finagle-thrift: Introduce ServiceClass.fqn that renders a Scrooge-gen…

…erated Thrift class name

Problem

We want a utility to convert Scrooge-generated service stub into a human-readable form that's also FQN.

Solution

Add `ThriftUtil.extractServiceFqn`.

JIRA Issues: CSL-10941

Differential Revision: https://phabricator.twitter.biz/D676897

finagle-thrift/src/main/scala/com/twitter/finagle/Thrift.scala

@@ -212,7 +212,40 @@ object Thrift
       val default = PerEndpointStats(false)
     }
 
-    final case class ServiceClass(clazz: Option[Class[_]])
+    // This is based on the generated stubs from Scrooge.
+    private val ScroogeGeneratedSuffixes = Seq(
+      "$ServiceIface",
+      "$FutureIface",
+      "$MethodPerEndpoint",
+      "$ServicePerEndpoint",
+      "$MethodIface",
+      "$MethodPerEndpoint$MethodPerEndpointImpl",
+      "$ReqRepServicePerEndpoint",
+      "$ReqRepMethodPerEndpoint$ReqRepMethodPerEndpointImpl"
+    )
+
+    private def stripSuffix(iface: Class[_]): Option[String] = {
+      val ifaceName = iface.getName
+      ScroogeGeneratedSuffixes.find(s => ifaceName.endsWith(s)).map(s => ifaceName.stripSuffix(s))
+    }
+
+    /**
+     * A `Param` that captures a class of a Scrooge-generated service stub that's associated
+     * with a given client or server.
+     */
+    final case class ServiceClass(clazz: Option[Class[_]]) {
+
+      /**
+       * Extracts the Thrift IDL FQN from the Scrooge-generated service class in `clazz`. The main
+       * purpose of this method is to drop the Scrooge-specific suffix from the class name, leaving
+       * only domain-relevant name behind.
+       */
+      val fullyQualifiedName: Option[String] = clazz.flatMap { c =>
+        val all = Seq(c) ++ c.getInterfaces.toSeq ++ Option(c.getSuperclass)
+        all.flatMap(stripSuffix).headOption
+      }
+    }
+
     implicit object ServiceClass extends Stack.Param[ServiceClass] {
       val default = ServiceClass(None)
     }

finagle-thrift/src/test/scala/com/twitter/finagle/thrift/ServiceClassParamTest.scala

@@ -0,0 +1,61 @@
+package com.twitter.finagle.thrift
+
+import com.twitter.finagle.Service
+import com.twitter.finagle.Thrift.param.ServiceClass
+import com.twitter.finagle.thrift.thriftscala.{Echo => ScalaEcho}
+import com.twitter.finagle.thrift.thriftjava.{Echo => JavaEcho}
+import com.twitter.finagle.thrift.thriftscala.Echo.Echo
+import com.twitter.scrooge.{Request, Response}
+import com.twitter.util.Future
+import org.scalatest.funsuite.AnyFunSuite
+import scala.reflect.{ClassTag, classTag}
+
+object ServiceClassParamTest {
+  class EchoMPE extends ScalaEcho.MethodPerEndpoint {
+    override def echo(msg: String): Future[String] = ???
+  }
+
+  class EchoSPE extends ScalaEcho.ServicePerEndpoint {
+    override def echo: Service[Echo.Args, String] = ???
+  }
+
+  class EchoReqRepSPE extends ScalaEcho.ReqRepServicePerEndpoint {
+    override def echo: Service[Request[Echo.Args], Response[String]] = ???
+  }
+
+  class EchoFutureIface extends ScalaEcho.FutureIface {
+    override def echo(msg: String): Future[String] = ???
+  }
+
+  class EchoServiceIface extends JavaEcho.ServiceIface {
+    override def echo(msg: String): Future[String] = ???
+  }
+}
+
+class ServiceClassParamTest extends AnyFunSuite {
+  import ServiceClassParamTest._
+
+  private def fqn[A: ClassTag]: String = ServiceClass(
+    Some(classTag[A].runtimeClass)).fullyQualifiedName.get
+
+  test("extractServiceFqn for Scala clients") {
+    assert(fqn[ScalaEcho.MethodPerEndpoint] == "com.twitter.finagle.thrift.thriftscala.Echo")
+    assert(fqn[ScalaEcho.ServicePerEndpoint] == "com.twitter.finagle.thrift.thriftscala.Echo")
+    assert(fqn[ScalaEcho.ServiceIface] == "com.twitter.finagle.thrift.thriftscala.Echo")
+  }
+
+  test("extractServiceFqn for Java clients") {
+    assert(fqn[JavaEcho.ServiceIface] == "com.twitter.finagle.thrift.thriftjava.Echo")
+  }
+
+  test("extractServiceFqn for scala servers") {
+    assert(fqn[EchoMPE] == "com.twitter.finagle.thrift.thriftscala.Echo")
+    assert(fqn[EchoSPE] == "com.twitter.finagle.thrift.thriftscala.Echo")
+    assert(fqn[EchoReqRepSPE] == "com.twitter.finagle.thrift.thriftscala.Echo")
+    assert(fqn[EchoFutureIface] == "com.twitter.finagle.thrift.thriftscala.Echo")
+  }
+
+  test("extractServiceFqn for java servers") {
+    assert(fqn[EchoServiceIface] == "com.twitter.finagle.thrift.thriftjava.Echo")
+  }
+}