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The issue with AWS S3 Event notifications is that it replaces spaces with ‘+’ character sign in the object key name. This can cause issues when trying to access the object in S3. It will occurs NoSuchKey error if not handling this issue properly.

Background

Configured a S3 bucket put event notification to a Lambda function. The Lambda function will be triggered when a new object is uploaded to the S3 bucket. I upload a file named ‘2023 2nd quarter QE survey raw data.xlsx’ into S3 bucket, the Lambda function is triggered, but when I try to access the object in S3, I get NoSuchKey error in AWS CloudWatch Logs. Debugging shows that the object key name is ‘2023+2nd+quarter+QE+survey+raw+data.xlsx’ instead of ‘2023 2nd quarter QE survey raw data.xlsx’. It means the S3 event notification is replacing the space with ‘+’ character sign in the object key name.

The detail error is below:

[ERROR] NoSuchKey: An error occurred (NoSuchKey) when calling the GetObject operation: The specified key does not exist.

Solution

There are two solutions to fix this issue, one is from AWS S3 upload file side, another is from Lambda function side.

1. From AWS S3 upload file side:

If you have control over the upload process, ensure that the keys are properly URL-encoded.

import boto3
import urllib.parse

s3_client = boto3.client('s3')

# Example key with spaces
object_key = "2023 2nd quarter QE survey raw data.xlsx"
encoded_key = urllib.parse.quote(object_key)

# Upload the object
s3_client.upload_file("/tmp/2023 2nd quarter QE survey raw data.xlsx", "my-bucket-name", encoded_key)

This will ensure that the object key name is properly URL-encoded, which will prevent the S3 event notification from replacing spaces with ‘+’ character sign. The urllib.parse.quote function will replace spaces with ‘%20’ and ‘+’ with ‘%2B’.

2. From Lambda function side:

To fix this issue, we need to modify the Lambda function to handle the object key name with ‘+’ character sign. We can use the urllib.parse package to handle it. The package library provide the function unquote_plus to replace ‘+’ with space. Here is the code to handle the object key name with ‘+’ character sign:

import os
import urllib.parse as urlparse
import boto3

s3 = boto3.client('s3')

def lambda_handler(event, context):
    bucket_name = event['Records'][0]['s3']['bucket']['name']
    object_key = event['Records'][0]['s3']['object']['key']
    # Replace '+' with space
    object_key = urlparse.unquote_plus(object_key)
    # Download the object
    s3.download_file(bucket_name, object_key, '/tmp/file.txt')
    # Do something with the downloaded file
    #...

In the above code, we first get the bucket name and object key from the S3 event notification. We then use the urlparse.unquote_plus function to replace ‘+’ with space in the object key name. Finally, we download the object using the s3.download_file function.

Conclusion

To fix the issue with AWS S3 Event notifications replacing space with ‘+’ character sign in the object key name, we need to handle it properly in the Lambda function. We can use the urllib.parse package to handle it.