How to get the md5sum of a file on Amazon's S3

Question

If I have existing files on Amazon\'s S3, what\'s the easiest way to get their md5sum without having to download the files?

Thanks

Answer 1

Below that's work for me to compare local file checksum with s3 etag. I used Python

def md5_checksum(filename):
    m = hashlib.md5()
    with open(filename, 'rb') as f:
        for data in iter(lambda: f.read(1024 * 1024), b''):
            m.update(data)
   
    return m.hexdigest()


def etag_checksum(filename, chunk_size=8 * 1024 * 1024):
    md5s = []
    with open(filename, 'rb') as f:
        for data in iter(lambda: f.read(chunk_size), b''):
            md5s.append(hashlib.md5(data).digest())
    m = hashlib.md5(b"".join(md5s))
    print('{}-{}'.format(m.hexdigest(), len(md5s)))
    return '{}-{}'.format(m.hexdigest(), len(md5s))

def etag_compare(filename, etag):
    et = etag[1:-1] # strip quotes
    print('et',et)
    if '-' in et and et == etag_checksum(filename):
        return True
    if '-' not in et and et == md5_checksum(filename):
        return True
    return False


def main():   
    session = boto3.Session(
        aws_access_key_id=s3_accesskey,
        aws_secret_access_key=s3_secret
    )
    s3 = session.client('s3')
    obj_dict = s3.get_object(Bucket=bucket_name, Key=your_key)

    etag = (obj_dict['ETag'])
    print('etag', etag)
    
    validation = etag_compare(filename,etag)
    print(validation)
    etag_checksum(filename, chunk_size=8 * 1024 * 1024)
    return validation