How do I upload a gzip object to s3?

I am creating a gzip string and uploading it as an object to s3. However when I download the same file from s3 and decompress it locally with gunzip I get this error: gunzip: 111.gz: not in gzip format When I look at the mime_content_type returned in the file downloaded from s3 it is set as: application/zlib

Here is the code I am running to generate the gzip file and push it to s3:

for($i=0;$i<=100;$i++) {
    $content .= $i . "n";
}

$result = $this->s3->putObject(array(
   'Bucket' => 'my-bucket-name',
   'Key'    => '111.gz',
   'Body'   => gzcompress($content),
   'ACL' => 'authenticated-read',
   'Metadata' => [
       'ContentType' => 'text/plain',
       'ContentEncoding' => 'gzip'
   ]
));

The strange thing is that if I view the gzip content locally before I send it to s3 I am able to decompress it and see the original string. So I must be uploading the file incorrectly, any thoughts?

Answer

According to http://docs.aws.amazon.com/aws-sdk-php/v3/api/api-s3-2006-03-01.html#putobject the ContentType and ContentEncoding parameters belong on top level, and not under Metadata. So your call should look like:

$result = $this->s3->putObject(array(
   'Bucket' => 'my-bucket-name',
   'Key'    => '111.gz',
   'Body'   => gzencode($content),
   'ACL' => 'authenticated-read',
   'ContentType' => 'text/plain',
   'ContentEncoding' => 'gzip'
));

Also it’s possible that by setting ContentType to text/plain your file might be truncated whenever a null-byte occurs. I would try with’application/gzip’ if you still have problems unzipping the file.