Slack Slash Command - Image Not Unfurling - slack-api

Question

I have written a custom Slash command that takes in a query from the user and returns an image.
The Server side which receives the Slash command retrieves the query from the user, and forms the Image URL http://example.com/file1.png and it sends back the response as <http://example.com/file1.png>. This is shown as a link in the response and is not unfurled. What could be the problem?
I even tried the following:
1) I sent back a JSON payload as given below:
{
"text":"http://example.com/file1.gif","unfurl_media":true
}
But that displayed the link again and did not unfurl it.
2) I tried
{
"text":"<http://example.com/file1.gif>","unfurl_media":true
}
But same results.
What could be the problem? Do I absolutely need a incoming webhook integration and send the message there ?

Answer 1

Did it work the first time, or had the URL previously been unfurled?
Slack will only automatically unfurl a URL once per hour in a given channel. If a user manually posts the URL and it is not unfurled because of this limit they will get an ephemeral message from SlackBot about it, however the unfurl just silently fails for slash commands or webhooks. I've hit this before in testing and had to make sure to change either the URL or the channel to verify things are working.
You should not need a manual attachment or a webhook or even the unfurl_media flag in the response (it's on by default for messages posted via webhooks/slash command).

Answer 2

I was having a similar issue with slash commands returning the text of my image url.
What you need to change is to use an object with an image_url for your image, and put that inside an attachments array.
Below is an example that returns the link of the image as text and the image itself.
{
"parse": "full",
"response_type": "in_channel",
"text": "http://example.com/file1.png",
"attachments":[
{
"image_url": "http://example.com/file1.png"
}
],
"unfurl_media":true,
"unfurl_links":true
}

Answer 3

{
"parse": "full",
"text": "http://example.com/file1.png",
"attachments":[
{
"image_url": "http://example.com/file1.png"
}
],
"unfurl_media":true,
"unfurl_links":true
}