InterruptedIOException during calendar sync

[soeftware]

For about a week (might coincide with update to 4.2.2) there have been syncing problems for random calendars on my phone. The calendar the problem occurs in varies from call to call. Upload of new events does also not work. The server is running Nextcloud 24.0.2.

Relevant log excerpt (this occurs after several other calendars on the same account have run through correctly with the same settings):
2022-06-29 08:57:30 139622 [HttpClient] --> PROPFIND [Calendar URL redacted] h2
2022-06-29 08:57:30 139622 [HttpClient] Depth: 0
2022-06-29 08:57:30 139622 [HttpClient] User-Agent: DAVx5/4.2.2-gplay (2022/06/21; dav4jvm; okhttp/4.9.3) Android/11
2022-06-29 08:57:30 139622 [HttpClient] Accept-Language: de-DE, de;q=0.7, *;q=0.5
2022-06-29 08:57:30 139622 [HttpClient] Content-Type: application/xml; charset=utf-8
2022-06-29 08:57:30 139622 [HttpClient] Content-Length: 290
2022-06-29 08:57:30 139622 [HttpClient] Host: [Host redacted]
2022-06-29 08:57:30 139622 [HttpClient] Connection: Keep-Alive
2022-06-29 08:57:30 139622 [HttpClient] Accept-Encoding: gzip
2022-06-29 08:57:30 139622 [HttpClient] Cookie: [redacted]; __Host-nc_sameSiteCookielax=true; oc_sessionPassphrase=[redacted]; __Host-nc_sameSiteCookiestrict=true
2022-06-29 08:57:30 139622 [HttpClient]
2022-06-29 08:57:30 139622 [HttpClient] <CAL:max-resource-size /><n0:getctag xmlns:n0="http://calendarserver.org/ns/" />
2022-06-29 08:57:30 139622 [HttpClient] --> END PROPFIND (290-byte body)
2022-06-29 08:57:30 139622 [at.bitfire.dav4jvm.BasicDigestAuthHandler] Adding Basic authorization header for [Calendar URL redacted]
2022-06-29 08:57:38 139641 [syncadapter.SyncAdapterService] Sync thread cancelled! Interrupting sync
2022-06-29 08:57:38 139622 [HttpClient] <-- HTTP FAILED: java.io.InterruptedIOException
2022-06-29 08:57:38 139622 [syncadapter.CalendarsSyncAdapterService] Couldn't sync calendars
EXCEPTION java.io.InterruptedIOException
at okhttp3.internal.http2.Http2Stream.waitForIo$okhttp(Http2Stream.kt:3)
at okhttp3.internal.http2.Http2ExchangeCodec.readResponseHeaders(Http2ExchangeCodec.kt:5)
at okhttp3.internal.connection.Exchange.readResponseHeaders(Exchange.kt:1)
at okhttp3.internal.http.CallServerInterceptor.intercept(CallServerInterceptor.kt:39)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:16)
at at.bitfire.dav4jvm.BasicDigestAuthHandler.intercept(BasicDigestAuthHandler.kt:4)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:16)
at okhttp3.logging.HttpLoggingInterceptor.intercept(HttpLoggingInterceptor.kt:75)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:16)
at okhttp3.internal.connection.ConnectInterceptor.intercept(ConnectInterceptor.kt:32)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:16)
at okhttp3.internal.cache.CacheInterceptor.intercept(CacheInterceptor.kt:182)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:16)
at okhttp3.internal.http.BridgeInterceptor.intercept(BridgeInterceptor.kt:37)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:16)
at okhttp3.internal.http.RetryAndFollowUpInterceptor.intercept(RetryAndFollowUpInterceptor.kt:36)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:16)
at at.bitfire.davdroid.HttpClient$UserAgentInterceptor.intercept(HttpClient.kt:7)
at okhttp3.internal.http.RealInterceptorChain.proceed(RealInterceptorChain.kt:16)
at okhttp3.internal.connection.RealCall.getResponseWithInterceptorChain$okhttp(RealCall.kt:25)
at okhttp3.internal.connection.RealCall.execute(RealCall.kt:12)
at at.bitfire.dav4jvm.DavResource$propfind$2.invoke(DavResource.kt:8)
at at.bitfire.dav4jvm.DavResource$propfind$2.invoke(DavResource.kt:1)
at at.bitfire.dav4jvm.DavResource.followRedirects$build(DavResource.kt:1)
at at.bitfire.dav4jvm.DavResource.propfind(DavResource.kt:10)
at at.bitfire.davdroid.syncadapter.CalendarSyncManager$queryCapabilities$1.invoke(CalendarSyncManager.kt:3)
at at.bitfire.davdroid.syncadapter.CalendarSyncManager$queryCapabilities$1.invoke(CalendarSyncManager.kt:1)
at at.bitfire.davdroid.syncadapter.SyncManager.remoteExceptionContext(SyncManager.kt:1)
at at.bitfire.davdroid.syncadapter.SyncManager.remoteExceptionContext(SyncManager.kt:5)
at at.bitfire.davdroid.syncadapter.CalendarSyncManager.queryCapabilities(Unknown Source:5)
at at.bitfire.davdroid.syncadapter.SyncManager$performSync$1.invoke(SyncManager.kt:8)
at at.bitfire.davdroid.syncadapter.SyncManager$performSync$1.invoke(SyncManager.kt:1)
at at.bitfire.davdroid.syncadapter.SyncManager.unwrapExceptions(SyncManager.kt:1)
at at.bitfire.davdroid.syncadapter.SyncManager.performSync(SyncManager.kt:2)
at at.bitfire.davdroid.syncadapter.CalendarsSyncAdapterService$CalendarsSyncAdapter.sync(CalendarsSyncAdapterService.kt:14)
at at.bitfire.davdroid.syncadapter.SyncAdapterService$SyncAdapter$onPerformSync$1.invoke(SyncAdapterService.kt:6)
at at.bitfire.davdroid.syncadapter.SyncAdapterService$SyncAdapter$onPerformSync$1.invoke(SyncAdapterService.kt:1)
at at.bitfire.davdroid.ConcurrentUtils.runSingle(ConcurrentUtils.kt:2)
at at.bitfire.davdroid.syncadapter.SyncAdapterService$SyncAdapter.onPerformSync(SyncAdapterService.kt:3)
at android.content.AbstractThreadedSyncAdapter$SyncThread.run(AbstractThreadedSyncAdapter.java:334)

2022-06-29 08:57:38 139622 [syncadapter.CalendarsSyncAdapterService] Calendar sync complete
2022-06-29 08:57:38 139622 [syncadapter.SyncAdapterService] Sync for (com.android.calendar, Account {name=[redacted], type=bitfire.at.davdroid}) finished
PARAMETER #0 = SyncResult: stats []

[devvv4ever]

It seems that your Android is somehow disrupting the sync process. DAVx5 does never trigger or run the sync on its own. It's sync processes are always called and managed by the system (until we maybe sometime move away from the Android Sync Framework which is currently planned for the end of the year) and this process seems to be cancelled. DAVx5 is always syncing in background and many device manufacturers don't like that apps perform things on their own. You should have a look at certain battery optimizations on your device and make sure that DAVx5 is whitelisted. Please also have a look at dontklillmyapp.com and look for hints for your specific device (=like app pinning).

You can additionally try to put DAVx5 into "foreground" by activating a permanent notification in the DAVx5 settings. Maybe that helps, too.

[soeftware]

There have been no Android updates lately, so this is rather improbable for the recent problems. It has worked perfectly for some months until recently. Battery settings are correct, DAVx5 is exempted from battery optimizations.
I noticed that the sync abort / exception always happens immediately after the "Adding Basic authorization header" step in the logs. I also took a look into the changes introduced in 4.2.2 and found that that httpClient is now handled differently. Is it possible there are some changes in the used http client which handles authentication differently?

[soeftware]

I tried installing 4.2.1 manually and running the sync there. The same problem occurs, so it's probably not the 4.2.2 update.

[soeftware]

And another interesting tidbit: After reconnecting DAVx5 through the NextCloud app instead of manually adding the server & account, everything seems to work like a charm again.