Crash when connecting to a socket on iOS in distribution builds

I’m trying to build my project using Unreal Engine 5.4 for iOS. I use SocketIO 2.8.0 to connect to the backend. When trying to connect to the socket, a crash occurs. This only happens on iOS, only in Distribution builds, and only on Unreal 5.4. There are no problems on Unreal 5.2. Callstack: crashlog.txt

The callstack may be slightly different, but the problem is always when allocating or deallocating memory. I suspect that this may be a race condition and is related to some peculiarities of working with memory on iOS.

I tried using other versions of plugin, other versions of xcode, tried to build socket io using both c++20 and c++17, nothing helps.

likely related issues: #431 (5.3) and #402

iOS is not a primary platform I develop on, will likely have to depend on other devs to identify issue. Once a pull request with fix is opened I can merge it.

I was experiencing consistent crashes on iOS only in TestFlight / Distribution builds, while everything worked perfectly in Development builds.

The crash log showed:

___BUG_IN_CLIENT_OF_LIBMALLOC_POINTER_BEING_FREED_WAS_NOT_ALLOCATED

and the stack trace pointed into websocketpp / socket.io-client-cpp during HTTP header parsing.

Workaround That Fixed It

For me, the issue appears to be related to memory allocation differences in iOS Shipping/Distribution builds.

I resolved the crash by forcing Unreal Engine to use the ANSI allocator on iOS:

using UnrealBuildTool;
using System.Collections.Generic;

public class YourProjectTarget : TargetRules
{
    public YourProjectTarget(TargetInfo Target) : base(Target)
    {
        Type = TargetType.Game;

        if (Target.Platform == UnrealTargetPlatform.IOS)
        {
            GlobalDefinitions.Add("FORCE_ANSI_ALLOCATOR=1");
        }
    }
}

### Steps

Add the above to your Game Target (.Target.cs)

Delete:

Binaries
Intermediate
Regenerate project files
Rebuild and archive again

Notes

This issue seems specific to iOS distribution/TestFlight builds
Development builds may work fine, which can make this tricky to debug
Likely related to how Unreal’s allocator interacts with socket.io-client-cpp / websocketpp on iOS

Nice spot, if you make a pull request with the suggested code changes I'll merge it.

Thanks! I've implemented the fix and opened a pull request with the changes.

This resolved the iOS TestFlight/distribution crash on my side. Let me know if you'd like any adjustments.

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Crash when connecting to a socket on iOS in distribution builds #442

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Crash when connecting to a socket on iOS in distribution builds #442

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getnamo commented on Dec 2, 2024

omaralmasoud commented on Mar 17, 2026

Workaround That Fixed It

getnamo commented on Mar 18, 2026

omaralmasoud commented on Mar 19, 2026

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