[Bug]: Array to string conversion in CalDAV backend

[ChristophWurst]

⚠️ This issue respects the following points: ⚠️

• This is a bug, not a question or a configuration/webserver/proxy issue.
• This issue is not already reported on Github (I've searched it).
• Nextcloud Server is up to date. See Maintenance and Release Schedule for supported versions.
• Nextcloud Server is running on 64bit capable CPU, PHP and OS.
• I agree to follow Nextcloud's Code of Conduct.

Bug description

Array to string conversion at https://github.com/nextcloud/server/blob/v26.0.0rc1/apps/dav/lib/CalDAV/Activity/Backend.php#L561

server/apps/dav/lib/CalDAV/Activity/Backend.php

Line 561 in 6466c8e

$users = $this->getUsersForShares(array_intersect($sourceShares, $targetShares));

Steps to reproduce

1. Connect mac os to Nextcloud's CalDAV backend
2. ???

Expected behavior

No errors

Installation method

None

Operating system

None

PHP engine version

None

Web server

None

Database engine version

None

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

None

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

n/a

List of activated Apps

n/a

Nextcloud Signing status

No response

Nextcloud Logs

{
  "reqId": "9DlC6Z02DsTFC2tvNxU2",
  "level": 3,
  "time": "2023-03-03T06:56:13+00:00",
  "remoteAddr": "redacted",
  "user": "user123",
  "app": "PHP",
  "method": "MOVE",
  "url": "/remote.php/dav/calendars/user123/personal/sabredav-abc-def-ghi.ics",
  "message": "Array to string conversion at /var/www/cloud.nextcloud.com/nextcloud/apps/dav/lib/CalDAV/Activity/Backend.php#561",
  "userAgent": "macOS/13.1 (22C65) dataaccessd/1.0",
  "version": "26.0.0.8",
  "data": {
    "app": "PHP"
  },
  "id": "123def567"
}

Additional info

No response

[ChristophWurst]

array_intersect does not like nested array: https://3v4l.org/TYrqn

[tcitworld]

I just saw the same thing (in 25). I don't see how shares can contain an array itself. 🤔

[kartoffelheinz]

This bug prevents certain events from syncing (from Apple devices, mostly fantastical) and had been fixed in early 26 beta but apparently has now been re-introduced. Unfortunate. Any idea on when this is going to be fixed again?

[Pazu]

Still seeing this running 27.1.3:

{
    "reqId": "[removed]",
    "level": 3,
    "time": "2023-11-05T17:35:11+00:00",
    "remoteAddr": "[removed]",
    "user": "[removed]",
    "app": "PHP",
    "method": "MOVE",
    "url": "/remote.php/dav/calendars/[removed]/[removed]/[GUID].ics",
    "message": "Array to string conversion at /var/www/path_to_web_root/apps/dav/lib/CalDAV/Activity/Backend.php#561",
    "userAgent": "iOS/17.0.3 (21A360) dataaccessd/1.0",
    "version": "27.1.3.2",
    "data": {
        "app": "PHP"
    },
    "id": "[removed]"
}

[solracsf]

What if values are flatten before using the arrays, could this fix it?

$flatten = function ($array) use (&$flatten) {
	$result = [];
	foreach ($array as $value) {
		if (is_array($value)) {
			$result = array_merge($result, $flatten($value));
		} else {
			$result[] = $value;
		}
	}
	return $result;
};

$sourceShares = is_array($sourceShares) ? $flatten($sourceShares) : [];
$targetShares = is_array($targetShares) ? $flatten($targetShares) : [];

[jameskimmel]

Same error on 28.0.2

{
  "reqId": "removed",
  "level": 3,
  "time": "2024-02-21T11:07:11+00:00",
  "remoteAddr": "1.1.1.1",
  "user": "UserName1",
  "app": "PHP",
  "method": "MOVE",
  "url": "/remote.php/dav/calendars/UserName1/sitzungen_shared_by_UserName2/58B95D5D-32EA-490B-82E1-ADC31B854C3C.ics",
  "message": "Array to string conversion at /var/www/nextcloud/apps/dav/lib/CalDAV/Activity/Backend.php#561",
  "userAgent": "Mozilla/5.0 (iPad; CPU OS 15_6 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) CriOS/121.0.6167.171 Mobile/15E148 Safari/604.1",
  "version": "28.0.2.5",
  "data": {
    "app": "PHP"
  },
  "id": "65defd55416b7"
}

[joshtrichards]

Same solution as used in #43794 should work here (using array_map serialize/unserialize different approach taken in the final merged PR, but same idea). I don't have a test setup for this, so I'll leave trying it to someone that feels like giving it a shot + can also reproduce this situation on-demand.

[Quake85]

Also on my instance 30.0.1

What about a fix or update?

[Mer0me]

This bug prevents certain events from syncing (from Apple devices, mostly fantastical) and had been fixed in early 26 beta but apparently has now been re-introduced. Unfortunate. Any idea on when this is going to be fixed again?

We actually have some events not syncing only on some users' Iphones. Could you please develop your observations. It could help us to figure out what happened to these events.
The Array to string error throws every time we move an event from a calendar to another. But there is no evident correlation between moved events and missing events on Iphones.

[guckuck]

I have this problem too. I just updated to 30.0.2. I will observe this problem ...

{
  "reqId": "removed",
  "level": 3,
  "time": "2024-11-05T05:39:20+00:00",
  "remoteAddr": "IP",
  "user": "user.name",
  "app": "PHP",
  "method": "MOVE",
  "url": "/remote.php/dav/calendars/user.name/personal/A2829EA6-94ED-4E01-8FAD-D1879CAA78BF.ics",
  "message": "Array to string conversion at /var/www/nextcloud/apps/dav/lib/CalDAV/Activity/Backend.php#541",
  "userAgent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:132.0) Gecko/20100101 Firefox/132.0",
  "version": "30.0.1.2",
  "data": {
    "app": "PHP"
  },
  "id": "..."
}

[thibs43]

Hello,
Also got this error here, nextcloud server Nextcloud Hub 9 (30.0.2)
Client is on a Android phone syncing with calDav

[PHP] Error: Array to string conversion at /var/www/html/apps/dav/lib/CalDAV/Activity/Backend.php#541
	MOVE /remote.php/dav/calendars/---/personal/F3D54AEF-000-4D86-BB5A-D********75FAE.ics
	from 192.168.1.254 by *** at Nov 13, 2024, 10:13:11 PM

[Quake85]

Yes, i also Updated to 30.0.2, Same Problem. Also fresh/new Installation in my testing environment.

Ist’s clear, that this is a bug.

So please dear developers clear this Problem.

Thanks a lot

[jameskimmel]

I know this does not help most of you guys, but I can only say that the issue is gone for me.

I updated to 30.0.2, reconfigured my NGINX reverse proxy to include this

    location /.well-known/carddav {
    return 301 $scheme://$host/remote.php/dav;
    }

    location /.well-known/caldav {
    return 301 $scheme://$host/remote.php/dav;
    }

and also installed the calender via profiles on my iPhone. Works perfect and nothing in the logs.

[SebastianKrupinski]

Hi Everyone,

Would anyone with this issue here be able to provide a transmission intercept capture? As I don't have a Mac or iDevice to test with.

This seems to be caused by the MOVE method, but I need a reliable way to reproduce this issue to test and fix.

[Quake85]

Hey Sebastian,
If you could describe me what exactly to do, I can do this.
At the Moment I don‘t know exactly what you mean.

[SebastianKrupinski]

Hey Sebastian, If you could describe me what exactly to do, I can do this. At the Moment I don‘t know exactly what you mean.

I need to see the commands that the mac app is sending, the easiest way to do this would be to use tcpdump on the server and setup the Mac client to connect to NC over non encrypted HTTP.

tcpdump -i <interface> -w <output_file> port 80

[SebastianKrupinski]

You could also use something like mitmproxy to capture the encrypted connection if a HTTP setup or connection is not possible.

[Quake85]

Ok. I will try it the next days. Perhaps someone else who has this Problem is faster than me, but i will give my best to help you finding the fault.

[ChristophWurst]

I don't see how shares can contain an array itself. 🤔

Could it be cache value deserialization? Shares loaded from the db should not be nested.