In writing my new Outlook Add-in (Send to Trello), I got stuck on attachments. The first version did not include an attachments option because of two unique problems that compounded each other:
- The Office Add-in API no longer provides a Media Type/MIME Type with an attachment request. I am able to get the “blob()” from Office, but other than the file extension there is not a way to determine the type. But sometimes a file does not have an extension, or the extension is wrong, etc.
- The Trello API will not let you upload without supplying a MIME type, you cannot just give it a Base64 string as an attachment and let them figure it out.
So, I found out something interesting while researching a workaround. Most every base64 string of a specific file type starts with the same “prolog” of text. Using this, combined with the fallback of the file extensions, I was able to get attachments to work (for the attachment types supported by Trello). So, v1.02 will now include attachments.
Anway, as for the workaround I found, this might be ugly, but wanted to share it anyway: