feat(exp/base): Add service registry for cloud services

This change adds a new module called opendc-experiments-base which will
provide a base for doing experiments with OpenDC. The initial feature we
introduce is the service registry which acts as DNS for services to
register during experimentation.

3 files changed, 168 insertions, 0 deletions

diff --git a/opendc-experiments/opendc-experiments-base/src/main/kotlin/org/opendc/experiments/MutableServiceRegistry.kt b/opendc-experiments/opendc-experiments-base/src/main/kotlin/org/opendc/experiments/MutableServiceRegistry.kt
new file mode 100644
index 00000000..94fe56fa
--- /dev/null
+++ b/opendc-experiments/opendc-experiments-base/src/main/kotlin/org/opendc/experiments/MutableServiceRegistry.kt
@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2022 AtLarge Research
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package org.opendc.experiments
+
+/**
+ * A mutable [ServiceRegistry].
+ */
+public interface MutableServiceRegistry : ServiceRegistry {
+    /**
+     * Register [service] for the specified [name] in this registry.
+     *
+     * @param name The name of the service to register, which should follow the rules for domain names as defined by
+     *             DNS.
+     * @param type The interface provided by the service.
+     * @param service A reference to the actual implementation of the service.
+     */
+    public fun <T : Any> register(name: String, type: Class<T>, service: T)
+
+    /**
+     * Remove the service with [name] and [type] from this registry.
+     *
+     * @param name The name of the service to remove, which should follow the rules for domain names as defined by DNS.
+     * @param type The type of the service to remove.
+     */
+    public fun remove(name: String, type: Class<*>)
+
+    /**
+     * Remove all services registered with [name].
+     *
+     * @param name The name of the services to remove, which should follow the rules for domain names as defined by DNS.
+     */
+    public fun remove(name: String)
+
+    /**
+     * Create a copy of the registry.
+     */
+    public fun clone(): MutableServiceRegistry
+}
diff --git a/opendc-experiments/opendc-experiments-base/src/main/kotlin/org/opendc/experiments/ServiceRegistry.kt b/opendc-experiments/opendc-experiments-base/src/main/kotlin/org/opendc/experiments/ServiceRegistry.kt
new file mode 100644
index 00000000..a6776e14
--- /dev/null
+++ b/opendc-experiments/opendc-experiments-base/src/main/kotlin/org/opendc/experiments/ServiceRegistry.kt
@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2022 AtLarge Research
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package org.opendc.experiments
+
+import org.opendc.experiments.broker.Broker
+
+/**
+ * A read-only registry of services accessible by a [Broker] during an experiment.
+ *
+ * The service registry is similar conceptually to the Domain Name System (DNS), which is a naming system used to
+ * identify computers reachable via the Internet. The service registry should be used in a similar fashion.
+ */
+public interface ServiceRegistry {
+    /**
+     * Lookup the service with the specified [name] and [type].
+     *
+     * @param name The name of the service to resolve, which should follow the rules for domain names as defined by DNS.
+     * @param type The type of the service to resolve, identified by the interface that is implemented by the service.
+     * @return The service with specified [name] and implementing [type] or `null` if it does not exist.
+     */
+    public fun <T : Any> resolve(name: String, type: Class<T>): T?
+}
diff --git a/opendc-experiments/opendc-experiments-base/src/main/kotlin/org/opendc/experiments/internal/ServiceRegistryImpl.kt b/opendc-experiments/opendc-experiments-base/src/main/kotlin/org/opendc/experiments/internal/ServiceRegistryImpl.kt
new file mode 100644
index 00000000..c2e91730
--- /dev/null
+++ b/opendc-experiments/opendc-experiments-base/src/main/kotlin/org/opendc/experiments/internal/ServiceRegistryImpl.kt
@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2022 AtLarge Research
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package org.opendc.experiments.internal
+
+import org.opendc.experiments.MutableServiceRegistry
+
+/**
+ * Implementation of the [MutableServiceRegistry] interface.
+ */
+internal class ServiceRegistryImpl(private val registry: MutableMap<String, MutableMap<Class<*>, Any>> = mutableMapOf()) :
+    MutableServiceRegistry {
+    override fun <T : Any> resolve(name: String, type: Class<T>): T? {
+        val servicesForName = registry[name] ?: return null
+
+        @Suppress("UNCHECKED_CAST")
+        return servicesForName[type] as T?
+    }
+
+    override fun <T : Any> register(name: String, type: Class<T>, service: T) {
+        val services = registry.computeIfAbsent(name) { mutableMapOf() }
+
+        if (type in services) {
+            throw IllegalStateException("Duplicate service $type registered for name $name")
+        }
+
+        services[type] = service
+    }
+
+    override fun remove(name: String, type: Class<*>) {
+        val services = registry[name] ?: return
+        services.remove(type)
+    }
+
+    override fun remove(name: String) {
+        registry.remove(name)
+    }
+
+    override fun clone(): MutableServiceRegistry {
+        val res = mutableMapOf<String, MutableMap<Class<*>, Any>>()
+        registry.mapValuesTo(res) { (_, v) -> v.toMutableMap() }
+        return ServiceRegistryImpl(res)
+    }
+
+    override fun toString(): String {
+        val entries = registry.map { "${it.key}=${it.value}" }.joinToString()
+        return "ServiceRegistry{$entries}"
+    }
+}