Generate a presigned URL to download an S3 object

s3_presigned_url.py

#!/usr/bin/env python3
"""Generate a presigned URL to download an S3 object

<cmd> bucket_name key_name [expiration_days]"""

import sys

import boto3
from botocore.client import Config

if len(sys.argv) < 3 or len(sys.argv) > 4:
    print(__doc__)
    quit()

BUCKET = sys.argv[1]  # S3 bucket name
KEY = sys.argv[2]     # S3 object key

# URL Expiration in days (default: 1)
DAYS = int(sys.argv[3]) if len(sys.argv) > 3 else 1

# boto3 defaults to 'virtual' bucket addressing which does not work for
# the presigned URL, we need 'path'
# Thanks to https://github.com/boto/boto3/issues/1644#issuecomment-417550879
# for this way to fix the 403 SignatureDoesNotMatch return code.
S3_CLIENT = boto3.client(
    's3',
    config=Config(signature_version='s3v4',
                  s3={'addressing_style': 'path'}))

URL = S3_CLIENT.generate_presigned_url(
    ClientMethod='get_object',
    Params={'Bucket': BUCKET, 'Key': KEY},
    ExpiresIn=DAYS*3600*24)

print(URL)