Post activity with attachment should upload metadata

[compulim]

Background

We recently updated our /upload endpoint to support metadata (e.g. thumbnailUrl) for attachments. The service work is carried out by @NickEricson and did not introduce backward compatibility issues.

This work is required for microsoft/BotFramework-WebChat#2422.

Changes

Instead of removing activity.attachments, we leave the attachments array but only removing activity.attachments[].contentUrl. This will send contentType and thumbnailUrl to the service.

The service will match metadata by looking at:

• activity.attachments[].name
• filename of multipart, where the multipart has name equals to file

Quicklook

Today

-------boundary
Content-Disposition: form-data; name="activity"; filename="blob"
Content-Type: application/vnd.microsoft.activity

{
  "from": {
    "id": "dl_1234567"
  },
  "type": "message",
  ...
}
-------boundary
Content-Disposition: form-data; name="file"; filename="abc.png"
Content-Type: image/png

...
-------boundary

Tomorrow

  -------boundary
  Content-Disposition: form-data; name="activity"; filename="blob"
  Content-Type: application/vnd.microsoft.activity

  {
+   "attachments": [{
+     "contentType": "image/png",
+     "name": "abc.png",
+     "thumbnailUrl": "data:image/jpeg;base64,..."
+   }],
    "from": {
      "id": "dl_1234567"
    },
    "type": "message",
    ...
  }
  -------boundary
  Content-Disposition: form-data; name="file"; filename="abc.png"
  Content-Type: image/png

  ...
  -------boundary

Note: the filename field on multipart is used for matching the corresponding item in the attachments array.