Storage Content-Type

[brendanhay]

Changes the custom Servant multipart/related instances to allow passing in of the non-root object payload's Content-Type.

This Content-Type (of type HttpMedia from http-media) is passed in as an additional parameter to upload.

The following example would align with the Google Storage documentation:

example = do
    l <- newLogger Debug stdout
    e <- newEnv <&> (envLogger .~ l) . allow storageReadWriteScope

    -- This will guess the MIME type as "image/jpeg" due to the file extension.
    b <- sourceBody "/path/to/image.jpg"

    -- An example of explicitly setting the MIME type would be:
    -- b <- sourceBody "/path/to/image.jpg" <&> bodyContentType .~ "image" // "png"

    let bkt = "bucket-name"
        key = "object-key.jpg"

    runResourceT . runGoogle e $ do
        _ <- upload (objectsInsert bkt object' & oiName ?~ key) b
        _ <- download (objectsGet bkt key)
        pure ()

POST https://www.googleapis.com/upload/storage/v1/b/myBucket/o?uploadType=multipart HTTP/1.1
Authorization: Bearer [YOUR_AUTH_TOKEN]
Content-Type: multipart/related; boundary=foo_bar_baz
Content-Length: [NUMBER_OF_BYTES_IN_ENTIRE_REQUEST_BODY]

--foo_bar_baz
Content-Type: application/json; charset=UTF-8

{
  "name": "myObject"
}

--foo_bar_baz
Content-Type: image/jpeg

[JPEG_DATA]
--foo_bar_baz--

Fixes #16.