net: add RAII socket and use it instead of bare SOCKET

Introduce a class to manage the lifetime of a socket - when the object
that contains the socket goes out of scope, the underlying socket will
be closed.

In addition, the new `Sock` class has a `Send()`, `Recv()` and `Wait()`
methods that can be overridden by unit tests to mock the socket
operations.

The `Wait()` method also hides the
`#ifdef USE_POLL poll() #else select() #endif` technique from higher
level code.

src/util/sock.cpp

@@ -6,12 +6,97 @@
 #include <logging.h>
 #include <tinyformat.h>
 #include <util/sock.h>
+#include <util/system.h>
+#include <util/time.h>
 
 #include <codecvt>
 #include <cwchar>
 #include <locale>
 #include <string>
 
+#ifdef USE_POLL
+#include <poll.h>
+#endif
+
+Sock::Sock() : m_socket(INVALID_SOCKET) {}
+
+Sock::Sock(SOCKET s) : m_socket(s) {}
+
+Sock::Sock(Sock&& other)
+{
+    m_socket = other.m_socket;
+    other.m_socket = INVALID_SOCKET;
+}
+
+Sock::~Sock() { Reset(); }
+
+Sock& Sock::operator=(Sock&& other)
+{
+    Reset();
+    m_socket = other.m_socket;
+    other.m_socket = INVALID_SOCKET;
+    return *this;
+}
+
+SOCKET Sock::Get() const { return m_socket; }
+
+SOCKET Sock::Release()
+{
+    const SOCKET s = m_socket;
+    m_socket = INVALID_SOCKET;
+    return s;
+}
+
+void Sock::Reset() { CloseSocket(m_socket); }
+
+ssize_t Sock::Send(const void* data, size_t len, int flags) const
+{
+    return send(m_socket, static_cast<const char*>(data), len, flags);
+}
+
+ssize_t Sock::Recv(void* buf, size_t len, int flags) const
+{
+    return recv(m_socket, static_cast<char*>(buf), len, flags);
+}
+
+bool Sock::Wait(std::chrono::milliseconds timeout, Event requested) const
+{
+#ifdef USE_POLL
+    pollfd fd;
+    fd.fd = m_socket;
+    fd.events = 0;
+    if (requested & RECV) {
+        fd.events |= POLLIN;
+    }
+    if (requested & SEND) {
+        fd.events |= POLLOUT;
+    }
+
+    return poll(&fd, 1, count_milliseconds(timeout)) != SOCKET_ERROR;
+#else
+    if (!IsSelectableSocket(m_socket)) {
+        return false;
+    }
+
+    fd_set fdset_recv;
+    fd_set fdset_send;
+    FD_ZERO(&fdset_recv);
+    FD_ZERO(&fdset_send);
+
+    if (requested & RECV) {
+        FD_SET(m_socket, &fdset_recv);
+    }
+
+    if (requested & SEND) {
+        FD_SET(m_socket, &fdset_send);
+    }
+
+    timeval timeout_struct = MillisToTimeval(timeout);
+
+    return select(m_socket + 1, &fdset_recv, &fdset_send, nullptr, &timeout_struct) != SOCKET_ERROR;
+#endif /* USE_POLL */
+}
+
 #ifdef WIN32
 std::string NetworkErrorString(int err)
 {