Closes #9821 - DownloadService will use a default mime type if otherwise empty

[Mugurell]

Speculative fix (cannot reproduce the issue) for crashes where based on the
stacktrace the download's mime type was empty.

Pull Request checklist

• Quality: This PR builds and passes detekt/ktlint checks (A pre-push hook is recommended)
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry or does not need one
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features

After merge

• Milestone: Make sure issues closed by this pull request are added to the milestone of the version currently in development.
• Breaking Changes: If this is a breaking change, please push a draft PR on Reference Browser to address the breaking issues.

[codecov]

Codecov Report

Merging #9822 (d860b7d) into master (7e3b610) will increase coverage by 0.00%.
The diff coverage is 66.66%.

@@             Coverage Diff             @@
##             master    #9822     +/-   ##
===========================================
  Coverage     74.06%   74.07%             
+ Complexity     5656     5056    -600     
===========================================
  Files           772      702     -70     
  Lines         28763    25601   -3162     
  Branches       4741     4203    -538     
===========================================
- Hits          21303    18963   -2340     
+ Misses         4981     4430    -551     
+ Partials       2479     2208    -271     

Impacted Files	Coverage Δ	Complexity Δ
...va/mozilla/components/support/ktx/kotlin/String.kt	77.58% <0.00%> (-1.37%)	0.00 <0.00> (ø)
.../feature/downloads/AbstractFetchDownloadService.kt	75.24% <72.72%> (+1.47%)	96.00 <0.00> (ø)
...ozilla/components/feature/downloads/ext/Context.kt	55.00% <0.00%> (-45.00%)	0.00% <0.00%> (ø%)
...mponents/feature/downloads/DownloadNotification.kt	96.57% <0.00%> (-1.37%)	21.00% <0.00%> (-1.00%)
...s/concept/push/exceptions/SubscriptionException.kt
...ava/mozilla/components/concept/push/PushService.kt
...onents/lib/dataprotect/SecureAbove22Preferences.kt
...va/mozilla/components/service/sync/logins/Types.kt
...s/support/android/test/espresso/ViewInteraction.kt
...java/mozilla/components/feature/push/Connection.kt
... and 64 more

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[Amejia481]

We could re-use getSafeContentType that has the same logic plus it tries to extract the MimeTypefrom the physical file, what do you think?

[Mugurell]

Adding this new safety net allows for a quick and easy way to ensure we don't get that crash anymore.
Using getSafeContentType would mean taking another stab at inferring the mime type (which I would've preferred to not do if not neded (it is a bit of code executed..) but maybe it would help reducing the number of times */* is returned).
In the current implementation getSafeContentType returns DownloadUtils.sanitizeMimeType(resultContentType) ?: "*/*" and so it still has the possibility of returning an empty String.
Instead of wrapping getSafeContentType and others in getNotEmptyMimeType we could add one last check for empty strings in that method and use that.
Thank you!

[Mugurell]

I've updated the patch to use getSafeContentType.
Would appreciate if you could comment on the approach, if it's okay.
I'll work next on updating tests and documentation.

[mergify]

This pull request has conflicts when rebasing. Could you fix it @Mugurell? 🙏

[Amejia481]

Looks good, could we add tests for the new extension function.