Android 5.8.3: Sporadic E033: Redirect detected with Linkwarden backend behind Synology reverse proxy, no option to disable redirect check

[hscheele]

Which version of floccus are you using?

5.8.3

How many bookmarks do you have, roughly?

450

Are you using other means to sync bookmarks in parallel to floccus?

No

Sync method

Linkwarden

Which browser are you using? In case you are using the phone App, specify the Android or iOS version and device please.

Android 16

Which version of Nextcloud Bookmarks are you using? (if relevant)

No response

Which version of Nextcloud? (if relevant)

No response

What kind of WebDAV server are you using? (if relevant)

No response

Describe the Bug

On Android, Floccus sometimes fails to sync with the Linkwarden backend and shows the following error:

E033: Weiterleitung festgestellt. Vergewissern Sie sich, dass der angegebene Server die ausgewählte Synchronisierungsmethode unterstützt und die URL stimmt, die Sie eingegeben haben und nicht auf eine andere URL weiterleitet. Falls die Weiterleitung teil Ihres Server-Setups ist, können Sie diese Kontrolle in den Einstellungen deaktivieren.

In English: E033 “Redirect detected… If redirects are part of your server setup, you can disable this check in the settings.”
However, in the Android app (v5.8.3) I cannot find any setting to disable the redirect check, even though the error message suggests that this should be possible.

Important characteristics

The error is sporadic:

• Sometimes sync works.
• Sometimes sync fails with E033 on the same server and same network.

I have multiple Floccus instances.
Sometimes it helps to import the profile from one of my other working instances into this problematic instance.
After such an import, sync may work again for some time, but the error can come back later.

The Linkwarden instance is only reachable via the above Synology reverse proxy configuration (see details below). There is no extra redirect configured in Linkwarden

Observed behavior

Sometimes sync works without any errors.
Sometimes the same sync fails with E033: Redirect detected on Android.
In the Android app, there is no visible option to disable redirect detection, even though the error text explicitly mentions such an option.

---

Reverse proxy: Synology NAS Reverse Proxy

Source:

• Protocol: HTTPS
• Hostname: XXXXX (hidden here!)
• Port: 443
• HSTS: enabled

Destination:

• Protocol: HTTP
• Hostname: 10.10.1.100
• Port: 7461

Custom header tab

• Upgrade → $ http_upgrade
• Connection → $ connection_upgrade

Advanced tab

• Proxy connection timeout: 60 seconds
• Proxy send timeout: 60 seconds
• Proxy read timeout: 60 seconds
• Proxy HTTP version: HTTP 1.1
• “Use the error page returned by the target server”: enabled

Expected Behavior

Either:

• Floccus Android should not incorrectly detect a redirect in this setup (or should handle it more gracefully),or
• The Android app should provide the same “allow redirects / disable redirect check” setting that the error message refers to, so users behind reverse proxies can still use Floccus.

To Reproduce

1. Set up Linkwarden behind a Synology reverse proxy as described above.
2. Install Floccus 5.8.3 on Android.
3. Create a new account in Floccus with:

• Backend: Linkwarden
• Server URL: https://XXX (through Synology reverse proxy)
• Correct credentials.

4. Trigger a sync.

Debug log provided

• I have provided a debug log file

[github-actions]

Hello! 👋

Thank you for taking the time to open this issue with floccus. I know it's frustrating when software causes problems. You have made the right choice to come here and open an issue to make sure your problem gets looked at and if possible solved. Let me give you a short introduction on what to expect from this issue tracker to avoid misunderstandings. I'm Marcel. I created floccus a few years ago, and have been maintaining it since. I currently work for Nextcloud which leaves me with less time for side projects like this one than I used to have. I still try to answer all issues and if possible fix all bugs here, but it sometimes takes a while until I get to it. Until then, please be patient. It helps when you stick around to answer follow up questions I may have, as very few bugs can be fixed directly from the first bug report, without any interaction. If information is missing in your bug report and the issue cannot be solved without it, I will have to close the issue after a while. Note also that GitHub in general is a place where people meet to make software better together. Nobody here is under any obligation to help you, solve your problems or deliver on any expectations or demands you may have, but if enough people come together we can collaborate to make this software better. For everyone. Thus, if you can, you could also have a look at other issues to see whether you can help other people with your knowledge and experience. If you have coding experience it would also be awesome if you could step up to dive into the code and try to fix the odd bug yourself. Everyone will be thankful for extra helping hands! If you cannot lend a helping hand, to continue the development and maintenance of this project in a sustainable way, I ask that you donate to the project when opening an issue (or at least once your issue is solved), if you're not a donor already. You can find donation options at https://floccus.org/donate/. Thank you!

One last word: If you feel, at any point, like you need to vent, this is not the place for it; you can go to the Nextcloud forum, to twitter or somewhere else. But this is a technical issue tracker, so please make sure to focus on the tech and keep your opinions to yourself.

Thank you for reading through this primer. I look forward to working with you on this issue! Cheers! 💙

[marcelklehr]

Hey @hscheele
thank you for taking the time to give feedback by opening this issue!

In the Android app, there is no visible option to disable redirect detection, even though the error text explicitly mentions such an option.

That would indeed be a bug. I will fix this.

As this only happens on mobile, I think we can rule out the reverse proxy being wrongly configured. Linkwarden itself also doesn't even use redirects in its API code, I just checked that. That leaves more exotic redirects like access points that you have to pay for e.g. in airports or similar locations, where URLs might get redirected to a Captive portal. Is that possible?

[hscheele]

Hi @marcelklehr

Coming straight to your question: No, as URL is not redirected in an exotic way! What Synology is providing is very basic and also very limited in being further configured above what whas stated before. So, purely adding the option to disable redirect detection would probably do the job.

Feel free to get back to me directly if testing a later solution would make sense before an official release!