feat: port join_hub to ipc

Author: mworzala

bin/api-server/src/main/java/net/hollowcube/apiserver/session/SessionServiceImpl.java

@@ -1,7 +1,9 @@
 package net.hollowcube.apiserver.session;
 
 import net.hollowcube.apiserver.db.ApiDatabase;
+import net.hollowcube.ipc.session.GameServer;
 import net.hollowcube.ipc.session.SessionService;
+import org.jetbrains.annotations.Nullable;
 
 /// Player sessions, served out of the `player_sessions` table the Go api-server writes.
 public final class SessionServiceImpl implements SessionService {
@@ -17,4 +19,10 @@ public int onlinePlayers() {
         // Every row, hidden players and all, the way the player count graphs count them.
         return (int) db.sessions.countPlayerSessions();
     }
+
+    @Override
+    public @Nullable GameServer findHub(@Nullable String exclude) {
+        var hub = db.servers.findHub(exclude);
+        return hub == null ? null : new GameServer(hub.id(), hub.clusterIp(), hub.protocolVersion());
+    }
 }

bin/api-server/src/test/java/net/hollowcube/apiserver/session/SessionServiceImplTest.java

@@ -2,6 +2,7 @@
 
 import com.sun.net.httpserver.HttpServer;
 import net.hollowcube.apiserver.db.ApiDatabase;
+import net.hollowcube.ipc.session.GameServer;
 import net.hollowcube.ipc.session.SessionClient;
 import net.hollowcube.ipc.session.SessionServer;
 import net.hollowcube.sqlgen.testing.TestDb;
@@ -15,6 +16,7 @@
 import java.net.http.HttpClient;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNull;
 
 /// Sessions end to end, the same way as the head database: a real Postgres under the service, the
 /// generated server over it, and the generated client talking to that over a real socket.
@@ -61,4 +63,29 @@ insert into player_sessions (player_id, proxy_id, skin_texture, skin_signature,
 
         assertEquals(3, sessions.onlinePlayers());
     }
+
+    @Test
+    void findHub_returnsAReadyHubWithItsProtocol() {
+        TEST_DB.seed(
+            """
+            insert into server_states (id, role, status, cluster_ip, protocol_version) values
+                ('hub-starting', 'hub', 0, '10.0.0.1', 0),
+                ('map-a', 'map', 1, '10.0.0.2', 777),
+                ('hub-a', 'hub', 1, '10.0.0.3', 777)"""
+        );
+
+        assertEquals(new GameServer("hub-a", "10.0.0.3", 777), sessions.findHub(null));
+    }
+
+    @Test
+    void findHub_skipsTheExcludedHub() {
+        TEST_DB.seed(
+            """
+            insert into server_states (id, role, status, cluster_ip) values
+                ('hub-a', 'hub', 1, '10.0.0.3')"""
+        );
+
+        assertNull(sessions.findHub("hub-a"));
+        assertEquals(new GameServer("hub-a", "10.0.0.3", 0), sessions.findHub("hub-b"));
+    }
 }

modules/api/src/generated/java/net/hollowcube/apiserver/db/ApiDatabase.java

@@ -0,0 +1,6 @@
+-- Describe-time mirror of Go's 000006, 000007 and 000012, in the order they ran. Nothing to apply.
+alter table server_states add column if not exists status_v2 varchar(10) default 'starting';
+alter table server_states alter column status_v2 set not null;
+alter table server_states add column if not exists status_since timestamptz not null default now();
+-- 0 until the tracker has asked the server, and for a build too old to answer.
+alter table server_states add column if not exists protocol_version int not null default 0;

modules/api/src/generated/java/net/hollowcube/apiserver/db/ServerStates.java

@@ -0,0 +1,8 @@
+-- name: findHub :one
+-- Ready as of the Go tracker's last pod sync, which runs every 5s.
+select id, cluster_ip, protocol_version
+from server_states
+where role = 'hub'
+  and status = 1
+  and ($exclude::text is null or id != $exclude)
+limit 1;

modules/api/src/generated/java/net/hollowcube/apiserver/db/ServersQueries.java

@@ -0,0 +1,8 @@
+package net.hollowcube.ipc.session;
+
+/// A server a player can be sent to, as the proxy connects to it.
+///
+/// @param id              the pod name
+/// @param protocolVersion what the server speaks, or 0 when the tracker has not learned it yet
+public record GameServer(String id, String clusterIp, int protocolVersion) {
+}

modules/api/src/generated/java/net/hollowcube/apiserver/db/ServersQueriesImpl.java

@@ -1,6 +1,7 @@
 package net.hollowcube.ipc.session;
 
 import net.hollowcube.ipc.util.Ipc;
+import org.jetbrains.annotations.Nullable;
 
 /// Player sessions: the one row per player online anywhere on the network. The rest of the Go
 /// `/v3/internal/session` surface lands here as it is ported.
@@ -11,4 +12,8 @@ public interface SessionService {
     /// shows: a single proxy only knows its own.
     int onlinePlayers();
 
+    /// A ready hub other than `exclude`, or null when there is none.
+    @Nullable
+    GameServer findHub(@Nullable String exclude);
+
 }