net: allow selection of Wait() API by specifying SocketEventsMode

No behavior has changed as we don't support any additional APIs and
SEM_LT_DEFAULT preserves old behavior but upcoming commits will utilize
this to able to effectuate the preferences set by `-socketevents`.

Author: kwvg

src/i2p.cpp

@@ -160,7 +160,7 @@ bool Session::Accept(Connection& conn)
 
     while (!*m_interrupt) {
         Sock::Event occurred;
-        if (!conn.sock->Wait(MAX_WAIT_FOR_IO, Sock::RECV, &occurred)) {
+        if (!conn.sock->Wait(MAX_WAIT_FOR_IO, Sock::RECV, SEM_LT_DEFAULT, &occurred)) {
             errmsg = "wait on socket failed";
             break;
         }

src/netbase.cpp

@@ -572,7 +572,7 @@ static bool ConnectToSocket(const Sock& sock, struct sockaddr* sockaddr, socklen
             // synchronously to check for successful connection with a timeout.
             const Sock::Event requested = Sock::RECV | Sock::SEND;
             Sock::Event occurred;
-            if (!sock.Wait(std::chrono::milliseconds{nConnectTimeout}, requested, &occurred)) {
+            if (!sock.Wait(std::chrono::milliseconds{nConnectTimeout}, requested, SEM_LT_DEFAULT, &occurred)) {
                 LogPrintf("wait for connect to %s failed: %s\n",
                           dest_str,
                           NetworkErrorString(WSAGetLastError()));

src/test/fuzz/util.cpp

@@ -270,7 +270,7 @@ bool FuzzedSock::IsSelectable() const
     return m_selectable;
 }
 
-bool FuzzedSock::Wait(std::chrono::milliseconds timeout, Event requested, Event* occurred) const
+bool FuzzedSock::Wait(std::chrono::milliseconds timeout, Event requested, SocketEventsMode event_mode, Event* occurred) const
 {
     constexpr std::array wait_errnos{
         EBADF,

src/test/fuzz/util.h

@@ -89,7 +89,7 @@ class FuzzedSock : public Sock
 
     bool IsSelectable() const override;
 
-    bool Wait(std::chrono::milliseconds timeout, Event requested, Event* occurred = nullptr) const override;
+    bool Wait(std::chrono::milliseconds timeout, Event requested, SocketEventsMode event_mode = SEM_LT_DEFAULT, Event* occurred = nullptr) const override;
 
     bool IsConnected(std::string& errmsg) const override;
 };

src/test/util/net.h

@@ -202,6 +202,7 @@ class StaticContentsSock : public Sock
 
     bool Wait(std::chrono::milliseconds timeout,
               Event requested,
+              SocketEventsMode event_mode = SEM_LT_DEFAULT,
               Event* occurred = nullptr) const override
     {
         if (occurred != nullptr) {

src/util/sock.cpp

@@ -140,8 +140,36 @@ bool Sock::IsSelectable() const
 #endif
 }
 
-bool Sock::Wait(std::chrono::milliseconds timeout, Event requested, Event* occurred) const
+bool Sock::Wait(std::chrono::milliseconds timeout, Event requested, SocketEventsMode event_mode, Event* occurred) const
 {
+    std::string debug_str;
+
+    switch (event_mode)
+    {
+        case SocketEventsMode::Poll:
+#ifdef USE_POLL
+            return WaitPoll(timeout, requested, occurred);
+#else
+            debug_str += "Sock::Wait -- Support for poll not compiled in, falling back on ";
+            break;
+#endif /* USE_POLL */
+        case SocketEventsMode::Select:
+            return WaitSelect(timeout, requested, occurred);
+        case SocketEventsMode::EPoll:
+            debug_str += "Sock::Wait -- Unimplemented for epoll, falling back on ";
+            break;
+        case SocketEventsMode::KQueue:
+            debug_str += "Sock::Wait -- Unimplemented for kqueue, falling back on ";
+            break;
+        default:
+            assert(false);
+    }
+#ifdef USE_POLL
+    debug_str += "poll";
+#else
+    debug_str += "select";
+#endif /* USE_POLL*/
+    LogPrint(BCLog::NET, "%s\n", debug_str);
 #ifdef USE_POLL
     return WaitPoll(timeout, requested, occurred);
 #else

src/util/sock.h

@@ -28,6 +28,12 @@ enum class SocketEventsMode : int8_t {
     Unknown = -1
 };
 
+#ifdef USE_POLL
+#define SEM_LT_DEFAULT SocketEventsMode::Poll
+#else
+#define SEM_LT_DEFAULT SocketEventsMode::Select
+#endif /* USE_POLL */
+
 /* Converts SocketEventsMode value to string with additional check to report modes not compiled for as unknown */
 constexpr std::string_view SEMToString(const SocketEventsMode val) {
     switch (val) {
@@ -212,6 +218,7 @@ class Sock
      * Wait for readiness for input (recv) or output (send).
      * @param[in] timeout Wait this much for at least one of the requested events to occur.
      * @param[in] requested Wait for those events, bitwise-or of `RECV` and `SEND`.
+     * @param[in] event_mode Wait using the API specified.
      * @param[out] occurred If not nullptr and the function returns `true`, then this
      * indicates which of the requested events occurred (`ERR` will be added, even if
      * not requested, if an exceptional event occurs on the socket).
@@ -220,6 +227,7 @@ class Sock
      */
     [[nodiscard]] virtual bool Wait(std::chrono::milliseconds timeout,
                                     Event requested,
+                                    SocketEventsMode event_mode = SEM_LT_DEFAULT,
                                     Event* occurred = nullptr) const;
 #ifdef USE_POLL
     bool WaitPoll(std::chrono::milliseconds timeout, Event requested, Event* occurred = nullptr) const;