feat: syncing etag and overall improvement. (#1155)

* chore: don't log the access token from google.

Signed-off-by: KaiserBh <kaiserbh@proton.me>

* chore: don't log the access token from google.

Signed-off-by: KaiserBh <kaiserbh@proton.me>

* chore: forgot to add sy stuff.

The customInfo and readEntries wasn't taken into account, so when it was disabled it will always sync it because it's true by default in BackupOptions.kt. Should be fixed and now it doesn't reset the check mark.

Signed-off-by: KaiserBh <kaiserbh@proton.me>

* fix: same device sync.

When same device is initiating the sync just update the remote that.

Signed-off-by: KaiserBh <kaiserbh@proton.me>

* refactor: throw early.

When there is network failure or any sort during downloading just throw exception and stop syncing.

Signed-off-by: KaiserBh <kaiserbh@proton.me>

* refactor(gdrive): stream the json.

People with over 3k library can't sync because we are hitting OOM ```java.util.concurrent.ExecutionException: java.lang.OutOfMemoryError: Failed to allocate a 370950192 byte allocation with 25165824 free bytes and 281MB until OOM, target footprint 333990992, growth limit 603979776```. This should fix that for them but only gdrive.

Signed-off-by: KaiserBh <kaiserbh@proton.me>

* feat: a demo for sync with new api

* refactor: perform early null checks

* feat: restore even if push failed

* feat: switch to protobuf

* chore: show error notification when sync fails.

Signed-off-by: KaiserBh <kaiserbh@proton.me>

* fix: update order by merge

* fix: call pushSyncData twice

---------

Signed-off-by: KaiserBh <kaiserbh@proton.me>
Co-authored-by: Cologler <skyoflw@gmail.com>

app/src/main/java/eu/kanade/domain/sync/SyncPreferences.kt

@@ -13,6 +13,8 @@ class SyncPreferences(
     fun clientAPIKey() = preferenceStore.getString("sync_client_api_key", "")
     fun lastSyncTimestamp() = preferenceStore.getLong(Preference.appStateKey("last_sync_timestamp"), 0L)
 
+    fun lastSyncEtag() =  preferenceStore.getString("sync_etag", "")
+
     fun syncInterval() = preferenceStore.getInt("sync_interval", 0)
     fun syncService() = preferenceStore.getInt("sync_service", 0)
 
@@ -53,6 +55,11 @@ class SyncPreferences(
             appSettings = preferenceStore.getBoolean("appSettings", true).get(),
             sourceSettings = preferenceStore.getBoolean("sourceSettings", true).get(),
             privateSettings = preferenceStore.getBoolean("privateSettings", true).get(),
+
+            // SY -->
+            customInfo = preferenceStore.getBoolean("customInfo", true).get(),
+            readEntries = preferenceStore.getBoolean("readEntries", true).get()
+            // SY <--
         )
     }
 
@@ -65,6 +72,11 @@ class SyncPreferences(
         preferenceStore.getBoolean("appSettings", true).set(syncSettings.appSettings)
         preferenceStore.getBoolean("sourceSettings", true).set(syncSettings.sourceSettings)
         preferenceStore.getBoolean("privateSettings", true).set(syncSettings.privateSettings)
+
+        // SY -->
+        preferenceStore.getBoolean("customInfo", true).set(syncSettings.customInfo)
+        preferenceStore.getBoolean("readEntries", true).set(syncSettings.readEntries)
+        // SY <--
     }
 
     fun getSyncTriggerOptions(): SyncTriggerOptions {

app/src/main/java/eu/kanade/domain/sync/models/SyncSettings.kt

@@ -9,4 +9,9 @@ data class SyncSettings(
     val appSettings: Boolean = true,
     val sourceSettings: Boolean = true,
     val privateSettings: Boolean = false,
+
+    // SY -->
+    val customInfo: Boolean = true,
+    val readEntries: Boolean = true
+    // SY <--
 )

app/src/main/java/eu/kanade/presentation/more/settings/screen/data/SyncSettingsSelector.kt

@@ -124,6 +124,11 @@ private class SyncSettingsSelectorModel(
                 appSettings = syncSettings.appSettings,
                 sourceSettings = syncSettings.sourceSettings,
                 privateSettings = syncSettings.privateSettings,
+
+                // SY -->
+                customInfo = syncSettings.customInfo,
+                readEntries = syncSettings.readEntries,
+                // SY <--
             )
         }
 
@@ -137,6 +142,11 @@ private class SyncSettingsSelectorModel(
                 appSettings = backupOptions.appSettings,
                 sourceSettings = backupOptions.sourceSettings,
                 privateSettings = backupOptions.privateSettings,
+
+                // SY -->
+                customInfo = backupOptions.customInfo,
+                readEntries = backupOptions.readEntries,
+                // SY <--
             )
         }
     }

app/src/main/java/eu/kanade/tachiyomi/data/sync/SyncManager.kt

@@ -88,7 +88,14 @@ class SyncManager(
             appSettings = syncOptions.appSettings,
             sourceSettings = syncOptions.sourceSettings,
             privateSettings = syncOptions.privateSettings,
+
+            // SY -->
+            customInfo = syncOptions.customInfo,
+            readEntries = syncOptions.readEntries,
+            // SY <--
         )
+
+        logcat(LogPriority.DEBUG) { "Begin create backup" }
         val backup = Backup(
             backupManga = backupCreator.backupMangas(databaseManga, backupOptions),
             backupCategories = backupCreator.backupCategories(backupOptions),
@@ -100,9 +107,11 @@ class SyncManager(
             backupSavedSearches = backupCreator.backupSavedSearches(),
             // SY <--
         )
+        logcat(LogPriority.DEBUG) { "End create backup" }
 
         // Create the SyncData object
         val syncData = SyncData(
+            deviceId = syncPreferences.uniqueDeviceID(),
             backup = backup,
         )
 
@@ -129,8 +138,22 @@ class SyncManager(
 
         val remoteBackup = syncService?.doSync(syncData)
 
+        if (remoteBackup == null) {
+            logcat(LogPriority.DEBUG) { "Skip restore due to network issues" }
+            // should we call showSyncError?
+            return
+        }
+
+        if (remoteBackup === syncData.backup){
+            // nothing changed
+            logcat(LogPriority.DEBUG) { "Skip restore due to remote was overwrite from local" }
+            syncPreferences.lastSyncTimestamp().set(Date().time)
+            notifier.showSyncSuccess("Sync completed successfully")
+            return
+        }
+
         // Stop the sync early if the remote backup is null or empty
-        if (remoteBackup?.backupManga?.size == 0) {
+        if (remoteBackup.backupManga?.size == 0) {
             notifier.showSyncError("No data found on remote server.")
             return
         }
@@ -143,7 +166,6 @@ class SyncManager(
             return
         }
 
-        if (remoteBackup != null) {
         val (filteredFavorites, nonFavorites) = filterFavoritesAndNonFavorites(remoteBackup)
         updateNonFavorites(nonFavorites)
 
@@ -187,7 +209,6 @@ class SyncManager(
             logcat(LogPriority.ERROR) { "Failed to write sync data to file" }
         }
     }
-    }
 
     private fun writeSyncDataToCache(context: Context, backup: Backup): Uri? {
         val cacheFile = File(context.cacheDir, "tachiyomi_sync_data.proto.gz")

app/src/main/java/eu/kanade/tachiyomi/data/sync/service/GoogleDriveSyncService.kt

@@ -11,6 +11,7 @@ import com.google.api.client.googleapis.auth.oauth2.GoogleClientSecrets
 import com.google.api.client.googleapis.auth.oauth2.GoogleCredential
 import com.google.api.client.googleapis.auth.oauth2.GoogleTokenResponse
 import com.google.api.client.http.ByteArrayContent
+import com.google.api.client.http.InputStreamContent
 import com.google.api.client.http.javanet.NetHttpTransport
 import com.google.api.client.json.JsonFactory
 import com.google.api.client.json.jackson2.JacksonFactory
@@ -18,9 +19,12 @@ import com.google.api.services.drive.Drive
 import com.google.api.services.drive.DriveScopes
 import com.google.api.services.drive.model.File
 import eu.kanade.domain.sync.SyncPreferences
+import eu.kanade.tachiyomi.data.backup.models.Backup
 import kotlinx.coroutines.delay
-import kotlinx.serialization.encodeToString
+import kotlinx.coroutines.launch
 import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.decodeFromStream
+import kotlinx.serialization.json.encodeToStream
 import logcat.LogPriority
 import logcat.logcat
 import tachiyomi.core.common.i18n.stringResource
@@ -30,8 +34,9 @@ import tachiyomi.i18n.MR
 import tachiyomi.i18n.sy.SYMR
 import uy.kohesive.injekt.Injekt
 import uy.kohesive.injekt.api.get
-import java.io.ByteArrayOutputStream
 import java.io.IOException
+import java.io.PipedInputStream
+import java.io.PipedOutputStream
 import java.time.Instant
 import java.util.zip.GZIPInputStream
 import java.util.zip.GZIPOutputStream
@@ -65,7 +70,43 @@ class GoogleDriveSyncService(context: Context, json: Json, syncPreferences: Sync
 
     private val googleDriveService = GoogleDriveService(context)
 
-    override suspend fun beforeSync() {
+    override suspend fun doSync(syncData: SyncData): Backup? {
+        beforeSync()
+
+        try {
+            val remoteSData = pullSyncData()
+
+            if (remoteSData != null ){
+                // Get local unique device ID
+                val localDeviceId = syncPreferences.uniqueDeviceID()
+                val lastSyncDeviceId = remoteSData.deviceId
+
+                // Log the device IDs
+                logcat(LogPriority.DEBUG, "SyncService") {
+                    "Local device ID: $localDeviceId, Last sync device ID: $lastSyncDeviceId"
+                }
+
+                // check if the last sync was done by the same device if so overwrite the remote data with the local data
+                return if (lastSyncDeviceId == localDeviceId) {
+                    pushSyncData(syncData)
+                    syncData.backup
+                }else{
+                    // Merge the local and remote sync data
+                    val mergedSyncData = mergeSyncData(syncData, remoteSData)
+                    pushSyncData(mergedSyncData)
+                    mergedSyncData.backup
+                }
+            }
+
+            pushSyncData(syncData)
+            return syncData.backup
+        } catch (e: Exception) {
+            logcat(LogPriority.ERROR, "SyncService") { "Error syncing: ${e.message}" }
+            return null
+        }
+    }
+
+    private suspend fun beforeSync() {
         try {
             googleDriveService.refreshToken()
             val drive = googleDriveService.driveService
@@ -121,13 +162,9 @@ class GoogleDriveSyncService(context: Context, json: Json, syncPreferences: Sync
         }
     }
 
-    override suspend fun pullSyncData(): SyncData? {
+    private fun pullSyncData(): SyncData? {
-        val drive = googleDriveService.driveService
+        val drive = googleDriveService.driveService ?:
-
-        if (drive == null) {
-            logcat(LogPriority.DEBUG) { "Google Drive service not initialized" }
         throw Exception(context.stringResource(SYMR.strings.google_drive_not_signed_in))
-        }
 
         val fileList = getAppDataFileList(drive)
         if (fileList.isEmpty()) {
@@ -138,75 +175,53 @@ class GoogleDriveSyncService(context: Context, json: Json, syncPreferences: Sync
         val gdriveFileId = fileList[0].id
         logcat(LogPriority.DEBUG) { "Google Drive File ID: $gdriveFileId" }
 
-        val outputStream = ByteArrayOutputStream()
         try {
-            drive.files().get(gdriveFileId).executeMediaAndDownloadTo(outputStream)
+            drive.files().get(gdriveFileId).executeMediaAsInputStream().use { inputStream ->
-            logcat(LogPriority.DEBUG) { "File downloaded successfully" }
+                GZIPInputStream(inputStream).use { gzipInputStream ->
+                    return Json.decodeFromStream(SyncData.serializer(), gzipInputStream)
+                }
+            }
         } catch (e: Exception) {
             logcat(LogPriority.ERROR, throwable = e) { "Error downloading file" }
-            return null
+            throw Exception("Failed to download sync data: ${e.message}", e)
-        }
-
-        return withIOContext {
-            try {
-                val gzipInputStream = GZIPInputStream(outputStream.toByteArray().inputStream())
-                val jsonString = gzipInputStream.bufferedReader().use { it.readText() }
-                val syncData = json.decodeFromString(SyncData.serializer(), jsonString)
-                this@GoogleDriveSyncService.logcat(LogPriority.DEBUG) { "JSON deserialized successfully" }
-                syncData
-            } catch (e: Exception) {
-                this@GoogleDriveSyncService.logcat(
-                    LogPriority.ERROR,
-                    throwable = e,
-                ) { "Failed to convert json to sync data with kotlinx.serialization" }
-                throw Exception(e.message, e)
-            }
         }
     }
 
-    override suspend fun pushSyncData(syncData: SyncData) {
+    private suspend fun pushSyncData(syncData: SyncData) {
-        val jsonData = json.encodeToString(syncData)
         val drive = googleDriveService.driveService
             ?: throw Exception(context.stringResource(SYMR.strings.google_drive_not_signed_in))
 
         val fileList = getAppDataFileList(drive)
-        val byteArrayOutputStream = ByteArrayOutputStream()
+
+        PipedOutputStream().use { pos ->
+            PipedInputStream(pos).use { pis ->
                 withIOContext {
-            GZIPOutputStream(byteArrayOutputStream).use { gzipOutputStream ->
+                    // Start a coroutine or a background thread to write JSON to the PipedOutputStream
-                gzipOutputStream.write(jsonData.toByteArray(Charsets.UTF_8))
+                    launch {
+                        GZIPOutputStream(pos).use { gzipOutputStream ->
+                            Json.encodeToStream(SyncData.serializer(), syncData, gzipOutputStream)
                         }
-            this@GoogleDriveSyncService.logcat(LogPriority.DEBUG) { "JSON serialized successfully" }
                     }
 
-        val byteArrayContent = ByteArrayContent("application/octet-stream", byteArrayOutputStream.toByteArray())
-
-        try {
                     if (fileList.isNotEmpty()) {
-                // File exists, so update it
                         val fileId = fileList[0].id
-                drive.files().update(fileId, null, byteArrayContent).execute()
+                        val mediaContent = InputStreamContent("application/gzip", pis)
+                        drive.files().update(fileId, null, mediaContent).execute()
                         logcat(LogPriority.DEBUG) { "Updated existing sync data file in Google Drive with file ID: $fileId" }
                     } else {
-                // File doesn't exist, so create it
                         val fileMetadata = File().apply {
                             name = remoteFileName
                             mimeType = "application/gzip"
                             parents = listOf("appDataFolder")
                         }
-                val uploadedFile = drive.files().create(fileMetadata, byteArrayContent)
+                        val mediaContent = InputStreamContent("application/gzip", pis)
+                        val uploadedFile = drive.files().create(fileMetadata, mediaContent)
                             .setFields("id")
                             .execute()
-
+                        logcat(LogPriority.DEBUG) { "Created new sync data file in Google Drive with file ID: ${uploadedFile.id}" }
-                logcat(
+                    }
-                    LogPriority.DEBUG,
+                }
-                ) { "Created new sync data file in Google Drive with file ID: ${uploadedFile.id}" }
             }
-
-            // Data has been successfully pushed or updated, delete the lock file
-            deleteLockFile(drive)
-        } catch (e: Exception) {
-            logcat(LogPriority.ERROR, throwable = e) { "Failed to push or update sync data" }
-            throw Exception(context.stringResource(SYMR.strings.error_uploading_sync_data) + ": ${e.message}", e)
         }
     }
 
@@ -393,7 +408,6 @@ class GoogleDriveService(private val context: Context) {
     }
     internal suspend fun refreshToken() = withIOContext {
         val refreshToken = syncPreferences.googleDriveRefreshToken().get()
-        val accessToken = syncPreferences.googleDriveAccessToken().get()
 
         val jsonFactory: JsonFactory = JacksonFactory.getDefaultInstance()
         val secrets = GoogleClientSecrets.load(
@@ -413,16 +427,12 @@ class GoogleDriveService(private val context: Context) {
 
         credential.refreshToken = refreshToken
 
-        this@GoogleDriveService.logcat(LogPriority.DEBUG) { "Refreshing access token with: $refreshToken" }
-
         try {
             credential.refreshToken()
             val newAccessToken = credential.accessToken
             // Save the new access token
             syncPreferences.googleDriveAccessToken().set(newAccessToken)
             setupGoogleDriveService(newAccessToken, credential.refreshToken)
-            this@GoogleDriveService
-                .logcat(LogPriority.DEBUG) { "Google Access token refreshed old: $accessToken new: $newAccessToken" }
         } catch (e: TokenResponseException) {
             if (e.details.error == "invalid_grant") {
                 // The refresh token is invalid, prompt the user to sign in again

app/src/main/java/eu/kanade/tachiyomi/data/sync/service/SyncService.kt

@@ -17,6 +17,7 @@ import logcat.logcat
 
 @Serializable
 data class SyncData(
+    val deviceId: String = "",
     val backup: Backup? = null,
 )
 
@@ -25,38 +26,7 @@ abstract class SyncService(
     val json: Json,
     val syncPreferences: SyncPreferences,
 ) {
-    open suspend fun doSync(syncData: SyncData): Backup? {
+    abstract suspend fun doSync(syncData: SyncData): Backup?;
-        beforeSync()
-
-        val remoteSData = pullSyncData()
-
-        val finalSyncData =
-            if (remoteSData == null) {
-                pushSyncData(syncData)
-                syncData
-            } else {
-                val mergedSyncData = mergeSyncData(syncData, remoteSData)
-                pushSyncData(mergedSyncData)
-                mergedSyncData
-            }
-
-        return finalSyncData.backup
-    }
-
-    /**
-     * For refreshing tokens and other possible operations before connecting to the remote storage
-     */
-    open suspend fun beforeSync() {}
-
-    /**
-     * Download sync data from the remote storage
-     */
-    abstract suspend fun pullSyncData(): SyncData?
-
-    /**
-     * Upload sync data to the remote storage
-     */
-    abstract suspend fun pushSyncData(syncData: SyncData)
 
     /**
      * Merges the local and remote sync data into a single JSON string.
@@ -65,11 +35,17 @@ abstract class SyncService(
      * @param remoteSyncData The SData containing the remote sync data.
      * @return The JSON string containing the merged sync data.
      */
-    private fun mergeSyncData(localSyncData: SyncData, remoteSyncData: SyncData): SyncData {
+    protected fun mergeSyncData(localSyncData: SyncData, remoteSyncData: SyncData): SyncData {
-        val mergedMangaList = mergeMangaLists(localSyncData.backup?.backupManga, remoteSyncData.backup?.backupManga)
         val mergedCategoriesList =
             mergeCategoriesLists(localSyncData.backup?.backupCategories, remoteSyncData.backup?.backupCategories)
 
+        val mergedMangaList = mergeMangaLists(
+            localSyncData.backup?.backupManga,
+            remoteSyncData.backup?.backupManga,
+            localSyncData.backup?.backupCategories ?: emptyList(),
+            remoteSyncData.backup?.backupCategories ?: emptyList(),
+            mergedCategoriesList)
+
         val mergedSourcesList =
             mergeSourcesLists(localSyncData.backup?.backupSources, remoteSyncData.backup?.backupSources)
         val mergedPreferencesList =
@@ -101,6 +77,7 @@ abstract class SyncService(
 
         // Create the merged SData object
         return SyncData(
+            deviceId = syncPreferences.uniqueDeviceID(),
             backup = mergedBackup,
         )
     }
@@ -117,6 +94,9 @@ abstract class SyncService(
     private fun mergeMangaLists(
         localMangaList: List<BackupManga>?,
         remoteMangaList: List<BackupManga>?,
+        localCategories: List<BackupCategory>,
+        remoteCategories: List<BackupCategory>,
+        mergedCategories: List<BackupCategory>,
     ): List<BackupManga> {
         val logTag = "MergeMangaLists"
 
@@ -135,6 +115,18 @@ abstract class SyncService(
         val localMangaMap = localMangaListSafe.associateBy { mangaCompositeKey(it) }
         val remoteMangaMap = remoteMangaListSafe.associateBy { mangaCompositeKey(it) }
 
+        val localCategoriesMapByOrder = localCategories.associateBy { it.order }
+        val remoteCategoriesMapByOrder = remoteCategories.associateBy { it.order }
+        val mergedCategoriesMapByName = mergedCategories.associateBy { it.name }
+
+        fun updateCategories(theManga: BackupManga, theMap: Map<Long, BackupCategory>): BackupManga {
+            return theManga.copy(categories = theManga.categories.mapNotNull {
+                theMap[it]?.let { category ->
+                    mergedCategoriesMapByName[category.name]?.order
+                }
+            })
+        }
+
         logcat(LogPriority.DEBUG, logTag) {
             "Starting merge. Local list size: ${localMangaListSafe.size}, Remote list size: ${remoteMangaListSafe.size}"
         }
@@ -145,20 +137,26 @@ abstract class SyncService(
 
             // New version comparison logic
             when {
-                local != null && remote == null -> local
+                local != null && remote == null -> updateCategories(local, localCategoriesMapByOrder)
-                local == null && remote != null -> remote
+                local == null && remote != null -> updateCategories(remote, remoteCategoriesMapByOrder)
                 local != null && remote != null -> {
                     // Compare versions to decide which manga to keep
                     if (local.version >= remote.version) {
                         logcat(LogPriority.DEBUG, logTag) {
                             "Keeping local version of ${local.title} with merged chapters."
                         }
-                        local.copy(chapters = mergeChapters(local.chapters, remote.chapters))
+                        updateCategories(
+                            local.copy(chapters = mergeChapters(local.chapters, remote.chapters)),
+                            localCategoriesMapByOrder
+                        )
                     } else {
                         logcat(LogPriority.DEBUG, logTag) {
                             "Keeping remote version of ${remote.title} with merged chapters."
                         }
-                        remote.copy(chapters = mergeChapters(local.chapters, remote.chapters))
+                        updateCategories(
+                            remote.copy(chapters = mergeChapters(local.chapters, remote.chapters)),
+                            remoteCategoriesMapByOrder
+                        )
                     }
                 }
                 else -> null // No manga found for key

app/src/main/java/eu/kanade/tachiyomi/data/sync/service/SyncYomiSyncService.kt

@@ -2,23 +2,26 @@ package eu.kanade.tachiyomi.data.sync.service
 
 import android.content.Context
 import eu.kanade.domain.sync.SyncPreferences
+import eu.kanade.tachiyomi.data.backup.models.Backup
+import eu.kanade.tachiyomi.data.backup.models.BackupSerializer
 import eu.kanade.tachiyomi.data.sync.SyncNotifier
 import eu.kanade.tachiyomi.network.GET
-import eu.kanade.tachiyomi.network.PATCH
+import eu.kanade.tachiyomi.network.PUT
-import eu.kanade.tachiyomi.network.POST
 import eu.kanade.tachiyomi.network.await
-import kotlinx.coroutines.delay
+import kotlinx.serialization.SerializationException
-import kotlinx.serialization.SerialName
-import kotlinx.serialization.Serializable
-import kotlinx.serialization.encodeToString
 import kotlinx.serialization.json.Json
+import kotlinx.serialization.protobuf.ProtoBuf
 import logcat.LogPriority
+import logcat.logcat
 import okhttp3.Headers
-import okhttp3.MediaType.Companion.toMediaTypeOrNull
+import okhttp3.MediaType.Companion.toMediaType
 import okhttp3.OkHttpClient
-import okhttp3.RequestBody.Companion.gzip
 import okhttp3.RequestBody.Companion.toRequestBody
-import tachiyomi.core.common.util.system.logcat
+import org.apache.http.HttpStatus
+import tachiyomi.core.common.i18n.stringResource
+import tachiyomi.i18n.MR
+import uy.kohesive.injekt.Injekt
+import uy.kohesive.injekt.api.get
 import java.util.concurrent.TimeUnit
 
 class SyncYomiSyncService(
@@ -26,140 +29,117 @@ class SyncYomiSyncService(
     json: Json,
     syncPreferences: SyncPreferences,
     private val notifier: SyncNotifier,
+
+    private val protoBuf: ProtoBuf = Injekt.get(),
 ) : SyncService(context, json, syncPreferences) {
 
-    @Serializable
+    private class SyncYomiException(message: String?) : Exception(message)
-    enum class SyncStatus {
-        @SerialName("pending")
-        Pending,
 
-        @SerialName("syncing")
+    override suspend fun doSync(syncData: SyncData): Backup? {
-        Syncing,
+        try {
+            val (remoteData, etag) = pullSyncData()
 
-        @SerialName("success")
+            val finalSyncData = if (remoteData != null){
-        Success,
+                assert(etag.isNotEmpty()) { "ETag should never be empty if remote data is not null" }
+                logcat(LogPriority.DEBUG, "SyncService") {
+                    "Try update remote data with ETag($etag)"
+                }
+                mergeSyncData(syncData, remoteData)
+            } else {
+                // init or overwrite remote data
+                logcat(LogPriority.DEBUG) {
+                    "Try overwrite remote data with ETag($etag)"
+                }
+                syncData
             }
 
-    @Serializable
+            pushSyncData(finalSyncData, etag)
-    data class LockFile(
+            return finalSyncData.backup
-        @SerialName("id")
-        val id: Int?,
-        @SerialName("user_api_key")
-        val userApiKey: String?,
-        @SerialName("acquired_by")
-        val acquiredBy: String?,
-        @SerialName("last_synced")
-        val lastSynced: String?,
-        @SerialName("status")
-        val status: SyncStatus,
-        @SerialName("acquired_at")
-        val acquiredAt: String?,
-        @SerialName("expires_at")
-        val expiresAt: String?,
-    )
 
-    @Serializable
+        } catch (e: Exception) {
-    data class LockfileCreateRequest(
+            logcat(LogPriority.ERROR) { "Error syncing: ${e.message}" }
-        @SerialName("acquired_by")
+            notifier.showSyncError(e.message)
-        val acquiredBy: String,
+            return null
-    )
+        }
+    }
 
-    @Serializable
+    private suspend fun pullSyncData(): Pair<SyncData?, String> {
-    data class LockfilePatchRequest(
-        @SerialName("user_api_key")
-        val userApiKey: String,
-        @SerialName("acquired_by")
-        val acquiredBy: String,
-    )
-
-    override suspend fun beforeSync() {
         val host = syncPreferences.clientHost().get()
         val apiKey = syncPreferences.clientAPIKey().get()
-        val lockFileApi = "$host/api/sync/lock"
+        val downloadUrl = "$host/api/sync/content"
-        val deviceId = syncPreferences.uniqueDeviceID()
-        val client = OkHttpClient()
-        val headers = Headers.Builder().add("X-API-Token", apiKey).build()
-        val json = Json { ignoreUnknownKeys = true }
 
-        val createLockfileRequest = LockfileCreateRequest(deviceId)
+        val headersBuilder = Headers.Builder().add("X-API-Token", apiKey)
-        val createLockfileJson = json.encodeToString(createLockfileRequest)
+        val lastETag = syncPreferences.lastSyncEtag().get()
-
+        if (lastETag != "") {
-        val patchRequest = LockfilePatchRequest(apiKey, deviceId)
+            headersBuilder.add("If-None-Match", lastETag)
-        val patchJson = json.encodeToString(patchRequest)
-
-        val lockFileRequest = GET(
-            url = lockFileApi,
-            headers = headers,
-        )
-
-        val lockFileCreate = POST(
-            url = lockFileApi,
-            headers = headers,
-            body = createLockfileJson.toRequestBody("application/json; charset=utf-8".toMediaTypeOrNull()),
-        )
-
-        val lockFileUpdate = PATCH(
-            url = lockFileApi,
-            headers = headers,
-            body = patchJson.toRequestBody("application/json; charset=utf-8".toMediaTypeOrNull()),
-        )
-
-        // create lock file first
-        client.newCall(lockFileCreate).await()
-        // update lock file acquired_by
-        client.newCall(lockFileUpdate).await()
-
-        var backoff = 2000L // Start with 2 seconds
-        val maxBackoff = 32000L // Maximum backoff time e.g., 32 seconds
-        var lockFile: LockFile
-        do {
-            val response = client.newCall(lockFileRequest).await()
-            val responseBody = response.body.string()
-            lockFile = json.decodeFromString<LockFile>(responseBody)
-            logcat(LogPriority.DEBUG) { "SyncYomi lock file status: ${lockFile.status}" }
-
-            if (lockFile.status != SyncStatus.Success) {
-                logcat(LogPriority.DEBUG) { "Lock file not ready, retrying in $backoff ms..." }
-                delay(backoff)
-                backoff = (backoff * 2).coerceAtMost(maxBackoff)
         }
-        } while (lockFile.status != SyncStatus.Success)
+        val headers = headersBuilder.build()
-
-        // update lock file acquired_by
-        client.newCall(lockFileUpdate).await()
-    }
-
-    override suspend fun pullSyncData(): SyncData? {
-        val host = syncPreferences.clientHost().get()
-        val apiKey = syncPreferences.clientAPIKey().get()
-        val downloadUrl = "$host/api/sync/download"
-
-        val client = OkHttpClient()
-        val headers = Headers.Builder().add("X-API-Token", apiKey).build()
 
         val downloadRequest = GET(
             url = downloadUrl,
             headers = headers,
         )
 
+        val client = OkHttpClient()
         val response = client.newCall(downloadRequest).await()
-        val responseBody = response.body.string()
 
-        return if (response.isSuccessful) {
+        if (response.code == HttpStatus.SC_NOT_MODIFIED) {
-            json.decodeFromString<SyncData>(responseBody)
+            // not modified
+            assert(lastETag.isNotEmpty())
+            logcat(LogPriority.INFO) {
+                "Remote server not modified"
+            }
+            return Pair(null, lastETag)
+        } else if (response.code == HttpStatus.SC_NOT_FOUND) {
+            // maybe got deleted from remote
+            return Pair(null, "")
+        }
+
+        if (response.isSuccessful) {
+            val newETag = response.headers["ETag"]
+                .takeIf { it?.isNotEmpty() == true } ?: throw SyncYomiException("Missing ETag")
+
+            val byteArray = response.body.byteStream().use {
+                return@use it.readBytes()
+            }
+
+            return try {
+                val backup = protoBuf.decodeFromByteArray(BackupSerializer, byteArray)
+                return Pair(SyncData(backup = backup), newETag)
+            } catch (_: SerializationException) {
+                logcat(LogPriority.INFO) {
+                    "Bad content responsed from server"
+                }
+                // the body is invalid
+                // return default value so we can overwrite it
+                Pair(null, "")
+            }
+
         } else {
+            val responseBody = response.body.string()
             notifier.showSyncError("Failed to download sync data: $responseBody")
-            responseBody.let { logcat(LogPriority.ERROR) { "SyncError:$it" } }
+            logcat(LogPriority.ERROR) { "SyncError: $responseBody" }
-            null
+            throw SyncYomiException("Failed to download sync data: $responseBody")
         }
     }
 
-    override suspend fun pushSyncData(syncData: SyncData) {
+    /**
+     * Return true if update success
+     */
+    private suspend fun pushSyncData(syncData: SyncData, eTag: String) {
+        val backup = syncData.backup ?: return
+
         val host = syncPreferences.clientHost().get()
         val apiKey = syncPreferences.clientAPIKey().get()
-        val uploadUrl = "$host/api/sync/upload"
+        val uploadUrl = "$host/api/sync/content"
         val timeout = 30L
 
+        val headersBuilder = Headers.Builder().add("X-API-Token", apiKey)
+        if (eTag.isNotEmpty()) {
+            headersBuilder.add("If-Match", eTag)
+        }
+        val headers = headersBuilder.build()
+
         // Set timeout to 30 seconds
         val client = OkHttpClient.Builder()
             .connectTimeout(timeout, TimeUnit.SECONDS)
@@ -167,32 +147,34 @@ class SyncYomiSyncService(
             .writeTimeout(timeout, TimeUnit.SECONDS)
             .build()
 
-        val headers = Headers.Builder().add(
+        val byteArray = protoBuf.encodeToByteArray(BackupSerializer, backup)
-            "Content-Type",
+        if (byteArray.isEmpty()) {
-            "application/gzip",
+            throw IllegalStateException(context.stringResource(MR.strings.empty_backup_error))
-        ).add("Content-Encoding", "gzip").add("X-API-Token", apiKey).build()
+        }
+        val body = byteArray.toRequestBody("application/octet-stream".toMediaType())
 
-        val mediaType = "application/gzip".toMediaTypeOrNull()
+        val uploadRequest = PUT(
-
-        val jsonData = json.encodeToString(syncData)
-        val body = jsonData.toRequestBody(mediaType).gzip()
-
-        val uploadRequest = POST(
             url = uploadUrl,
             headers = headers,
             body = body,
         )
 
-        client.newCall(uploadRequest).await().use {
+        val response = client.newCall(uploadRequest).await()
-            if (it.isSuccessful) {
+
-                logcat(
+        if (response.isSuccessful) {
-                    LogPriority.DEBUG,
+            val newETag = response.headers["ETag"]
-                ) { "SyncYomi sync completed!" }
+                .takeIf { it?.isNotEmpty() == true } ?: throw SyncYomiException("Missing ETag")
+            syncPreferences.lastSyncEtag().set(newETag)
+            logcat(LogPriority.DEBUG) { "SyncYomi sync completed" }
+
+        } else if (response.code == HttpStatus.SC_PRECONDITION_FAILED) {
+            // other clients updated remote data, will try next time
+            logcat(LogPriority.DEBUG) { "SyncYomi sync failed with 412" }
+
         } else {
-                val responseBody = it.body.string()
+            val responseBody = response.body.string()
             notifier.showSyncError("Failed to upload sync data: $responseBody")
-                responseBody.let { logcat(LogPriority.ERROR) { "SyncError:$it" } }
+            logcat(LogPriority.ERROR) { "SyncError: $responseBody" }
-            }
         }
     }
 }