HLAPI Serialization changes between 5.1.1f1 and 5.1.2f1?

Multiplayer & Networking
1

My project is running into serialization mismatch when built with 5.1.2f1 (and 5.1.3f1), which we don’t experience with 5.1.1f1. I see there are a lot of networking changes in the 5.1.2 release notes, is there anything that might cause such mismatches between OnSerialize/OnDeserialize in older code? I doubt this is enough information, but perhaps this sounds familiar to someone.

IndexOutOfRangeException: NetworkReader:ReadByte out of range:NetBuf sz:135 pos:135
UnityEngine.Networking.NetBuffer.ReadByte () (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkBuffer.cs:35)
UnityEngine.Networking.NetworkReader.ReadInt32 () (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkReader.cs:191)
[our scripts…]
UnityEngine.Networking.NetworkIdentity.OnUpdateVars (UnityEngine.Networking.NetworkReader reader, Boolean initialState) (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkIdentity.cs:552)
UnityEngine.Networking.ClientScene.OnUpdateVarsMessage (UnityEngine.Networking.NetworkMessage netMsg) (at C:/buildslave/unity/build/Extensions/Networking/Runtime/ClientScene.cs:591)
UnityEngine.Networking.NetworkConnection.HandleMessage (System.Collections.Generic.Dictionary`2 handler, UnityEngine.Networking.NetworkReader reader, Int32 receivedSize, Int32 channelId) (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkConnection.cs:302)
UnityEngine.Networking.NetworkClient.Update () (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkClient.cs:472)
UnityEngine.Networking.NetworkClient.UpdateClients () (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkClient.cs:686)
UnityEngine.Networking.NetworkIdentity.UNetStaticUpdate () (at C:/buildslave/unity/build/Extensions/Networking/Runtime/NetworkIdentity.cs:725)

2

So, in 5.1.1f1, OnSerialize is not called for NetworkBehaviours with 0 dirty bits, while in 5.1.2f1 and on, OnSerialize will be called even if dirty bits are zero, as long as one NetworkBehaviour on the same object has non-zero dirty bits. If you have an OnSerialize function that didn’t check the dirty bits due to this assumption, but your OnDeserialize did check the dirty bits, you will send too much data with 5.1.2 and you will also get out of sync in your OnDeserialize.