Add a client_state.json admin endpoint to expose the client address set

linkerd/admin/src/main/scala/com/twitter/finagle/client/buoyant/ClientStateHandler.scala

@@ -0,0 +1,41 @@
+package com.twitter.finagle.client.buoyant
+
+import com.twitter.finagle.{Addr, Address, Path, Service}
+import com.twitter.finagle.client.ClientRegistry
+import com.twitter.finagle.http.{MediaType, Request, Response}
+import com.twitter.finagle.loadbalancer.LoadBalancerFactory
+import com.twitter.util.{Future, Try}
+import io.buoyant.config.Parser
+
+class ClientStateHandler extends Service[Request, Response] {
+
+  private case class ClientState(state: String, addresses: Seq[String] = Nil)
+
+  private[this] val mapper = Parser.jsonObjectMapper(Nil)
+
+  override def apply(request: Request): Future[Response] = {
+    val entries = ClientRegistry.registrants
+      .filter { entry =>
+        // only display clients with a Path name
+        Try(Path.read(entry.addr)).isReturn
+      }.map { entry =>
+        val LoadBalancerFactory.Dest(va) = entry.params[LoadBalancerFactory.Dest]
+        val clientState = va.sample() match {
+          case Addr.Bound(addresses, _) =>
+            ClientState("bound", addresses.map {
+              case Address.Inet(isa, _) => s"${isa.getHostString}:${isa.getPort}"
+              case a => a.toString
+            }.toSeq)
+          case Addr.Failed(why) => ClientState(s"Failed: ${why.getMessage}")
+          case a@Addr.Pending => ClientState(a.toString)
+          case a@Addr.Neg => ClientState(a.toString)
+        }
+        entry.addr -> clientState
+      }.toMap
+
+    val response = Response()
+    response.contentType = MediaType.Json + ";charset=UTF-8"
+    response.contentString = mapper.writeValueAsString(entries)
+    Future.value(response)
+  }
+}

linkerd/admin/src/main/scala/io/buoyant/linkerd/admin/LinkerdAdmin.scala

@@ -2,6 +2,7 @@ package io.buoyant.linkerd
 package admin
 
 import com.twitter.finagle._
+import com.twitter.finagle.client.buoyant.ClientStateHandler
 import com.twitter.finagle.http.Request
 import com.twitter.finagle.naming.buoyant.DstBindingFactory
 import com.twitter.finagle.naming.NameInterpreter
@@ -42,6 +43,8 @@ object LinkerdAdmin {
     )
   }
 
+  val clientState: Handler = Handler("/client_state.json", new ClientStateHandler)
+
   def static(adminHandler: AdminHandler): Seq[Handler] = Seq(
     Handler("/", new DashboardHandler(adminHandler)),
     Handler("/files/", StaticFilter.andThen(ResourceHandler.fromDirectoryOrJar(
@@ -102,6 +105,6 @@ object LinkerdAdmin {
     static(adminHandler) ++ config(lc) ++
       boundNames(linker.namers.map { case (_, n) => n }) ++
       delegator(adminHandler, linker.routers) ++
-      extHandlers
+      extHandlers :+ clientState
   }
 }