ]
}

And the results look like this (I've trimmed off the timestamp and Request ID texts):

INFO    Bucket = s3://wgtiplists
INFO    key = tiplist.txt
INFO    Checking file existence
INFO    { Bucket: 's3://wgtiplists', Key: 'tiplist.txt' }
INFO    Calling s3.getObject

From this, I conclude that the S3 function is not being called, although I might be mistaken.

What am I doing wrong?

Answer 1

I believe you need parenthesis here:

const s3 = new aws.S3();

You should not be adding s3:// to the bucket name, just do this:

const bucket = event.Records[0].s3.bucket.name;

Answer 2

Look for the Cloudwatch logs. You might get some insight from there. Probably, as @Marck B mentioned, should be given bucket name is wrong