Moved a couple of folders and wrote some code

Assets/Packages/FishNet/Runtime/Managing/Utility/Utility.cs

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+using FishNet.Object;
+using FishNet.Serializing;
+using FishNet.Transporting;
+using UnityEngine;
+
+namespace FishNet.Managing.Utility
+{
+
+    public class Packets
+    {
+        /// <summary>
+        /// Returns written data length for packet.
+        /// </summary>
+        internal static int GetPacketLength(ushort packetId, PooledReader reader, Channel channel)
+        {
+            /* Broadcast is a special circumstance where data
+            * will not be purged even if unreliable.
+            * This is because a broadcast receiver may not
+            * be set, which could be intentional. Because of this
+            * length is always sent to skip
+            * past the broadcast data. 
+            *
+            * Reliables also need length read in the instance a client
+            * sends data to an object which server is despawning. Without
+            * parsing length the remainer data from client will be corrupt. */
+            PacketId pid = (PacketId)packetId;
+            if (channel == Channel.Reliable ||
+                pid == PacketId.Broadcast ||
+                pid == PacketId.SyncVar
+                )
+            {
+                return reader.ReadInt32();
+            }
+            //Unreliable purges remaining.
+            else if (channel == Channel.Unreliable)
+            {
+                return (int)MissingObjectPacketLength.PurgeRemaiming;
+            }
+            /* Unhandled. This shouldn't be possible
+             * since both reliable and unreliable is checked.
+             * There are no other options. This is merely here
+             * for a sanity check. */
+            else
+            {
+                LogError($"Operation is unhandled for packetId {(PacketId)packetId} on channel {channel}.");
+                return (int)MissingObjectPacketLength.PurgeRemaiming;
+            }
+
+            //Logs an error message.
+            void LogError(string message)
+            {
+                if (reader.NetworkManager != null)
+                    reader.NetworkManager.LogError(message);
+                else
+                    NetworkManager.StaticLogError(message);
+            }
+
+        }
+
+    }
+
+
+}

Assets/Packages/FishNet/Runtime/Managing/Utility/Utility.cs.meta

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