net: also wait for exceptional events in Sock::Wait()

This mimics closely `CConnman::SocketEvents()` and the underlying
`poll(2)`.

Author: vasild

src/i2p.cpp

@@ -150,8 +150,8 @@ bool Session::Accept(Connection& conn)
                 throw std::runtime_error("wait on socket failed");
             }
 
-            if ((occurred & Sock::RECV) == 0) {
-                // Timeout, no incoming connections within MAX_WAIT_FOR_IO.
+            if (occurred == 0) {
+                // Timeout, no incoming connections or errors within MAX_WAIT_FOR_IO.
                 continue;
             }
 

src/util/sock.cpp

@@ -136,6 +136,9 @@ bool Sock::Wait(std::chrono::milliseconds timeout, Event requested, Event* occur
         if (fd.revents & POLLOUT) {
             *occurred |= SEND;
         }
+        if (fd.revents & (POLLERR | POLLHUP)) {
+            *occurred |= ERR;
+        }
     }
 
     return true;
@@ -146,8 +149,10 @@ bool Sock::Wait(std::chrono::milliseconds timeout, Event requested, Event* occur
 
     fd_set fdset_recv;
     fd_set fdset_send;
+    fd_set fdset_err;
     FD_ZERO(&fdset_recv);
     FD_ZERO(&fdset_send);
+    FD_ZERO(&fdset_err);
 
     if (requested & RECV) {
         FD_SET(m_socket, &fdset_recv);
@@ -157,9 +162,11 @@ bool Sock::Wait(std::chrono::milliseconds timeout, Event requested, Event* occur
         FD_SET(m_socket, &fdset_send);
     }
 
+    FD_SET(m_socket, &fdset_err);
+
     timeval timeout_struct = MillisToTimeval(timeout);
 
-    if (select(m_socket + 1, &fdset_recv, &fdset_send, nullptr, &timeout_struct) == SOCKET_ERROR) {
+    if (select(m_socket + 1, &fdset_recv, &fdset_send, &fdset_err, &timeout_struct) == SOCKET_ERROR) {
         return false;
     }
 
@@ -171,6 +178,9 @@ bool Sock::Wait(std::chrono::milliseconds timeout, Event requested, Event* occur
         if (FD_ISSET(m_socket, &fdset_send)) {
             *occurred |= SEND;
         }
+        if (FD_ISSET(m_socket, &fdset_err)) {
+            *occurred |= ERR;
+        }
     }
 
     return true;

src/util/sock.h

@@ -130,21 +130,28 @@ class Sock
     /**
      * If passed to `Wait()`, then it will wait for readiness to read from the socket.
      */
-    static constexpr Event RECV = 0b01;
+    static constexpr Event RECV = 0b001;
 
     /**
      * If passed to `Wait()`, then it will wait for readiness to send to the socket.
      */
-    static constexpr Event SEND = 0b10;
+    static constexpr Event SEND = 0b010;
+
+    /**
+     * Ignored if passed to `Wait()`, but could be set in the occurred events if an
+     * exceptional condition has occurred on the socket or if it has been disconnected.
+     */
+    static constexpr Event ERR = 0b100;
 
     /**
      * 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[out] occurred If not nullptr and `true` is returned, then upon return this
-     * indicates which of the requested events occurred. A timeout is indicated by return
-     * value of `true` and `occurred` being set to 0.
-     * @return true on success and false otherwise
+     * @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).
+     * A timeout is indicated by return value of `true` and `occurred` being set to 0.
+     * @return true on success (or timeout, if `occurred` of 0 is returned), false otherwise
      */
     [[nodiscard]] virtual bool Wait(std::chrono::milliseconds timeout,
                                     Event requested,