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fix: Fixed an issue where BatchedSendQueue was including the HeadIndex twice when copying data, which was causing stream corruption when the data exceeded a certain throughput. [NCCBUG-187] #2332

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ShadauxCat merged 3 commits into from
Dec 5, 2022
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fix: Fixed an issue where BatchedSendQueue was including the HeadIndex twice when copying data, which was causing stream corruption when the data exceeded a certain throughput. [NCCBUG-187] #2332

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fix: Fixed an issue where BatchedSendQueue was including the HeadInde…
ShadauxCat Dec 2, 2022
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Added a test
ShadauxCat Dec 5, 2022
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ShadauxCat Dec 5, 2022
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2 changes: 1 addition & 1 deletion com.unity.netcode.gameobjects/Runtime/Transports/UTP/BatchedSendQueue.cs
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Expand Up @@ -226,7 +226,7 @@ public int FillWriterWithMessages(ref DataStreamWriter writer)
{
writer.WriteInt(messageLength);

var messageOffset = HeadIndex + reader.GetBytesRead();
var messageOffset = reader.GetBytesRead();
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@ShadauxCat ShadauxCat Dec 2, 2022

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If you look above here, there's readerOffset = HeadIndex. This was changed in #2224 from readerOffset = 0 because reader was changed from being a slice of m_data to containing all of m_data and reading from that offset. The return value of GetBytesRead() here already includes HeadIndex, so this results in HeadIndex being applied twice when calculating messageOffset.

When HeadIndex is 0 that has no effect, but when the queue gets filled more, it starts resulting in things being skipped over, data being corrupted, and - sometimes - data from completely outside the stream (i.e., garbage data) being copied into the stream.

WriteBytes(ref writer, (byte*)m_Data.GetUnsafePtr() + messageOffset, messageLength);

writerAvailable -= sizeof(int) + messageLength;
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