fix(spigot): look up fields/methods based on type and predicate inste…

…ad of hardcoding obfuscated field names

gradle.properties

@@ -8,7 +8,7 @@ yarn_mappings=1.21.1+build.3
 loader_version=0.16.7
 
 # Mod Properties
-version=2.1.0
+version=2.1.1
 group=net.mcbrawls.inject
 id=inject
 

spigot/src/main/java/net/mcbrawls/inject/spigot/InjectSpigot.java

@@ -17,11 +17,25 @@ public class InjectSpigot implements InjectPlatform {
     private InjectSpigot() {
     }
 
+    private boolean isRunningPaper() {
+        try {
+            Class.forName("com.destroystokyo.paper.PaperConfig");
+            return true;
+        } catch (ClassNotFoundException e) {
+            return false;
+        }
+    }
+
     @Override
     public void registerInjector(Injector injector) {
         injectors.add(injector);
 
         if (!hasInitialized) {
+            if (isRunningPaper()) {
+                LOGGER.warning("It looks like you are running Paper - Inject Spigot is unsupported on Paper!");
+                LOGGER.warning("Please use Inject Paper instead!");
+            }
+
             new ClientConnectionInterceptor().install((channel) -> {
                 var pipeline = channel.pipeline();
                 injectors.forEach(pipeline::addFirst);

spigot/src/main/java/net/mcbrawls/inject/spigot/interceptor/ClientConnectionInterceptor.java

@@ -6,8 +6,11 @@
 import java.lang.reflect.Field;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
+import java.util.Arrays;
 import java.util.List;
 import java.util.function.Consumer;
+import java.util.function.Function;
 
 public class ClientConnectionInterceptor {
 
@@ -44,6 +47,22 @@ public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception
         }
     }
 
+    private Method getMethodByReturnType(Class<?> clazz, Class<?> returnType) {
+        return Arrays.stream(clazz.getDeclaredMethods())
+                .filter((method) -> method.getReturnType().equals(returnType))
+                .findFirst()
+                .get();
+    }
+
+    // Predicate is needed to make sure we find the `List<ChannelFuture> channels` instead of `List<Connection> connections`
+    // since `channels` is private.
+    private Field getFieldByTypeAndPredicate(Class<?> clazz, Class<?> type, Function<Field, Boolean> predicate) {
+        return Arrays.stream(clazz.getDeclaredFields())
+                .filter((field) -> field.getType().equals(type) && predicate.apply(field))
+                .findFirst()
+                .get();
+    }
+
     private List<ChannelFuture> getChannels() {
         final String serverVersion = this.getServerVersion();
 
@@ -55,15 +74,14 @@ private List<ChannelFuture> getChannels() {
             final Method craftServerGetServerMethod = craftServerClass.getDeclaredMethod("getServer");
 
             final Object minecraftServer = craftServerGetServerMethod.invoke(craftServerObject);
-            final Method getConnectionMethod = minecraftServerClass.getDeclaredMethod("ai");
+            final Method getConnectionMethod = getMethodByReturnType(minecraftServerClass, Class.forName("net.minecraft.server.network.ServerConnection"));
 
             final Object serverConnection = getConnectionMethod.invoke(minecraftServer);
-            final Field channelsField = serverConnection.getClass().getDeclaredField("f");
+            final Field channelsField = getFieldByTypeAndPredicate(serverConnection.getClass(), List.class, (field) -> Modifier.isPrivate(field.getModifiers()));
 
             channelsField.setAccessible(true);
             return (List<ChannelFuture>) channelsField.get(serverConnection);
-        } catch (ClassNotFoundException | NoSuchMethodException | InvocationTargetException | IllegalAccessException |
-                 NoSuchFieldException e) {
+        } catch (ClassNotFoundException | NoSuchMethodException | InvocationTargetException | IllegalAccessException e) {
             throw new RuntimeException(e);
         }
     }