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Mime types of attachments uploaded to Trello

Adrian Sutton_phcu8v

I'm attempting to upload MP3 attachments to a Trello card (using the API, with the Python Trello module). I'm taking care to make sure the mimeType is set to 'audio/mpeg3', and that the file is encoded as multipart/form-data.

The upload itself happens fine, and the response data shows that Trello thinks it's a MIME type of 'audio/mpeg3' as I specified.

However, looking at the card, the attachment doesn't appear as an MP3, just a generic link, meaning that when clicking on the attachment in the card, it thinks I want to download it (i.e. a generic file) rather than listen to it.

Can anyone explain what's happening here?

Accepted answers

Fabio Barbon

I've just noticed that this issue happens only for certain mime types. For instance image files (such as "image/jpeg") work as expected, but neither MP3s nor PDFs do.
Also, note that mp3s uploaded via the GUI result as "audio/mp3" (via the get card attachments endpoint). And unfortunately no, it doesn't work even by "patching" the mime type in this way before posting

All comments

Iain Dooley

@Adrian Sutton yep I've never been able to get Trello uploads to work via the API the same way they do if you upload via the app. What I concluded is that, internally, all attachments are just links and there's something that happens in the Trello interface to set "isUpload" to true and set the mimetype so the icon is displayed differently on the card, but that never happens in the API.

Adrian Sutton_phcu8v

Thanks Iain

Adrian Sutton_phcu8v

Are there any devs from Atlassian here that can explain why this happens?..

Fabio Barbon

Ok, I think I've figured out the issue. Here's a snippet of the body multi-part data generated by the trello.com website when adding attachments:

------WebKitFormBoundaryMpa8IFEcwGeZ3C67
Content-Disposition: form-data; name="token"

5360ecf0889ea2ef01811bc2/bIZEBmZCuwzhyYVrj75WEpC21t1lebRyWKRZgdjLWBZuBg4H92rpWqqthVuvDVdG
------WebKitFormBoundaryMpa8IFEcwGeZ3C67
Content-Disposition: form-data; name="file"; filename="funky-phone.mp3"
Content-Type: audio/mpeg


------WebKitFormBoundaryMpa8IFEcwGeZ3C67--

Not all http client libs include the "filename" entry. By manually adding it the attachment mime-type seems correct.
For example, in PHP with Guzzle you need to explicitly add a "filename" attribute within the request:

'multipart' => [ 
  [ 'name' => 'name', 'contents' => $file->getName() ], 
  [ 'name' => 'token', 'contents' => $this::$trelloToken ],
[ 'name' => 'file', 'contents' => $file->fopen('rb'), 'filename'=>$file->getName() ] 
]

Hope this helps.

Iain Dooley

@Fabio Barbon awesome! Keen to give this a try

Adrian Sutton_phcu8v

Thanks Fabio, will try

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