fix: dynamically select port for DDB Local

Author: ianbotsf

hll/dynamodb-mapper/dynamodb-mapper/build.gradle.kts

@@ -9,8 +9,10 @@ import com.amazonaws.services.dynamodbv2.local.server.DynamoDBProxyServer
 import com.google.devtools.ksp.gradle.KspTaskJvm
 import com.google.devtools.ksp.gradle.KspTaskMetadata
 import org.jetbrains.kotlin.gradle.tasks.KotlinCompilationTask
+import java.net.ServerSocket
 import java.nio.file.Files
 import java.nio.file.StandardCopyOption
+import kotlin.properties.Delegates
 
 description = "High level DynamoDbMapper client"
 extra["displayName"] = "AWS :: SDK :: Kotlin :: HLL :: DynamoDbMapper"
@@ -128,29 +130,41 @@ if (project.NATIVE_ENABLED) {
 }
 
 open class DynamoDbLocalInstance : DefaultTask() {
-    private val port = 44212 // Keep in sync with DdbLocalTest.kt
+    private var port: Int by Delegates.notNull()
+
+    @OutputFile
+    val portFile = project.objects.fileProperty()
 
     @Internal
     var runner: DynamoDBProxyServer? = null
         private set
 
     @TaskAction
     fun exec() {
-        println("Running DynamoDB local instance on port $port")
+        port = ServerSocket(0).use { it.localPort }
+
+        println("Starting DynamoDB local instance on port $port")
         runner = ServerRunner
             .createServerFromCommandLineArgs(arrayOf("-inMemory", "-port", port.toString(), "-disableTelemetry"))
             .also { it.start() }
+
+        portFile.asFile.get().writeText(port.toString())
     }
 
     fun stop() {
+        runCatching { portFile.asFile.get().delete() }.onFailure { t -> println("Failed to delete $portFile: $t") }
+
         runner?.let {
             println("Stopping DynamoDB local instance on port $port")
             it.stop()
         }
     }
 }
 
-val startDdbLocal = task<DynamoDbLocalInstance>("startDdbLocal")
+val startDdbLocal = task<DynamoDbLocalInstance>("startDdbLocal") {
+    portFile.set(file("build/ddblocal/port.info")) // Keep in sync with DdbLocalTest.kt
+    outputs.upToDateWhen { false } // Always run this task even if a portFile already exists
+}
 
 tasks.withType<Test> {
     dependsOn(startDdbLocal)

hll/dynamodb-mapper/dynamodb-mapper/jvm/test/aws/sdk/kotlin/hll/dynamodbmapper/testutils/DdbLocalTest.kt

@@ -20,12 +20,11 @@ import aws.smithy.kotlin.runtime.net.Scheme
 import aws.smithy.kotlin.runtime.net.url.Url
 import io.kotest.core.spec.style.AnnotationSpec
 import kotlinx.coroutines.runBlocking
+import java.io.File
 import kotlin.test.assertContains
 import kotlin.test.assertEquals
 import kotlin.test.assertNotNull
 
-private const val DDB_LOCAL_PORT = 44212 // Keep in sync with build.gradle.kts
-
 /**
  * The base class for test classes which need DynamoDB Local running. This class provides a few convenience declarations
  * for subclasses:
@@ -50,11 +49,14 @@ abstract class DdbLocalTest : AnnotationSpec() {
     private val requestInterceptor = RequestCapturingInterceptor(this@DdbLocalTest.requests)
 
     private val ddbHolder = lazy {
+        val portFile = File("build/ddblocal/port.info").absoluteFile // Keep in sync with build.gradle.kts
+        val port = portFile.readText().toInt()
+
         DynamoDbClient {
             endpointUrl = Url {
                 scheme = Scheme.HTTP
                 host = Host.Domain("localhost")
-                port = DDB_LOCAL_PORT
+                this.port = port
             }
 
             region = "DUMMY"