Improve zombie client connection detection

src/connection.h

@@ -404,8 +404,8 @@ static inline int connIsClosing(connection *conn) {
     return conn->type->is_closing(conn);
 }
 
-/* Shared is_closing implementation for socket-based connections. */
-int connSocketIsClosing(connection *conn);
+/* Shared is_closing implementation for TCP socket-based connections. */
+int connTcpSocketIsClosing(connection *conn);
 
 /* Associate a private data pointer with the connection */
 static inline void connSetPrivateData(connection *conn, void *data) {

src/server.c

@@ -1228,6 +1228,9 @@ void getExpensiveClientsInfo(size_t *in_usage, size_t *out_usage) {
 static bool clientsCronTcpIsClosing(client *c) {
     if (!c->conn) return false;
 
+    /* If the fd is still watched by the event loop, it detects the close and frees the client itself. */
+    if (connHasReadHandler(c->conn) || connHasWriteHandler(c->conn)) return false;
+
     if (!connIsClosing(c->conn)) return false;
 
     if (server.verbosity <= LL_VERBOSE) {
@@ -1291,10 +1294,10 @@ static void clientsCron(int clients_this_cycle) {
          * The protocol is that they return non-zero if the client was
          * terminated. */
         if (clientsCronHandleTimeout(c, now)) continue;
+        if (clientsCronTcpIsClosing(c)) continue;
         if (clientsCronResizeQueryBuffer(c)) continue;
         if (clientsCronResizeOutputBuffer(c, now)) continue;
         if (clientsCronTrackExpensiveClients(c, curr_peak_mem_usage_slot)) continue;
-        if (clientsCronTcpIsClosing(c)) continue;
 
         /* Iterating all the clients in getMemoryOverheadData() is too slow and
          * in turn would make the INFO command too slow. So we perform this

src/socket.c

@@ -422,17 +422,20 @@ static int connSocketGetType(void) {
     return CONN_TYPE_SOCKET;
 }
 
-int connSocketIsClosing(connection *conn) {
-    if (aeGetFileEvents(server.el, conn->fd) != AE_NONE) return false;
+int connTcpSocketIsClosing(connection *conn) {
 #if defined(__linux__)
     struct tcp_info info;
     socklen_t infolen = sizeof(info);
-    if (getsockopt(conn->fd, IPPROTO_TCP, TCP_INFO, &info, &infolen) != 0 || infolen < sizeof(info)) return false; // Cannot retrieve TCP info
+    if (getsockopt(conn->fd, IPPROTO_TCP, TCP_INFO, &info, &infolen) != 0 ||
+        infolen < offsetof(struct tcp_info, tcpi_state) + sizeof(info.tcpi_state))
+        return false; /* Cannot retrieve TCP info, or the state field was not returned. */
     return (info.tcpi_state == TCP_CLOSE_WAIT || info.tcpi_state == TCP_CLOSE);
 #elif defined(__APPLE__)
     struct tcp_connection_info info;
     socklen_t infolen = sizeof(info);
-    if (getsockopt(conn->fd, IPPROTO_TCP, TCP_CONNECTION_INFO, &info, &infolen) != 0 || infolen < sizeof(info)) return false; // Cannot retrieve TCP info
+    if (getsockopt(conn->fd, IPPROTO_TCP, TCP_CONNECTION_INFO, &info, &infolen) != 0 ||
+        infolen < offsetof(struct tcp_connection_info, tcpi_state) + sizeof(info.tcpi_state))
+        return false; /* Cannot retrieve TCP info, or the state field was not returned. */
     return (info.tcpi_state == TCPS_CLOSE_WAIT || info.tcpi_state == TCPS_CLOSED);
 #else
     /* Unsupported platform: zombie connection detection is not available. */
@@ -488,7 +491,7 @@ static ConnectionType CT_Socket = {
 
     /* Miscellaneous */
     .connIntegrityChecked = NULL,
-    .is_closing = connSocketIsClosing,
+    .is_closing = connTcpSocketIsClosing,
 };
 
 int connBlock(connection *conn) {

src/tls.c

@@ -2022,7 +2022,7 @@ static ConnectionType CT_TLS = {
 
     /* Miscellaneous */
     .connIntegrityChecked = connTLSIsIntegrityChecked,
-    .is_closing = connSocketIsClosing,
+    .is_closing = connTcpSocketIsClosing,
 
 };