Attachment uploads

You can send attachments as files[n] parts in a multipart message, or upload them first and attach them by their upload key (upload_filename). Uploading first takes four steps.

1. Request an upload plan.
2. Send the bytes to its upload URLs.
3. Complete the upload if it is multipart.
4. Attach the upload by its upload key when you create or edit a message or start a thread.

Uploading first needs presigned_attachment_uploads set to true in instance features. When it is off, the plan and completion requests return 403 FEATURE_TEMPORARILY_DISABLED.

Request an upload plan

Call Request attachment upload URLs with up to 10 files, each with its exact byte count. Each file in the plan has an upload_mode that decides which fields it gets.

Value	When	Added fields
singlepart	A file_size of at most 10485760 bytes (10 MiB)	upload_url
multipart	A file_size above 10485760 bytes	upload_id, part_size and parts

Each parts entry has a part_number starting at 1 and its own upload_url.

Upload the bytes

Send a PUT to each upload_url exactly as returned, with no Authorization header. Fluxer picks content_type from the file name, and a singlepart upload must send the whole file with it as Content-Type. A multipart upload sends each part to its own URL, with exactly part_size bytes in every part except the last.

An upload URL points to storage or to the upload relay, and it expires after the time below.

Upload URL	Lifetime
Storage, singlepart	5 minutes
Storage, multipart part	1 hour
Upload relay	15 minutes by default, and the instance can change it

Keep upload URLs out of logs, because anyone who has one can upload to it until it expires. When a URL expires, request a new plan and upload the file again.

Complete a multipart upload

After every part has uploaded, call Complete attachment upload with the upload_filename and upload_id of up to 10 uploads. Fluxer checks permissions and the file size limit again. If completion fails because no parts arrived, the parts are too large or storage can't finish the upload, Fluxer cancels the upload and you need a new plan.

Attach the upload

Put the upload_filename in a pre-uploaded attachment when you call Create message, Modify message or Start thread in a forum or media channel.

An upload key works once, for the user and channel that requested it. Using a key that belongs to someone else, was requested for another channel or was already used returns 400 INVALID_FORM_BODY with UPLOADED_ATTACHMENT_NOT_FOUND. A key whose bytes never uploaded returns the same error with FILE_NOT_FOUND.

Stream previews

A stream preview is a JPEG of at most 1000000 bytes that shows for a voice stream. You can upload it with either of these Streams API endpoints.

• Upload stream preview takes the image as canonical base64 in JSON, using the standard alphabet with padding. Other encodings return 400 INVALID_STREAM_THUMBNAIL_PAYLOAD.
• Create stream preview upload URL returns a URL. Send the JPEG to it with PUT and the returned content_type before expires_at, and keep it at or under max_bytes.

A preview expires one day after you upload it or request its upload URL, and after that Get stream preview returns 404.