Dynamic buffers become corrupted

Unity Engine
,
1

I’ve been having a problem with garbage data appearing in dynamic buffers on the client, and after finally getting something more reproducible I think I found the problem.

This is around line 576 in GhostReceiveSystem.c:

buf.ResizeUninitialized((int)newCapacity);
//Move buffer content around (because the slot size is changed)
var sourcePtr = (byte*)buf.GetUnsafePtr() + GhostSystemConstants.SnapshotHistorySize*slotCapacity;
var destPtr = (byte*)buf.GetUnsafePtr() + GhostSystemConstants.SnapshotHistorySize*newSlotCapacity;
for (int i=0;i<GhostSystemConstants.SnapshotHistorySize;++i)
{
    destPtr -= newSlotCapacity;
    sourcePtr -= slotCapacity;
    UnsafeUtility.MemMove(destPtr, sourcePtr, slotCapacity);
}
slotCapacity = newSlotCapacity;

Both sourcePtr and destPtr doesn’t take into account the buffer header so the buffer is corrupted after the copy.

After adding the header size to those two pointers I stopped getting corrupted values:

var sourcePtr = (byte*)buf.GetUnsafePtr() + SnapshotDynamicBuffersHelper.GetHeaderSize()+ GhostSystemConstants.SnapshotHistorySize*slotCapacity;
var destPtr = (byte*)buf.GetUnsafePtr() + SnapshotDynamicBuffersHelper.GetHeaderSize()+ GhostSystemConstants.SnapshotHistorySize*newSlotCapacity;

Also, there is a variable baselineDynamicDataPtr in the same file that seems to refer to that buffer. It looks like it might be used after the buffer reallocation, but not sure.

2

Hi Skiplist,

There were some bug in relation to dynamic buffer in 0.6-preview-7. One of them was exactly here (the memory was not moved correctly).
Has been already fixed (amoung others) in later version of NetCode. So sorry we didn’t ship yet a new update in a while.
The baselineDynamicDataPtr is used to decompressed the snapshot sent by server in case it is delta-compressed.
In relation to baselineDynamicDataPtr there was another problem (again, already fixed) that was causing reading memory from a release memory location, ending in garbage data inside the buffer.

I attached a diff with all the changes (not many) in case you need to locally fix also these.

7332817–890908–GhostReceiveSystem__diff.txt (6.39 KB)

1 Like
3

Thanks, that is very helpful. With this fixed I’m pretty happy with 0.6, but if we can get access to something newer soonish that would still be nice :slight_smile: