net: reintroduce IsSelectableSocket() and make it SEM-aware

`IsSelectableSocket()` was subsumed into `Sock` for mockability's sake
but creates problems when our event-socket map uses the raw `SOCKET`
and not `Sock`, so we need to bring it back. On top of that,
`IsSelectableSocket()`'s behavior was defined at compile-time when it
should've been sensitive to the runtime capabilities we give it.

Currently, this does not cause a change in behavior but makes way for
future changes.

Author: kwvg

src/test/fuzz/util.cpp

@@ -265,7 +265,7 @@ bool FuzzedSock::SetNonBlocking() const
     return true;
 }
 
-bool FuzzedSock::IsSelectable() const
+bool FuzzedSock::IsSelectable(bool is_select) const
 {
     return m_selectable;
 }

src/test/fuzz/util.h

@@ -87,7 +87,7 @@ class FuzzedSock : public Sock
 
     bool SetNonBlocking() const override;
 
-    bool IsSelectable() const override;
+    bool IsSelectable(bool is_select) const override;
 
     bool Wait(std::chrono::milliseconds timeout, Event requested, SocketEventsMode event_mode = SEM_LT_DEFAULT, Event* occurred = nullptr) const override;
 

src/test/util/net.h

@@ -198,7 +198,7 @@ class StaticContentsSock : public Sock
 
     bool SetNonBlocking() const override { return true; }
 
-    bool IsSelectable() const override { return true; }
+    bool IsSelectable(bool is_select) const override { return true; }
 
     bool Wait(std::chrono::milliseconds timeout,
               Event requested,

src/util/sock.cpp

@@ -24,6 +24,15 @@ static inline bool IOErrorIsPermanent(int err)
     return err != WSAEAGAIN && err != WSAEINTR && err != WSAEWOULDBLOCK && err != WSAEINPROGRESS;
 }
 
+static inline bool IsSelectableSocket(const SOCKET& s, bool is_select)
+{
+#if defined(WIN32)
+    return true;
+#else
+    return is_select ? (s < FD_SETSIZE) : true;
+#endif
+}
+
 Sock::Sock() : m_socket(INVALID_SOCKET) {}
 
 Sock::Sock(SOCKET s) : m_socket(s) {}
@@ -131,13 +140,9 @@ bool Sock::SetNonBlocking() const
     return true;
 }
 
-bool Sock::IsSelectable() const
+bool Sock::IsSelectable(bool is_select) const
 {
-#if defined(USE_POLL) || defined(WIN32)
-    return true;
-#else
-    return m_socket < FD_SETSIZE;
-#endif
+    return IsSelectableSocket(m_socket, is_select);
 }
 
 bool Sock::Wait(std::chrono::milliseconds timeout, Event requested, SocketEventsMode event_mode, Event* occurred) const
@@ -213,7 +218,7 @@ bool Sock::WaitPoll(std::chrono::milliseconds timeout, Event requested, Event* o
 
 bool Sock::WaitSelect(std::chrono::milliseconds timeout, Event requested, Event* occurred) const
 {
-    if (!IsSelectable()) {
+    if (!IsSelectableSocket(m_socket, /*is_select=*/true)) {
         return false;
     }
 

src/util/sock.h

@@ -194,7 +194,7 @@ class Sock
      * Check if the underlying socket can be used for `select(2)` (or the `Wait()` method).
      * @return true if selectable
      */
-    [[nodiscard]] virtual bool IsSelectable() const;
+    [[nodiscard]] virtual bool IsSelectable(bool is_select = (SEM_LT_DEFAULT == SocketEventsMode::Select)) const;
 
     using Event = uint8_t;