Accept multipart_upload parameters (supports ServerSideEncryption) for S3

[eschwartz]

Accept a multipart_upload parameter for S3 operations. Accepts the same arguments as S3.initiate_multipart_upload. Allows for, among other things, using S3 server-side encryption.

eg.

smart_open('s3://path/to/file', 'wb', multipart_upload={
  'ServerSideEncryption': 'AES256'
})

[eschwartz]

Again, I wasn't sure how to test this. The integration test is from #194.

Here's the script I ran locally to validate my changes:

import os
import random
import string
import boto3

os.sys.path.insert(0, './')
from smart_open import smart_open



def main():
    uid = ''.join(random.choice(string.ascii_letters) for n in range(12))

    bucket = '[bucket name]'
    key = f"test_file_{uid}"
    s3_uri = f"s3://{bucket}/{key}"

    print(f"Writing to {s3_uri}")
    write_stream = smart_open(
        s3_uri, 'wb', encoding='utf-8',
        multipart_upload={
            'ServerSideEncryption': 'AES256'
        }
    )
    with write_stream as write_stream:
        write_stream.write("test data")

    # Check that the file is encrypted
    res = boto3.client('s3').get_object(
        Bucket=bucket,
        Key=key
    )
    assert res['ServerSideEncryption'] == 'AES256'




main()

[eschwartz]

I borrowed test coverage from #196, which apparently does the same thing as this PR.

[eschwartz]

I figured out how to add unit tests for this.

I also renamed the argument to s3_upload, in consideration of @mpenkov's comments here. It also gives us flexibility to add a s3_download argument later, to support args for S3#get

[eschwartz]

@mpenkov or @piskvorky -- Can we get this merged?

[piskvorky]

Minor doc nit picks, otherwise looks good!

[piskvorky]

PEP8: two blank lines between module-level classes or functions.

[eschwartz]

fixed

[piskvorky]

One-liner please (like the other examples).

[eschwartz]

fixed

[eschwartz]

Requested changes were made.

[piskvorky]

LGTM.

[menshikh-iv]

Looks good for me too 👍, ping @mpenkov

[menshikh-iv]

Thanks @eschwartz congratz with your first contribution 🥇