Can not install apks from File Manager or browser?

Question

In the answer to this question I specifically discovered that I could not install the VLC nightlies. It had nothing to do with that answer, which was on a question about which version of VLC was right for that device. But that question was in fact inspired by this problem: I never previously had an APK I couldn't install by merely downloading, when I am in the Android Web Browser, and it downloads the APK, I can click on it in the notification applet at the top. When I do, it says

Can not open file

When I open that file up with the LineageOS Files Manager, com.android.documentsui I get the same error. Now, I'm wanting to know what specifically is borked about just the VLC packages? Does anyone else get this problem? Why is that pm install ./appname.apk in the shell works, but the GUI doesn't?

I'm using LineageOS 14.1-20180616, based on Android 7.1.2.

— Evan Carroll | Sources

Answer

Installing

With the LineageOS File Manager

It seems that inside the File Manager, there are two discrete things Download a directory, and Downloads some broken nonsense shortcut link:

Does not work: On the left nav, you'll see Images Videos Audio Recent, and then Downloads Documents, and SM-P600. Installing from the Downloads on the right bar, gives this error.

Works: Going into the device at the bottom of the left nav (which is actually just a link to /data/media/0 and then clicking on Download will take you Download which is actually different from Downloads (plural and on the Left Nav). From this you can install the APK.

With the CLI

Enable ADB in the Settings

Run adb shell on the host

Browse to /sdcard/Downloads or /data/media/0/Download with cd. If you're unsure where the apk is located try running
```
find / -name 'VLC*-ARMv7.apk
```

Locate the apk and install with pm
```
pm install ./VLC*-ARMv7.apk
```

The problem

The problem seems to be that VLC web server answers the request with a response that has content-type: application/octet-stream like this,

$ curl -s -I "https://nightlies.videolan.org/build/android-armv7/VLC-Android-3.0.11-20180618-0249-ARMv7.apk" 

HTTP/2 200 

server: nginx/1.15.0

date: Tue, 19 Jun 2018 03:16:06 GMT

content-type: application/octet-stream

content-length: 25048251

last-modified: Mon, 18 Jun 2018 06:05:02 GMT

etag: "5b274b8e-17e34bb"

accept-ranges: bytes

x-clacks-overhead: GNU Terry Pratchett

strict-transport-security: max-age=31536000

Rather than application/vnd.android.package-archive. This means that you can't install through the browser, or the Downloads shortcut. This is because APK files are just zip files:

$ file VLC-Android-3.0.11-20180618-0249-ARMv7.apk 

VLC-Android-3.0.11-20180618-0249-ARMv7.apk: Zip archive data, at least v2.0 to extract

So what the File Manager and browser are trying to do is open them as such -- and you don't have something that hands Zip archive data 2.0+