fix(file.controller.js): set headers for file extensions from MIME -I1218

[elit-altum]

I have verified that this pull request:

• has no linting errors (npm run lint)
• is from a uniquely-named feature branch and has been rebased on top of the latest master. (If I was asked to make more changes, I have made sure to rebase onto master then too)
• is descriptively named and links to an issue number, i.e. Fixes #123

Fixes #1218

• Adds mime-types as a dependency to check for the file's MIME and then set an appropriate header.

[elit-altum]

@stalgiag Is this the right approach ? Please review!

[stalgiag]

Hi @elit-altum one thing that I am noticing is that this is failing the linting test with the error Absolute imports should come before relative imports. Try moving up the import for mime-types.`

Other than that, this looks like it should work but I don't have the opportunity to test currently. Are you able to test successfully with the appropriate file types?

[elit-altum]

Oh that's my bad @stalgiag. Thanks for pointing it out. I am really sorry
I tried logging the output of the return from mime.lookup and that seems to be working fine. But I am new to this so wanted a second opinion

[andrewn]

Thanks for opening this PR!

resolvedFile is an object, and mime.lookup() requires a filename string so I've changed this to resolvedFile.name.

Also, lookup() returns false if no mime-type is found, so I've added a fallback to application/octet-stream as recommended by the library otherwise the server crashes.