Initial version of Ktor sync server

server/.gitignore

@@ -0,0 +1,7 @@
+/.gradle
+/.idea
+/out
+/build
+*.iml
+*.ipr
+*.iws

server/build.gradle

@@ -0,0 +1,61 @@
+/*
+ * 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/>.
+ */
+
+buildscript {
+    repositories {
+        jcenter()
+    }
+    
+    dependencies {
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
+    }
+}
+
+apply plugin: 'kotlin'
+apply plugin: 'application'
+
+group 'org.isoron.uhabits'
+version '0.0.1'
+mainClassName = "io.ktor.server.netty.EngineMain"
+
+sourceSets {
+    main.kotlin.srcDirs = main.java.srcDirs = ['src']
+    test.kotlin.srcDirs = test.java.srcDirs = ['test']
+    main.resources.srcDirs = ['resources']
+    test.resources.srcDirs = ['testresources']
+}
+
+repositories {
+    mavenLocal()
+    jcenter()
+    maven { url 'https://kotlin.bintray.com/ktor' }
+    maven { url 'https://kotlin.bintray.com/kotlin-js-wrappers' }
+}
+
+dependencies {
+    implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk8:$kotlin_version"
+    implementation "io.ktor:ktor-server-netty:$ktor_version"
+    implementation "ch.qos.logback:logback-classic:$logback_version"
+    implementation "io.ktor:ktor-server-core:$ktor_version"
+    implementation "io.ktor:ktor-html-builder:$ktor_version"
+    implementation "io.ktor:ktor-jackson:$ktor_version"
+    implementation "org.jetbrains:kotlin-css-jvm:1.0.0-pre.31-kotlin-1.2.41"
+    testImplementation "io.ktor:ktor-server-tests:$ktor_version"
+    testImplementation "org.mockito:mockito-core:2.+"
+}

server/gradle.properties

@@ -0,0 +1,23 @@
+#
+# 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/>.
+#
+
+ktor_version=1.4.2
+kotlin.code.style=official
+kotlin_version=1.4.10
+logback_version=1.2.1

server/gradle/wrapper/gradle-wrapper.properties

@@ -0,0 +1,5 @@
+distributionBase=GRADLE_USER_HOME
+distributionPath=wrapper/dists
+distributionUrl=https\://services.gradle.org/distributions/gradle-6.6.1-all.zip
+zipStoreBase=GRADLE_USER_HOME
+zipStorePath=wrapper/dists

server/gradlew

@@ -0,0 +1,191 @@
+#!/usr/bin/env sh
+
+#
+# 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/>.
+#
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS=""
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=$((i+1))
+    done
+    case $i in
+        (0) set -- ;;
+        (1) set -- "$args0" ;;
+        (2) set -- "$args0" "$args1" ;;
+        (3) set -- "$args0" "$args1" "$args2" ;;
+        (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
+}
+APP_ARGS=$(save "$@")
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+# by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong
+if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then
+  cd "$(dirname "$0")"
+fi
+
+exec "$JAVACMD" "$@"

server/gradlew.bat

@@ -0,0 +1,84 @@
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS=
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto init
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto init
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:init
+@rem Get command-line arguments, handling Windows variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

server/resources/application.conf

@@ -0,0 +1,9 @@
+ktor {
+    deployment {
+        port = 8080
+        port = ${?PORT}
+    }
+    application {
+        modules = [ org.isoron.uhabits.sync.app.SyncApplicationKt.main ]
+    }
+}

server/resources/logback.xml

@@ -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/>.
+  -->
+
+<configuration>
+    <appender name="STDOUT" class="ch.qos.logback.core.ConsoleAppender">
+        <encoder>
+            <pattern>%d{YYYY-MM-dd HH:mm:ss.SSS} [%thread] %-5level %logger{36} - %msg%n</pattern>
+        </encoder>
+    </appender>
+    <root level="trace">
+        <appender-ref ref="STDOUT"/>
+    </root>
+    <logger name="org.eclipse.jetty" level="INFO"/>
+    <logger name="io.netty" level="INFO"/>
+</configuration>

server/settings.gradle

@@ -0,0 +1,20 @@
+/*
+ * 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/>.
+ */
+
+rootProject.name = "syncserver"

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

@@ -0,0 +1,48 @@
+/*
+ * 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
+
+interface AbstractSyncServer {
+    /**
+     * Generates and returns a new sync key, which can be used to store and retrive
+     * data.
+     *
+     * @throws RegistrationUnavailableException If key cannot be generated at this
+     *      time, for example, due to insufficient server resources or temporary
+     *      maintenance.
+     */
+    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.
+     */
+    fun put(key: String, newData: SyncData)
+
+    /**
+     * Returns data for a given sync key.
+     *
+     * @throws KeyNotFoundException If key is not found
+     */
+    fun get(key: String): SyncData
+}

server/src/org/isoron/uhabits/sync/MemorySyncServer.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
+
+import java.util.*
+import kotlin.streams.*
+
+/**
+ * An AbstractSyncServer that stores all data in memory.
+ */
+class MemorySyncServer : AbstractSyncServer {
+    private val db = mutableMapOf<String, SyncData>()
+
+    override fun register(): String {
+        synchronized(db) {
+            val key = generateKey()
+            db[key] = SyncData(0, "")
+            return key
+        }
+    }
+
+    override fun put(key: String, newData: SyncData) {
+        synchronized(db) {
+            if (!db.containsKey(key)) {
+                throw KeyNotFoundException()
+            }
+            val prevData = db.getValue(key)
+            if (newData.version != prevData.version + 1) {
+                throw EditConflictException()
+            }
+            db[key] = newData
+        }
+    }
+
+    override fun get(key: String): SyncData {
+        synchronized(db) {
+            if (!db.containsKey(key)) {
+                throw KeyNotFoundException()
+            }
+            return db.getValue(key)
+        }
+    }
+
+    private fun generateKey(): String {
+        val chars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"
+        while (true) {
+            val key = Random().ints(64, 0, chars.length)
+                .asSequence()
+                .map(chars::get)
+                .joinToString("")
+            if (!db.containsKey(key))
+                return key
+        }
+
+    }
+}

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

@@ -0,0 +1,30 @@
+/*
+ * 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: Int,
+    val content: String,
+)
+
+val defaultMapper = ObjectMapper()
+fun SyncData.toJson(): String = defaultMapper.writeValueAsString(this)

server/src/org/isoron/uhabits/sync/SyncException.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
+
+/**
+ * Generic class for all exceptions thrown by SyncServer.
+ */
+open class SyncException: RuntimeException()
+
+class KeyNotFoundException: SyncException()
+
+class RegistrationUnavailableException: SyncException()
+
+class EditConflictException: SyncException()

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, mapOf("key" to key))
+        } catch (e: RegistrationUnavailableException) {
+            call.respond(HttpStatusCode.ServiceUnavailable)
+        }
+    }
+}

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

@@ -0,0 +1,54 @@
+/*
+ * 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.get(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) {
+                val currData = app.server.get(key)
+                call.respond(HttpStatusCode.Conflict, currData)
+            }
+        }
+    }
+}

server/src/org/isoron/uhabits/sync/app/SyncApplication.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.features.*
+import io.ktor.jackson.*
+import io.ktor.routing.*
+import org.isoron.uhabits.sync.*
+
+fun Application.main() = SyncApplication().apply { main() }
+
+class SyncApplication(
+    val server: AbstractSyncServer = MemorySyncServer(),
+) {
+    fun Application.main() {
+        install(DefaultHeaders)
+        install(CallLogging)
+        install(ContentNegotiation) {
+            jackson { }
+        }
+        routing {
+            registration(this@SyncApplication)
+            storage(this@SyncApplication)
+        }
+    }
+}

server/test/org/isoron/uhabits/sync/MemorySyncServerTest.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
+
+import org.junit.Test
+import kotlin.test.*
+
+class MemorySyncServerTest {
+
+    private val server = MemorySyncServer()
+    private val key = server.register()
+
+    @Test
+    fun testUsage() {
+        val data0 = SyncData(0, "")
+        assertEquals(server.get(key), data0)
+
+        val data1 = SyncData(1, "Hello world")
+        server.put(key, data1)
+        assertEquals(server.get(key), data1)
+
+        val data2 = SyncData(2, "Hello new world")
+        server.put(key, data2)
+        assertEquals(server.get(key), data2)
+
+        assertFailsWith<EditConflictException> {
+            server.put(key, data2)
+        }
+
+        assertFailsWith<KeyNotFoundException> {
+            server.get("INVALID")
+        }
+
+        assertFailsWith<KeyNotFoundException> {
+            server.put("INVALID", data0)
+        }
+    }
+}

server/test/org/isoron/uhabits/sync/app/BaseApplicationTest.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.app
+
+import io.ktor.application.*
+import org.isoron.uhabits.sync.*
+import org.mockito.Mockito.*
+
+open class BaseApplicationTest {
+
+    protected val server: AbstractSyncServer = mock(AbstractSyncServer::class.java)
+
+    protected fun app(): Application.() -> Unit = {
+        SyncApplication(server).apply {
+            main()
+        }
+    }
+}

server/test/org/isoron/uhabits/sync/app/RegistrationModuleTest.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.app
+
+import io.ktor.http.*
+import io.ktor.server.testing.*
+import org.isoron.uhabits.sync.*
+import org.junit.Test
+import org.mockito.*
+import org.mockito.Mockito.*
+import kotlin.test.*
+
+class RegistrationModuleTest : BaseApplicationTest() {
+    @Test
+    fun `when register succeeds should return generated key`() {
+        `when`(server.register()).thenReturn("ABCDEF")
+        withTestApplication(app()) {
+            val call = handleRequest(HttpMethod.Post, "/register")
+            assertEquals(HttpStatusCode.OK, call.response.status())
+            assertEquals("{\"key\":\"ABCDEF\"}", call.response.content)
+        }
+    }
+
+    @Test
+    fun `when registration is unavailable should return 503`() {
+        `when`(server.register()).thenThrow(RegistrationUnavailableException())
+        withTestApplication(app()) {
+            val call = handleRequest(HttpMethod.Post, "/register")
+            assertEquals(HttpStatusCode.ServiceUnavailable, call.response.status())
+        }
+    }
+}

server/test/org/isoron/uhabits/sync/app/StorageModuleTest.kt

@@ -0,0 +1,97 @@
+/*
+ * 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.http.*
+import io.ktor.server.testing.*
+import org.isoron.uhabits.sync.*
+import org.junit.Test
+import org.mockito.Mockito.*
+import kotlin.test.*
+
+class StorageModuleTest : BaseApplicationTest() {
+    private val data1 = SyncData(1, "Hello world")
+    private val data2 = SyncData(2, "Hello new world")
+
+    @Test
+    fun `when get succeeds should return data`() {
+        `when`(server.get("k1")).thenReturn(data1)
+        withTestApplication(app()) {
+            handleGet("/db/k1").apply {
+                assertEquals(HttpStatusCode.OK, response.status())
+                assertEquals(data1.toJson(), response.content)
+            }
+        }
+    }
+
+    @Test
+    fun `when get with invalid key should return 404`() {
+        `when`(server.get("k1")).thenThrow(KeyNotFoundException())
+        withTestApplication(app()) {
+            handleGet("/db/k1").apply {
+                assertEquals(HttpStatusCode.NotFound, response.status())
+            }
+        }
+    }
+
+
+    @Test
+    fun `when put succeeds should return OK`() {
+        withTestApplication(app()) {
+            handlePut("/db/k1", data1).apply {
+                assertEquals(HttpStatusCode.OK, response.status())
+                verify(server).put("k1", data1)
+            }
+        }
+    }
+
+    @Test
+    fun `when put with invalid key should return 404`() {
+        `when`(server.put("k1", data1)).thenThrow(KeyNotFoundException())
+        withTestApplication(app()) {
+            handlePut("/db/k1", data1).apply {
+                assertEquals(HttpStatusCode.NotFound, response.status())
+            }
+        }
+    }
+
+    @Test
+    fun `when put with invalid version should return 409 and current data`() {
+        `when`(server.put("k1", data1)).thenThrow(EditConflictException())
+        `when`(server.get("k1")).thenReturn(data2)
+        withTestApplication(app()) {
+            handlePut("/db/k1", data1).apply {
+                assertEquals(HttpStatusCode.Conflict, response.status())
+                assertEquals(data2.toJson(), response.content)
+            }
+        }
+    }
+
+    private fun TestApplicationEngine.handlePut(url: String, data: SyncData): TestApplicationCall {
+        return handleRequest(HttpMethod.Put, url) {
+            addHeader(HttpHeaders.ContentType, ContentType.Application.Json.toString())
+            setBody(data.toJson())
+        }
+    }
+
+    private fun TestApplicationEngine.handleGet(url: String): TestApplicationCall {
+        return handleRequest(HttpMethod.Get, url)
+    }
+}