Client Attachments

Historical Context

This section is SPECULATIVE.

Discord wants to provide more benefits for Nitro users to drive Nitro adoption, one of them being bumping the attachment size limit from 100MB to 500MB, however, Cloudflare only allows for client requests sized 100MB in the Free plan.

Cloudflare can bump this limit to 500MB for Enterprise customers, but users are able to upload up to 10 attachments in a single message, so the upper limit would be 5GB. What to do then?

The answer: New API for asynchronous attachment uploads.

How it currently works

From the official docs, you use multipart form data to attach your file and then reference it in another part called payload_json. This is all part of a single request to POST /messages.

How the new method works

We do not know if Discord will open this API to bots. Use this at your own caution.

A new POST /attachments is created which creates an "attachment slot" (unofficial name) inside Discord, that "slot" has a Google Cloud Storage bucket URL that the client directly uploads to, then references it in POST /messages.

POST /attachments

Receives a list of attachment slot requests.

field	type	description
files	List[AttachmentSlotRequest]	requests

Returns a list of attachment slots.

field	type	description
attachments	List[AttachmentSlot]	slots

AttachmentSlotRequest

field	type	description
filename	string	file name
file_size	int	file size
id	string	slot id (random int by client, ASSUMPTION: this is scoped to either session or user id. ASSUMPTION: must be a number, as its casted on AttachmentSlot)

Example:

{
  "filename": "myfile.png",
  "file_size": 533389,
  "id": "3821"
}

AttachmentSlot

Contains a reserved attachment slot the client shall upload the actual file to.

field	type	description
id	int	slot id from the request
upload_filename	string	filename of that slot
upload_url	string	url for the client to directly upload the file to

Example:

{
  "id": 3821,
  "upload_url": "https://discord-attachments-uploads-prd.storage.googleapis.com/b757d035-4dcb-44c6-b66e-2815f5042ede/myfile.png?upload_id=OHQlQNB7Mx1J8teeUPE1V__KLj0OZZdPkMmGaA7o1qY'",
  "upload_filename": "b757d035-4dcb-44c6-b66e-2815f5042ede/myfile.png"
}

referencing attachments in POST /messages

The partial attachment object gets a new field, uploaded_filename, which is the same value as the one returned in the AttachmentSlot.

Example of message containing an attachment slot reference:

{
  "content": "",
  "nonce": "123123123123123123",
  "channel_id": "123123123123123123",
  "type": 0,
  "sticker_ids": [],
  "attachments": [
    {
      "id": "0",
      "filename": "myfile.png",
      "uploaded_filename": "b757d035-4dcb-44c6-b66e-2815f5042ede/myfile.png"
    }
  ]
}