net: convert standalone IsSelectableSocket() to Sock::IsSelectable()

This makes the callers mockable.

src/net.cpp

@@ -961,8 +961,7 @@ void CConnman::CreateNodeFromAcceptedSocket(std::unique_ptr<Sock>&& sock,
         return;
     }
 
-    if (!IsSelectableSocket(sock->Get()))
-    {
+    if (!sock->IsSelectable()) {
         LogPrintf("connection from %s dropped: non-selectable socket\n", addr.ToString());
         return;
     }

src/netbase.cpp

@@ -503,7 +503,7 @@ std::unique_ptr<Sock> CreateSockTCP(const CService& address_family)
 
     // Ensure that waiting for I/O on this socket won't result in undefined
     // behavior.
-    if (!IsSelectableSocket(sock->Get())) {
+    if (!sock->IsSelectable()) {
         LogPrintf("Cannot create connection: non-selectable socket created (fd >= FD_SETSIZE ?)\n");
         return nullptr;
     }

src/test/fuzz/util.cpp

@@ -16,7 +16,7 @@
 #include <memory>
 
 FuzzedSock::FuzzedSock(FuzzedDataProvider& fuzzed_data_provider)
-    : m_fuzzed_data_provider{fuzzed_data_provider}
+    : m_fuzzed_data_provider{fuzzed_data_provider}, m_selectable{fuzzed_data_provider.ConsumeBool()}
 {
     m_socket = fuzzed_data_provider.ConsumeIntegralInRange<SOCKET>(INVALID_SOCKET - 1, INVALID_SOCKET);
 }
@@ -254,6 +254,11 @@ int FuzzedSock::GetSockName(sockaddr* name, socklen_t* name_len) const
     return 0;
 }
 
+bool FuzzedSock::IsSelectable() const
+{
+    return m_selectable;
+}
+
 bool FuzzedSock::Wait(std::chrono::milliseconds timeout, Event requested, Event* occurred) const
 {
     constexpr std::array wait_errnos{

src/test/fuzz/util.h

@@ -48,6 +48,13 @@ class FuzzedSock : public Sock
      */
     mutable std::optional<uint8_t> m_peek_data;
 
+    /**
+     * Whether to pretend that the socket is select(2)-able. This is randomly set in the
+     * constructor. It should remain constant so that repeated calls to `IsSelectable()`
+     * return the same value.
+     */
+    const bool m_selectable;
+
 public:
     explicit FuzzedSock(FuzzedDataProvider& fuzzed_data_provider);
 
@@ -73,6 +80,8 @@ public:
 
     int GetSockName(sockaddr* name, socklen_t* name_len) const override;
 
+    bool IsSelectable() const override;
+
     bool Wait(std::chrono::milliseconds timeout, Event requested, Event* occurred = nullptr) const override;
 
     bool WaitMany(std::chrono::milliseconds timeout, EventsPerSock& events_per_sock) const override;

src/test/util/net.h

@@ -166,6 +166,8 @@ public:
         return 0;
     }
 
+    bool IsSelectable() const override { return true; }
+
     bool Wait(std::chrono::milliseconds timeout,
               Event requested,
               Event* occurred = nullptr) const override

src/util/sock.cpp

@@ -117,11 +117,12 @@ int Sock::GetSockName(sockaddr* name, socklen_t* name_len) const
     return getsockname(m_socket, name, name_len);
 }
 
-bool IsSelectableSocket(const SOCKET& s) {
+bool Sock::IsSelectable() const
+{
 #if defined(USE_POLL) || defined(WIN32)
     return true;
 #else
-    return (s < FD_SETSIZE);
+    return m_socket < FD_SETSIZE;
 #endif
 }
 
@@ -193,10 +194,10 @@ bool Sock::WaitMany(std::chrono::milliseconds timeout, EventsPerSock& events_per
     SOCKET socket_max{0};
 
     for (const auto& [sock, events] : events_per_sock) {
-        const auto& s = sock->m_socket;
-        if (!IsSelectableSocket(s)) {
+        if (!sock->IsSelectable()) {
             return false;
         }
+        const auto& s = sock->m_socket;
         if (events.requested & RECV) {
             FD_SET(s, &recv);
         }

src/util/sock.h

@@ -133,6 +133,12 @@ public:
      */
     [[nodiscard]] virtual int GetSockName(sockaddr* name, socklen_t* name_len) const;
 
+    /**
+     * Check if the underlying socket can be used for `select(2)` (or the `Wait()` method).
+     * @return true if selectable
+     */
+    [[nodiscard]] virtual bool IsSelectable() const;
+
     using Event = uint8_t;
 
     /**
@@ -267,8 +273,6 @@ private:
     void Close();
 };
 
-bool IsSelectableSocket(const SOCKET& s);
-
 /** Return readable error string for a network error code */
 std::string NetworkErrorString(int err);