Prevent sendmsg/write raising SIGPIPE the TCP socket is closed:

This is observed by @gchiu etc when testing the http server:

    the problem is that the web server writes to the client when the
    client has closed the connection this happens when the browser
    client does a refresh while not having received yet the full
    response

    so the server code keeps writing to a broken pipe which doesn't seem
    to matter in windows but gives this signal in osx so it's seen on
    multiple refreshes with a browser client on the web server we saw
    the problem too on android but it went away when we trapped the
    writes

There are a few ways to prevent it crashing:
1. installing a signal handler for SIGPIPE
2. set SO_NOSIGPIPE option on the socket (only supported on some
platforms)
3. set MSG_NO_SIGNAL flag on the sendto (only supported on Linux)

This commit tries to do both 2 and/or 3 when supported.

See:
https://stackoverflow.com/questions/108183/how-to-prevent-sigpipes-or-handle-them-properly

src/os/dev-net.c

@@ -61,6 +61,13 @@ DEVICE_CMD Listen_Socket(REBREQ *sock);
     extern HWND Event_Handle; // For WSAAsync API
 #endif
 
+// Prevent sendmsg/write raising SIGPIPE the TCP socket is closed:
+// https://stackoverflow.com/questions/108183/how-to-prevent-sigpipes-or-handle-them-properly
+// Linux does not support SO_NOSIGPIPE
+//
+#ifndef MSG_NOSIGNAL
+#define MSG_NOSIGNAL 0
+#endif
 
 /***********************************************************************
 **
@@ -89,8 +96,17 @@ static void Get_Local_IP(struct devreq_net *sock)
     sock->local_port = ntohs(sa.sin_port);
 }
 
-static REBOOL Nonblocking_Mode(SOCKET sock)
+static REBOOL Set_Sock_Options(SOCKET sock)
 {
+    // Prevent sendmsg/write raising SIGPIPE the TCP socket is closed:
+    // https://stackoverflow.com/questions/108183/how-to-prevent-sigpipes-or-handle-them-properly
+#if defined(SO_NOSIGPIPE)
+    int on = 1;
+    if (setsockopt(sock, SOL_SOCKET, SO_NOSIGPIPE, &on, sizeof(on)) < 0) {
+        return FALSE;
+    }
+#endif
+
     // Set non-blocking mode. Return TRUE if no error.
 #ifdef FIONBIO
     unsigned long mode = 1;
@@ -190,7 +206,7 @@ DEVICE_CMD Open_Socket(REBREQ *sock)
     SET_FLAG(sock->state, RSM_OPEN);
 
     // Set socket to non-blocking async mode:
-    if (!Nonblocking_Mode(sock->requestee.socket)) {
+    if (!Set_Sock_Options(sock->requestee.socket)) {
         sock->error = GET_ERROR;
         return DR_ERROR;
     }
@@ -391,7 +407,7 @@ DEVICE_CMD Transfer_Socket(REBREQ *req)
         result = sendto(
             req->requestee.socket,
             s_cast(req->common.data), len,
-            0, // Flags
+            MSG_NOSIGNAL, // Flags
             cast(struct sockaddr*, &remote_addr), addr_len
         );
         WATCH2("send() len: %d actual: %d\n", len, result);
@@ -620,6 +636,12 @@ DEVICE_CMD Accept_Socket(REBREQ *req)
         return DR_ERROR;
     }
 
+    if (!Set_Sock_Options(result)) {
+        req->error = GET_ERROR;
+        //Signal_Device(sock, EVT_ERROR);
+        return DR_ERROR;
+    }
+
     // To report the new socket, the code here creates a temporary
     // request and copies the listen request to it. Then, it stores
     // the new values for IP and ports and links this request to the
@@ -637,8 +659,6 @@ DEVICE_CMD Accept_Socket(REBREQ *req)
     news->remote_port = ntohs(sa.sin_port);
     Get_Local_IP(news);
 
-    Nonblocking_Mode(news->devreq.requestee.socket);
-
     // There could be mulitple connections to be accepted.
     // Queue them at common.sock
     Attach_Request(cast(REBREQ**, &AS_REBREQ(sock)->common.sock), AS_REBREQ(news));