How to gzip while uploading into s3 using boto

I implemented the solution hinted at in the comments of the accepted answer by garnaat:

import cStringIO
import gzip

def sendFileGz(bucket, key, fileName, suffix='.gz'):
    key += suffix
    mpu = bucket.initiate_multipart_upload(key)
    stream = cStringIO.StringIO()
    compressor = gzip.GzipFile(fileobj=stream, mode='w')

    def uploadPart(partCount=[0]):
        partCount[0] += 1
        stream.seek(0)
        mpu.upload_part_from_file(stream, partCount[0])
        stream.seek(0)
        stream.truncate()

    with file(fileName) as inputFile:
        while True:  # until EOF
            chunk = inputFile.read(8192)
            if not chunk:  # EOF?
                compressor.close()
                uploadPart()
                mpu.complete_upload()
                break
            compressor.write(chunk)
            if stream.tell() > 10<<20:  # min size for multipart upload is 5242880
                uploadPart()

It seems to work without problems. And after all, streaming is in most cases just a chunking of the data. In this case, the chunks are about 10MB large, but who cares? As long as we aren't talking about several GB chunks, I'm fine with this.

---

Update for Python 3:

from io import BytesIO
import gzip

def sendFileGz(bucket, key, fileName, suffix='.gz'):
    key += suffix
    mpu = bucket.initiate_multipart_upload(key)
    stream = BytesIO()
    compressor = gzip.GzipFile(fileobj=stream, mode='w')

    def uploadPart(partCount=[0]):
        partCount[0] += 1
        stream.seek(0)
        mpu.upload_part_from_file(stream, partCount[0])
        stream.seek(0)
        stream.truncate()

    with open(fileName, "rb") as inputFile:
        while True:  # until EOF
            chunk = inputFile.read(8192)
            if not chunk:  # EOF?
                compressor.close()
                uploadPart()
                mpu.complete_upload()
                break
            compressor.write(chunk)
            if stream.tell() > 10<<20:  # min size for multipart upload is 5242880
                uploadPart()

You can also compress Bytes with gzip easily and upload it as the following easily:

import gzip
import boto3

cred = boto3.Session().get_credentials()

s3client = boto3.client('s3',
                            aws_access_key_id=cred.access_key,
                            aws_secret_access_key=cred.secret_key,
                            aws_session_token=cred.token
                            )

bucketname = 'my-bucket-name'      
key = 'filename.gz'  

s_in = b"Lots of content here"
gzip_object = gzip.compress(s_in)

s3client.put_object(Bucket=bucket, Body=gzip_object, Key=key)

It is possible to replace s_in by any Bytes, io.BytesIO, pickle dumps, files, etc.

If you want to upload compressed Json then here is a nice example: Upload compressed Json to S3

There really isn't a way to do this because S3 doesn't support true streaming input (i.e. chunked transfer encoding). You must know the Content-Length prior to upload and the only way to know that is to have performed the gzip operation first.