Show HN: Gander, an Android file viewer that asks for no permissions

> That means the app can open a system browser using a URL containing the data it wants to transmit.

This can be mitigated by using an app like URLCheck [1], which you set as your default browser, and it shows and lets you edit the URL being opened before handing it off to your real browser. It also has neat features like choosing to open in incognito (if you use Firefox) and automatically removing tracking parameters.

[1] https://f-droid.org/packages/com.trianguloy.urlchecker

This is all very true, unfortunately. Google designed Android as a an OS for internet appliances. They're not interested in local-only apps working on local files.

But I think the OP is to be complimented for what they've built and their intention in making it local-only. I've long felt that apps that *genuinely" respect privacy are one of the few areas of opportunity still left in the mobile space. I wish there were more develpers building things like this.

You're aware that the only really secure computing device has no way to connect to a network and is under armed guard?

Edit: also that LLMs are tuned for "engagement" not for answers like "it's secure enough, move along"?

AOSP allows the internet permission to be denied per app (hence LineageOS and Graphene exposing it), it's just most OEMs ROMs don't expose it, you can draw your own conclusions from that.

I guess that makes sense. Since most non-privacy-focused Android distributions don't let users turn off the internet permission, keeping the permission secure likely ceased to be a priority.

The full list of bypasses is likely much larger because it doesn't fall in the scope of bug bounties.

GrapheneOS asks for internet permission when you install any app.

Why post AI-generated answers? Anyone reading your comment could do the same.

"I just asked Gemini, and it turns out that Mossad can steal my data anyways".

- An app without the INTERNET permission will crash the moment you try to access the internet. It's like a rite of passage of every android developer with every new project, you forgot the permission.

- Launching an Intent is EXTREMELY visible. It opens a full on browser. It's limited to a GET with a dedicated URL, so what are they going to do, stuff your data in query params ?

- Even in the case of another app being installed that would silently receive this intent and not pop an activity, you need a different app. It cannot be an activity added by the same package.

- Loading a Chrome Custom Tab opens a whole ass browser in front of you, think you're going to miss it ?

- Shared user IDs also require two different app installations and you cannot declare multiple. You also cannot have sharedUserId if you do not sign the apps with the same key. you cannot sharedUserId with Facebook, you need once again a dedicated app installation.

- A ContentProvider needs a dedicated permission on the writing app AND on the reading app, which is once again very visible.

I'll add more to your list: an app can request to write a file inside your downloads folder, and another one can show a popup asking you to open it! And if someone shows up with a hammer at your door, he can also hit your fingers really hard to make you tell him the data.

Android apps are, by default, very well isolated. INTERNET is a permission like any other, just not surfaced as a dangerous one (like permanent access to your background location would be), or a runtime one (like access to your current location while the app is in foreground)

I use a rooted phone and afwall+ which uses the underlying Linux firewall. There's also the mobile and WiFi data permissions you can change manually.

Christ that's depressing.

I'm assuming that all works even with application sandboxing (1) or am I mis-reading how that is applied to applications.

Man I need to move my movement to GrapheneOS up to be sooner.

(1) https://source.android.com/docs/security/app-sandbox

> If two apps from the same developer share a User ID (sharedUserId), they run in the same process and share all permissions

Good grief. What a huge vulnerability. Is there some benefit that justifies this?

Yeah fair I was too flat in the post... No INTERNET means my process can't reach the network. It doesn't stop an app passing data to something that can, so your list is right.

It's not a guarantee then, it's just a lot less to check. There's no silent route out so all that's left is what the app chooses to send via intents and Gander sends two, both when you tap something ("Share" and "Show in file manager")

Nothing anywhere builds a URL out of the file contents. No browser launch, no Custom Tabs and no shared user ID. The only content provider is closed to other apps. The one time a file goes anywhere is when you hit Share and pick the app, and what it gets is read access to that one file.

In case you grep it there's an https:// in ViewerActivity.kt. That's the local virtual host WebViewAssetLoader serves the bundled renderers from, it never leaves the process.

Added, it's in the README under Install now. Thanks for bringing that up!

Obtainium works just fine with the github source

That is listed in the Roadmap section right at the end of the README.md file

ods actually already works.. it goes through the same SheetJS path as xlsx and csv. But your question made me check properly and there's a bug... I never registered the OpenDocument mime type so Gander wont show up in the "open with" list when you tap a .ods. Opening it from inside the app works fine.

Fixed in the manifest just now, it'll be in the next build.

odt and odp dont work at all. odt is a fair ask.. its the same shape of problem as docx so it's doable. Less sure about odp though.. the pptx renderer is already the weakest part of this.

And yeah, fewer apps on the phone was pretty much the whole reason I started building this.

Seconded.

pptx by a mile. A slide is absolutely positioned shapes with a whole layout inheritance thing going on so the JS renderer ends up reimplementing a whole layout engine, and it gets you to "approximately right" and stops there. Charts I gave up on.

docx was annoying in a different way. Bullets came out as junk characters for a while and I couldnt work out why. I then found that Word writes them as private use area codepoints in the Symbol font so unless you have that exact font you get some junk. I just map them back to unicode after the render.

xlsx was the easy one, SheetJS does the hard part.

On faithful though none of this is faithful the way LibreOffice is. Its more that "you can read the document and it looks roughly right" which is what I wanted out of an app of 14MB.

Why would rendering a document need internet access?

Could you please recommend a comfortable personal firewall app for Android?

No, most people do not.

Firewalls are already a pain for desktop OS. They are basically unusable on mobile for normal users.

I had the goal to eliminate annoying ads in some apps that I use. I deleted the user data for those apps and also applied restrictions so they could no longer access internet. Ads still showed up.

I mostly stopped using these types of apps and switched to F-Droid alternatives.

Sorry, that's on my README. That line is under "Build from source" so it's what you need to compile it, not to run it. minSdk is 26, so Android 8 and up.

Android 14 is well past the floor, you're good to go!

Just installed it in my Android 10 phone and it works.

Which is also weird considering most of formats are just opened in a WebView with a respective JS-based viewer. Surely it can be backported?

Fair enough, fixed that in the README.

Thanks, Claude