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fix: Survive a shutdown from inside receive dispatch - #73
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An application may shut its peer down, or drop a transfer, from a callback Receive is dispatching. Six live tests pin what must hold: a FileListTransfer receiver is dereferenced once whether its callback shuts the peer down or removes the receiver, a plugin's shutdown stops the packet before later plugins, and a returned packet survives Shutdown() and can still be deallocated.
Shutdown() cleared the packet pool even while Receive was dispatching a packet from it, or the application still held one Receive returned. Receive then handed the freed packet to the next plugin, and the application's DeallocatePacket released it into a pool that no longer existed. The pool is now only cleared once every packet has come back, and Receive stops dispatching -- and returns nothing -- for a packet whose callbacks shut the peer down.
A download callback that shuts the peer down, or calls RemoveReceiver or CancelReceive, frees its own receiver. DecodeSetHeader, DecodeFile and OnReferencePush then dereferenced and deleted it a second time, and Update() indexed past a list the callback had emptied. Each path now re-checks the receiver after every callback.
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WalkthroughFileListTransfer now checks receiver registration after callbacks. RakPeer tracks outstanding pooled packets and detects shutdown during Receive dispatch. Integration tests cover receiver removal, shutdown during plugin dispatch, and packet handling after shutdown. ChangesCallback-safe dispatch and shutdown
Priority: ⬆️ High Estimated code review effort: 3 (Moderate) | ~25 minutes Change: Bug fix Merge Risk: 🔵 Low · up to
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| Check name | Status | Explanation | Resolution |
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| Docstring Coverage |  |
Docstring coverage is 14.71% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 34 functions across 5 files. | Write docstrings for the functions missing them to satisfy the coverage threshold. |
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Check name Status Explanation Description Check Check skipped - CodeRabbit’s high-level summary is enabled. Title check The title clearly and concisely describes the primary change: preventing failures when shutdown occurs during receive dispatch. Linked Issues check Check skipped because no linked issues were found for this pull request. Out of Scope Changes check Check skipped because no linked issues were found for this pull request.
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A rabbit watched the callbacks run,
Then checked each receiver, one by one.
Pooled packets stayed safe in their place,
While shutdown changed the dispatch pace.
The bunny thumped: “The tests are done!”
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Review comments at @Tests/Integration/ShutdownDuringDispatchLiveTests.cpp:
- Around line 242-257: Update RunReactingTransfer and the affected
ShutdownDuringDispatch tests to use an ephemeral server port: bind to port 0,
obtain the assigned port with GetMyBoundAddress().GetPort(), and pass it to
Connect instead of using fixed port numbers.
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📒 Files selected for processing: 5
Source/include/mafianet/file_list_transfer.hSource/include/mafianet/peer.hSource/src/file_list_transfer.cppSource/src/peer.cppTests/Integration/ShutdownDuringDispatchLiveTests.cpp
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Reported in MafiaHub/Framework#315: a Framework client refusing a join from its asset download callback crashes in
FileListTransfer::DecodeSetHeader, with an access violation or a double free (0xC0000374).Cause
Shutdown()called from a callback thatReceiveis dispatching releases things its callers still use:FileListTransfer::Clear()deletes the receiver whose callback is running.DecodeSetHeader,DecodeFileandOnReferencePushthen dereference it and delete it again.RemoveReceiverandCancelReceivefrom a callback do the same.Receiveis still dispatching a packet from it, and while the application may still hold oneReceivereturned. That packet then goes to the next plugin, and the application'sDeallocatePacketputs it back into a pool that no longer exists.Fix
RakPeer: the pool is only cleared when every packet has come back; otherwise its pages are reused by the next session. A per-shutdown generation letsReceivestop a packet whose callbacks shut the peer down: no further plugins see it, andReceivereturns nothing for it.FileListTransfer: every path re-checks the receiver after each download callback before touching it again.Update()no longer indexes past a list that a handler emptied.Tests
ShutdownDuringDispatchLiveTests.cppadds six tests. Against the old code, the four receiver tests crash with0xC0000005(the issue's crash) and the plugin test fails because a later plugin still receives the packet.ReturnedPacketOutlivesShutdownonly fails in Debug, because Release doesn't scribble over freed memory.The full suite passes locally on Windows Release (287/287).
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