Make SyncManager suspending (first part) (#1451)

* Introduce coroutine dispatcher for sync operations * Make `logSyncTimeBlocking` and `insertOrReplace` suspend functions * Suspend first bunch of SyncManager methods; move sync dispatcher usage to SyncManager * [WIP] Fix tests TODO: extract test framework changes to separate PR * Remove mainDispatcher from SyncManagerTest * Remove explicit coroutineScope naming
2025-12-23 23:17:50 -05:00 · 2025-05-12 15:52:54 +02:00
parent a15902e586
commit cfeb6b3974
16 changed files with 166 additions and 142 deletions
--- a/app/src/androidTest/kotlin/at/bitfire/davdroid/sync/SyncManagerTest.kt
+++ b/app/src/androidTest/kotlin/at/bitfire/davdroid/sync/SyncManagerTest.kt
@@ -25,9 +25,10 @@ import dagger.hilt.android.testing.BindValue
 import dagger.hilt.android.testing.HiltAndroidRule
 import dagger.hilt.android.testing.HiltAndroidTest
 import io.mockk.every
-import io.mockk.impl.annotations.MockK
+import io.mockk.impl.annotations.RelaxedMockK
 import io.mockk.junit4.MockKRule
 import io.mockk.mockk
+import kotlinx.coroutines.test.runTest
 import okhttp3.Protocol
 import okhttp3.internal.http.StatusLine
 import okhttp3.mockwebserver.MockResponse
@@ -45,6 +46,12 @@ import javax.inject.Inject
@HiltAndroidTest
 class SyncManagerTest {

+    @get:Rule
+    val hiltRule = HiltAndroidRule(this)
+
+    @get:Rule
+    val mockKRule = MockKRule(this)
+
    @Inject
    lateinit var accountSettingsFactory: AccountSettings.Factory

@@ -58,24 +65,19 @@ class SyncManagerTest {
    lateinit var syncManagerFactory: TestSyncManager.Factory

    @BindValue
-    @MockK(relaxed = true)
+    @RelaxedMockK
    lateinit var syncStatsRepository: DavSyncStatsRepository

    @Inject
    lateinit var workerFactory: HiltWorkerFactory

-    @get:Rule
-    val hiltRule = HiltAndroidRule(this)
-
-    @get:Rule
-    val mockKRule = MockKRule(this)
-
    private lateinit var account: Account
    private lateinit var server: MockWebServer

    @Before
    fun setUp() {
        hiltRule.inject()
+
        TestUtils.setUpWorkManager(context, workerFactory)

        account = TestAccount.create()
@@ -122,7 +124,7 @@ class SyncManagerTest {


    @Test
-    fun testPerformSync_503RetryAfter_DelaySeconds() {
+    fun testPerformSync_503RetryAfter_DelaySeconds() = runTest {
        server.enqueue(MockResponse()
            .setResponseCode(503)
            .setHeader("Retry-After", "60"))    // 60 seconds
@@ -139,7 +141,7 @@ class SyncManagerTest {
    }

    @Test
-    fun testPerformSync_FirstSync_Empty() {
+    fun testPerformSync_FirstSync_Empty() = runTest {
        val collection = LocalTestCollection() /* no last known ctag */
        server.enqueue(queryCapabilitiesResponse())

@@ -154,7 +156,7 @@ class SyncManagerTest {
    }

    @Test
-    fun testPerformSync_UploadNewMember_ETagOnPut() {
+    fun testPerformSync_UploadNewMember_ETagOnPut() = runTest {
        val collection = LocalTestCollection().apply {
            lastSyncState = SyncState(SyncState.Type.CTAG, "old-ctag")
            entries += LocalTestResource().apply {
@@ -197,7 +199,7 @@ class SyncManagerTest {
    }

    @Test
-    fun testPerformSync_UploadModifiedMember_ETagOnPut() {
+    fun testPerformSync_UploadModifiedMember_ETagOnPut() = runTest {
        val collection = LocalTestCollection().apply {
            lastSyncState = SyncState(SyncState.Type.CTAG, "old-ctag")
            entries += LocalTestResource().apply {
@@ -244,7 +246,7 @@ class SyncManagerTest {
    }

    @Test
-    fun testPerformSync_UploadModifiedMember_NoETagOnPut() {
+    fun testPerformSync_UploadModifiedMember_NoETagOnPut() = runTest {
        val collection = LocalTestCollection().apply {
            lastSyncState = SyncState(SyncState.Type.CTAG, "old-ctag")
            entries += LocalTestResource().apply {
@@ -289,7 +291,7 @@ class SyncManagerTest {
    }

    @Test
-    fun testPerformSync_UploadModifiedMember_412PreconditionFailed() {
+    fun testPerformSync_UploadModifiedMember_412PreconditionFailed() = runTest {
        val collection = LocalTestCollection().apply {
            lastSyncState = SyncState(SyncState.Type.CTAG, "old-ctag")
            entries += LocalTestResource().apply {
@@ -335,7 +337,7 @@ class SyncManagerTest {
    }

    @Test
-    fun testPerformSync_NoopOnMemberWithSameETag() {
+    fun testPerformSync_NoopOnMemberWithSameETag() = runTest {
        val collection = LocalTestCollection().apply {
            lastSyncState = SyncState(SyncState.Type.CTAG, "ctag1")
            entries += LocalTestResource().apply {
@@ -372,7 +374,7 @@ class SyncManagerTest {
    }

    @Test
-    fun testPerformSync_DownloadNewMember() {
+    fun testPerformSync_DownloadNewMember() = runTest {
        val collection = LocalTestCollection().apply {
            lastSyncState = SyncState(SyncState.Type.CTAG, "old-ctag")
        }
@@ -406,7 +408,7 @@ class SyncManagerTest {
    }

    @Test
-    fun testPerformSync_DownloadUpdatedMember() {
+    fun testPerformSync_DownloadUpdatedMember() = runTest {
        val collection = LocalTestCollection().apply {
            lastSyncState = SyncState(SyncState.Type.CTAG, "old-ctag")
            entries += LocalTestResource().apply {
@@ -444,7 +446,7 @@ class SyncManagerTest {
    }

    @Test
-    fun testPerformSync_RemoveVanishedMember() {
+    fun testPerformSync_RemoveVanishedMember() = runTest {
        val collection = LocalTestCollection().apply {
            lastSyncState = SyncState(SyncState.Type.CTAG, "old-ctag")
            entries += LocalTestResource().apply {
@@ -464,7 +466,7 @@ class SyncManagerTest {
    }

    @Test
-    fun testPerformSync_CTagDidntChange() {
+    fun testPerformSync_CTagDidntChange() = runTest {
        val collection = LocalTestCollection().apply {
            lastSyncState = SyncState(SyncState.Type.CTAG, "ctag1")
        }
--- a/app/src/androidTest/kotlin/at/bitfire/davdroid/sync/TestSyncManager.kt
+++ b/app/src/androidTest/kotlin/at/bitfire/davdroid/sync/TestSyncManager.kt
@@ -11,13 +11,14 @@ import at.bitfire.dav4jvm.Response
 import at.bitfire.dav4jvm.property.caldav.GetCTag
 import at.bitfire.davdroid.db.Collection
 import at.bitfire.davdroid.db.SyncState
+import at.bitfire.davdroid.di.SyncDispatcher
 import at.bitfire.davdroid.network.HttpClient
 import at.bitfire.davdroid.resource.LocalResource
-import at.bitfire.davdroid.settings.AccountSettings
 import at.bitfire.davdroid.util.DavUtils.lastSegment
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedFactory
 import dagger.assisted.AssistedInject
+import kotlinx.coroutines.CoroutineDispatcher
 import okhttp3.HttpUrl
 import okhttp3.RequestBody
 import okhttp3.RequestBody.Companion.toRequestBody
@@ -30,7 +31,8 @@ class TestSyncManager @AssistedInject constructor(
    @Assisted httpClient: HttpClient,
    @Assisted syncResult: SyncResult,
    @Assisted localCollection: LocalTestCollection,
-    @Assisted collection: Collection
+    @Assisted collection: Collection,
+    @SyncDispatcher syncDispatcher: CoroutineDispatcher
 ): SyncManager<LocalTestResource, LocalTestCollection, DavCollection>(
    account,
    httpClient,
@@ -38,7 +40,8 @@ class TestSyncManager @AssistedInject constructor(
    authority,
    syncResult,
    localCollection,
-    collection
+    collection,
+    syncDispatcher
 ) {

    @AssistedFactory
--- a/app/src/main/kotlin/at/bitfire/davdroid/db/SyncStatsDao.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/db/SyncStatsDao.kt
@@ -14,7 +14,7 @@ import kotlinx.coroutines.flow.Flow
 interface SyncStatsDao {

    @Insert(onConflict = OnConflictStrategy.REPLACE)
-    fun insertOrReplace(syncStats: SyncStats)
+    suspend fun insertOrReplace(syncStats: SyncStats)

    @Query("SELECT * FROM syncstats WHERE collectionId=:id")
    fun getByCollectionIdFlow(id: Long): Flow<List<SyncStats>>
--- a/app/src/main/kotlin/at/bitfire/davdroid/repository/DavSyncStatsRepository.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/repository/DavSyncStatsRepository.kt
@@ -40,7 +40,7 @@ class DavSyncStatsRepository @Inject constructor(
            }
        }

-    fun logSyncTimeBlocking(collectionId: Long, authority: String, lastSync: Long = System.currentTimeMillis()) {
+    suspend fun logSyncTime(collectionId: Long, authority: String, lastSync: Long = System.currentTimeMillis()) {
        dao.insertOrReplace(SyncStats(
            id = 0,
            collectionId = collectionId,
--- a/app/src/main/kotlin/at/bitfire/davdroid/sync/AddressBookSyncer.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/sync/AddressBookSyncer.kt
@@ -18,6 +18,7 @@ import at.bitfire.davdroid.sync.account.setAndVerifyUserData
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedFactory
 import dagger.assisted.AssistedInject
+import kotlinx.coroutines.runBlocking
 import java.util.logging.Level

 /**
@@ -108,7 +109,9 @@ class AddressBookSyncer @AssistedInject constructor(
                addressBook,
                collection
            )
-            syncManager.performSync()
+            runBlocking {
+                syncManager.performSync()
+            }

        } catch(e: Exception) {
            logger.log(Level.SEVERE, "Couldn't sync contacts", e)
--- a/app/src/main/kotlin/at/bitfire/davdroid/sync/CalendarSyncManager.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/sync/CalendarSyncManager.kt
@@ -20,6 +20,7 @@ import at.bitfire.dav4jvm.property.webdav.SyncToken
 import at.bitfire.davdroid.R
 import at.bitfire.davdroid.db.Collection
 import at.bitfire.davdroid.db.SyncState
+import at.bitfire.davdroid.di.SyncDispatcher
 import at.bitfire.davdroid.network.HttpClient
 import at.bitfire.davdroid.resource.LocalCalendar
 import at.bitfire.davdroid.resource.LocalEvent
@@ -32,6 +33,7 @@ import at.bitfire.ical4android.util.DateUtils
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedFactory
 import dagger.assisted.AssistedInject
+import kotlinx.coroutines.CoroutineDispatcher
 import net.fortuna.ical4j.model.Component
 import net.fortuna.ical4j.model.component.VAlarm
 import net.fortuna.ical4j.model.property.Action
@@ -56,7 +58,8 @@ class CalendarSyncManager @AssistedInject constructor(
    @Assisted syncResult: SyncResult,
    @Assisted localCalendar: LocalCalendar,
    @Assisted collection: Collection,
-    private val accountSettingsFactory: AccountSettings.Factory
+    accountSettingsFactory: AccountSettings.Factory,
+    @SyncDispatcher syncDispatcher: CoroutineDispatcher
 ): SyncManager<LocalEvent, LocalCalendar, DavCalendar>(
    account,
    httpClient,
@@ -64,7 +67,8 @@ class CalendarSyncManager @AssistedInject constructor(
    authority,
    syncResult,
    localCalendar,
-    collection
+    collection,
+    syncDispatcher
 ) {

    @AssistedFactory
@@ -144,7 +148,7 @@ class CalendarSyncManager @AssistedInject constructor(
        return super.processLocallyDeleted()
    }

-    override fun uploadDirty(): Boolean {
+    override suspend fun uploadDirty(): Boolean {
        var modified = false
        if (localCollection.readOnly) {
            for (event in localCollection.findDirty()) {
--- a/app/src/main/kotlin/at/bitfire/davdroid/sync/CalendarSyncer.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/sync/CalendarSyncer.kt
@@ -15,6 +15,7 @@ import at.bitfire.ical4android.AndroidCalendar
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedFactory
 import dagger.assisted.AssistedInject
+import kotlinx.coroutines.runBlocking

 /**
 * Sync logic for calendars
@@ -64,7 +65,9 @@ class CalendarSyncer @AssistedInject constructor(
            localCollection,
            remoteCollection
        )
-        syncManager.performSync()
+        runBlocking {
+            syncManager.performSync()
+        }
    }

 }
--- a/app/src/main/kotlin/at/bitfire/davdroid/sync/ContactsSyncManager.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/sync/ContactsSyncManager.kt
@@ -24,6 +24,7 @@ import at.bitfire.dav4jvm.property.webdav.SyncToken
 import at.bitfire.davdroid.R
 import at.bitfire.davdroid.db.Collection
 import at.bitfire.davdroid.db.SyncState
+import at.bitfire.davdroid.di.SyncDispatcher
 import at.bitfire.davdroid.network.HttpClient
 import at.bitfire.davdroid.resource.LocalAddress
 import at.bitfire.davdroid.resource.LocalAddressBook
@@ -44,6 +45,7 @@ import dagger.assisted.AssistedFactory
 import dagger.assisted.AssistedInject
 import ezvcard.VCardVersion
 import ezvcard.io.CannotParseException
+import kotlinx.coroutines.CoroutineDispatcher
 import okhttp3.HttpUrl
 import okhttp3.HttpUrl.Companion.toHttpUrlOrNull
 import okhttp3.MediaType
@@ -104,7 +106,8 @@ class ContactsSyncManager @AssistedInject constructor(
    @Assisted collection: Collection,
    val dirtyVerifier: Optional<ContactDirtyVerifier>,
    accountSettingsFactory: AccountSettings.Factory,
-    private val httpClientBuilder: HttpClient.Builder
+    private val httpClientBuilder: HttpClient.Builder,
+    @SyncDispatcher syncDispatcher: CoroutineDispatcher
 ): SyncManager<LocalAddress, LocalAddressBook, DavAddressBook>(
    account,
    httpClient,
@@ -112,7 +115,8 @@ class ContactsSyncManager @AssistedInject constructor(
    authority,
    syncResult,
    localAddressBook,
-    collection
+    collection,
+    syncDispatcher
 ) {

    @AssistedFactory
@@ -228,7 +232,7 @@ class ContactsSyncManager @AssistedInject constructor(
                // mirror deletions to remote collection (DELETE)
                super.processLocallyDeleted()

-    override fun uploadDirty(): Boolean {
+    override suspend fun uploadDirty(): Boolean {
        var modified = false

        if (localCollection.readOnly) {
--- a/app/src/main/kotlin/at/bitfire/davdroid/sync/JtxSyncManager.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/sync/JtxSyncManager.kt
@@ -19,6 +19,7 @@ import at.bitfire.dav4jvm.property.webdav.SyncToken
 import at.bitfire.davdroid.R
 import at.bitfire.davdroid.db.Collection
 import at.bitfire.davdroid.db.SyncState
+import at.bitfire.davdroid.di.SyncDispatcher
 import at.bitfire.davdroid.network.HttpClient
 import at.bitfire.davdroid.resource.LocalJtxCollection
 import at.bitfire.davdroid.resource.LocalJtxICalObject
@@ -29,6 +30,7 @@ import at.bitfire.ical4android.JtxICalObject
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedFactory
 import dagger.assisted.AssistedInject
+import kotlinx.coroutines.CoroutineDispatcher
 import okhttp3.HttpUrl
 import okhttp3.RequestBody
 import okhttp3.RequestBody.Companion.toRequestBody
@@ -44,7 +46,8 @@ class JtxSyncManager @AssistedInject constructor(
    @Assisted authority: String,
    @Assisted syncResult: SyncResult,
    @Assisted localCollection: LocalJtxCollection,
-    @Assisted collection: Collection
+    @Assisted collection: Collection,
+    @SyncDispatcher syncDispatcher: CoroutineDispatcher
 ): SyncManager<LocalJtxICalObject, LocalJtxCollection, DavCalendar>(
    account,
    httpClient,
@@ -52,7 +55,8 @@ class JtxSyncManager @AssistedInject constructor(
    authority,
    syncResult,
    localCollection,
-    collection
+    collection,
+    syncDispatcher
 ) {

    @AssistedFactory
--- a/app/src/main/kotlin/at/bitfire/davdroid/sync/JtxSyncer.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/sync/JtxSyncer.kt
@@ -16,6 +16,7 @@ import at.bitfire.ical4android.TaskProvider
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedFactory
 import dagger.assisted.AssistedInject
+import kotlinx.coroutines.runBlocking

 /**
 * Sync logic for jtx board
@@ -77,7 +78,9 @@ class JtxSyncer @AssistedInject constructor(
            localCollection,
            remoteCollection
        )
-        syncManager.performSync()
+        runBlocking {
+            syncManager.performSync()
+        }
    }

 }
--- a/app/src/main/kotlin/at/bitfire/davdroid/sync/SyncManager.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/sync/SyncManager.kt
@@ -41,9 +41,10 @@ import at.bitfire.davdroid.sync.account.InvalidAccountException
 import at.bitfire.ical4android.CalendarStorageException
 import at.bitfire.vcard4android.ContactsStorageException
 import dagger.hilt.android.qualifiers.ApplicationContext
+import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.coroutineScope
 import kotlinx.coroutines.launch
-import kotlinx.coroutines.runBlocking
+import kotlinx.coroutines.withContext
 import okhttp3.HttpUrl
 import okhttp3.RequestBody
 import java.io.IOException
@@ -79,7 +80,8 @@ abstract class SyncManager<ResourceType: LocalResource<*>, out CollectionType: L
    val authority: String,
    val syncResult: SyncResult,
    val localCollection: CollectionType,
-    val collection: Collection
+    val collection: Collection,
+    val syncDispatcher: CoroutineDispatcher
 ) {

    enum class SyncAlgorithm {
@@ -87,13 +89,6 @@ abstract class SyncManager<ResourceType: LocalResource<*>, out CollectionType: L
        COLLECTION_SYNC
    }

-    companion object {
-
-        /** Maximum number of resources that are requested with one multiget request. */
-        const val MAX_MULTIGET_RESOURCES = 10
-
-    }
-

    @Inject
    lateinit var accountRepository: AccountRepository
@@ -135,7 +130,7 @@ abstract class SyncManager<ResourceType: LocalResource<*>, out CollectionType: L
        } ?: emptyMap()
    }

-    fun performSync() {
+    suspend fun performSync() = withContext(syncDispatcher) {
        // dismiss previous error notifications
        syncNotificationManager.dismissInvalidResource(localCollectionTag = localCollection.tag)

@@ -143,9 +138,9 @@ abstract class SyncManager<ResourceType: LocalResource<*>, out CollectionType: L
            logger.info("Preparing synchronization")
            if (!prepare()) {
                logger.info("No reason to synchronize, aborting")
-                return
+                return@withContext
            }
-            syncStatsRepository.logSyncTimeBlocking(collection.id, authority)
+            syncStatsRepository.logSyncTime(collection.id, authority)

            logger.info("Querying server capabilities")
            var remoteSyncState = queryCapabilities()
@@ -366,11 +361,10 @@ abstract class SyncManager<ResourceType: LocalResource<*>, out CollectionType: L
     *
     * @return whether local resources have been processed so that a synchronization is always necessary
     */
-    protected open fun uploadDirty(): Boolean {
+    protected open suspend fun uploadDirty(): Boolean {
        var numUploaded = 0

-        // upload dirty resources (parallelized)
-        runBlocking {
+        coroutineScope {    // structured concurrency
            for (local in localCollection.findDirty())
                launch {
                    SyncException.wrapWithLocalResource(local) {
@@ -546,80 +540,78 @@ abstract class SyncManager<ResourceType: LocalResource<*>, out CollectionType: L
     *
     * @param listRemote function to list remote resources (for instance, all since a certain sync-token)
     */
-    protected open fun syncRemote(listRemote: (MultiResponseCallback) -> Unit) {
-        runBlocking {
-            // download queue
-            val toDownload = LinkedBlockingQueue<HttpUrl>()
-            fun download(url: HttpUrl?) {
-                if (url != null)
-                    toDownload += url
+    protected open suspend fun syncRemote(listRemote: (MultiResponseCallback) -> Unit) = coroutineScope {    // structured concurrency
+        // download queue
+        val toDownload = LinkedBlockingQueue<HttpUrl>()
+        fun download(url: HttpUrl?) {
+            if (url != null)
+                toDownload += url

-                if (toDownload.size >= MAX_MULTIGET_RESOURCES || url == null) {
-                    while (toDownload.isNotEmpty()) {
-                        val bunch = LinkedList<HttpUrl>()
-                        toDownload.drainTo(bunch, MAX_MULTIGET_RESOURCES)
-                        launch {
-                            downloadRemote(bunch)
-                        }
+            if (toDownload.size >= MAX_MULTIGET_RESOURCES || url == null) {
+                while (toDownload.isNotEmpty()) {
+                    val bunch = LinkedList<HttpUrl>()
+                    toDownload.drainTo(bunch, MAX_MULTIGET_RESOURCES)
+                    launch {
+                        downloadRemote(bunch)
                    }
                }
            }
-
-            coroutineScope {    // structured concurrency: blocks until all inner coroutines are finished
-                listRemote { response, relation ->
-                    // ignore non-members
-                    if (relation != Response.HrefRelation.MEMBER)
-                        return@listRemote
-
-                    // ignore collections
-                    if (response[at.bitfire.dav4jvm.property.webdav.ResourceType::class.java]?.types?.contains(at.bitfire.dav4jvm.property.webdav.ResourceType.COLLECTION) == true)
-                        return@listRemote
-
-                    val name = response.hrefName()
-
-                    if (response.isSuccess()) {
-                        logger.fine("Found remote resource: $name")
-
-                        launch {
-                            val local = localCollection.findByName(name)
-                            SyncException.wrapWithLocalResource(local) {
-                                if (local == null) {
-                                    logger.info("$name has been added remotely, queueing download")
-                                    download(response.href)
-                                } else {
-                                    val localETag = local.eTag
-                                    val remoteETag = response[GetETag::class.java]?.eTag
-                                        ?: throw DavException("Server didn't provide ETag")
-                                    if (localETag == remoteETag) {
-                                        logger.info("$name has not been changed on server (ETag still $remoteETag)")
-                                    } else {
-                                        logger.info("$name has been changed on server (current ETag=$remoteETag, last known ETag=$localETag)")
-                                        download(response.href)
-                                    }
-
-                                    // mark as remotely present, so that this resource won't be deleted at the end
-                                    local.updateFlags(LocalResource.FLAG_REMOTELY_PRESENT)
-                                }
-                            }
-                        }
-
-                    } else if (response.status?.code == HttpURLConnection.HTTP_NOT_FOUND) {
-                        // collection sync: resource has been deleted on remote server
-                        launch {
-                            localCollection.findByName(name)?.let { local ->
-                                SyncException.wrapWithLocalResource(local) {
-                                    logger.info("$name has been deleted on server, deleting locally")
-                                    local.delete()
-                                }
-                            }
-                        }
-                    }
-                }
-            }
-
-            // download remaining resources
-            download(null)
        }
+
+        coroutineScope {    // structured concurrency
+            listRemote { response, relation ->
+                // ignore non-members
+                if (relation != Response.HrefRelation.MEMBER)
+                    return@listRemote
+
+                // ignore collections
+                if (response[at.bitfire.dav4jvm.property.webdav.ResourceType::class.java]?.types?.contains(at.bitfire.dav4jvm.property.webdav.ResourceType.COLLECTION) == true)
+                    return@listRemote
+
+                val name = response.hrefName()
+
+                if (response.isSuccess()) {
+                    logger.fine("Found remote resource: $name")
+
+                    launch {
+                        val local = localCollection.findByName(name)
+                        SyncException.wrapWithLocalResource(local) {
+                            if (local == null) {
+                                logger.info("$name has been added remotely, queueing download")
+                                download(response.href)
+                            } else {
+                                val localETag = local.eTag
+                                val remoteETag = response[GetETag::class.java]?.eTag
+                                    ?: throw DavException("Server didn't provide ETag")
+                                if (localETag == remoteETag) {
+                                    logger.info("$name has not been changed on server (ETag still $remoteETag)")
+                                } else {
+                                    logger.info("$name has been changed on server (current ETag=$remoteETag, last known ETag=$localETag)")
+                                    download(response.href)
+                                }
+
+                                // mark as remotely present, so that this resource won't be deleted at the end
+                                local.updateFlags(LocalResource.FLAG_REMOTELY_PRESENT)
+                            }
+                        }
+                    }
+
+                } else if (response.status?.code == HttpURLConnection.HTTP_NOT_FOUND) {
+                    // collection sync: resource has been deleted on remote server
+                    launch {
+                        localCollection.findByName(name)?.let { local ->
+                            SyncException.wrapWithLocalResource(local) {
+                                logger.info("$name has been deleted on server, deleting locally")
+                                local.delete()
+                            }
+                        }
+                    }
+                }
+            }
+        }
+
+        // download remaining resources
+        download(null)
    }

    protected abstract fun listAllRemote(callback: MultiResponseCallback)
@@ -771,4 +763,12 @@ abstract class SyncManager<ResourceType: LocalResource<*>, out CollectionType: L

    protected abstract fun notifyInvalidResourceTitle(): String

+
+    companion object {
+
+        /** Maximum number of resources that are requested with one multiget request. */
+        const val MAX_MULTIGET_RESOURCES = 10
+
+    }
+
 }
--- a/app/src/main/kotlin/at/bitfire/davdroid/sync/TaskSyncer.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/sync/TaskSyncer.kt
@@ -16,6 +16,7 @@ import at.bitfire.ical4android.TaskProvider
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedFactory
 import dagger.assisted.AssistedInject
+import kotlinx.coroutines.runBlocking

 /**
 * Sync logic for tasks in CalDAV collections ({@code VTODO}).
@@ -78,7 +79,9 @@ class TaskSyncer @AssistedInject constructor(
            localCollection,
            remoteCollection
        )
-        syncManager.performSync()
+        runBlocking {
+            syncManager.performSync()
+        }
    }

 }
--- a/app/src/main/kotlin/at/bitfire/davdroid/sync/TasksSyncManager.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/sync/TasksSyncManager.kt
@@ -18,6 +18,7 @@ import at.bitfire.dav4jvm.property.webdav.SyncToken
 import at.bitfire.davdroid.R
 import at.bitfire.davdroid.db.Collection
 import at.bitfire.davdroid.db.SyncState
+import at.bitfire.davdroid.di.SyncDispatcher
 import at.bitfire.davdroid.network.HttpClient
 import at.bitfire.davdroid.resource.LocalResource
 import at.bitfire.davdroid.resource.LocalTask
@@ -28,6 +29,7 @@ import at.bitfire.ical4android.Task
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedFactory
 import dagger.assisted.AssistedInject
+import kotlinx.coroutines.CoroutineDispatcher
 import okhttp3.HttpUrl
 import okhttp3.RequestBody
 import okhttp3.RequestBody.Companion.toRequestBody
@@ -46,7 +48,8 @@ class TasksSyncManager @AssistedInject constructor(
    @Assisted authority: String,
    @Assisted syncResult: SyncResult,
    @Assisted localCollection: LocalTaskList,
-    @Assisted collection: Collection
+    @Assisted collection: Collection,
+    @SyncDispatcher syncDispatcher: CoroutineDispatcher
 ): SyncManager<LocalTask, LocalTaskList, DavCalendar>(
    account,
    httpClient,
@@ -54,7 +57,8 @@ class TasksSyncManager @AssistedInject constructor(
    authority,
    syncResult,
    localCollection,
-    collection
+    collection,
+    syncDispatcher
 ) {

    @AssistedFactory
--- a/app/src/main/kotlin/at/bitfire/davdroid/sync/worker/BaseSyncWorker.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/sync/worker/BaseSyncWorker.kt
@@ -36,10 +36,8 @@ import at.bitfire.davdroid.sync.worker.BaseSyncWorker.Companion.commonTag
 import at.bitfire.davdroid.ui.NotificationRegistry
 import at.bitfire.ical4android.TaskProvider
 import dagger.Lazy
-import kotlinx.coroutines.CoroutineDispatcher
 import kotlinx.coroutines.delay
 import kotlinx.coroutines.runInterruptible
-import kotlinx.coroutines.withContext
 import java.util.Collections
 import java.util.logging.Level
 import java.util.logging.Logger
@@ -47,8 +45,7 @@ import javax.inject.Inject

 abstract class BaseSyncWorker(
    context: Context,
-    private val workerParams: WorkerParameters,
-    private val syncDispatcher: CoroutineDispatcher
+    private val workerParams: WorkerParameters
 ) : CoroutineWorker(context, workerParams) {

    @Inject
@@ -142,7 +139,7 @@ abstract class BaseSyncWorker(
        }
    }

-    suspend fun doSyncWork(account: Account, dataType: SyncDataType): Result = withContext(syncDispatcher) {
+    suspend fun doSyncWork(account: Account, dataType: SyncDataType): Result {
        logger.info("Running ${javaClass.name}: account=$account, dataType=$dataType")

        // pass possibly supplied flags to the selected syncer
@@ -176,7 +173,7 @@ abstract class BaseSyncWorker(
                        taskSyncer.create(account, currentProvider, extras, syncResult)
                    else -> {
                        logger.warning("No valid tasks provider found, aborting sync")
-                        return@withContext Result.failure()
+                        return Result.failure()
                    }
                }
            }
@@ -208,7 +205,7 @@ abstract class BaseSyncWorker(
                        delay(blockDuration * 1000)

                    logger.warning("Retrying on soft error (attempt $runAttemptCount of $MAX_RUN_ATTEMPTS)")
-                    return@withContext Result.retry()
+                    return Result.retry()
                }

                logger.warning("Max retries on soft errors reached ($runAttemptCount of $MAX_RUN_ATTEMPTS). Treating as failed")
@@ -225,7 +222,7 @@ abstract class BaseSyncWorker(
                }

                output.putBoolean(OUTPUT_TOO_MANY_RETRIES, true)
-                return@withContext Result.failure(output.build())
+                return Result.failure(output.build())
            }

            // If no soft error found, dismiss sync error notification
@@ -239,12 +236,12 @@ abstract class BaseSyncWorker(
            // Note: SyncManager should have notified the user
            if (syncResult.hasHardError()) {
                logger.log(Level.WARNING, "Hard error while syncing", syncResult)
-                return@withContext Result.failure(output.build())
+                return Result.failure(output.build())
            }
        }

        logger.log(Level.INFO, "Sync worker succeeded", syncResult)
-        return@withContext Result.success(output.build())
+        return Result.success(output.build())
    }


--- a/app/src/main/kotlin/at/bitfire/davdroid/sync/worker/OneTimeSyncWorker.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/sync/worker/OneTimeSyncWorker.kt
@@ -12,12 +12,10 @@ import androidx.work.ForegroundInfo
 import androidx.work.WorkManager
 import androidx.work.WorkerParameters
 import at.bitfire.davdroid.R
-import at.bitfire.davdroid.di.SyncDispatcher
 import at.bitfire.davdroid.sync.SyncDataType
 import at.bitfire.davdroid.ui.NotificationRegistry
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedInject
-import kotlinx.coroutines.CoroutineDispatcher

 /**
 * One-time sync worker.
@@ -29,9 +27,8 @@ import kotlinx.coroutines.CoroutineDispatcher
@HiltWorker
 class OneTimeSyncWorker @AssistedInject constructor(
    @Assisted appContext: Context,
-    @Assisted workerParams: WorkerParameters,
-    @SyncDispatcher syncDispatcher: CoroutineDispatcher
-) : BaseSyncWorker(appContext, workerParams, syncDispatcher) {
+    @Assisted workerParams: WorkerParameters
+) : BaseSyncWorker(appContext, workerParams) {

    /**
     * Used by WorkManager to show a foreground service notification for expedited jobs on Android <12.
--- a/app/src/main/kotlin/at/bitfire/davdroid/sync/worker/PeriodicSyncWorker.kt
+++ b/app/src/main/kotlin/at/bitfire/davdroid/sync/worker/PeriodicSyncWorker.kt
@@ -10,12 +10,10 @@ import androidx.annotation.VisibleForTesting
 import androidx.hilt.work.HiltWorker
 import androidx.work.WorkManager
 import androidx.work.WorkerParameters
-import at.bitfire.davdroid.di.SyncDispatcher
 import at.bitfire.davdroid.sync.SyncDataType
 import dagger.assisted.Assisted
 import dagger.assisted.AssistedFactory
 import dagger.assisted.AssistedInject
-import kotlinx.coroutines.CoroutineDispatcher

 /**
 * Handles scheduled sync requests.
@@ -36,9 +34,8 @@ import kotlinx.coroutines.CoroutineDispatcher
@HiltWorker
 class PeriodicSyncWorker @AssistedInject constructor(
    @Assisted appContext: Context,
-    @Assisted workerParams: WorkerParameters,
-    @SyncDispatcher syncDispatcher: CoroutineDispatcher
-) : BaseSyncWorker(appContext, workerParams, syncDispatcher) {
+    @Assisted workerParams: WorkerParameters
+) : BaseSyncWorker(appContext, workerParams) {

    @AssistedFactory
    @VisibleForTesting