Percentage is not displayed when downloading a .txt file

[SoftVision-CiprianMuresan]

[Notes]:

• The issue is also reproducible on the Dev page.
• The issue is not reproducible on the Prod page.
• I've tried to reproduce this with many other files with different extensions and it seems to only happen with .txt files.

[Affected versions]:

• Firefox Release, Beta, Nightly
• Chrome

[Affected Platforms]:

• All Windows
• All Mac
• All Linux

[Steps to reproduce]:

1. Open the browser and navigate to https://send.stage.mozaws.net/.
2. Upload a file .txt file (>100kb) and copy the download link.
3. Paste the link in a new tab and press enter.
4. Click the "Download" button and observe the behavior.

[Expected result]:

• Download percentage is displayed.

[Actual results]:

• Only the "%" symbol is displayed.

[Additional notes]:

• Here is a screen recording shot of the issue on Stage and Dev:
  

[ehuggett]

I was able to reproduce with the following on dev and stage

• Firefox 52.3.0 (64-bit) from debian package repositories (on Debian 9)
• Firefox Developer Edition 56.0b3 (64-bit) from Mozilla (tarball) (also on Debian 9)

Using a file created as follows:
dd if=/dev/urandom of=101kb.txt bs=1024 count=101 did trigger the bug

• But the progress bar works when I change the file extension to rzr
• I have not tested files with no extension
• a 27byte file does not appear to trigger the bug

[ehuggett]

Somebody seems to have set the content-type header to something other than octet stream, why? (not yet on production)

[ehuggett]

oh dear... this also breaks if you upload an html file, I strongly suspect the Content-Type header is related

That header will be set to "text/html" on the response from https://send.dev.mozaws.net/assets/download/, does this violate "Web APIs must set a non-HTML content-type on all responses, including 300s, 400s and 500s (APP-NOHTML)" from #202? (remember encryption is technically optional as it is performed by the client so could this potentially be used to host html files on send?)

edit: added screenshot

[dannycoates]

This should be fixed as of e9405f4 and is up on https://send.dev.mozaws.net

The content-type was added to support mobile browsers but only the decrypted blob should have that type. The encrypted download should just be application/octet-stream.

[SoftVision-CiprianMuresan]

The issue is no longer reproducible on the Dev and Stage pages. Marking as verified.