Fixed player walking speed changes due to heavy items

src/main/java/com/minelittlepony/unicopia/player/PlayerAttributes.java

@@ -28,6 +28,8 @@ class PlayerAttributes {
 
     private double loadStrength = 0;
 
+    private final WalkSpeed walker = new WalkSpeed();
+
     public void applyAttributes(EntityPlayer entity, Race race) {
         loadStrength = 0;
 
@@ -38,9 +40,7 @@ class PlayerAttributes {
             loadStrength += InventoryOfHolding.decodeStackWeight(item);
         }
 
-        if (entity.world.isRemote) {
-            entity.capabilities.setPlayerWalkSpeed(0.1F - (float)(loadStrength / 100000));
-        }
+        walker.setPlayerWalkSpeed(entity.capabilities, 0.1F - (float)(loadStrength / 100000));
 
         applyAttribute(entity, SharedMonsterAttributes.ATTACK_DAMAGE, EARTH_PONY_STRENGTH, race.canUseEarth());
         applyAttribute(entity, SharedMonsterAttributes.KNOCKBACK_RESISTANCE, EARTH_PONY_STRENGTH, race.canUseEarth());

src/main/java/com/minelittlepony/unicopia/player/WalkSpeed.java

@@ -0,0 +1,72 @@
+package com.minelittlepony.unicopia.player;
+
+import java.lang.reflect.Field;
+
+import com.minelittlepony.unicopia.forgebullshit.FUF;
+
+import net.minecraft.entity.player.PlayerCapabilities;
+import net.minecraft.nbt.NBTTagCompound;;
+
+/**
+ * Workaround for setting the player's walking speed.
+ */
+@FUF(reason = "`setPlayerWalkSpeed(v)` is marked as client-only. Waiting on mixins...")
+class WalkSpeed {
+
+    private static boolean regularMethodCheck = true;
+
+    private static boolean reflexiveMethodCheck = true;
+    private static Field walkSpeed;
+
+    public void setPlayerWalkSpeed(PlayerCapabilities capabilities, float speed) {
+        if (capabilities.getWalkSpeed() == speed) {
+            return;
+        }
+
+        if (!setNormally(capabilities, speed)) {
+            if (!setReflexively(capabilities, speed)) {
+                setTheMostSlow(capabilities, speed);
+            }
+        }
+    }
+
+    private boolean setNormally(PlayerCapabilities capabilities, float speed) {
+        if (regularMethodCheck) {
+            try {
+                capabilities.setPlayerWalkSpeed(speed);
+            } catch (Throwable t) {
+                regularMethodCheck = false;
+            }
+        }
+
+        return regularMethodCheck;
+    }
+
+    private boolean setReflexively(PlayerCapabilities capabilities, float speed) {
+        if (reflexiveMethodCheck) {
+            try {
+                if (walkSpeed == null) {
+                    Field[] f = PlayerCapabilities.class.getDeclaredFields();
+                    walkSpeed = f[f.length - 1];
+                    walkSpeed.setAccessible(true);
+                }
+
+                walkSpeed.set(capabilities, speed);
+            } catch (Throwable t) {
+                reflexiveMethodCheck = false;
+            }
+        }
+
+        return reflexiveMethodCheck;
+    }
+
+    private void setTheMostSlow(PlayerCapabilities capabilities, float speed) {
+        NBTTagCompound comp = new NBTTagCompound();
+
+        capabilities.writeCapabilitiesToNBT(comp);
+
+        comp.getCompoundTag("capabilities").setFloat("walkSpeed", speed);
+
+        capabilities.readCapabilitiesFromNBT(comp);
+    }
+}