From 8c05ccc39d01400e70f02cfe4c845536efff4fee Mon Sep 17 00:00:00 2001
From: Torsten Grote <t@grobox.de>
Date: Mon, 26 Aug 2024 11:00:20 -0300
Subject: [PATCH] Use new WebDavBackend in WebDavStoragePlugin

---
 .../seedvault/plugins/webdav/WebDavConfig.kt  |  12 -
 .../seedvault/plugins/webdav/WebDavFactory.kt |   3 +-
 .../seedvault/plugins/webdav/WebDavHandler.kt |   1 +
 .../plugins/webdav/WebDavProperties.kt        |   1 +
 .../seedvault/plugins/webdav/WebDavStorage.kt |   1 +
 .../plugins/webdav/WebDavStoragePlugin.kt     | 218 +++-------------
 .../seedvault/settings/SettingsManager.kt     |   2 +-
 .../seedvault/storage/WebDavStoragePlugin.kt  | 242 +++---------------
 .../seedvault/ui/storage/StorageViewModel.kt  |   2 +-
 .../plugins/webdav/WebDavStoragePluginTest.kt |  42 +--
 .../plugins/webdav/WebDavTestConfig.kt        |   1 +
 .../storage/WebDavStoragePluginTest.kt        |  51 +---
 .../test/resources/simplelogger.properties    |   1 +
 .../seedvault/core/backends/Backend.kt        |  25 +-
 .../seedvault/core/backends/FileHandle.kt     |   6 +
 .../seedvault/core/backends/saf/SafBackend.kt |  10 +
 .../core/backends/webdav/WebDavBackend.kt     | 167 ++++++++----
 .../calyxos/backup/storage/api/Snapshot.kt    |   4 +-
 18 files changed, 255 insertions(+), 534 deletions(-)
 delete mode 100644 app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavConfig.kt
 create mode 100644 app/src/test/resources/simplelogger.properties

diff --git a/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavConfig.kt b/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavConfig.kt
deleted file mode 100644
index b95ff71b..00000000
--- a/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavConfig.kt
+++ /dev/null
@@ -1,12 +0,0 @@
-/*
- * SPDX-FileCopyrightText: 2024 The Calyx Institute
- * SPDX-License-Identifier: Apache-2.0
- */
-
-package com.stevesoltys.seedvault.plugins.webdav
-
-data class WebDavConfig(
-    val url: String,
-    val username: String,
-    val password: String,
-)
diff --git a/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavFactory.kt b/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavFactory.kt
index 91a2d78c..bc8016b7 100644
--- a/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavFactory.kt
+++ b/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavFactory.kt
@@ -9,13 +9,14 @@ import android.annotation.SuppressLint
 import android.content.Context
 import android.provider.Settings
 import com.stevesoltys.seedvault.plugins.StoragePlugin
+import org.calyxos.seedvault.core.backends.webdav.WebDavConfig
 
 class WebDavFactory(
     private val context: Context,
 ) {
 
     fun createAppStoragePlugin(config: WebDavConfig): StoragePlugin<WebDavConfig> {
-        return WebDavStoragePlugin(context, config)
+        return WebDavStoragePlugin(config)
     }
 
     fun createFilesStoragePlugin(
diff --git a/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavHandler.kt b/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavHandler.kt
index 667b7568..d93f7f6c 100644
--- a/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavHandler.kt
+++ b/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavHandler.kt
@@ -14,6 +14,7 @@ import com.stevesoltys.seedvault.settings.SettingsManager
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.asStateFlow
 import okhttp3.HttpUrl.Companion.toHttpUrl
+import org.calyxos.seedvault.core.backends.webdav.WebDavConfig
 import java.io.IOException
 
 internal sealed interface WebDavConfigState {
diff --git a/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavProperties.kt b/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavProperties.kt
index 29ea84a9..7f06cf7c 100644
--- a/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavProperties.kt
+++ b/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavProperties.kt
@@ -7,6 +7,7 @@ package com.stevesoltys.seedvault.plugins.webdav
 
 import android.content.Context
 import com.stevesoltys.seedvault.plugins.StorageProperties
+import org.calyxos.seedvault.core.backends.webdav.WebDavConfig
 
 data class WebDavProperties(
     override val config: WebDavConfig,
diff --git a/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavStorage.kt b/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavStorage.kt
index faec3f84..b7175006 100644
--- a/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavStorage.kt
+++ b/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavStorage.kt
@@ -29,6 +29,7 @@ import okhttp3.MediaType.Companion.toMediaType
 import okhttp3.OkHttpClient
 import okhttp3.RequestBody
 import okio.BufferedSink
+import org.calyxos.seedvault.core.backends.webdav.WebDavConfig
 import org.xmlpull.v1.XmlPullParser
 import java.io.IOException
 import java.io.InputStream
diff --git a/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavStoragePlugin.kt b/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavStoragePlugin.kt
index da6976c1..bc48607f 100644
--- a/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavStoragePlugin.kt
+++ b/app/src/main/java/com/stevesoltys/seedvault/plugins/webdav/WebDavStoragePlugin.kt
@@ -5,233 +5,95 @@
 
 package com.stevesoltys.seedvault.plugins.webdav
 
-import android.content.Context
 import android.util.Log
-import at.bitfire.dav4jvm.DavCollection
-import at.bitfire.dav4jvm.Response.HrefRelation.SELF
-import at.bitfire.dav4jvm.exception.HttpException
-import at.bitfire.dav4jvm.exception.NotFoundException
-import at.bitfire.dav4jvm.property.webdav.DisplayName
-import at.bitfire.dav4jvm.property.webdav.QuotaAvailableBytes
-import at.bitfire.dav4jvm.property.webdav.ResourceType
 import com.stevesoltys.seedvault.plugins.EncryptedMetadata
 import com.stevesoltys.seedvault.plugins.StoragePlugin
-import com.stevesoltys.seedvault.plugins.chunkFolderRegex
 import com.stevesoltys.seedvault.plugins.saf.FILE_BACKUP_METADATA
-import com.stevesoltys.seedvault.plugins.saf.FILE_NO_MEDIA
-import com.stevesoltys.seedvault.plugins.tokenRegex
-import okhttp3.HttpUrl.Companion.toHttpUrl
-import org.calyxos.backup.storage.plugin.PluginConstants.SNAPSHOT_EXT
+import com.stevesoltys.seedvault.worker.FILE_BACKUP_ICONS
+import org.calyxos.seedvault.core.backends.LegacyAppBackupFile
+import org.calyxos.seedvault.core.backends.webdav.WebDavBackend
+import org.calyxos.seedvault.core.backends.webdav.WebDavConfig
 import java.io.IOException
 import java.io.InputStream
 import java.io.OutputStream
-import kotlin.coroutines.resume
-import kotlin.coroutines.suspendCoroutine
 
 internal class WebDavStoragePlugin(
-    context: Context,
     webDavConfig: WebDavConfig,
     root: String = DIRECTORY_ROOT,
 ) : WebDavStorage(webDavConfig, root), StoragePlugin<WebDavConfig> {
 
-    override suspend fun test(): Boolean {
-        val location = (if (baseUrl.endsWith('/')) baseUrl else "$baseUrl/").toHttpUrl()
-        val davCollection = DavCollection(okHttpClient, location)
+    private val delegate = WebDavBackend(webDavConfig, root)
 
-        val webDavSupported = suspendCoroutine { cont ->
-            davCollection.options { davCapabilities, response ->
-                debugLog { "test() = $davCapabilities $response" }
-                if (davCapabilities.contains("1")) cont.resume(true)
-                else if (davCapabilities.contains("2")) cont.resume(true)
-                else if (davCapabilities.contains("3")) cont.resume(true)
-                else cont.resume(false)
-            }
-        }
-        return webDavSupported
+    override suspend fun test(): Boolean {
+        return delegate.test()
     }
 
     override suspend fun getFreeSpace(): Long? {
-        val location = "$url/".toHttpUrl()
-        val davCollection = DavCollection(okHttpClient, location)
-
-        val availableBytes = suspendCoroutine { cont ->
-            davCollection.propfind(depth = 0, QuotaAvailableBytes.NAME) { response, _ ->
-                debugLog { "getFreeSpace() = $response" }
-                val quota = response.properties.getOrNull(0) as? QuotaAvailableBytes
-                val availableBytes = quota?.quotaAvailableBytes ?: -1
-                if (availableBytes > 0) {
-                    cont.resume(availableBytes)
-                } else {
-                    cont.resume(null)
-                }
-            }
-        }
-        return availableBytes
+        return delegate.getFreeSpace()
     }
 
     @Throws(IOException::class)
     override suspend fun startNewRestoreSet(token: Long) {
-        val location = "$url/$token/".toHttpUrl()
-        val davCollection = DavCollection(okHttpClient, location)
-
-        val response = davCollection.createFolder()
-        debugLog { "startNewRestoreSet($token) = $response" }
+        // no-op
     }
 
     @Throws(IOException::class)
     override suspend fun initializeDevice() {
-        // TODO does it make sense to delete anything
-        //  when [startNewRestoreSet] is always called first? Maybe unify both calls?
-        val location = "$url/".toHttpUrl()
-        val davCollection = DavCollection(okHttpClient, location)
-
-        try {
-            davCollection.head { response ->
-                debugLog { "Root exists: $response" }
-            }
-        } catch (e: NotFoundException) {
-            val response = davCollection.createFolder()
-            debugLog { "initializeDevice() = $response" }
-        } catch (e: Exception) {
-            if (e is IOException) throw e
-            else throw IOException(e)
-        }
+        // no-op
     }
 
     @Throws(IOException::class)
     override suspend fun getOutputStream(token: Long, name: String): OutputStream {
-        val location = "$url/$token/$name".toHttpUrl()
-        return try {
-            getOutputStream(location)
-        } catch (e: Exception) {
-            if (e is IOException) throw e
-            else throw IOException("Error getting OutputStream for $token and $name: ", e)
+        val handle = when (name) {
+            FILE_BACKUP_METADATA -> LegacyAppBackupFile.Metadata(token)
+            FILE_BACKUP_ICONS -> LegacyAppBackupFile.IconsFile(token)
+            else -> LegacyAppBackupFile.Blob(token, name)
         }
+        return delegate.save(handle).outputStream()
     }
 
     @Throws(IOException::class)
     override suspend fun getInputStream(token: Long, name: String): InputStream {
-        val location = "$url/$token/$name".toHttpUrl()
-        return try {
-            getInputStream(location)
-        } catch (e: Exception) {
-            if (e is IOException) throw e
-            else throw IOException("Error getting InputStream for $token and $name: ", e)
+        val handle = when (name) {
+            FILE_BACKUP_METADATA -> LegacyAppBackupFile.Metadata(token)
+            FILE_BACKUP_ICONS -> LegacyAppBackupFile.IconsFile(token)
+            else -> LegacyAppBackupFile.Blob(token, name)
         }
+        return delegate.load(handle).inputStream()
     }
 
     @Throws(IOException::class)
     override suspend fun removeData(token: Long, name: String) {
-        val location = "$url/$token/$name".toHttpUrl()
-        val davCollection = DavCollection(okHttpClient, location)
-
-        try {
-            val response = suspendCoroutine { cont ->
-                davCollection.delete { response ->
-                    cont.resume(response)
-                }
-            }
-            debugLog { "removeData($token, $name) = $response" }
-        } catch (e: Exception) {
-            if (e is IOException) throw e
-            else throw IOException(e)
+        val handle = when (name) {
+            FILE_BACKUP_METADATA -> LegacyAppBackupFile.Metadata(token)
+            FILE_BACKUP_ICONS -> LegacyAppBackupFile.IconsFile(token)
+            else -> LegacyAppBackupFile.Blob(token, name)
         }
+        delegate.remove(handle)
     }
 
     override suspend fun getAvailableBackups(): Sequence<EncryptedMetadata>? {
         return try {
-            doGetAvailableBackups()
+            // get all restore set tokens in root folder that have a metadata file
+            val tokens = ArrayList<Long>()
+            delegate.list(null, LegacyAppBackupFile.Metadata::class) { fileInfo ->
+                val handle = fileInfo.fileHandle as LegacyAppBackupFile.Metadata
+                tokens.add(handle.token)
+            }
+            val tokenIterator = tokens.iterator()
+            return generateSequence {
+                if (!tokenIterator.hasNext()) return@generateSequence null // end sequence
+                val token = tokenIterator.next()
+                EncryptedMetadata(token) {
+                    getInputStream(token, FILE_BACKUP_METADATA)
+                }
+            }
         } catch (e: Throwable) { // NoClassDefFound isn't an [Exception], can get thrown by dav4jvm
             Log.e(TAG, "Error getting available backups: ", e)
             null
         }
     }
 
-    private suspend fun doGetAvailableBackups(): Sequence<EncryptedMetadata> {
-        val location = "$url/".toHttpUrl()
-        val davCollection = DavCollection(okHttpClient, location)
-
-        // get all restore set tokens in root folder
-        val tokens = ArrayList<Long>()
-        try {
-            davCollection.propfind(
-                depth = 2,
-                reqProp = arrayOf(DisplayName.NAME, ResourceType.NAME),
-            ) { response, relation ->
-                debugLog { "getAvailableBackups() = $response" }
-                // This callback will be called for every file in the folder
-                if (relation != SELF && !response.isFolder() && response.href.pathSize >= 2 &&
-                    response.hrefName() == FILE_BACKUP_METADATA
-                ) {
-                    val tokenName = response.href.pathSegments[response.href.pathSegments.size - 2]
-                    getTokenOrNull(tokenName)?.let { token ->
-                        tokens.add(token)
-                    }
-                }
-            }
-        } catch (e: HttpException) {
-            if (e.isUnsupportedPropfind()) getBackupTokenWithDepthOne(davCollection, tokens)
-            else throw e
-        }
-        val tokenIterator = tokens.iterator()
-        return generateSequence {
-            if (!tokenIterator.hasNext()) return@generateSequence null // end sequence
-            val token = tokenIterator.next()
-            EncryptedMetadata(token) {
-                getInputStream(token, FILE_BACKUP_METADATA)
-            }
-        }
-    }
-
-    private fun getBackupTokenWithDepthOne(davCollection: DavCollection, tokens: ArrayList<Long>) {
-        davCollection.propfind(
-            depth = 1,
-            reqProp = arrayOf(DisplayName.NAME, ResourceType.NAME),
-        ) { response, relation ->
-            debugLog { "getBackupTokenWithDepthOne() = $response" }
-
-            // we are only interested in sub-folders, skip rest
-            if (relation == SELF || !response.isFolder()) return@propfind
-
-            val token = getTokenOrNull(response.hrefName()) ?: return@propfind
-            val tokenUrl = response.href.newBuilder()
-                .addPathSegment(FILE_BACKUP_METADATA)
-                .build()
-            // check if .backup.metadata file exists using HEAD request,
-            // because some servers (e.g. nginx don't list hidden files with PROPFIND)
-            try {
-                DavCollection(okHttpClient, tokenUrl).head {
-                    debugLog { "getBackupTokenWithDepthOne() = $response" }
-                    tokens.add(token)
-                }
-            } catch (e: Exception) {
-                // just log exception and continue, we want to find all files that are there
-                Log.e(TAG, "Error retrieving $tokenUrl: ", e)
-            }
-        }
-    }
-
-    private fun getTokenOrNull(name: String): Long? {
-        val looksLikeToken = name.isNotEmpty() && tokenRegex.matches(name)
-        if (looksLikeToken) {
-            return try {
-                name.toLong()
-            } catch (e: NumberFormatException) {
-                throw AssertionError(e) // regex must be wrong
-            }
-        }
-        if (isUnexpectedFile(name)) {
-            Log.w(TAG, "Found invalid backup set folder: $name")
-        }
-        return null
-    }
-
-    private fun isUnexpectedFile(name: String): Boolean {
-        return name != FILE_NO_MEDIA &&
-            !chunkFolderRegex.matches(name) &&
-            !name.endsWith(SNAPSHOT_EXT)
-    }
-
-    override val providerPackageName: String = context.packageName // 100% built-in plugin
+    override val providerPackageName: String? = null // 100% built-in plugin
 
 }
diff --git a/app/src/main/java/com/stevesoltys/seedvault/settings/SettingsManager.kt b/app/src/main/java/com/stevesoltys/seedvault/settings/SettingsManager.kt
index f62ce688..13cbc75a 100644
--- a/app/src/main/java/com/stevesoltys/seedvault/settings/SettingsManager.kt
+++ b/app/src/main/java/com/stevesoltys/seedvault/settings/SettingsManager.kt
@@ -15,11 +15,11 @@ import com.stevesoltys.seedvault.permitDiskReads
 import com.stevesoltys.seedvault.plugins.StoragePlugin
 import com.stevesoltys.seedvault.plugins.saf.DocumentsProviderStoragePlugin
 import com.stevesoltys.seedvault.plugins.saf.SafStorage
-import com.stevesoltys.seedvault.plugins.webdav.WebDavConfig
 import com.stevesoltys.seedvault.plugins.webdav.WebDavHandler.Companion.createWebDavProperties
 import com.stevesoltys.seedvault.plugins.webdav.WebDavProperties
 import com.stevesoltys.seedvault.plugins.webdav.WebDavStoragePlugin
 import com.stevesoltys.seedvault.transport.backup.BackupCoordinator
+import org.calyxos.seedvault.core.backends.webdav.WebDavConfig
 import java.util.concurrent.ConcurrentSkipListSet
 
 internal const val PREF_KEY_TOKEN = "token"
diff --git a/app/src/main/java/com/stevesoltys/seedvault/storage/WebDavStoragePlugin.kt b/app/src/main/java/com/stevesoltys/seedvault/storage/WebDavStoragePlugin.kt
index e77a2a6d..7f458a30 100644
--- a/app/src/main/java/com/stevesoltys/seedvault/storage/WebDavStoragePlugin.kt
+++ b/app/src/main/java/com/stevesoltys/seedvault/storage/WebDavStoragePlugin.kt
@@ -5,187 +5,75 @@
 
 package com.stevesoltys.seedvault.storage
 
-import android.util.Log
-import at.bitfire.dav4jvm.DavCollection
-import at.bitfire.dav4jvm.Response.HrefRelation.SELF
-import at.bitfire.dav4jvm.exception.NotFoundException
-import at.bitfire.dav4jvm.property.webdav.DisplayName
-import at.bitfire.dav4jvm.property.webdav.ResourceType
-import com.stevesoltys.seedvault.plugins.chunkFolderRegex
 import com.stevesoltys.seedvault.plugins.webdav.DIRECTORY_ROOT
-import com.stevesoltys.seedvault.plugins.webdav.WebDavConfig
-import com.stevesoltys.seedvault.plugins.webdav.WebDavStorage
-import okhttp3.HttpUrl.Companion.toHttpUrl
 import org.calyxos.backup.storage.api.StoragePlugin
 import org.calyxos.backup.storage.api.StoredSnapshot
-import org.calyxos.backup.storage.plugin.PluginConstants.SNAPSHOT_EXT
-import org.calyxos.backup.storage.plugin.PluginConstants.chunkRegex
-import org.calyxos.backup.storage.plugin.PluginConstants.snapshotRegex
-import org.koin.core.time.measureDuration
+import org.calyxos.seedvault.core.backends.FileBackupFileType
+import org.calyxos.seedvault.core.backends.TopLevelFolder
+import org.calyxos.seedvault.core.backends.webdav.WebDavBackend
+import org.calyxos.seedvault.core.backends.webdav.WebDavConfig
 import java.io.IOException
 import java.io.InputStream
 import java.io.OutputStream
-import kotlin.coroutines.resume
-import kotlin.coroutines.suspendCoroutine
 
 internal class WebDavStoragePlugin(
     /**
      * The result of Settings.Secure.getString(context.contentResolver, Settings.Secure.ANDROID_ID)
      */
-    androidId: String,
+    private val androidId: String,
     webDavConfig: WebDavConfig,
     root: String = DIRECTORY_ROOT,
-) : WebDavStorage(webDavConfig, root), StoragePlugin {
+) : StoragePlugin {
 
-    /**
-     * The folder name is our user ID plus .sv extension (for SeedVault).
-     * The user or `androidId` is unique to each combination of app-signing key, user, and device
-     * so we don't leak anything by not hashing this and can use it as is.
-     */
-    private val folder: String = "$androidId.sv"
+    private val topLevelFolder = TopLevelFolder("$androidId.sv")
+    private val delegate = WebDavBackend(webDavConfig, root)
 
     @Throws(IOException::class)
     override suspend fun init() {
-        val location = "$url/".toHttpUrl()
-        val davCollection = DavCollection(okHttpClient, location)
-
-        try {
-            davCollection.head { response ->
-                debugLog { "Root exists: $response" }
-            }
-        } catch (e: NotFoundException) {
-            val response = davCollection.createFolder()
-            debugLog { "init() = $response" }
-        } catch (e: Exception) {
-            if (e is IOException) throw e
-            else throw IOException(e)
-        }
+        // no-op
     }
 
     @Throws(IOException::class)
     override suspend fun getAvailableChunkIds(): List<String> {
-        val location = "$url/$folder/".toHttpUrl()
-        val davCollection = DavCollection(okHttpClient, location)
-        debugLog { "getAvailableChunkIds($location)" }
-
-        val expectedChunkFolders = (0x00..0xff).map {
-            Integer.toHexString(it).padStart(2, '0')
-        }.toHashSet()
         val chunkIds = ArrayList<String>()
-        try {
-            val duration = measureDuration {
-                davCollection.propfindDepthTwo { response, relation ->
-                    debugLog { "getAvailableChunkIds() = $response" }
-                    // This callback will be called for every file in the folder
-                    if (relation != SELF && response.isFolder()) {
-                        val name = response.hrefName()
-                        if (chunkFolderRegex.matches(name)) {
-                            expectedChunkFolders.remove(name)
-                        }
-                    } else if (relation != SELF && response.href.pathSize >= 2) {
-                        val folderName =
-                            response.href.pathSegments[response.href.pathSegments.size - 2]
-                        if (folderName != folder && chunkFolderRegex.matches(folderName)) {
-                            val name = response.hrefName()
-                            if (chunkRegex.matches(name)) chunkIds.add(name)
-                        }
-                    }
-                }
-            }
-            Log.i(TAG, "Retrieving chunks took $duration")
-        } catch (e: NotFoundException) {
-            debugLog { "Folder not found: $location" }
-            davCollection.createFolder()
-        } catch (e: Exception) {
-            if (e is IOException) throw e
-            else throw IOException("Error populating chunk folders: ", e)
+        delegate.list(topLevelFolder, FileBackupFileType.Blob::class) { fileInfo ->
+            chunkIds.add(fileInfo.fileHandle.name)
         }
-        Log.i(TAG, "Got ${chunkIds.size} available chunks")
-        createMissingChunkFolders(expectedChunkFolders)
         return chunkIds
     }
 
-    @Throws(IOException::class)
-    private suspend fun createMissingChunkFolders(
-        missingChunkFolders: Set<String>,
-    ) {
-        val s = missingChunkFolders.size
-        for ((i, chunkFolderName) in missingChunkFolders.withIndex()) {
-            val location = "$url/$folder/$chunkFolderName/".toHttpUrl()
-            val davCollection = DavCollection(okHttpClient, location)
-            val response = davCollection.createFolder()
-            debugLog { "Created missing folder $chunkFolderName (${i + 1}/$s) $response" }
-        }
-    }
-
     @Throws(IOException::class)
     override suspend fun getChunkOutputStream(chunkId: String): OutputStream {
-        val chunkFolderName = chunkId.substring(0, 2)
-        val location = "$url/$folder/$chunkFolderName/$chunkId".toHttpUrl()
-        debugLog { "getChunkOutputStream($location) for $chunkId" }
-        return try {
-            getOutputStream(location)
-        } catch (e: Exception) {
-            if (e is IOException) throw e
-            else throw IOException("Error getting OutputStream for $chunkId: ", e)
-        }
+        val fileHandle = FileBackupFileType.Blob(androidId, chunkId)
+        return delegate.save(fileHandle).outputStream()
     }
 
     @Throws(IOException::class)
     override suspend fun getBackupSnapshotOutputStream(timestamp: Long): OutputStream {
-        val location = "$url/$folder/$timestamp$SNAPSHOT_EXT".toHttpUrl()
-        debugLog { "getBackupSnapshotOutputStream($location)" }
-        return try {
-            getOutputStream(location)
-        } catch (e: Exception) {
-            if (e is IOException) throw e
-            else throw IOException("Error getting OutputStream for $timestamp$SNAPSHOT_EXT: ", e)
-        }
+        val fileHandle = FileBackupFileType.Snapshot(androidId, timestamp)
+        return delegate.save(fileHandle).outputStream()
     }
 
     /************************* Restore *******************************/
 
     @Throws(IOException::class)
     override suspend fun getBackupSnapshotsForRestore(): List<StoredSnapshot> {
-        val location = "$url/".toHttpUrl()
-        val davCollection = DavCollection(okHttpClient, location)
-        debugLog { "getBackupSnapshotsForRestore($location)" }
-
         val snapshots = ArrayList<StoredSnapshot>()
-        try {
-            davCollection.propfindDepthTwo { response, relation ->
-                debugLog { "getBackupSnapshotsForRestore() = $response" }
-                // This callback will be called for every file in the folder
-                if (relation != SELF && !response.isFolder() && response.href.pathSize >= 2) {
-                    val name = response.hrefName()
-                    val match = snapshotRegex.matchEntire(name)
-                    if (match != null) {
-                        val timestamp = match.groupValues[1].toLong()
-                        val folderName =
-                            response.href.pathSegments[response.href.pathSegments.size - 2]
-                        val storedSnapshot = StoredSnapshot(folderName, timestamp)
-                        snapshots.add(storedSnapshot)
-                    }
-                }
-            }
-        } catch (e: Exception) {
-            if (e is IOException) throw e
-            else throw IOException("Error getting snapshots for restore: ", e)
+        delegate.list(null, FileBackupFileType.Snapshot::class) { fileInfo ->
+            val handle = fileInfo.fileHandle as FileBackupFileType.Snapshot
+            val folderName = handle.topLevelFolder.name
+            val timestamp = handle.time
+            val storedSnapshot = StoredSnapshot(folderName, timestamp)
+            snapshots.add(storedSnapshot)
         }
         return snapshots
     }
 
     @Throws(IOException::class)
     override suspend fun getBackupSnapshotInputStream(storedSnapshot: StoredSnapshot): InputStream {
-        val timestamp = storedSnapshot.timestamp
-        val location = "$url/${storedSnapshot.userId}/$timestamp$SNAPSHOT_EXT".toHttpUrl()
-        debugLog { "getBackupSnapshotInputStream($location)" }
-        return try {
-            getInputStream(location)
-        } catch (e: Exception) {
-            if (e is IOException) throw e
-            else throw IOException("Error getting InputStream for $storedSnapshot: ", e)
-        }
+        val androidId = storedSnapshot.androidId
+        val handle = FileBackupFileType.Snapshot(androidId, storedSnapshot.timestamp)
+        return delegate.load(handle).inputStream()
     }
 
     @Throws(IOException::class)
@@ -193,92 +81,38 @@ internal class WebDavStoragePlugin(
         snapshot: StoredSnapshot,
         chunkId: String,
     ): InputStream {
-        val chunkFolderName = chunkId.substring(0, 2)
-        val location = "$url/${snapshot.userId}/$chunkFolderName/$chunkId".toHttpUrl()
-        debugLog { "getChunkInputStream($location) for $chunkId" }
-        return try {
-            getInputStream(location)
-        } catch (e: Exception) {
-            if (e is IOException) throw e
-            else throw IOException("Error getting InputStream for $chunkFolderName/$chunkId: ", e)
-        }
+        val handle = FileBackupFileType.Blob(snapshot.androidId, chunkId)
+        return delegate.load(handle).inputStream()
     }
 
     /************************* Pruning *******************************/
 
     @Throws(IOException::class)
     override suspend fun getCurrentBackupSnapshots(): List<StoredSnapshot> {
-        val location = "$url/$folder/".toHttpUrl()
-        val davCollection = DavCollection(okHttpClient, location)
-        debugLog { "getCurrentBackupSnapshots($location)" }
-
         val snapshots = ArrayList<StoredSnapshot>()
-        try {
-            val duration = measureDuration {
-                davCollection.propfind(
-                    depth = 1,
-                    reqProp = arrayOf(DisplayName.NAME, ResourceType.NAME),
-                ) { response, relation ->
-                    debugLog { "getCurrentBackupSnapshots() = $response" }
-                    // This callback will be called for every file in the folder
-                    if (relation != SELF && !response.isFolder()) {
-                        val match = snapshotRegex.matchEntire(response.hrefName())
-                        if (match != null) {
-                            val timestamp = match.groupValues[1].toLong()
-                            val storedSnapshot = StoredSnapshot(folder, timestamp)
-                            snapshots.add(storedSnapshot)
-                        }
-                    }
-                }
-            }
-            Log.i(TAG, "getCurrentBackupSnapshots took $duration")
-        } catch (e: Exception) {
-            if (e is IOException) throw e
-            else throw IOException("Error getting current snapshots: ", e)
+        delegate.list(topLevelFolder, FileBackupFileType.Snapshot::class) { fileInfo ->
+            val handle = fileInfo.fileHandle as FileBackupFileType.Snapshot
+            val folderName = handle.topLevelFolder.name
+            val timestamp = handle.time
+            val storedSnapshot = StoredSnapshot(folderName, timestamp)
+            snapshots.add(storedSnapshot)
         }
-        Log.i(TAG, "Got ${snapshots.size} snapshots.")
         return snapshots
     }
 
     @Throws(IOException::class)
     override suspend fun deleteBackupSnapshot(storedSnapshot: StoredSnapshot) {
-        val timestamp = storedSnapshot.timestamp
-        Log.d(TAG, "Deleting snapshot $timestamp")
-
-        val location = "$url/${storedSnapshot.userId}/$timestamp$SNAPSHOT_EXT".toHttpUrl()
-        val davCollection = DavCollection(okHttpClient, location)
-
-        try {
-            val response = suspendCoroutine { cont ->
-                davCollection.delete { response ->
-                    cont.resume(response)
-                }
-            }
-            debugLog { "deleteBackupSnapshot() = $response" }
-        } catch (e: Exception) {
-            if (e is IOException) throw e
-            else throw IOException(e)
-        }
+        val androidId = storedSnapshot.androidId
+        val handle = FileBackupFileType.Snapshot(androidId, storedSnapshot.timestamp)
+        delegate.remove(handle)
     }
 
     @Throws(IOException::class)
     override suspend fun deleteChunks(chunkIds: List<String>) {
         chunkIds.forEach { chunkId ->
-            val chunkFolderName = chunkId.substring(0, 2)
-            val location = "$url/$folder/$chunkFolderName/$chunkId".toHttpUrl()
-            val davCollection = DavCollection(okHttpClient, location)
-
-            try {
-                val response = suspendCoroutine { cont ->
-                    davCollection.delete { response ->
-                        cont.resume(response)
-                    }
-                }
-                debugLog { "deleteChunks($chunkId) = $response" }
-            } catch (e: Exception) {
-                if (e is IOException) throw e
-                else throw IOException(e)
-            }
+            val androidId = topLevelFolder.name.substringBefore(".sv")
+            val handle = FileBackupFileType.Blob(androidId, chunkId)
+            delegate.remove(handle)
         }
     }
 }
diff --git a/app/src/main/java/com/stevesoltys/seedvault/ui/storage/StorageViewModel.kt b/app/src/main/java/com/stevesoltys/seedvault/ui/storage/StorageViewModel.kt
index 61d0f2e7..927646a1 100644
--- a/app/src/main/java/com/stevesoltys/seedvault/ui/storage/StorageViewModel.kt
+++ b/app/src/main/java/com/stevesoltys/seedvault/ui/storage/StorageViewModel.kt
@@ -16,7 +16,6 @@ import com.stevesoltys.seedvault.R
 import com.stevesoltys.seedvault.plugins.StoragePluginManager
 import com.stevesoltys.seedvault.plugins.saf.SafHandler
 import com.stevesoltys.seedvault.plugins.saf.SafStorage
-import com.stevesoltys.seedvault.plugins.webdav.WebDavConfig
 import com.stevesoltys.seedvault.plugins.webdav.WebDavHandler
 import com.stevesoltys.seedvault.plugins.webdav.WebDavProperties
 import com.stevesoltys.seedvault.plugins.webdav.WebDavStoragePlugin
@@ -26,6 +25,7 @@ import com.stevesoltys.seedvault.ui.MutableLiveEvent
 import com.stevesoltys.seedvault.ui.storage.StorageOption.SafOption
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
+import org.calyxos.seedvault.core.backends.webdav.WebDavConfig
 
 internal abstract class StorageViewModel(
     private val app: Application,
diff --git a/app/src/test/java/com/stevesoltys/seedvault/plugins/webdav/WebDavStoragePluginTest.kt b/app/src/test/java/com/stevesoltys/seedvault/plugins/webdav/WebDavStoragePluginTest.kt
index ed1c2844..7aa321e1 100644
--- a/app/src/test/java/com/stevesoltys/seedvault/plugins/webdav/WebDavStoragePluginTest.kt
+++ b/app/src/test/java/com/stevesoltys/seedvault/plugins/webdav/WebDavStoragePluginTest.kt
@@ -8,23 +8,20 @@ package com.stevesoltys.seedvault.plugins.webdav
 import androidx.test.ext.junit.runners.AndroidJUnit4
 import com.stevesoltys.seedvault.TestApp
 import com.stevesoltys.seedvault.getRandomByteArray
-import com.stevesoltys.seedvault.getRandomString
 import com.stevesoltys.seedvault.plugins.EncryptedMetadata
 import com.stevesoltys.seedvault.plugins.saf.FILE_BACKUP_METADATA
 import com.stevesoltys.seedvault.transport.TransportTest
 import kotlinx.coroutines.runBlocking
+import org.calyxos.seedvault.core.backends.webdav.WebDavConfig
 import org.junit.Test
 import org.junit.jupiter.api.Assertions.assertArrayEquals
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Assertions.assertFalse
-import org.junit.jupiter.api.Assertions.assertNull
 import org.junit.jupiter.api.Assertions.assertTrue
 import org.junit.jupiter.api.Assertions.fail
 import org.junit.jupiter.api.assertThrows
 import org.junit.runner.RunWith
 import org.robolectric.annotation.Config
-import java.io.IOException
-import kotlin.random.Random
 
 @RunWith(AndroidJUnit4::class)
 @Config(
@@ -33,13 +30,13 @@ import kotlin.random.Random
 )
 internal class WebDavStoragePluginTest : TransportTest() {
 
-    private val plugin = WebDavStoragePlugin(context, WebDavTestConfig.getConfig())
+    private val plugin = WebDavStoragePlugin(WebDavTestConfig.getConfig())
 
     @Test
     fun `test self-test`() = runBlocking {
         assertTrue(plugin.test())
 
-        val plugin2 = WebDavStoragePlugin(context, WebDavConfig("https://github.com/", "", ""))
+        val plugin2 = WebDavStoragePlugin(WebDavConfig("https://github.com/", "", ""))
         val e = assertThrows<Exception> {
             assertFalse(plugin2.test())
         }
@@ -86,37 +83,4 @@ internal class WebDavStoragePluginTest : TransportTest() {
         }
     }
 
-    @Test
-    fun `test streams for non-existent data`() = runBlocking {
-        val token = Random.nextLong(System.currentTimeMillis(), 9999999999999)
-        val file = getRandomString()
-
-        assertFalse(plugin.hasData(token, file))
-
-        assertThrows<IOException> {
-            plugin.getOutputStream(token, file).use { it.write(getRandomByteArray()) }
-        }
-
-        assertThrows<IOException> {
-            plugin.getInputStream(token, file).use {
-                it.readAllBytes()
-            }
-        }
-        Unit
-    }
-
-    @Test
-    fun `test missing root dir`() = runBlocking {
-        val plugin = WebDavStoragePlugin(context, WebDavTestConfig.getConfig(), getRandomString())
-
-        assertNull(plugin.getAvailableBackups())
-
-        assertFalse(plugin.hasData(42L, "foo"))
-
-        assertThrows<IOException> {
-            plugin.removeData(42L, "foo")
-        }
-        Unit
-    }
-
 }
diff --git a/app/src/test/java/com/stevesoltys/seedvault/plugins/webdav/WebDavTestConfig.kt b/app/src/test/java/com/stevesoltys/seedvault/plugins/webdav/WebDavTestConfig.kt
index e7f5c674..bb6099b8 100644
--- a/app/src/test/java/com/stevesoltys/seedvault/plugins/webdav/WebDavTestConfig.kt
+++ b/app/src/test/java/com/stevesoltys/seedvault/plugins/webdav/WebDavTestConfig.kt
@@ -5,6 +5,7 @@
 
 package com.stevesoltys.seedvault.plugins.webdav
 
+import org.calyxos.seedvault.core.backends.webdav.WebDavConfig
 import org.junit.Assume.assumeFalse
 import org.junit.jupiter.api.Assertions.fail
 
diff --git a/app/src/test/java/com/stevesoltys/seedvault/storage/WebDavStoragePluginTest.kt b/app/src/test/java/com/stevesoltys/seedvault/storage/WebDavStoragePluginTest.kt
index c393d15d..62bdb785 100644
--- a/app/src/test/java/com/stevesoltys/seedvault/storage/WebDavStoragePluginTest.kt
+++ b/app/src/test/java/com/stevesoltys/seedvault/storage/WebDavStoragePluginTest.kt
@@ -6,7 +6,6 @@
 package com.stevesoltys.seedvault.storage
 
 import com.stevesoltys.seedvault.getRandomByteArray
-import com.stevesoltys.seedvault.getRandomString
 import com.stevesoltys.seedvault.plugins.webdav.WebDavTestConfig
 import com.stevesoltys.seedvault.transport.backup.BackupTest
 import kotlinx.coroutines.runBlocking
@@ -14,14 +13,13 @@ import org.calyxos.backup.storage.api.StoredSnapshot
 import org.junit.Assert.assertArrayEquals
 import org.junit.Assert.assertEquals
 import org.junit.Test
-import org.junit.jupiter.api.assertThrows
-import java.io.IOException
 
 internal class WebDavStoragePluginTest : BackupTest() {
 
-    private val plugin = WebDavStoragePlugin("foo", WebDavTestConfig.getConfig())
+    private val androidId = "abcdef0123456789"
+    private val plugin = WebDavStoragePlugin(androidId, WebDavTestConfig.getConfig())
 
-    private val snapshot = StoredSnapshot("foo.sv", System.currentTimeMillis())
+    private val snapshot = StoredSnapshot("$androidId.sv", System.currentTimeMillis())
 
     @Test
     fun `test chunks`() = runBlocking {
@@ -82,8 +80,9 @@ internal class WebDavStoragePluginTest : BackupTest() {
             )
 
             // other device writes another snapshot
-            val otherPlugin = WebDavStoragePlugin("bar", WebDavTestConfig.getConfig())
-            val otherSnapshot = StoredSnapshot("bar.sv", System.currentTimeMillis())
+            val androidId2 = "0123456789abcdef"
+            val otherPlugin = WebDavStoragePlugin(androidId2, WebDavTestConfig.getConfig())
+            val otherSnapshot = StoredSnapshot("$androidId2.sv", System.currentTimeMillis())
             val otherSnapshotBytes = getRandomByteArray()
             assertEquals(emptyList<String>(), otherPlugin.getAvailableChunkIds())
             otherPlugin.getBackupSnapshotOutputStream(otherSnapshot.timestamp).use {
@@ -104,44 +103,6 @@ internal class WebDavStoragePluginTest : BackupTest() {
         }
     }
 
-    @Test
-    fun `test missing root dir`() = runBlocking {
-        val plugin = WebDavStoragePlugin(
-            androidId = "foo",
-            webDavConfig = WebDavTestConfig.getConfig(),
-            root = getRandomString(),
-        )
-
-        assertThrows<IOException> {
-            plugin.getCurrentBackupSnapshots()
-        }
-        assertThrows<IOException> {
-            plugin.getBackupSnapshotsForRestore()
-        }
-        assertThrows<IOException> {
-            plugin.getAvailableChunkIds()
-        }
-        assertThrows<IOException> {
-            plugin.deleteChunks(listOf("foo"))
-        }
-        assertThrows<IOException> {
-            plugin.deleteBackupSnapshot(snapshot)
-        }
-        assertThrows<IOException> {
-            plugin.getBackupSnapshotOutputStream(snapshot.timestamp).close()
-        }
-        assertThrows<IOException> {
-            plugin.getBackupSnapshotInputStream(snapshot).use { it.readAllBytes() }
-        }
-        assertThrows<IOException> {
-            plugin.getChunkOutputStream("foo").close()
-        }
-        assertThrows<IOException> {
-            plugin.getChunkInputStream(snapshot, "foo").use { it.readAllBytes() }
-        }
-        Unit
-    }
-
 }
 
 private fun ByteArray.toHexString() = joinToString("") { "%02x".format(it) }
diff --git a/app/src/test/resources/simplelogger.properties b/app/src/test/resources/simplelogger.properties
new file mode 100644
index 00000000..e0f0d79d
--- /dev/null
+++ b/app/src/test/resources/simplelogger.properties
@@ -0,0 +1 @@
+org.slf4j.simpleLogger.defaultLogLevel=trace
diff --git a/core/src/main/java/org/calyxos/seedvault/core/backends/Backend.kt b/core/src/main/java/org/calyxos/seedvault/core/backends/Backend.kt
index cd275b69..4ae19495 100644
--- a/core/src/main/java/org/calyxos/seedvault/core/backends/Backend.kt
+++ b/core/src/main/java/org/calyxos/seedvault/core/backends/Backend.kt
@@ -5,12 +5,26 @@
 
 package org.calyxos.seedvault.core.backends
 
+import androidx.annotation.VisibleForTesting
 import okio.BufferedSink
 import okio.BufferedSource
 import kotlin.reflect.KClass
 
 public interface Backend {
 
+    /**
+     * Returns true if the plugin is working, or false if it isn't.
+     * @throws Exception any kind of exception to provide more info on the error
+     */
+    public suspend fun test(): Boolean
+
+    /**
+     * Retrieves the available storage space in bytes.
+     * @return the number of bytes available or null if the number is unknown.
+     * Returning a negative number or zero to indicate unknown is discouraged.
+     */
+    public suspend fun getFreeSpace(): Long?
+
     public suspend fun save(handle: FileHandle): BufferedSink
 
     public suspend fun load(handle: FileHandle): BufferedSource
@@ -25,7 +39,16 @@ public interface Backend {
 
     public suspend fun rename(from: TopLevelFolder, to: TopLevelFolder)
 
-    // TODO really all?
+    @VisibleForTesting
     public suspend fun removeAll()
 
+    /**
+     * Returns the package name of the app that provides the storage backend
+     * which is used for the current backup location.
+     *
+     * Backends are advised to cache this as it will be requested frequently.
+     *
+     * @return null if no package name could be found
+     */
+    public val providerPackageName: String?
 }
diff --git a/core/src/main/java/org/calyxos/seedvault/core/backends/FileHandle.kt b/core/src/main/java/org/calyxos/seedvault/core/backends/FileHandle.kt
index 88e1321d..0b242b57 100644
--- a/core/src/main/java/org/calyxos/seedvault/core/backends/FileHandle.kt
+++ b/core/src/main/java/org/calyxos/seedvault/core/backends/FileHandle.kt
@@ -43,6 +43,12 @@ public sealed class LegacyAppBackupFile : FileHandle() {
 
 public sealed class FileBackupFileType : FileHandle() {
     public abstract val androidId: String
+
+    /**
+     * The folder name is our user ID plus .sv extension (for SeedVault).
+     * The user or `androidId` is unique to each combination of app-signing key, user, and device
+     * so we don't leak anything by not hashing this and can use it as is.
+     */
     public val topLevelFolder: TopLevelFolder get() = TopLevelFolder("$androidId.sv")
 
     public data class Blob(
diff --git a/core/src/main/java/org/calyxos/seedvault/core/backends/saf/SafBackend.kt b/core/src/main/java/org/calyxos/seedvault/core/backends/saf/SafBackend.kt
index e1a70632..2c262235 100644
--- a/core/src/main/java/org/calyxos/seedvault/core/backends/saf/SafBackend.kt
+++ b/core/src/main/java/org/calyxos/seedvault/core/backends/saf/SafBackend.kt
@@ -45,6 +45,14 @@ public class SafBackend(
     private val context: Context get() = appContext.getBackendContext { safConfig.isUsb }
     private val cache = DocumentFileCache(context, safConfig.getDocumentFile(context), root)
 
+    override suspend fun test(): Boolean {
+        TODO("Not yet implemented")
+    }
+
+    override suspend fun getFreeSpace(): Long? {
+        TODO("Not yet implemented")
+    }
+
     override suspend fun save(handle: FileHandle): BufferedSink {
         val file = cache.getFile(handle)
         return file.getOutputStream(context.contentResolver).sink().buffer()
@@ -148,4 +156,6 @@ public class SafBackend(
         }
     }
 
+    override val providerPackageName: String? get() = TODO("Not yet implemented")
+
 }
diff --git a/core/src/main/java/org/calyxos/seedvault/core/backends/webdav/WebDavBackend.kt b/core/src/main/java/org/calyxos/seedvault/core/backends/webdav/WebDavBackend.kt
index b479a733..d611f581 100644
--- a/core/src/main/java/org/calyxos/seedvault/core/backends/webdav/WebDavBackend.kt
+++ b/core/src/main/java/org/calyxos/seedvault/core/backends/webdav/WebDavBackend.kt
@@ -11,6 +11,7 @@ import at.bitfire.dav4jvm.PropertyRegistry
 import at.bitfire.dav4jvm.Response.HrefRelation.SELF
 import at.bitfire.dav4jvm.exception.HttpException
 import at.bitfire.dav4jvm.exception.NotFoundException
+import at.bitfire.dav4jvm.property.webdav.QuotaAvailableBytes
 import io.github.oshai.kotlinlogging.KLogger
 import io.github.oshai.kotlinlogging.KotlinLogging
 import kotlinx.coroutines.DelicateCoroutinesApi
@@ -51,7 +52,7 @@ import kotlin.reflect.KClass
 private const val DEBUG_LOG = true
 
 @OptIn(DelicateCoroutinesApi::class)
-internal class WebDavBackend(
+public class WebDavBackend(
     webDavConfig: WebDavConfig,
     root: String = DIRECTORY_ROOT,
 ) : Backend {
@@ -75,13 +76,53 @@ internal class WebDavBackend(
         .retryOnConnectionFailure(true)
         .build()
 
-    private val url = "${webDavConfig.url}/$root"
+    private val baseUrl = webDavConfig.url.trimEnd('/')
+    private val url = "$baseUrl/$root"
     private val folders = mutableSetOf<HttpUrl>() // cache for existing/created folders
 
     init {
         PropertyRegistry.register(GetLastModified.Factory)
     }
 
+    override suspend fun test(): Boolean {
+        val location = "$baseUrl/".toHttpUrl()
+        val davCollection = DavCollection(okHttpClient, location)
+
+        val hasCaps = suspendCoroutine { cont ->
+            davCollection.options { davCapabilities, response ->
+                log.debugLog { "test() = $davCapabilities $response" }
+                if (davCapabilities.contains("1")) cont.resume(true)
+                else if (davCapabilities.contains("2")) cont.resume(true)
+                else if (davCapabilities.contains("3")) cont.resume(true)
+                else cont.resume(false)
+            }
+        }
+        if (!hasCaps) return false
+
+        val rootCollection = DavCollection(okHttpClient, "$url/foo".toHttpUrl())
+        rootCollection.ensureFoldersExist(log, folders) // only considers parents, so foo isn't used
+        return true
+    }
+
+    override suspend fun getFreeSpace(): Long? {
+        val location = "$url/".toHttpUrl()
+        val davCollection = DavCollection(okHttpClient, location)
+
+        val availableBytes = suspendCoroutine { cont ->
+            davCollection.propfind(depth = 0, QuotaAvailableBytes.NAME) { response, _ ->
+                log.debugLog { "getFreeSpace() = $response" }
+                val quota = response.properties.getOrNull(0) as? QuotaAvailableBytes
+                val availableBytes = quota?.quotaAvailableBytes ?: -1
+                if (availableBytes > 0) {
+                    cont.resume(availableBytes)
+                } else {
+                    cont.resume(null)
+                }
+            }
+        }
+        return availableBytes
+    }
+
     override suspend fun save(handle: FileHandle): BufferedSink {
         val location = handle.toHttpUrl()
         val davCollection = DavCollection(okHttpClient, location)
@@ -118,10 +159,15 @@ internal class WebDavBackend(
         val location = handle.toHttpUrl()
         val davCollection = DavCollection(okHttpClient, location)
 
-        val response = davCollection.get(accept = "", headers = null)
+        val response = try {
+            davCollection.get(accept = "", headers = null)
+        } catch (e: Exception) {
+            if (e is IOException) throw e
+            else throw IOException("Error loading $location", e)
+        }
         log.debugLog { "load($location) = $response" }
         if (response.code / 100 != 2) throw IOException("HTTP error ${response.code}")
-        return response.body?.source() ?: throw IOException()
+        return response.body?.source() ?: throw IOException("Body was null for $location")
     }
 
     override suspend fun list(
@@ -145,58 +191,67 @@ internal class WebDavBackend(
         }
         val davCollection = DavCollection(okHttpClient, location)
         val tokenFolders = mutableSetOf<HttpUrl>()
-        davCollection.propfindDepthInfinity(depth) { response, relation ->
-            log.debugLog { "list() = $response" }
+        try {
+            davCollection.propfindDepthInfinity(depth) { response, relation ->
+                log.debugLog { "list() = $response" }
 
-            // work around nginx's inability to find files starting with .
-            if (relation != SELF && LegacyAppBackupFile.Metadata::class in fileTypes &&
-                response.isFolder() && response.hrefName().matches(tokenRegex)
-            ) {
-                tokenFolders.add(response.href)
-            }
-            if (relation != SELF && !response.isFolder() && response.href.pathSize >= 2) {
-                val name = response.hrefName()
-                val parentName = response.href.pathSegments[response.href.pathSegments.size - 2]
+                // work around nginx's inability to find files starting with .
+                if (relation != SELF && LegacyAppBackupFile.Metadata::class in fileTypes &&
+                    response.isFolder() && response.hrefName().matches(tokenRegex)
+                ) {
+                    tokenFolders.add(response.href)
+                }
+                if (relation != SELF && !response.isFolder() && response.href.pathSize >= 2) {
+                    val name = response.hrefName()
+                    val parentName = response.href.pathSegments[response.href.pathSegments.size - 2]
 
-                if (LegacyAppBackupFile.Metadata::class in fileTypes) {
-                    if (name == FILE_BACKUP_METADATA && parentName.matches(tokenRegex)) {
-                        val metadata = LegacyAppBackupFile.Metadata(parentName.toLong())
-                        val size = response.properties.contentLength()
-                        callback(FileInfo(metadata, size))
-                        // we can find .backup.metadata files, so no need for nginx workaround
-                        tokenFolders.clear()
-                    }
-                }
-                if (FileBackupFileType.Snapshot::class in fileTypes ||
-                    FileBackupFileType::class in fileTypes
-                ) {
-                    val match = snapshotRegex.matchEntire(name)
-                    if (match != null) {
-                        val size = response.properties.contentLength()
-                        val snapshot = FileBackupFileType.Snapshot(
-                            androidId = parentName.substringBefore('.'),
-                            time = match.groupValues[1].toLong(),
-                        )
-                        callback(FileInfo(snapshot, size))
-                    }
-                }
-                if ((FileBackupFileType.Blob::class in fileTypes ||
-                        FileBackupFileType::class in fileTypes) && response.href.pathSize >= 3
-                ) {
-                    val androidIdSv =
-                        response.href.pathSegments[response.href.pathSegments.size - 3]
-                    if (folderRegex.matches(androidIdSv) && chunkFolderRegex.matches(parentName)) {
-                        if (chunkRegex.matches(name)) {
-                            val blob = FileBackupFileType.Blob(
-                                androidId = androidIdSv.substringBefore('.'),
-                                name = name,
-                            )
+                    if (LegacyAppBackupFile.Metadata::class in fileTypes) {
+                        if (name == FILE_BACKUP_METADATA && parentName.matches(tokenRegex)) {
+                            val metadata = LegacyAppBackupFile.Metadata(parentName.toLong())
                             val size = response.properties.contentLength()
-                            callback(FileInfo(blob, size))
+                            callback(FileInfo(metadata, size))
+                            // we can find .backup.metadata files, so no need for nginx workaround
+                            tokenFolders.clear()
+                        }
+                    }
+                    if (FileBackupFileType.Snapshot::class in fileTypes ||
+                        FileBackupFileType::class in fileTypes
+                    ) {
+                        val match = snapshotRegex.matchEntire(name)
+                        if (match != null) {
+                            val size = response.properties.contentLength()
+                            val snapshot = FileBackupFileType.Snapshot(
+                                androidId = parentName.substringBefore('.'),
+                                time = match.groupValues[1].toLong(),
+                            )
+                            callback(FileInfo(snapshot, size))
+                        }
+                    }
+                    if ((FileBackupFileType.Blob::class in fileTypes ||
+                            FileBackupFileType::class in fileTypes) && response.href.pathSize >= 3
+                    ) {
+                        val androidIdSv =
+                            response.href.pathSegments[response.href.pathSegments.size - 3]
+                        if (folderRegex.matches(androidIdSv) &&
+                            chunkFolderRegex.matches(parentName)
+                        ) {
+                            if (chunkRegex.matches(name)) {
+                                val blob = FileBackupFileType.Blob(
+                                    androidId = androidIdSv.substringBefore('.'),
+                                    name = name,
+                                )
+                                val size = response.properties.contentLength()
+                                callback(FileInfo(blob, size))
+                            }
                         }
                     }
                 }
             }
+        } catch (e: NotFoundException) {
+            log.warn(e) { "$location not found" }
+        } catch (e: Exception) {
+            if (e is IOException) throw e
+            else throw IOException("Error listing $location", e)
         }
         // direct query for .backup.metadata as nginx doesn't support listing hidden files
         tokenFolders.forEach { url ->
@@ -251,8 +306,13 @@ internal class WebDavBackend(
         val location = "$url/${from.name}/".toHttpUrl()
         val toUrl = "$url/${to.name}/".toHttpUrl()
         val davCollection = DavCollection(okHttpClient, location)
-        davCollection.move(toUrl, false) { response ->
-            log.debugLog { "rename(${from.name}, ${to.name}) = $response" }
+        try {
+            davCollection.move(toUrl, false) { response ->
+                log.debugLog { "rename(${from.name}, ${to.name}) = $response" }
+            }
+        } catch (e: Exception) {
+            if (e is IOException) throw e
+            else throw IOException("Error renaming $location to ${to.name}", e)
         }
     }
 
@@ -265,9 +325,14 @@ internal class WebDavBackend(
             }
         } catch (e: NotFoundException) {
             log.info { "Not found: $location" }
+        } catch (e: Exception) {
+            if (e is IOException) throw e
+            else throw IOException("Error removing all at $location", e)
         }
     }
 
+    override val providerPackageName: String? = null // 100% built-in plugin
+
     private fun FileHandle.toHttpUrl(): HttpUrl = when (this) {
         // careful with trailing slashes, use only for folders/collections
         is TopLevelFolder -> "$url/$name/".toHttpUrl()
diff --git a/storage/lib/src/main/java/org/calyxos/backup/storage/api/Snapshot.kt b/storage/lib/src/main/java/org/calyxos/backup/storage/api/Snapshot.kt
index a0135283..e9998bd1 100644
--- a/storage/lib/src/main/java/org/calyxos/backup/storage/api/Snapshot.kt
+++ b/storage/lib/src/main/java/org/calyxos/backup/storage/api/Snapshot.kt
@@ -29,7 +29,9 @@ public data class StoredSnapshot(
      * The timestamp identifying a snapshot of the [userId].
      */
     public val timestamp: Long,
-)
+) {
+    public val androidId: String = userId.substringBefore(".sv")
+}
 
 /**
  * Defines which backup snapshots should be retained when pruning backups.