使用AWS Lambda从AWS S3访问元数据

Question

每次将对象上传到S3时，我都想检索添加的一些元数据（使用控制台x-amz-meta-my_variable）。

我已经通过控制台设置了lambda，以在每次将对象上传到存储桶时触发

我想知道是否可以使用类似的方法variable = event['Records'][0]['s3']['object']['my_variable']来检索此数据，或者是否必须使用存储桶和密钥连接回S3，然后调用一些函数来检索它？

下面是代码：

from __future__ import print_function

import json
import urllib
import boto3

print('Loading function')

s3 = boto3.client('s3')


def lambda_handler(event, context):

    # Get the object from the event and show its content type
    bucket = event['Records'][0]['s3']['bucket']['name']
    key = urllib.unquote_plus(event['Records'][0]['s3']['object']['key']).decode('utf8')

    # variable = event['Records'][0]['s3']['object']['my_variable']

    try:
        response = s3.get_object(Bucket=bucket, Key=key)

        # Call some function here?

        print("CONTENT TYPE: " + response['ContentType'])
        return response['ContentType']

    except Exception as e:
        print(e)
        print('Error getting object {} from bucket {}. Make sure they exist and your bucket is in the same region as this function.'.format(key, bucket))
        raise e

Answer 1

元数据不是在事件中，而是在head对象中。

HEAD操作从对象检索元数据，而不返回对象本身。如果您仅对对象的元数据感兴趣，则此操作很有用。要使用HEAD，您必须具有对该对象的READ访问权限。

HEAD请求具有与对对象的GET操作相同的选项。除了没有响应主体外，该响应与GET响应相同。

s3.head_object（桶=水桶，钥匙=钥匙）

下面的代码是获取元数据的代码段。

from __future__ import print_function
import boto3, logging

s3 = boto3.client('s3')
logger = logging.getLogger()
logger.setLevel(logging.INFO)

def lambda_handler(event, context):
  for record in event['Records']
    bucket = record['s3']['bucket']['name']
    key = record['s3']['object']['key']
    response = s3.head_object(Bucket=bucket, Key=key)

    logger.info('Response: {}'.format(response))

    print("Author : " + response['Metadata']['author'])
    print("Description : " + response['Metadata']['description'])

输出：

[INFO]  2016-05-18T01:30:47.900Z    241f0cfc-1c98-12e6-b9a7-cf406f32a0dc    Response: {u'AcceptRanges': 'bytes', u'ContentType': 'binary/octet-stream', 'ResponseMetadata': {'HTTPStatusCode': 200, 'HostId': 'K8JMVbEt5xA+qXuXOedb1y5nxuv6scMXnNH/rHVtxcg=', 'RequestId': 'D05BE92E55E0'}, u'LastModified': datetime.datetime(2016, 5, 17, 22, 54, 37, tzinfo=tzutc()), u'ContentLength': 94320, u'ETag': '"0e4d457d912bce9ff81952"', u'Metadata': {'author': 'Satyajit Ray', 'description':'He was an Indian filmmaker, widely regarded as one of the greatest filmmakers of the 20th century.'}}
Author : Satyajit Ray
Description : He was an Indian filmmaker, widely regarded as one of the greatest filmmakers of the 20th century.