object storage v1: Helper functions for Uploading and Downloading

[jtopjian]

Gophercloud contains fairly feature complete support for Object Storage, however the functions are very basic and low-level. One would have to write a good amount of code in order to have more robust uploading and downloading.

It would be beneficial to include these functions here. The functionality could/should use python-swiftclient as the basis:

https://github.com/openstack/python-swiftclient/blob/e65070964c7b1e04119c87e5f344d39358780d18/swiftclient/service.py

[majewsky]

I see you implemented something like this already in #47. Alternatively, you could have the documentation point users to https://github.com/majewsky/schwift, which provides a nice object-oriented Swift client API on top of Gophercloud auth.

For example, this is what segmented uploading looks like in Schwift: (error handling elided)

var client *gophercloud.ServiceClient //has already been obtained
account, err := gopherschwift.Wrap(client)
container, err := account.Container("example").EnsureExists()
segmentContainer, err := account.Container("example_segments").EnsureExists()
largeObj, err := container.Object("linux-5.0.0.tar.gz").AsNewLargeObject(
  schwift.SegmentingOptions{SegmentContainer: segmentContainer},
  &schwift.TruncateOptions{DeleteSegments: true}, //cleanup existing segments, if necessary
)
file, err := os.Open("./linux-5.0.0.tar.gz")
segmentSize := 1<<30
err := largeObj.Append(file, segmentSize, nil)
err := largeObj.WriteManifest(nil)

If you want to add extra metadata to the object, replace the last line by something like:

hdr := NewObjectHeaders()
obj.ContentType().Set("application/tar")
obj.ExpiresAt().Set(time.Now().Add(24 * time.Hour))
err := largeObj.WriteManifest(hdr.ToOpts())