refactor: factors out config loader.

core/api/src/main/java/io/gatehill/imposter/config/LoadedConfig.kt

@@ -46,8 +46,14 @@ package io.gatehill.imposter.config
 /**
  * Holds a loaded configuration and its reference.
  */
-data class LoadedConfig(
-    val ref: ConfigReference,
-    val serialised: String,
-    val plugin: String,
-)
+interface LoadedConfig {
+    val ref: ConfigReference
+    val serialised: String
+    val plugin: String
+}
+
+data class LoadedConfigImpl(
+    override val ref: ConfigReference,
+    override val serialised: String,
+    override val plugin: String,
+) : LoadedConfig

core/config/build.gradle

@@ -14,11 +14,6 @@ dependencies {
     implementation "com.fasterxml.jackson.datatype:jackson-datatype-jsr310:$version_jackson"
     implementation "com.fasterxml.jackson.module:jackson-module-kotlin:$version_jackson"
 
-    implementation "com.esotericsoftware:kryo:5.6.0"
-
-//    implementation "de.ruedigermoeller:fst:2.56"
-    implementation "de.ruedigermoeller:fst:3.0.1"
-
     // test
     testImplementation "junit:junit:$version_junit"
     testImplementation group: 'org.hamcrest', name: 'hamcrest', version: version_hamcrest

core/config/src/main/java/io/gatehill/imposter/config/loader/ConfigLoader.kt

@@ -0,0 +1,59 @@
+/*
+ * Copyright (c) 2024.
+ *
+ * This file is part of Imposter.
+ *
+ * "Commons Clause" License Condition v1.0
+ *
+ * The Software is provided to you by the Licensor under the License, as
+ * defined below, subject to the following condition.
+ *
+ * Without limiting other conditions in the License, the grant of rights
+ * under the License will not include, and the License does not grant to
+ * you, the right to Sell the Software.
+ *
+ * For purposes of the foregoing, "Sell" means practicing any or all of
+ * the rights granted to you under the License to provide to third parties,
+ * for a fee or other consideration (including without limitation fees for
+ * hosting or consulting/support services related to the Software), a
+ * product or service whose value derives, entirely or substantially, from
+ * the functionality of the Software. Any license notice or attribution
+ * required by the License must also include this Commons Clause License
+ * Condition notice.
+ *
+ * Software: Imposter
+ *
+ * License: GNU Lesser General Public License version 3
+ *
+ * Licensor: Peter Cornish
+ *
+ * Imposter is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Imposter 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with Imposter.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package io.gatehill.imposter.config.loader
+
+import io.gatehill.imposter.config.ConfigReference
+import io.gatehill.imposter.config.LoadedConfig
+import io.gatehill.imposter.plugin.config.BasicPluginConfig
+import java.io.File
+
+/**
+ * Reads configuration files and deserialises them to plugin configuration instances.
+ *
+ * @author Pete Cornish
+ */
+interface ConfigLoader<C : LoadedConfig> {
+    fun readPluginConfig(configRef: ConfigReference): C
+    fun <T : BasicPluginConfig> loadConfig(configFile: File, loadedConfig: C, configClass: Class<T>): T
+}

core/config/src/main/java/io/gatehill/imposter/config/loader/YamlConfigLoaderImpl.kt

@@ -0,0 +1,108 @@
+/*
+ * Copyright (c) 2024.
+ *
+ * This file is part of Imposter.
+ *
+ * "Commons Clause" License Condition v1.0
+ *
+ * The Software is provided to you by the Licensor under the License, as
+ * defined below, subject to the following condition.
+ *
+ * Without limiting other conditions in the License, the grant of rights
+ * under the License will not include, and the License does not grant to
+ * you, the right to Sell the Software.
+ *
+ * For purposes of the foregoing, "Sell" means practicing any or all of
+ * the rights granted to you under the License to provide to third parties,
+ * for a fee or other consideration (including without limitation fees for
+ * hosting or consulting/support services related to the Software), a
+ * product or service whose value derives, entirely or substantially, from
+ * the functionality of the Software. Any license notice or attribution
+ * required by the License must also include this Commons Clause License
+ * Condition notice.
+ *
+ * Software: Imposter
+ *
+ * License: GNU Lesser General Public License version 3
+ *
+ * Licensor: Peter Cornish
+ *
+ * Imposter is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU Lesser General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * Imposter 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 Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with Imposter.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+package io.gatehill.imposter.config.loader
+
+import com.fasterxml.jackson.databind.JsonMappingException
+import io.gatehill.imposter.config.ConfigReference
+import io.gatehill.imposter.config.LoadedConfig
+import io.gatehill.imposter.config.LoadedConfigImpl
+import io.gatehill.imposter.config.expression.EnvEvaluator
+import io.gatehill.imposter.config.expression.SystemEvaluator
+import io.gatehill.imposter.config.model.LightweightConfig
+import io.gatehill.imposter.config.util.ConfigUtil
+import io.gatehill.imposter.config.util.EnvVars
+import io.gatehill.imposter.expression.eval.ExpressionEvaluator
+import io.gatehill.imposter.expression.util.ExpressionUtil
+import io.gatehill.imposter.plugin.config.BasicPluginConfig
+import java.io.File
+import java.io.IOException
+
+/**
+ * YAML (and JSON) implementation of a configuration loader.
+ *
+ * @author Pete Cornish
+ */
+class YamlConfigLoaderImpl : ConfigLoader<LoadedConfig> {
+    private var expressionEvaluators: Map<String, ExpressionEvaluator<*>> = emptyMap()
+
+    init {
+        initInterpolators(EnvVars.getEnv())
+    }
+
+    fun initInterpolators(environment: Map<String, String>) {
+        // reset the environment used by the expression evaluator
+        expressionEvaluators = mapOf(
+            "env" to EnvEvaluator(environment),
+            "system" to SystemEvaluator,
+        )
+    }
+
+    /**
+     * Reads the contents of the configuration file, performing necessary string substitutions.
+     *
+     * @param configRef             the configuration reference
+     * @return the loaded configuration
+     */
+    override fun readPluginConfig(configRef: ConfigReference): LoadedConfig {
+        val configFile = configRef.file
+        try {
+            val rawContents = configFile.readText()
+            val parsedContents = ExpressionUtil.eval(rawContents, expressionEvaluators, nullifyUnsupported = false)
+
+            val config = ConfigUtil.lookupMapper(configFile).readValue(parsedContents, LightweightConfig::class.java)
+            config.plugin
+                ?: throw IllegalStateException("No plugin specified in configuration file: $configFile")
+
+            return LoadedConfigImpl(configRef, parsedContents, config.plugin)
+
+        } catch (e: JsonMappingException) {
+            throw RuntimeException("Error reading configuration file: " + configFile.absolutePath + ", reason: ${e.message}")
+        } catch (e: IOException) {
+            throw RuntimeException("Error reading configuration file: " + configFile.absolutePath, e)
+        }
+    }
+
+    override fun <T : BasicPluginConfig> loadConfig(configFile: File, loadedConfig: LoadedConfig, configClass: Class<T>): T =
+        ConfigUtil.lookupMapper(configFile).readValue(loadedConfig.serialised, configClass)!!
+}