Genericize object storage backend for private storage

In reality, most "S3-compatible" service providers are not, in fact,
S3-compatible and so waste our time by causing compatibility issues with
our code when we choose to use a S3 feature not supported by the service
provider we currently happen to be using.

Instead, genericize the object storage backend as preliminary work
toward implementing proper first-party support for other object storage
backends.

Author: lberrymage

.run/console.run.xml

@@ -14,6 +14,7 @@ SPDX-License-Identifier: AGPL-3.0-only
       <env name="DEBUG_USER_REVIEWER_EMAIL" value="[email protected]" />
       <env name="POSTGRESQL_PASSWORD" value="password" />
       <env name="POSTGRESQL_SSL_MODE" value="disable" />
+      <env name="PRIVATE_STORAGE_BACKEND" value="S3" />
       <env name="GITHUB_OAUTH2_REDIRECT_URL" value="http://localhost:4200/auth/github/callback" />
       <env name="HOST" value="0.0.0.0" />
       <env name="PORT" value="8080" />

console/src/main/kotlin/app/accrescent/parcelo/console/Application.kt

@@ -61,13 +61,20 @@ fun Application.module() {
             password = System.getenv("POSTGRESQL_PASSWORD"),
             sslMode = System.getenv("POSTGRESQL_SSL_MODE") ?: POSTGRESQL_DEFAULT_SSL_MODE,
         ),
-        privateStorage = Config.S3(
-            endpointUrl = System.getenv("PRIVATE_STORAGE_ENDPOINT_URL"),
-            region = System.getenv("PRIVATE_STORAGE_REGION"),
-            bucket = System.getenv("PRIVATE_STORAGE_BUCKET"),
-            accessKeyId = System.getenv("PRIVATE_STORAGE_ACCESS_KEY_ID"),
-            secretAccessKey = System.getenv("PRIVATE_STORAGE_SECRET_ACCESS_KEY"),
-        ),
+        privateStorage = System.getenv("PRIVATE_STORAGE_BACKEND")?.let {
+            when (it) {
+                "S3" -> Config.ObjectStorage.S3(
+                    endpointUrl = System.getenv("PRIVATE_STORAGE_ENDPOINT_URL"),
+                    region = System.getenv("PRIVATE_STORAGE_REGION"),
+                    bucket = System.getenv("PRIVATE_STORAGE_BUCKET"),
+                    accessKeyId = System.getenv("PRIVATE_STORAGE_ACCESS_KEY_ID"),
+                    secretAccessKey = System.getenv("PRIVATE_STORAGE_SECRET_ACCESS_KEY"),
+                )
+
+                else ->
+                    throw Exception("invalid private storage backend $it; must be one of [S3]")
+            }
+        } ?: throw Exception("PRIVATE_STORAGE_BACKEND is not specified in the environment"),
         s3 = Config.S3(
             endpointUrl = System.getenv("S3_ENDPOINT_URL"),
             region = System.getenv("S3_REGION"),
@@ -90,13 +97,15 @@ fun Application.module() {
         val mainModule = module {
             single { config }
             single<FileStorageService> {
-                S3FileStorageService(
-                    Url.parse(config.privateStorage.endpointUrl),
-                    config.privateStorage.region,
-                    config.privateStorage.bucket,
-                    config.privateStorage.accessKeyId,
-                    config.privateStorage.secretAccessKey,
-                )
+                when (config.privateStorage) {
+                    is Config.ObjectStorage.S3 -> S3FileStorageService(
+                        Url.parse(config.privateStorage.endpointUrl),
+                        config.privateStorage.region,
+                        config.privateStorage.bucket,
+                        config.privateStorage.accessKeyId,
+                        config.privateStorage.secretAccessKey,
+                    )
+                }
             }
             single { HttpClient { install(HttpTimeout) } }
             single<PublishService> {

console/src/main/kotlin/app/accrescent/parcelo/console/Config.kt

@@ -8,7 +8,7 @@ data class Config(
     val application: Application,
     val cors: Cors,
     val postgresql: Postgresql,
-    val privateStorage: S3,
+    val privateStorage: ObjectStorage,
     val s3: S3,
     val github: GitHub,
 ) {
@@ -25,6 +25,16 @@ data class Config(
         val sslMode: String,
     )
 
+    sealed class ObjectStorage {
+        data class S3(
+            val endpointUrl: String,
+            val region: String,
+            val bucket: String,
+            val accessKeyId: String,
+            val secretAccessKey: String,
+        ) : ObjectStorage()
+    }
+
     data class S3(
         val endpointUrl: String,
         val region: String,