Access Slack files from a slack bot - ruby

Question

I need a slack bot that's able to receive and save files send from slack chatrooms.
The problem is: slack doesn't send file contents, but an array of links pointing to the file. Most of them, including download link are private and cannot be accessed via bot. It does send one public link, but that link points at the file preview, which does not have the file itself (here's an example).
How can I access uploaded files via bot?

Answer 1

You can access private URLs from your bot by providing an access token in the HTTP header when you are doing you CURL request.
Your token needs to have the scope files.read in order to get access.
The format is:
Authorization: Bearer A_VALID_TOKEN
Replace A_VALID_TOKEN with your slack access token.
I just tested it with a simple PHP script to retrieve a file by its "url_private" and it works nicely.
Source: Slack API documententation / file object / Authentication

Answer 2

Example for using the Python requests library to fetch an example file:
import requests
url = 'https://slack-files.com/T0JU09BGC-F0UD6SJ21-a762ad74d3'
token = 'xoxp-8853424449-8820034832-8891394196-faf6f0'
requests.get(url, headers={'Authorization': 'Bearer %s' % token})

Answer 3

for those wanting to accomplish this with Bash & cURL, here's a helpful function! It will download the file to the current directory with a filename that uniquely identifies the file, even if the file has the same name as others in your file listing.
function slack_download {
URL="$1";
TOKEN="$2"
FILENAME=`echo "$URL" | sed -r 's/.*\/(T.+)\/([^\/]+)$/\1-\2/'`;
curl -o "$FILENAME" -H "Authorization: Bearer $TOKEN" "$URL";
}
# Usage:
# Downloads as ./TJOLLYDAY-FANGBEARD-NSFW_PIC.jpg
slack_download "https://files.slack.com/files-pri/TJOLLYDAY-FANGBEARD/NSFW_PIC.jpg" xoxp-12345678901-01234567890-123456789012-abcdef0123456789abcdef0123456789

Answer 4

Tested with Python3 - just replace SLACK_TOKEN with your token.
Downloads and creates an output file.
#!/usr/bin/env python3
# Usage: python3 download_files_from_slack.py <URL>
import sys
import re
import requests
url = " ".join(sys.argv[1:])
token = 'SLACK_TOKEN'
resp = requests.get(url, headers={'Authorization': 'Bearer %s' % token})
headers = resp.headers['content-disposition']
fname = re.findall("filename=(.*?);", headers)[0].strip("'").strip('"')
assert not os.path.exists(fname), print("File already exists. Please remove/rename and re-run")
out_file = open(fname, mode="wb+")
out_file.write(resp.content)
out_file.close()