feat(presence): count players by server across the network

common/build.gradle.kts

@@ -11,7 +11,7 @@ repositories {
 }
 
 dependencies {
-    protobuf("gg.grounds:library-grpc-contracts-player:0.3.0")
+    protobuf("gg.grounds:library-grpc-contracts-player:0.4.0")
 
     testImplementation("org.junit.jupiter:junit-jupiter-api:5.13.4")
     testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.13.4")

common/src/main/kotlin/gg/grounds/player/presence/GrpcPlayerPresenceClient.kt

@@ -1,5 +1,7 @@
 package gg.grounds.player.presence
 
+import gg.grounds.grpc.player.CountPlayersByServerReply
+import gg.grounds.grpc.player.CountPlayersByServerRequest
 import gg.grounds.grpc.player.GetPlayerSessionRequest
 import gg.grounds.grpc.player.PlayerHeartbeatBatchReply
 import gg.grounds.grpc.player.PlayerHeartbeatBatchRequest
@@ -124,6 +126,16 @@ private constructor(
         }
     }
 
+    fun countPlayersByServer(): CountPlayersByServerReply? {
+        return try {
+            stub
+                .withDeadlineAfter(DEFAULT_TIMEOUT_MS, TimeUnit.MILLISECONDS)
+                .countPlayersByServer(CountPlayersByServerRequest.newBuilder().build())
+        } catch (e: RuntimeException) {
+            null
+        }
+    }
+
     fun updateServer(playerId: UUID, serverName: String): Boolean {
         return try {
             stub

velocity/build.gradle.kts

@@ -14,11 +14,14 @@ dependencies {
     implementation(project(":common"))
     // plugin-proxy owns the ProxyServiceRegistry at runtime — compileOnly, never shaded, or the
     // registry this plugin writes into would be a different class from the one chat/social read.
-    compileOnly("gg.grounds:plugin-proxy-api:0.1.0")
+    compileOnly("gg.grounds:plugin-proxy-api:0.2.0")
     implementation("tools.jackson.dataformat:jackson-dataformat-yaml:3.0.4")
     implementation("tools.jackson.module:jackson-module-kotlin:3.0.4")
     implementation("io.grpc:grpc-netty-shaded:1.78.0")
 
+    // compileOnly above is not visible to tests; PlayerSessionQueryImplTest needs the interface's
+    // types.
+    testImplementation("gg.grounds:plugin-proxy-api:0.2.0")
     testImplementation("org.junit.jupiter:junit-jupiter-api:5.13.4")
     testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.13.4")
     testRuntimeOnly("org.junit.platform:junit-platform-launcher:1.13.4")

velocity/src/main/kotlin/gg/grounds/presence/PlayerPresenceService.kt

@@ -1,5 +1,6 @@
 package gg.grounds.presence
 
+import gg.grounds.grpc.player.CountPlayersByServerReply
 import gg.grounds.grpc.player.PlayerLogoutReply
 import gg.grounds.grpc.player.PlayerSessionInfo
 import gg.grounds.player.presence.GrpcPlayerPresenceClient
@@ -57,6 +58,14 @@ class PlayerPresenceService : AutoCloseable {
         }
     }
 
+    fun countPlayersByServer(): CountPlayersByServerReply? {
+        return try {
+            client.countPlayersByServer()
+        } catch (e: RuntimeException) {
+            null
+        }
+    }
+
     fun updateServer(playerId: UUID, serverName: String): Boolean {
         return try {
             client.updateServer(playerId, serverName)

velocity/src/main/kotlin/gg/grounds/presence/PlayerSessionQueryImpl.kt

@@ -1,5 +1,7 @@
 package gg.grounds.presence
 
+import gg.grounds.grpc.player.CountPlayersByServerReply
+import gg.grounds.proxy.api.NetworkPlayerCounts
 import gg.grounds.proxy.api.PlayerSessionInfo
 import gg.grounds.proxy.api.PlayerSessionQuery
 import java.util.UUID
@@ -23,6 +25,9 @@ class PlayerSessionQueryImpl(private val presenceService: PlayerPresenceService)
     override fun suggestNames(prefix: String, limit: Int): List<String> =
         presenceService.suggestNames(prefix, limit)
 
+    override fun countPlayersByServer(): NetworkPlayerCounts? =
+        presenceService.countPlayersByServer()?.let(::toNetworkPlayerCounts)
+
     /**
      * A session with no usable id or name tells the caller nothing — drop it rather than
      * half-answer.
@@ -38,4 +43,14 @@ class PlayerSessionQueryImpl(private val presenceService: PlayerPresenceService)
             connectedAt = session.connectedAtMillis,
         )
     }
+
+    /**
+     * `servers` has one row per occupied backend server — a server nobody is on is absent, not a
+     * zero entry.
+     */
+    internal fun toNetworkPlayerCounts(reply: CountPlayersByServerReply): NetworkPlayerCounts =
+        NetworkPlayerCounts(
+            byServer = reply.serversList.associate { it.serverName to it.players },
+            total = reply.total,
+        )
 }

velocity/src/test/kotlin/gg/grounds/presence/PlayerSessionQueryImplTest.kt

@@ -0,0 +1,43 @@
+package gg.grounds.presence
+
+import gg.grounds.grpc.player.CountPlayersByServerReply
+import gg.grounds.grpc.player.ServerPlayerCount
+import java.net.ServerSocket
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Assertions.assertNull
+import org.junit.jupiter.api.Test
+
+class PlayerSessionQueryImplTest {
+
+    @Test
+    fun countPlayersByServerMapsServersAndCarriesTotal() {
+        val reply =
+            CountPlayersByServerReply.newBuilder()
+                .addServers(
+                    ServerPlayerCount.newBuilder().setServerName("lobby-1").setPlayers(2).build()
+                )
+                .addServers(
+                    ServerPlayerCount.newBuilder().setServerName("lobby-2").setPlayers(5).build()
+                )
+                .setTotal(8)
+                .build()
+
+        val counts = PlayerSessionQueryImpl(PlayerPresenceService()).toNetworkPlayerCounts(reply)
+
+        assertEquals(mapOf("lobby-1" to 2, "lobby-2" to 5), counts.byServer)
+        assertEquals(8, counts.total)
+    }
+
+    @Test
+    fun countPlayersByServerReturnsNullWhenPresenceServiceIsUnavailable() {
+        val presenceService = PlayerPresenceService()
+        val unusedPort = ServerSocket(0).use { it.localPort }
+        presenceService.configure("localhost:$unusedPort")
+
+        try {
+            assertNull(PlayerSessionQueryImpl(presenceService).countPlayersByServer())
+        } finally {
+            presenceService.close()
+        }
+    }
+}