added gzip support

Author: darthbear

README.md

@@ -182,3 +182,8 @@ psql> select * from animals;
  tortoise | 205
 (4 rows)
 ```
+
+## Support for gzip files
+
+If the file has the metadata `Content-Encoding=gzip` in S3, then the file will be automatically unzipped prior to be copied to the table.
+One can update the metadata in S3 by following the instructions described [here](https://docs.aws.amazon.com/AmazonS3/latest/user-guide/add-object-metadata.html).

aws_s3--0.0.1.sql

@@ -65,6 +65,8 @@ AS $$
 
  boto3 = cache_import('boto3')
  tempfile = cache_import('tempfile')
+ gzip = cache_import('gzip')
+ shutil = cache_import('shutil')
 
  plan = plpy.prepare('select current_setting($1, true)::int', ['TEXT'])
 
@@ -76,8 +78,18 @@ AS $$
  region_name=region
  )
 
+ response = s3.head_object(Bucket=bucket, Key=file_path)
+ content_encoding = response.get('ContentEncoding')
+
  with tempfile.NamedTemporaryFile() as fd:
- s3.download_fileobj(bucket, file_path, fd)
+ if content_encoding and content_encoding.lower() == 'gzip':
+ with tempfile.NamedTemporaryFile() as gzfd:
+ s3.download_fileobj(bucket, file_path, gzfd)
+ gzfd.flush()
+ gzfd.seek(0)
+ shutil.copyfileobj(gzip.GzipFile(fileobj=gzfd, mode='rb'), fd)
+ else:
+ s3.download_fileobj(bucket, file_path, fd)
  fd.flush()
  res = plpy.execute("COPY {table_name} {column_list} FROM {filename} {options};".format(
  table_name=table_name,