Hand UDP sockets over on a reload too

A UDP service's socket is kept as a listener like a TCP one, the
protocol part of what must match: on a reload a new UDP service on the
same address takes it over. It is the way the old service's sessions
answer as well, and they go on answering through it; the new service
reads what comes, a datagram of an old session forwarded to it as
before, sessions being found by the service's and the client's
addresses whichever service made them. The socket stays open while the
old sessions do.

The takeover case keeps a udppm session going through three reloads
and wants every datagram back; with the build before this datagrams
were lost.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/proxymain.c

@@ -875,11 +875,14 @@ static int srvprepare(struct srvstart *s, int argc, char **argv){
    reload, a service of the new configuration listening on the same
    address, port, network namespace and device with the same options takes
    it over. The old service stops accepting once its configuration is no
-   longer in force; whoever lets go of the socket last closes it. TCP only:
-   a UDP service's clients read from its socket. */
+   longer in force; whoever lets go of the socket last closes it. A UDP
+   service's socket is the way its sessions answer too: the old sessions go
+   on answering through it, the new service reading what comes, the
+   sessions found by client address whichever service made them. */
 struct listener {
 	struct listener *next;
 	SOCKET sock;
+	int isudp;
 	PROXYSOCKADDRTYPE sa;
 	char *netns, *device;
 	struct sockoptset opts;
@@ -892,7 +895,7 @@ struct listener {
 static struct listener *listeners = NULL;
 _3proxy_mutex_t listener_mutex;
 
-static int listenerkeep(struct srvparam *srv, SOCKET sock);
+static int listenerkeep(struct srvparam *srv, SOCKET sock, int isudp);
 static void listenerstop(struct srvparam *srv);
 static void listenerrelease(struct srvparam *srv);
 #endif
@@ -912,6 +915,10 @@ static int srvlisten(struct srvstart *s){
 	/* taken over from a service of the configuration before: listening
 	   already, only the backlog may be new */
 	sock = srv->srvsock = srv->listener->sock;
+#ifndef NOUDPMAIN
+	if(s->isudp) defparam->clisock = sock;
+	else
+#endif
 	if(srv->so._listen (srv->so.state, sock, srv->backlog?srv->backlog : 1+(srv->maxchild>>3))==-1) {
 		sprintf((char *)buf, "listen(): %s", strerror(errno));
 		if(!srv->silent)dolog(defparam, buf);
@@ -981,13 +988,17 @@ static int srvlisten(struct srvstart *s){
 #ifndef STDMAIN
 	/* kept for a service of a later configuration to take over; without
 	   memory for it the service closes the socket itself */
-	listenerkeep(srv, sock);
+	listenerkeep(srv, sock, 0);
 #endif
  }
 #endif
 #ifndef NOUDPMAIN
- if(s->isudp)
+ if(s->isudp){
 	defparam->clisock = sock;
+#ifndef STDMAIN
+	listenerkeep(srv, sock, 1);
+#endif
+ }
 #endif
  srv->fds.fd = sock;
  srv->fds.events = POLLIN;
@@ -1524,7 +1535,8 @@ static int samestr(const char *a, const char *b){
  return (!a && !b) || (a && b && !strcmp(a, b));
 }
 
-static int samelistener(struct listener *l, struct srvparam *srv){
+static int samelistener(struct listener *l, struct srvparam *srv, int isudp){
+ if(l->isudp != isudp) return 0;
 #ifdef __linux__
  if(!samestr(l->netns, srv->inetns)) return 0;
 #endif
@@ -1544,10 +1556,10 @@ void mainclaim(void *service){
  struct srvparam *srv = &s->srv;
  struct listener *l;
 
- if(s->isudp || s->iscbc) return;
+ if(!s->isudp && s->iscbc) return;	/* connects back: no socket of its own */
  _3proxy_mutex_lock(&listener_mutex);
  for(l = listeners; l; l = l->next){
-	if(l->owner && l->sock != INVALID_SOCKET && l->owner->config != srv->config && samelistener(l, srv)){
+	if(l->owner && l->sock != INVALID_SOCKET && l->owner->config != srv->config && samelistener(l, srv, s->isudp)){
 		l->owner = srv;
 		l->users++;
 		srv->listener = l;
@@ -1559,12 +1571,13 @@ void mainclaim(void *service){
 
 /* A socket a service opened and bound itself, kept for whoever may take it
    over; 0, or 1 for want of memory, when the service closes it itself. */
-static int listenerkeep(struct srvparam *srv, SOCKET sock){
+static int listenerkeep(struct srvparam *srv, SOCKET sock, int isudp){
  struct listener *l;
 
  if(!(l = malloc(sizeof(*l)))) return 1;
  memset(l, 0, sizeof(*l));
  l->sock = sock;
+ l->isudp = isudp;
  l->sa = srv->intsa;
  l->opts = srv->lissockopts;
 #ifdef __linux__
@@ -1650,7 +1663,7 @@ int reattach(struct clientparam *param){
  struct srvparam *cur = PSRV(param), *newest, *orig;
  int version = runconf->version, res;
 
- /* without a listener (UDP, connecting back) nothing replaces it */
+ /* without a listener (connecting back) nothing replaces it */
  if(!cur->listener){
 	param->version = version;
 	return 0;

tests/cases/takeover.py

@@ -67,6 +67,57 @@ def run(t):
     t.eq(0, done["failed"], "no request is refused or reset by a reload "
          f"(first errors: {done['errors']})")
 
+    # --- UDP: the socket is handed over too, and a session of the old
+    # service goes on through it, its datagrams forwarded by the new one ---
+    echo = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    echo.bind(("127.0.0.1", 0))
+    echo_port = echo.getsockname()[1]
+
+    def echo_server():
+        while True:
+            try:
+                data, addr = echo.recvfrom(2048)
+            except OSError:
+                return
+            echo.sendto(data, addr)
+
+    threading.Thread(target=echo_server, daemon=True).start()
+    udp = t.free_port()
+    uconf = conf + f"\n        udppm {udp} 127.0.0.1 {echo_port}\n"
+    t.write_config("takeover", uconf)
+    t.http(f"http://127.0.0.1:{adm}/R")
+    time.sleep(1.5)
+
+    client = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
+    client.settimeout(1)
+    sent = lost = 0
+    stopudp = time.time() + 5
+    reloads = 0
+    next_reload = time.time() + 0.5
+    while time.time() < stopudp:
+        if reloads < 3 and time.time() >= next_reload:
+            t.write_config("takeover", uconf)
+            t.http(f"http://127.0.0.1:{adm}/R")
+            reloads += 1
+            next_reload = time.time() + 1.2
+        msg = f"n{sent}".encode()
+        client.sendto(msg, ("127.0.0.1", udp))
+        sent += 1
+        try:
+            data, _ = client.recvfrom(2048)
+            if data != msg:
+                lost += 1
+        except OSError:
+            lost += 1
+        time.sleep(0.02)
+    client.close()
+    echo.close()
+    t.ok(f"a UDP session sends through three reloads ({sent} datagrams)") if sent > 100 else \
+        t.fail("a UDP session sends through three reloads", "more than 100", sent)
+    t.eq(0, lost, "and every datagram comes back, the socket handed over")
+    t.contains(server.output(), f"{udp} 0.0.0.0:0 0 0 0 Accepting connections, taken over",
+               "the UDP service takes the socket over")
+
     # a changed port is a new socket: the old one closes, the new one opens
     moved = t.free_port()
     t.write_config("takeover", conf.replace(f"proxy -p{proxy}", f"proxy -p{moved}"))