Helper function to download a file

I suggest adding a method on the Web API to download a file from slack, symmetrical to files.upload.

[aoberoi]

i think the SDK could provide a helper function to download actual files. what i’m imagining is a function web.helpers.fileDownload(fileId, [opts]) and the opts could allow you to specify if you want the return value to be a readable stream or a Buffer.

[clavin]

First off, this repository is for handling the client that uses the Web API, which is produced by some lovely engineers at Slack. We have no control over what is and isn’t in the API. Nonetheless, such a method (one that downloads files) isn’t exactly possible with the Web API (can’t force a client to download something, you can only send data).

But, there is a way to do what you’re looking for: simply use an http client (such as request) to go to the file’s url (which you can get using the files.list method) and save the file’s response to disk.

Further, there’s a special little bit of authentication you need to do in your request to get the file (using it’s url_private field), as specified by the file type documentation. Simply, there must be an Authorization header present in the request that’s set to Bearer YOUR_TOKEN (which may be the bot’s token or a OAuth token).

Here’s an example of what all of that would look like:

const fs = require('fs');
const request = require('request');
const WebClient = require('@slack/client').WebClient;

const web = new WebClient(your token and options);

web.files.list({}, function(err, fileListResp) {
  if (err)
    return console.log(err);

  // Strategically choose a file to download.
  let filePrivateUrl = fileListResp.files[Math.floor(
    Math.random() * fileListResp.files.length)].url_private;

  // If you don't want to write the returned data to a file then just remove the
  // `pipe` call and supply `request` with a callback.
  request({
    url: filePrivateUrl,
    headers: {
      'Authorization': 'Bearer ' + YOUR_TOKEN // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
    }
  }).pipe(fs.createWriteStream('./thefile'));
});

I didn’t test the code, it could error. I’m also unaware of any situation in which a file doesn’t have a url_private field. You’ll have to do your own testing to make sure the above approach is sound (sorry). It should still be a solid basis for what you’re attempting to achieve. Good luck!