AWS Lambda function to fix metadata for Unity WebGL build files

lambda_function.py

# This function should be invoked from event triggers from objects being created, filtered by the .br or .gz suffix
# Note that for system-defined values like Content-Encoding and Content-Type, we have to assign them directly
# Reference https://stackoverflow.com/a/66009750

import boto3

s3 = boto3.client('s3')

def lambda_handler(event, context):

    bucket_name = event['Records'][0]['s3']['bucket']['name']
    object_name = event['Records'][0]['s3']['object']['key']

    response = s3.head_object(Bucket=bucket_name, Key=object_name)
    
    if object_name.endswith(".br"):
        contentEncoding = "br"
    elif object_name.endswith(".gz"):
        contentEncoding = "gzip"
    # else contentEncoding = response['ContentEncoding']
    
    if object_name.endswith(".data.br") or object_name.endswith(".data.gz"):
        contentType = "application/octet-stream"
    elif object_name.endswith(".framework.js.br") or object_name.endswith(".framework.js.gz"):
        contentType = "application/javascript"
    elif object_name.endswith(".wasm.br") or object_name.endswith(".wasm.gz"):
        contentType = "application/wasm"
    elif object_name.endswith("symbols.json.br") or object_name.endswith("symbols.json.gz"):
        contentType = "application/octet-stream"
    # else contentType = response['ContentType']
    
    # use this for user-defined metadata
    # response['Metadata']['metadata-key'] = "value"

    result = s3.copy_object(Bucket = bucket_name, Key = object_name,
                            CopySource = {'Bucket': bucket_name, 'Key': object_name},
                            # Metadata = response['Metadata'],
                            MetadataDirective = 'REPLACE', TaggingDirective = 'COPY',
                            ContentEncoding = contentEncoding,
                            ContentType = contentType)