Split network macro conditions

On Windows, interrupting a socket with shutdown() does not wake up
accept() or read() calls, the socket must be closed.

Introduce a new macro constant SC_SOCKET_CLOSE_ON_INTERRUPT, distinct of
_WIN32, because Windows will not be the only platform exhibiting this
behavior.

Refs #5536 <#5536>

app/src/util/net.c

@@ -9,8 +9,6 @@
 #ifdef _WIN32
 # include <ws2tcpip.h>
   typedef int socklen_t;
-  typedef SOCKET sc_raw_socket;
-# define SC_RAW_SOCKET_NONE INVALID_SOCKET
 #else
 # include <sys/types.h>
 # include <sys/socket.h>
@@ -23,8 +21,6 @@
   typedef struct sockaddr_in SOCKADDR_IN;
   typedef struct sockaddr SOCKADDR;
   typedef struct in_addr IN_ADDR;
-  typedef int sc_raw_socket;
-# define SC_RAW_SOCKET_NONE -1
 #endif
 
 bool
@@ -47,17 +43,26 @@ net_cleanup(void) {
 #endif
 }
 
+static inline bool
+sc_raw_socket_close(sc_raw_socket raw_sock) {
+#ifndef _WIN32
+    return !close(raw_sock);
+#else
+    return !closesocket(raw_sock);
+#endif
+}
+
 static inline sc_socket
 wrap(sc_raw_socket sock) {
-#ifdef _WIN32
-    if (sock == INVALID_SOCKET) {
+#ifdef SC_SOCKET_CLOSE_ON_INTERRUPT
+    if (sock == SC_RAW_SOCKET_NONE) {
         return SC_SOCKET_NONE;
     }
 
-    struct sc_socket_windows *socket = malloc(sizeof(*socket));
+    struct sc_socket_wrapper *socket = malloc(sizeof(*socket));
     if (!socket) {
         LOG_OOM();
-        closesocket(sock);
+        sc_raw_socket_close(sock);
         return SC_SOCKET_NONE;
     }
 
@@ -72,9 +77,9 @@ wrap(sc_raw_socket sock) {
 
 static inline sc_raw_socket
 unwrap(sc_socket socket) {
-#ifdef _WIN32
+#ifdef SC_SOCKET_CLOSE_ON_INTERRUPT
     if (socket == SC_SOCKET_NONE) {
-        return INVALID_SOCKET;
+        return SC_RAW_SOCKET_NONE;
     }
 
     return socket->socket;
@@ -83,17 +88,6 @@ unwrap(sc_socket socket) {
 #endif
 }
 
-#ifndef HAVE_SOCK_CLOEXEC // avoid unused-function warning
-static inline bool
-sc_raw_socket_close(sc_raw_socket raw_sock) {
-#ifndef _WIN32
-    return !close(raw_sock);
-#else
-    return !closesocket(raw_sock);
-#endif
-}
-#endif
-
 #ifndef HAVE_SOCK_CLOEXEC
 // If SOCK_CLOEXEC does not exist, the flag must be set manually once the
 // socket is created
@@ -248,9 +242,9 @@ net_interrupt(sc_socket socket) {
 
     sc_raw_socket raw_sock = unwrap(socket);
 
-#ifdef _WIN32
+#ifdef SC_SOCKET_CLOSE_ON_INTERRUPT
     if (!atomic_flag_test_and_set(&socket->closed)) {
-        return !closesocket(raw_sock);
+        return sc_raw_socket_close(raw_sock);
     }
     return true;
 #else
@@ -262,15 +256,15 @@ bool
 net_close(sc_socket socket) {
     sc_raw_socket raw_sock = unwrap(socket);
 
-#ifdef _WIN32
+#ifdef SC_SOCKET_CLOSE_ON_INTERRUPT
     bool ret = true;
     if (!atomic_flag_test_and_set(&socket->closed)) {
-        ret = !closesocket(raw_sock);
+        ret = sc_raw_socket_close(raw_sock);
     }
     free(socket);
     return ret;
 #else
-    return !close(raw_sock);
+    return sc_raw_socket_close(raw_sock);
 #endif
 }
 

app/src/util/net.h

@@ -7,21 +7,36 @@
 #include <stdint.h>
 
 #ifdef _WIN32
-
 # include <winsock2.h>
+  typedef SOCKET sc_raw_socket;
+# define SC_RAW_SOCKET_NONE INVALID_SOCKET
+#else // not _WIN32
+# include <sys/socket.h>
+  typedef int sc_raw_socket;
+# define SC_RAW_SOCKET_NONE -1
+#endif
+
+#ifdef _WIN32
+// On Windows, shutdown() does not interrupt accept() or read() calls, so
+// net_interrupt() must call close() instead, and net_close() must behave
+// accordingly.
+// This causes a small race condition (once the socket is closed, its
+// handle becomes invalid and may in theory be reassigned before another
+// thread calls accept() or read()), but it is deemed acceptable as a
+// workaround.
+# define SC_SOCKET_CLOSE_ON_INTERRUPT
+#endif
+
+#ifdef SC_SOCKET_CLOSE_ON_INTERRUPT
 # include <stdatomic.h>
 # define SC_SOCKET_NONE NULL
-  typedef struct sc_socket_windows {
-      SOCKET socket;
+  typedef struct sc_socket_wrapper {
+      sc_raw_socket socket;
       atomic_flag closed;
   } *sc_socket;
-
-#else // not _WIN32
-
-# include <sys/socket.h>
+#else
 # define SC_SOCKET_NONE -1
-  typedef int sc_socket;
-
+  typedef sc_raw_socket sc_socket;
 #endif
 
 #define IPV4_LOCALHOST 0x7F000001