Reusing the same SocketAsyncEventArgs for different udp remote endpoints does not work anymore

[rmja]

Description

It has been introduced in .NET 8 that the _socketAddress inside the SocketAsyncEventArgs is only serialized if it is null. This means that it is only serialized the first time the SocketAsyncEventArgs is used for a socket operation. However, e.g. in https://github.com/chronoxor/NetCoreServer/blob/master/source/NetCoreServer/UdpServer.cs#L692-L694 the SocketAsyncEventArgs is used multiple times for different remote endpoints.

This is what is going on in .NET 8:
https://github.com/dotnet/runtime/blob/v8.0.1/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs#L3098-L3107

This is the previous same file in .NET 7:
https://github.com/dotnet/runtime/blob/v7.0.15/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs#L3027

When comparing the two files, it seems that, if one changes the remote endpoint and calls e.g. Socket.SendToAsync() then it will not re-serialize the _socketAddress and the payload will not be transmitted to the socket address of the newly configured remote endpoint - instead they whill be transmitted to the first configured remote endpoint.

Reproduction Steps

• Create a single instance of var ea = SocketAsyncEventArgs.
• Call ea.RemoteEndPoint = firstEndpoint.
• Call socket.SendToAsync(ea).
• The data is correctly sent to firstEndpoint, now set a different remote endpoint ea.RemoteEndpoint = secondEndpoint
• Call socket.SendToAsync(ea).
• The data is not sent secondEndpoint , it is sent to the old firstEndpoint which is clearly not correct.

Expected behavior

It is expected that consequitive calls to e.g. Socket.SendToAsync() with the same instance of SocketAsyncEventArgs but with reconfigured RemoteEndpoint, actually transmits to different endpoints.

Actual behavior

All consequitive calls to e.g. Socket.SendToAsync() are transmitted to the remote endpoint configured when Socket.SendToAsync() is first called. This is verified in wireshark.

Regression?

This worked fine in .NET 7.

Known Workarounds

I made the following PR in NetCoreServer in case the re-use of SocketAsyncEventArgs for different remote endpoints is in fact not legal, see: chronoxor/NetCoreServer#284

Configuration

No response

Other information

No response

[ghost]

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Issue Details

---

Description

It has been introduced in .NET 8 that the _socketAddress inside the SocketAsyncEventArgs is only serialized if it is null. This means that it is only serialized the first time the SocketAsyncEventArgs is used for a socket operation. However, e.g. in https://github.com/chronoxor/NetCoreServer/blob/master/source/NetCoreServer/UdpServer.cs#L692-L694 the SocketAsyncEventArgs is used multiple times for different remote endpoints.

This is what is going on in .NET 8:
https://github.com/dotnet/runtime/blob/v8.0.1/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs#L3098-L3107

This is the previous same file in .NET 7:
https://github.com/dotnet/runtime/blob/v7.0.15/src/libraries/System.Net.Sockets/src/System/Net/Sockets/Socket.cs#L3027

When comparing the two files, it seems that, if one changes the remote endpoint and calls e.g. Socket.SendToAsync() then it will not re-serialize the _socketAddress and the payload will not be transmitted to the socket address of the newly configured remote endpoint - instead they whill be transmitted to the first configured remote endpoint.

Reproduction Steps

• Create a single instance of var ea = SocketAsyncEventArgs.
• Call ea.RemoteEndPoint = firstEndpoint.
• Call socket.SendToAsync(ea).
• The data is correctly sent to firstEndpoint, now set a different remote endpoint ea.RemoteEndpoint = secondEndpoint
• Call socket.SendToAsync(ea).
• The data is not sent secondEndpoint , it is sent to the old firstEndpoint which is clearly not correct.

Expected behavior

It is expected that consequitive calls to e.g. Socket.SendToAsync() with the same instance of SocketAsyncEventArgs but with reconfigured RemoteEndpoint, actually transmits to different endpoints.

Actual behavior

All consequitive calls to e.g. Socket.SendToAsync() are transmitted to the remote endpoint configured when Socket.SendToAsync() is first called. This is verified in wireshark.

Regression?

This worked fine in .NET 7.

Known Workarounds

I made the following PR in NetCoreServer in case the re-use of SocketAsyncEventArgs for different remote endpoints is in fact not legal, see: chronoxor/NetCoreServer#284

Configuration

No response

Other information

No response

Author:	rmja
Assignees:	-
Labels:	area-System.Net.Sockets, untriaged
Milestone:	-

[stephentoub]

cc: @wfurt

[wfurt]

I'll take a look.

[rmja]

May I ask whether this was triaged to be a regression in .NET 8 or if the use of SocketAsyncEventArgs for different remote endpoints is a "too aggressive" optimization inside the NetCoreServer library? This would give some insight to whether chronoxor/NetCoreServer#284 should be merged or not, and maybe with a specific .NET 8 "fix" as I can see that this is not added to a .NET 8 patch milestone.

[wfurt]

it is certainly unintended regression @rmja and the linked code looks fine to me. I should have PR up today to fix it. Once fixed and merged to main, we can reopen it for servicing request. I'm not sure what exact timing it would be.

[wfurt]

re-opening for backport

[gmeena]

it is certainly unintended regression @rmja and the linked code looks fine to me. I should have PR up today to fix it. Once fixed and merged to main, we can reopen it for servicing request. I'm not sure what exact timing it would be.

@wfurt do we know when it will be available in 8.0.x? any approximation

[wfurt]

the fix missed 8.0.5 by day or so ;(
It should be in next update around mid June.

[gmeena]

the fix missed 8.0.5 by day or so ;( It should be in next update around mid June.

:( we just updated our services to .NET 8 and found this issue, now in spot. Any workaround?

[wfurt]

use fresh SocketAsyncEventArgs for each round or have one used based on the RemoteEndPoint

[gmeena]

@wfurt Is this included in .NET 8.0.6 - May 28, 2024

[wfurt]

no, my post had wrong version e.g. it missed 8.0.6 and it should be out mid June.

[wfurt]

8.0 fixed by #99695. it should be out in 8.0.7

[karelz]

Fixed in main (9.0) in PR #98134 and in 8.0.7 (July release) in PR #99695.