Nodejs adm-zip在Lambda中因访问被拒绝错误而失败

Question

我的目标是读取Lambda的zip文件中的文件，该文件由S3 Put调用，这是代码，但是Access Denied失败，即使Lambda具有对S3的完全访问权限：

var AWS = require('aws-sdk');  
var fs = require('fs');  
var s3 = new AWS.S3();
var AdmZip = require('adm-zip');

exports.handler = function(event, context, callback) {
    const bucket = event.Records[0].s3.bucket.name;
    const key = event.Records[0].s3.object.key;
    var params = {Bucket: 'bucket', Key: 'key'};
    console.log('Bucket Name:', bucket);
    console.log('Object Name:', key);
    var buffer = s3.getObject(params).createReadStream();   
    var zip = new AdmZip(buffer);
    var zipEntries = zip.getEntries();
    zipEntries.forEach(function(zipEntry) {
        console.log(zipEntry.toString());
        console.log('File Name: ',zipEntry.entryName); 
        if (zipEntry.entryName == "text.txt") {
             console.log(zipEntry.data.toString('utf8')); 
        }
    });
};

我收到以下错误：

START RequestId: fc524797-4d28-11e6-a092-5b3299c063a6 Version: $LATEST
2016-07-18T20:48:33.983Z    fc524797-4d28-11e6-a092-5b3299c063a6    Bucket Name: myTestBucket123
2016-07-18T20:48:33.984Z    fc524797-4d28-11e6-a092-5b3299c063a6    Object Name: test.zip
2016-07-18T20:48:35.145Z    fc524797-4d28-11e6-a092-5b3299c063a6    AccessDenied: Access Denied
    at Request.extractError (/var/runtime/node_modules/aws-sdk/lib/services/s3.js:524:35)
    at Request.callListeners (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:105:20)
    at Request.emit (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:77:10)
    at Request.emit (/var/runtime/node_modules/aws-sdk/lib/request.js:615:14)
    at Request.transition (/var/runtime/node_modules/aws-sdk/lib/request.js:22:10)
    at AcceptorStateMachine.runTo (/var/runtime/node_modules/aws-sdk/lib/state_machine.js:14:12)
    at /var/runtime/node_modules/aws-sdk/lib/state_machine.js:26:10
    at Request.<anonymous> (/var/runtime/node_modules/aws-sdk/lib/request.js:38:9)
    at Request.<anonymous> (/var/runtime/node_modules/aws-sdk/lib/request.js:617:12)
    at Request.callListeners (/var/runtime/node_modules/aws-sdk/lib/sequential_executor.js:115:18)
END RequestId: fc524797-4d28-11e6-a092-5b3299c063a6
REPORT RequestId: fc524797-4d28-11e6-a092-5b3299c063a6  Duration: 4318.87 ms    Billed Duration: 4400 ms    Memory Size: 128 MB Max Memory Used: 24 MB  
Process exited before completing request

以下是Lambda正在使用的角色的政策：

    {
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": [
                "logs:CreateLogGroup",
                "logs:CreateLogStream",
                "logs:PutLogEvents"
            ],
            "Resource": "arn:aws:logs:*:*:*"
        },
        {
            "Effect": "Allow",
            "Action": [
                "s3:*"
            ],
            "Resource": [
                "arn:aws:s3:::*"
            ]
        }
    ]
}