Fixed RD-15359: Implement the internal cache monitoring web server (#25)

![Screenshot 2025-02-21 at 10 57
54](https://github.com/user-attachments/assets/dfdc55c1-35d1-496a-82c3-c0bfdc7c356b)

---------

Co-authored-by: Miguel Branco <miguel@raw-labs.com>

src/main/resources/reference.conf

@@ -3,7 +3,7 @@ akka.license-key=${?AKKA_LICENSE_KEY}
 das {
     server {
         port = 50051 # the port the server listens on
-        monitoring-port = 8080 # http port for monitoring
+        monitoring-port = 8080 # the port the monitoring server listens on
         batch-latency = 100 millis # how long we wait for more rows before we send a batch
     }
     cache {

src/main/scala/com/rawlabs/das/server/DASServer.scala

@@ -32,11 +32,12 @@ import akka.actor.typed.{ActorSystem, Scheduler}
 import akka.stream.Materializer
 import io.grpc.{Server, ServerBuilder}
 
-class DASServer()(
+class DASServer(resultCache: QueryResultCache)(
     implicit settings: DASSettings,
     implicit val ec: ExecutionContext,
     implicit val materializer: Materializer,
-    implicit val scheduler: Scheduler) {
+    implicit val scheduler: Scheduler,
+    implicit val system: ActorSystem[Nothing]) {
 
   private[this] var server: Server = _
 
@@ -47,11 +48,6 @@ class DASServer()(
   private val registrationService = RegistrationServiceGrpc
     .bindService(new RegistrationServiceGrpcImpl(dasSdkManager))
 
-  private val resultCache =
-    new QueryResultCache(
-      maxEntries = settings.getInt("das.cache.max-entries"),
-      maxChunksPerEntry = settings.getInt("das.cache.max-chunks-per-entry"))
-
   private val tablesService = {
     val batchLatency = settings.getDuration("das.server.batch-latency").toScala
     TablesServiceGrpc
@@ -79,26 +75,33 @@ class DASServer()(
 object DASServer {
 
   def main(args: Array[String]): Unit = {
+    // 1) Load settings
     implicit val settings: DASSettings = new DASSettings()
 
-    // 1) Create a typed ActorSystem
+    // 2) Start the actor system
     implicit val system: ActorSystem[Nothing] = ActorSystem[Nothing](Behaviors.empty, "das-server")
-
-    val port = settings.getInt("das.server.port")
-    val monitoringPort = settings.getInt("das.server.monitoring-port")
-
     implicit val ec: ExecutionContext = system.executionContext
     implicit val mat: Materializer = Materializer(system)
     implicit val scheduler: Scheduler = system.scheduler
 
-    // 4) Start the grpc server
-    val dasServer = new DASServer()
-    dasServer.start(port)
+    // 3) Start the results cache
+    val resultCache =
+      new QueryResultCache(
+        maxEntries = settings.getInt("das.cache.max-entries"),
+        maxChunksPerEntry = settings.getInt("das.cache.max-chunks-per-entry"))
+
+    // 4) Start the web monitoring UI
+    settings.getIntOpt("das.server.monitoring-port").ifPresent { monitoringPort =>
+      val debugService = new DebugAppService(resultCache)
+      DASWebUIServer.startHttpInterface("0.0.0.0", monitoringPort, debugService)
+    }
 
-    // 5) Start the new server-side HTML UI
-    val debugService = new DebugAppService()
-    DASWebUIServer.startHttpInterface("0.0.0.0", monitoringPort, debugService)
+    // 5) Start the grpc server
+    val port = settings.getInt("das.server.port")
+    val dasServer = new DASServer(resultCache)
+    dasServer.start(port)
 
+    // Block until shutdown
     dasServer.blockUntilShutdown()
   }
 

src/main/scala/com/rawlabs/das/server/cache/QueryResultCache.scala

@@ -13,6 +13,7 @@
 package com.rawlabs.das.server.cache
 
 import scala.collection.mutable
+import scala.jdk.CollectionConverters.ConcurrentMapHasAsScala
 
 import com.google.common.cache.{Cache, CacheBuilder, RemovalNotification}
 import com.rawlabs.protocol.das.v1.services.ExecuteTableRequest
@@ -95,4 +96,11 @@ class QueryResultCache(maxEntries: Int, maxChunksPerEntry: Int) extends StrictLo
     cache.put(key.toString, result)
   }
 
+  /**
+   * Returns a list of cache keys and their sizes.
+   */
+  def getCacheStats: Seq[(String, Int, Seq[Int])] = {
+    cache.asMap().asScala.map { case (key, value) => (key, value.size, value.map(_.getSerializedSize)) }.toSeq
+  }
+
 }

src/main/scala/com/rawlabs/das/server/webui/DASWebUIServer.scala

@@ -28,12 +28,18 @@ object DASWebUIServer {
       ec: ExecutionContext): Unit = {
 
     val route =
-      concat(pathSingleSlash {
-        get {
-          // Synchronous: debugService.renderOverviewPage() => HttpEntity
-          complete(debugService.renderOverviewPage())
-        }
-      })
+      concat(
+        pathSingleSlash {
+          get {
+            // Synchronous: debugService.renderOverviewPage() => HttpEntity
+            complete(debugService.renderOverviewPage())
+          }
+        },
+        path("cache") {
+          get {
+            complete(debugService.renderCacheCatalog()) // GET /cache
+          }
+        })
 
     val bindingF = Http().newServerAt(host, port).bind(route)
 

src/main/scala/com/rawlabs/das/server/webui/DebugAppService.scala

@@ -12,16 +12,16 @@
 
 package com.rawlabs.das.server.webui
 
-import scala.concurrent.ExecutionContext
+import com.rawlabs.das.server.cache.QueryResultCache
 
 import akka.http.scaladsl.model._
 import scalatags.Text.all._
 import scalatags.Text.tags2.title
 
 /**
- * A service that uses the real CacheManager to fetch data, and returns the resulting HTML as a Future.
+ * A service that uses
  */
-class DebugAppService()(implicit ec: ExecutionContext, scheduler: akka.actor.typed.Scheduler) {
+class DebugAppService(queryResultCache: QueryResultCache) {
 
   // --------------------------------------------------------------------------
   // 2) RENDER “OVERVIEW” PAGE (SYNCHRONOUS EXAMPLE)
@@ -37,7 +37,30 @@ class DebugAppService()(implicit ec: ExecutionContext, scheduler: akka.actor.typ
         div(cls := "container my-5")(
           h1(cls := "mb-4")("Welcome to DAS Debug UI"),
           p("Use the links below to see system status:"),
-          ul(li(a(href := "/cache")("Cache Catalog")), li(a(href := "/actors")("Actors State"))))))
+          ul(li(a(href := "/cache")("Cache content"))))))
+    htmlToEntity(htmlContent)
+  }
+
+  // --------------------------------------------------------------------------
+  // Show the cache statistics
+  // --------------------------------------------------------------------------
+  def renderCacheCatalog(): HttpEntity.Strict = {
+    val cacheStats = queryResultCache.getCacheStats
+    val htmlContent = html(
+      head(
+        meta(charset := "UTF-8"),
+        title("DAS Debug UI - Cache Catalog"),
+        link(rel := "stylesheet", href := "https://cdn.jsdelivr.net/npm/bootstrap@5.3.0/dist/css/bootstrap.min.css")),
+      body(cls := "bg-light")(
+        div(cls := "container my-5")(
+          h1(cls := "mb-4")("Cache content"),
+          p("Cache statistics:"),
+          // Convert the cacheStats map into a table with column keys, nChunks, and chunkSizes
+          table(cls := "table")(
+            thead(tr(th("Key"), th("Number of chunks"), th("Chunk sizes"))),
+            tbody(cacheStats.map { case (key, nChunks, chunkSizes) =>
+              tr(td(pre(key)), td(nChunks.toString), td(chunkSizes.map(n => s"${n}B").mkString(", ")))
+            }.toSeq)))))
     htmlToEntity(htmlContent)
   }