Reorganize top level directory

uhabits-server/src/org/isoron/uhabits/sync/SyncData.kt

@@ -0,0 +1,35 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync
+
+import com.fasterxml.jackson.databind.*
+
+data class SyncData(
+    val version: Long,
+    val content: String
+)
+
+data class RegisterReponse(val key: String)
+
+data class GetDataVersionResponse(val version: Long)
+
+val defaultMapper = ObjectMapper()
+fun SyncData.toJson(): String = defaultMapper.writeValueAsString(this)
+fun GetDataVersionResponse.toJson(): String = defaultMapper.writeValueAsString(this)

uhabits-server/src/org/isoron/uhabits/sync/SyncException.kt

@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync
+
+open class SyncException: RuntimeException()
+
+class KeyNotFoundException: SyncException()
+
+class ServiceUnavailable: SyncException()
+
+class EditConflictException: SyncException()

uhabits-server/src/org/isoron/uhabits/sync/app/LinkModule.kt

@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync.app
+
+import io.ktor.application.*
+import io.ktor.http.*
+import io.ktor.request.*
+import io.ktor.response.*
+import io.ktor.routing.*
+import org.isoron.uhabits.sync.*
+
+data class LinkRegisterRequestData(
+    val syncKey: String,
+)
+fun LinkRegisterRequestData.toJson(): String = defaultMapper.writeValueAsString(this)
+
+fun Routing.links(app: SyncApplication) {
+    post("/links") {
+        try {
+            val data = call.receive<LinkRegisterRequestData>()
+            val link = app.server.registerLink(data.syncKey)
+            call.respond(HttpStatusCode.OK, link)
+        } catch (e: ServiceUnavailable) {
+            call.respond(HttpStatusCode.ServiceUnavailable)
+        }
+    }
+    get("/links/{id}") {
+        try {
+            val id = call.parameters["id"]!!
+            val link = app.server.getLink(id)
+            call.respond(HttpStatusCode.OK, link)
+        } catch (e: ServiceUnavailable) {
+            call.respond(HttpStatusCode.ServiceUnavailable)
+        } catch (e: KeyNotFoundException) {
+            call.respond(HttpStatusCode.NotFound)
+        }
+    }
+}

uhabits-server/src/org/isoron/uhabits/sync/app/MetricsModule.kt

@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync.app
+
+import io.ktor.application.*
+import io.ktor.http.*
+import io.ktor.response.*
+import io.ktor.routing.*
+import io.prometheus.client.*
+import io.prometheus.client.exporter.common.*
+import io.prometheus.client.hotspot.*
+import java.io.*
+
+
+fun Routing.metrics(app: SyncApplication) {
+    // Register JVM metrics
+    DefaultExports.initialize()
+
+    get("/metrics") {
+        val writer = StringWriter()
+        TextFormat.write004(
+            writer,
+            CollectorRegistry.defaultRegistry.filteredMetricFamilySamples(setOf<String>()),
+        )
+        call.respond(HttpStatusCode.OK, writer.toString())
+    }
+}

uhabits-server/src/org/isoron/uhabits/sync/app/RegistrationModule.kt

@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync.app
+
+import io.ktor.application.*
+import io.ktor.http.*
+import io.ktor.response.*
+import io.ktor.routing.*
+import org.isoron.uhabits.sync.*
+
+fun Routing.registration(app: SyncApplication) {
+    post("/register") {
+        try {
+            val key = app.server.register()
+            call.respond(HttpStatusCode.OK, RegisterReponse(key))
+        } catch (e: ServiceUnavailable) {
+            call.respond(HttpStatusCode.ServiceUnavailable)
+        }
+    }
+}

uhabits-server/src/org/isoron/uhabits/sync/app/StorageModule.kt

@@ -0,0 +1,62 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync.app
+
+import io.ktor.application.*
+import io.ktor.http.*
+import io.ktor.request.*
+import io.ktor.response.*
+import io.ktor.routing.*
+import org.isoron.uhabits.sync.*
+
+fun Routing.storage(app: SyncApplication) {
+    route("/db/{key}") {
+        get {
+            val key = call.parameters["key"]!!
+            try {
+                val data = app.server.getData(key)
+                call.respond(HttpStatusCode.OK, data)
+            } catch(e: KeyNotFoundException) {
+                call.respond(HttpStatusCode.NotFound)
+            }
+        }
+        put {
+            val key = call.parameters["key"]!!
+            val data = call.receive<SyncData>()
+            try {
+                app.server.put(key, data)
+                call.respond(HttpStatusCode.OK)
+            } catch (e: KeyNotFoundException) {
+                call.respond(HttpStatusCode.NotFound)
+            } catch (e: EditConflictException) {
+                call.respond(HttpStatusCode.Conflict)
+            }
+        }
+        get("version") {
+            val key = call.parameters["key"]!!
+            try {
+                val version = app.server.getDataVersion(key)
+                call.respond(HttpStatusCode.OK, GetDataVersionResponse(version))
+            } catch(e: KeyNotFoundException) {
+                call.respond(HttpStatusCode.NotFound)
+            }
+        }
+    }
+}

uhabits-server/src/org/isoron/uhabits/sync/app/SyncApplication.kt

@@ -0,0 +1,53 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync.app
+
+import io.ktor.application.*
+import io.ktor.features.*
+import io.ktor.jackson.*
+import io.ktor.routing.*
+import org.isoron.uhabits.sync.*
+import org.isoron.uhabits.sync.repository.*
+import org.isoron.uhabits.sync.server.*
+import java.nio.file.*
+
+fun Application.main() = SyncApplication().apply { main() }
+
+val REPOSITORY_PATH: Path = Paths.get(System.getenv("LOOP_REPO_PATH")!!)
+
+class SyncApplication(
+    val server: AbstractSyncServer = RepositorySyncServer(
+        FileRepository(REPOSITORY_PATH),
+    ),
+) {
+    fun Application.main() {
+        install(DefaultHeaders)
+        install(CallLogging)
+        install(ContentNegotiation) {
+            jackson { }
+        }
+        routing {
+            registration(this@SyncApplication)
+            storage(this@SyncApplication)
+            links(this@SyncApplication)
+            metrics(this@SyncApplication)
+        }
+    }
+}

uhabits-server/src/org/isoron/uhabits/sync/links/Link.kt

@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync.links
+
+import org.isoron.uhabits.sync.*
+import java.time.*
+
+/**
+ * A Link maps a public URL (such as https://sync.loophabits.org/links/B752A6)
+ * to a synchronization key. They are used to transfer sync keys between devices
+ * without ever exposing the original sync key. Unlike sync keys, links expire
+ * after a few minutes.
+ */
+data class Link(
+    val id: String,
+    val syncKey: String,
+    val createdAt: Long,
+)
+
+fun Link.toJson(): String = defaultMapper.writeValueAsString(this)

uhabits-server/src/org/isoron/uhabits/sync/links/LinkManager.kt

@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync.links
+
+import org.isoron.uhabits.sync.*
+import org.isoron.uhabits.sync.utils.*
+
+class LinkManager(
+    private val timeoutInMillis: Long = 900_000,
+) {
+    private val links = HashMap<String, Link>()
+
+    fun register(syncKey: String): Link {
+        val link = Link(
+            id = randomString(64),
+            syncKey = syncKey,
+            createdAt = System.currentTimeMillis(),
+        )
+        links[link.id] = link
+        return link
+    }
+
+    fun get(id: String): Link {
+        val link = links[id] ?: throw KeyNotFoundException()
+        val ageInMillis = System.currentTimeMillis() - link.createdAt
+        if (ageInMillis > timeoutInMillis) {
+            links.remove(id)
+            throw KeyNotFoundException()
+        }
+        return link
+    }
+}

uhabits-server/src/org/isoron/uhabits/sync/repository/FileRepository.kt

@@ -0,0 +1,73 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync.repository
+
+import org.isoron.uhabits.sync.*
+import java.io.*
+import java.nio.file.*
+
+class FileRepository(
+    private val basepath: Path,
+) : Repository {
+
+    override suspend fun put(key: String, data: SyncData) {
+        // Create directory
+        val dataPath = key.toDataPath()
+        val dataDir = dataPath.toFile()
+        dataDir.mkdirs()
+
+        // Create metadata
+        val metadataFile = dataPath.resolve("version").toFile()
+        metadataFile.outputStream().use { outputStream ->
+            PrintWriter(outputStream).use { printWriter ->
+                printWriter.print(data.version)
+            }
+        }
+
+        // Create data file
+        val dataFile = dataPath.resolve("content").toFile()
+        dataFile.outputStream().use { outputStream ->
+            PrintWriter(outputStream).use { printWriter ->
+                printWriter.print(data.content)
+            }
+        }
+    }
+
+    override suspend fun get(key: String): SyncData {
+        val dataPath = key.toDataPath()
+        val contentFile = dataPath.resolve("content").toFile()
+        val versionFile = dataPath.resolve("version").toFile()
+        if (!contentFile.exists() || !versionFile.exists()) {
+            throw KeyNotFoundException()
+        }
+        val version = versionFile.readText().trim().toLong()
+        return SyncData(version, contentFile.readText())
+    }
+
+    override suspend fun contains(key: String): Boolean {
+        val dataPath = key.toDataPath()
+        val versionFile = dataPath.resolve("version").toFile()
+        return versionFile.exists()
+    }
+
+    private fun String.toDataPath(): Path {
+        return basepath.resolve("${this[0]}/${this[1]}/${this[2]}/${this[3]}/$this")
+    }
+}

uhabits-server/src/org/isoron/uhabits/sync/repository/Repository.kt

@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync.repository
+
+import com.sun.org.apache.xpath.internal.operations.*
+import org.isoron.uhabits.sync.*
+
+/**
+ * A class that knows how to store and retrieve a large number of [SyncData] items.
+ */
+interface Repository {
+    /**
+     * Stores a data item, under the provided key. The item can be later retrieved with [get].
+     * Replaces existing items silently.
+     */
+    suspend fun put(key: String, data: SyncData)
+
+    /**
+     * Retrieves a data item that was previously stored using [put].
+     * @throws KeyNotFoundException If no such key exists.
+     */
+    suspend fun get(key: String): SyncData
+
+    /**
+     * Returns true if the repository contains a given key.
+     */
+    suspend fun contains(key: String): Boolean
+}
+

uhabits-server/src/org/isoron/uhabits/sync/server/AbstractSyncServer.kt

@@ -0,0 +1,81 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync.server
+
+import org.isoron.uhabits.sync.*
+import org.isoron.uhabits.sync.links.*
+
+interface AbstractSyncServer {
+    /**
+     * Generates and returns a new sync key, which can be used to store and retrive
+     * data.
+     *
+     * @throws ServiceUnavailable If key cannot be generated at this time, for example,
+     *      due to insufficient server resources, temporary server maintenance or network problems.
+     */
+    suspend fun register(): String
+
+    /**
+     * Replaces data for a given sync key.
+     *
+     * @throws KeyNotFoundException If key is not found
+     * @throws EditConflictException If the version of the data provided is not
+     *      exactly the current data version plus one.
+     * @throws ServiceUnavailable If data cannot be put at this time, for example, due
+     *      to insufficient server resources or network problems.
+     */
+    suspend fun put(key: String, newData: SyncData)
+
+    /**
+     * Returns data for a given sync key.
+     *
+     * @throws KeyNotFoundException If key is not found
+     * @throws ServiceUnavailable If data cannot be retrieved at this time, for example, due
+     *      to insufficient server resources or network problems.
+     */
+    suspend fun getData(key: String): SyncData
+
+    /**
+     * Returns the current data version for the given key
+     *
+     * @throws KeyNotFoundException If key is not found
+     * @throws ServiceUnavailable If data cannot be retrieved at this time, for example, due
+     *      to insufficient server resources or network problems.
+     */
+    suspend fun getDataVersion(key: String): Long
+
+    /**
+     * Registers a new temporary link (mapping to the given sync key) and returns it.
+     *
+     * @throws ServiceUnavailable If the link cannot be generated at this time due to
+     *      insufficient server resources.
+     */
+    suspend fun registerLink(syncKey: String): Link
+
+    /**
+     * Retrieves the syncKey associated with the given link id.
+     *
+     * @throws ServiceUnavailable If the link cannot be resolved at this time due to
+     *      insufficient server resources.
+     * @throws KeyNotFoundException If the link id cannot be found, or if it has
+     *      expired.
+     */
+    suspend fun getLink(id: String): Link
+}

uhabits-server/src/org/isoron/uhabits/sync/server/RepositorySyncServer.kt

@@ -0,0 +1,94 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync.server
+
+import io.prometheus.client.*
+import org.isoron.uhabits.sync.*
+import org.isoron.uhabits.sync.links.*
+import org.isoron.uhabits.sync.repository.*
+import org.isoron.uhabits.sync.utils.*
+
+/**
+ * An AbstractSyncServer that stores all data in a [Repository].
+ */
+class RepositorySyncServer(
+    private val repo: Repository,
+    private val linkManager: LinkManager = LinkManager(),
+) : AbstractSyncServer {
+
+    private val requestsCounter: Counter = Counter.build()
+        .name("requests_total")
+        .help("Total number of requests")
+        .labelNames("method")
+        .register()
+
+    override suspend fun register(): String {
+        requestsCounter.labels("register").inc()
+        val key = generateKey()
+        repo.put(key, SyncData(0, ""))
+        return key
+    }
+
+    override suspend fun put(key: String, newData: SyncData) {
+        requestsCounter.labels("put").inc()
+        if (!repo.contains(key)) {
+            throw KeyNotFoundException()
+        }
+        val prevData = repo.get(key)
+        if (newData.version != prevData.version + 1) {
+            throw EditConflictException()
+        }
+        repo.put(key, newData)
+    }
+
+    override suspend fun getData(key: String): SyncData {
+        requestsCounter.labels("getData").inc()
+        if (!repo.contains(key)) {
+            throw KeyNotFoundException()
+        }
+        return repo.get(key)
+    }
+
+    override suspend fun getDataVersion(key: String): Long {
+        requestsCounter.labels("getDataVersion").inc()
+        if (!repo.contains(key)) {
+            throw KeyNotFoundException()
+        }
+        return repo.get(key).version
+    }
+
+    override suspend fun registerLink(syncKey: String): Link {
+        requestsCounter.labels("registerLink").inc()
+        return linkManager.register(syncKey)
+    }
+
+    override suspend fun getLink(id: String): Link {
+        requestsCounter.labels("getLink").inc()
+        return linkManager.get(id)
+    }
+
+    private suspend fun generateKey(): String {
+        while (true) {
+            val key = randomString(64)
+            if (!repo.contains(key))
+                return key
+        }
+    }
+}

uhabits-server/src/org/isoron/uhabits/sync/utils/String.kt

@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2016-2020 Alinson Santos Xavier <git@axavier.org>
+ *
+ * This file is part of Loop Habit Tracker.
+ *
+ * Loop Habit Tracker is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or (at your
+ * option) any later version.
+ *
+ * Loop Habit Tracker is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package org.isoron.uhabits.sync.utils
+
+import java.util.*
+import kotlin.streams.*
+
+fun randomString(length: Long): String {
+    val chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+    return Random().ints(length, 0, chars.length)
+        .asSequence()
+        .map(chars::get)
+        .joinToString("")
+}