File sharing

[poga]

Currently, we only support text-based(text, action) messages. Although we can easily support file sharing via putting files into hyperdrive. There're some concerns:

• The performance impact of storing large binary blob in a merkle-log
• Operation: Storing large file on local disk increases operation burden.
• There're already many great platforms for sharing static files, such as BitTorrent, IPFS.

For simplicity sake, we can provide a simple "upload to BT/IPFS/S3" middleware and save the signed URL to the hyperdrive for now.

[poga]

The simplest way to do this might be with postToTopic in the frontend. We can post a new message to the topic with type = 'blob' and value = base64(blob).

pros:

• pure frontend solution, no new API needed
• Simple to implement

cons:

• everyone in channel will download the whole file instantly, wasting bandwidth.

[poga]

Preliminary support for file upload is implemented in #13.

However, it directly embed file blob into chat history. All uploaded files will be downloaded when user open the chat. This severely impact performance.

A proper way would be upload file to an external storage and only the save url in PTT.ai