C4CurlSystem: Unset CURLMOPT_SOCKETFUNCTION and CURLMOPT_TIMERFUNCTIO…

…N before calling curl_multi_cleanup

curl_multi_cleanup may call the socket function with an internal easy handle,
which will then attempt to insert that handle into the map. However, at that
point the map has already been destroyed, as curl_multi_cleanup is called
from the destructor of C4CurlSystem's multiHandle member. As we don't want to
know about that extra handle at this stage anyway, we ensure that all user
callbacks are reset to their default (nullptr) before curl_multi_cleanup
is called.

src/C4CurlSystem.cpp

@@ -84,6 +84,35 @@ C4CurlSystem::AddedEasyHandle::~AddedEasyHandle()
 	}
 }
 
+C4CurlSystem::MultiHandleWithCallbacks::MultiHandleWithCallbacks(
+		MultiHandle multiHandle,
+		C4CurlSystem &system,
+		SocketFunction *const socketFunction,
+		TimerFunction *const timerFunction)
+	: multiHandle{std::move(multiHandle)}
+{
+	if (this->multiHandle)
+	{
+		curl_multi_setopt(this->multiHandle.get(), CURLMOPT_SOCKETFUNCTION, socketFunction);
+		curl_multi_setopt(this->multiHandle.get(), CURLMOPT_SOCKETDATA, &system);
+
+		curl_multi_setopt(this->multiHandle.get(), CURLMOPT_TIMERFUNCTION, timerFunction);
+		curl_multi_setopt(this->multiHandle.get(), CURLMOPT_TIMERDATA, &system);
+	}
+}
+
+C4CurlSystem::MultiHandleWithCallbacks::~MultiHandleWithCallbacks()
+{
+	if (multiHandle)
+	{
+		curl_multi_setopt(multiHandle.get(), CURLMOPT_SOCKETFUNCTION, nullptr);
+		curl_multi_setopt(multiHandle.get(), CURLMOPT_SOCKETDATA, nullptr);
+
+		curl_multi_setopt(multiHandle.get(), CURLMOPT_TIMERFUNCTION, nullptr);
+		curl_multi_setopt(multiHandle.get(), CURLMOPT_TIMERDATA, nullptr);
+	}
+}
+
 C4CurlSystem::Awaiter::Awaiter(C4CurlSystem &system, EasyHandle &&easyHandle)
 	: system{system},
 	  easyHandle{std::move(easyHandle)},
@@ -145,7 +174,7 @@ void C4CurlSystem::Awaiter::Resume()
 }
 
 C4CurlSystem::C4CurlSystem()
-	: multiHandle{curl_multi_init()}
+	: multiHandle{MultiHandle{curl_multi_init()}, *this, &C4CurlSystem::SocketFunction, &C4CurlSystem::TimerFunction}
 {
 	if (!multiHandle)
 	{
@@ -154,12 +183,6 @@ C4CurlSystem::C4CurlSystem()
 		throw CStdApp::StartupException{std::move(message)};
 	}
 
-	curl_multi_setopt(multiHandle.get(), CURLMOPT_SOCKETFUNCTION, &C4CurlSystem::SocketFunction);
-	curl_multi_setopt(multiHandle.get(), CURLMOPT_SOCKETDATA, this);
-
-	curl_multi_setopt(multiHandle.get(), CURLMOPT_TIMERFUNCTION, &C4CurlSystem::TimerFunction);
-	curl_multi_setopt(multiHandle.get(), CURLMOPT_TIMERDATA, this);
-
 	multiTask = Execute();
 }
 

src/C4CurlSystem.h

@@ -97,6 +97,24 @@ class C4CurlSystem
 		~GlobalInit();
 	};
 
+	class MultiHandleWithCallbacks
+	{
+	public:
+		using SocketFunction = int(CURL *, curl_socket_t, int, void *) noexcept;
+		using TimerFunction = int(CURLM *, long, void *) noexcept;
+
+	public:
+		MultiHandleWithCallbacks(MultiHandle multiHandle, C4CurlSystem &system, SocketFunction *socketFunction, TimerFunction *timerFunction);
+		~MultiHandleWithCallbacks();
+
+	public:
+		auto get() const { return multiHandle.get(); }
+		explicit operator bool() const noexcept { return !!multiHandle; }
+
+	private:
+		MultiHandle multiHandle;
+	};
+
 	class Awaiter : public C4Task::CancellableAwaiter<Awaiter>
 	{
 	public:
@@ -171,7 +189,7 @@ class C4CurlSystem
 	std::atomic_uint32_t timeout{StdSync::Infinite};
 	[[NO_UNIQUE_ADDRESS]] GlobalInit globalInit;
 
-	MultiHandle multiHandle;
+	MultiHandleWithCallbacks multiHandle;
 
 #ifdef _WIN32
 	CStdEvent event;