Created
November 25, 2020 17:19
-
-
Save sweenzor/f11af4a9c7f08e196b093e3650609f56 to your computer and use it in GitHub Desktop.
Calculating the S3 ETag for a local file
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
| #!/usr/bin/env python3.6 | |
| import os | |
| import sys | |
| from hashlib import md5 | |
| from argparse import ArgumentParser | |
| parser = ArgumentParser(description='Compare an S3 etag to a local file') | |
| parser.add_argument('inputfile', help='The local file') | |
| parser.add_argument('etag', help='The etag from s3') | |
| args = parser.parse_args() | |
| def factor_of_1MB(filesize, num_parts): | |
| x = filesize / int(num_parts) | |
| y = x % 1048576 | |
| return int(x + 1048576 - y) | |
| def calc_etag(inputfile, partsize): | |
| md5_digests = [] | |
| with open(inputfile, 'rb') as f: | |
| for chunk in iter(lambda: f.read(partsize), b''): | |
| md5_digests.append(md5(chunk).digest()) | |
| return md5(b''.join(md5_digests)).hexdigest() + '-' + str(len(md5_digests)) | |
| def possible_partsizes(filesize, num_parts): | |
| return lambda partsize: partsize < filesize and (float(filesize) / float(partsize)) <= num_parts | |
| def main(): | |
| filesize = os.path.getsize(args.inputfile) | |
| num_parts = int(args.etag.split('-')[1]) | |
| partsizes = [ ## Default Partsizes Map | |
| 8388608, # aws_cli/boto3 | |
| 15728640, # s3cmd | |
| factor_of_1MB(filesize, num_parts) # Used by many clients to upload large files | |
| ] | |
| for partsize in filter(possible_partsizes(filesize, num_parts), partsizes): | |
| if args.etag == calc_etag(args.inputfile, partsize): | |
| print('Local file matches') | |
| sys.exit(0) | |
| print('Couldn\'t validate etag') | |
| sys.exit(1) | |
| if __name__ == "__main__": | |
| main() |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Source: https://teppen.io/2018/10/23/aws_s3_verify_etags/