Why does Slack's files.list endpoint return an empty files array?

Question

I'd like to use the Slack API to delete old files from my workspace, as we are running out of space to upload new ones.

I registered an application, installed it on the target workspace, granted the application the files:read and files:write permissions, and then generated a bot token for the application that has the prefix xoxb.

With this token, I made a GET request to the files.list endpoint using Postman:

GET https://slack.com/api/files.list?token=xoxb-xxxxxxxxxxxx-xxxxxxxxxxxxx-xxxxxxxxxxxxxxxxxxxxxxxx&count=100&page=1&show_files_hidden_by_limit=true
HTTP/1.1
User-Agent: PostmanRuntime/7.24.1
Accept: */*
Cache-Control: no-cache
Postman-Token: 29879ef1-6da3-4863-8bb9-da8b4d5f740c
Host: slack.com
Accept-Encoding: gzip, deflate, br
Connection: keep-alive

HTTP/1.1 200 OK
date: Sat, 09 Jan 2021 18:18:42 GMT
server: Apache
x-xss-protection: 0
pragma: no-cache
cache-control: private, no-cache, no-store, must-revalidate
access-control-allow-origin: *
strict-transport-security: max-age=31536000; includeSubDomains; preload
x-slack-req-id: d972daab31ff4fe7a477eb3149ad5260
x-content-type-options: nosniff
referrer-policy: no-referrer
access-control-expose-headers: x-slack-req-id, retry-after
x-slack-backend: r
x-oauth-scopes: files:read,files:write
x-accepted-oauth-scopes: files:read
expires: Mon, 26 Jul 1997 05:00:00 GMT
vary: Accept-Encoding
access-control-allow-headers: slack-route, x-slack-version-ts, x-b3-traceid, x-b3-spanid, x-b3-parentspanid, x-b3-sampled, x-b3-flags
content-encoding: gzip
content-length: 87
content-type: application/json; charset=utf-8
x-envoy-upstream-service-time: 444
x-backend: files_normal files_canary_with_overflow files_control_with_overflow
x-server: slack-www-hhvm-files-iad-jc2v
x-via: envoy-www-iad-4782, haproxy-edge-iad-y1wa
x-slack-shared-secret-outcome: shared-secret
via: envoy-www-iad-4782
{
  "ok": true,
  "files": [],
  "paging": {
    "count": 100,
    "total": 1803,
    "page": 1,
    "pages": 19
  }
}

As you can see, the response contains an empty files[] array, but the paging attribute tells me that there are 1803 files in the workspace.

Why can't I see any of the files in the workspace, even though I have the appropriate scopes and got an HTTP 200 in response?

Answer 1

I don't know if this is the answer, but it's a workaround:

• Grant the application the channels:read and channels:join scopes
• Call the conversations.list endpoint to get a list of channels in the workspace
• Grab the id attribute of one of the channels that you would like to list files for
• Call the conversations.join endpoint to add the application to the channel
• Call the files.list endpoint to get a list of files in that channel.

Presumably, you can iterate over every public channel in the workspace, join each, list its files, and then delete the files older than a certain date.