protocol: hello carries five fields; the released client reads no serverName

Upstream's git HEAD appends serverName to server_installed, but the shipped
1.0.4 client (fabric-26.2) decodes exactly version/lastGen/interval/mode/
ticks and vanilla disconnects the player with "8 bytes extra" on the first
hello. Verified with javap on the release jar; the other three codecs match.
Drops the server-name option (a leftover key now only warns).

Claude-Session: https://claude.ai/code/session_011FePLXwBsCGLTzaSkk1Z6V

gradle.properties

@@ -1,5 +1,5 @@
 group = lv.janhouse
-version = 0.1.0
+version = 0.1.1
 
 # Paper dev bundle (Mojang-mapped server + API) the plugin compiles against.
 # Must match the server it is deployed on: Paper 26.2 on JDK 25. The renderer

src/main/java/lv/janhouse/mapsyncer/Settings.java

@@ -34,8 +34,6 @@ public final class Settings {
     public final int clientPollIntervalTicks;
     public final int helloDelayTicks;
 
-    public final String serverName;
-
     public final WorldSettings defaultWorld;
     public final Map<String, WorldSettings> worlds;
 
@@ -66,7 +64,9 @@ public final class Settings {
         clientPollIntervalTicks = clamp(c.getInt("sync.client-poll-interval-ticks", 6000), 1200, 72000, "sync.client-poll-interval-ticks", warn);
         helloDelayTicks = clamp(c.getInt("sync.hello-delay-ticks", 100), 1, 1200, "sync.hello-delay-ticks", warn);
 
-        serverName = c.getString("server-name", "");
+        if (c.contains("server-name")) {
+            warn.accept("server-name is ignored: the released MapSyncer client cannot read that hello field.");
+        }
 
         ConfigurationSection ws = c.getConfigurationSection("worlds");
         WorldSettings def = new WorldSettings(true, TrackedWorld.Layers.AUTO);

src/main/java/lv/janhouse/mapsyncer/net/Protocol.java

@@ -74,16 +74,20 @@ public final class Protocol {
 
     // -------------------------------------------------------------- encoders
 
+    /**
+     * Five fields, no more. Upstream's git HEAD appends a sixth (serverName), but
+     * the released 1.0.4 client reads exactly five and vanilla disconnects on
+     * "8 bytes extra" if anything follows — verified against the shipped jar.
+     */
     public static byte[] encodeServerInstalled(String version, long lastGenerationTimestamp,
                                                int autoSyncIntervalMinutes, UpdateMode mode,
-                                               int incrementalUpdateIntervalTicks, String serverName) {
+                                               int incrementalUpdateIntervalTicks) {
         return new PacketWriter(64)
                 .writeUtf(version)
                 .writeLong(lastGenerationTimestamp)
                 .writeInt(autoSyncIntervalMinutes)
                 .writeByte(mode.ordinal())
                 .writeInt(incrementalUpdateIntervalTicks)
-                .writeUtf(serverName == null ? "" : serverName)
                 .toByteArray();
     }
 

src/main/java/lv/janhouse/mapsyncer/net/SyncService.java

@@ -199,7 +199,7 @@ public final class SyncService implements PluginMessageListener, Listener {
         int minutes = Math.max(1, ticks / 20 / 60);
         byte[] payload = Protocol.encodeServerInstalled(
                 "mapsyncer-paper/" + plugin.getPluginMeta().getVersion(),
-                lastGen, minutes, Protocol.UpdateMode.TICK, ticks, settings.serverName);
+                lastGen, minutes, Protocol.UpdateMode.TICK, ticks);
         player.sendPluginMessage(plugin, Protocol.SERVER_INSTALLED, payload);
         s.helloSent = true;
         helloCount.incrementAndGet();

src/main/resources/config.yml

@@ -58,10 +58,6 @@ sync:
   # cache, otherwise it forgets what it already has and re-syncs on every join.
   hello-delay-ticks: 100
 
-# Optional stable name sent to clients. The client mod uses it to recognise this
-# server when it is reached under a different address. Leave empty to disable.
-server-name: ""
-
 # Per-world settings. Keys are Bukkit world names. Anything not listed uses
 # "default". `layers` controls what is rendered:
 #   auto     surface for worlds with a sky, cave layers for worlds with a ceiling

src/test/java/lv/janhouse/mapsyncer/net/ProtocolTest.java

@@ -138,6 +138,20 @@ class ProtocolTest {
         assertFalse(Protocol.split(0, 0, "null", new byte[100], 1, Protocol.SURFACE_LAYER).get(0).isSplit());
     }
 
+    @Test
+    void helloHasExactlyFiveFields() {
+        // The released 1.0.4 client reads utf, long, int, byte, int and nothing
+        // else; a trailing byte disconnects the player.
+        byte[] hello = Protocol.encodeServerInstalled("v", 123L, 5, Protocol.UpdateMode.TICK, 6000);
+        PacketReader r = new PacketReader(hello);
+        assertEquals("v", r.readUtf());
+        assertEquals(123L, r.readLong());
+        assertEquals(5, r.readInt());
+        assertEquals(1, r.readByte());
+        assertEquals(6000, r.readInt());
+        assertEquals(0, r.readableBytes());
+    }
+
     @Test
     void hashValidity() {
         assertTrue(Protocol.isValidHash("a1b2c3d4"));