server: follow TCP port fallback on all interfaces

src/config.cpp

@@ -416,7 +416,12 @@ void _fromDefs(Config& self, const std::map<std::string, std::string>& defs, boo
     }
 
     if(pickone({"EPICS_PVAS_INTF_ADDR_LIST"})) {
-        split_addr_into(pickone.name.c_str(), self.interfaces, pickone.val, self.tcp_port, true);
+        // defaultPort=0, matching the client EPICS_PVA_INTF_ADDR_LIST path below.
+        // A port-less interface stays at port 0 so the acceptor loop can follow the
+        // server onto the port actually bound -- including a conflict fallback chosen
+        // while binding the first interface.  Filling in tcp_port here erases that
+        // "follow me" signal and strands the interface on the unbindable port.
+        split_addr_into(pickone.name.c_str(), self.interfaces, pickone.val, 0, true);
     }
 
     if(pickone({"EPICS_PVAS_IGNORE_ADDR_LIST"})) {

test/testconfig.cpp

@@ -141,7 +141,9 @@ void testDefs()
         testEq(conf.tcp_port, 5678);
         testFalse(conf.auto_beacon);
         testEq(conf.beaconDestinations, std::vector<std::string>({"1.2.1.2:1234", "4.3.2.1:1234"}));
-        testEq(conf.interfaces, std::vector<std::string>({"1.1.1.1:5678", "1.2.3.4:5678"}));
+        // server INTF list round-trips port-less, matching the client path above
+        // (a port-less interface follows the server's bound TCP port at bind time).
+        testEq(conf.interfaces, std::vector<std::string>({"1.1.1.1", "1.2.3.4"}));
     }
 }
 

test/testwild.cpp

@@ -80,11 +80,39 @@ void testconflict(const char* addr)
     testNotEq(iconf.tcp_port, fconf.tcp_port)<<"w/ "<<addr;
 }
 
+// as testconflict(), but configured as a user would.
+// $EPICS_PVAS_INTF_ADDR_LIST fills in $EPICS_PVAS_SERVER_PORT for each interface
+// which does not name a port, so the interfaces arrive here carrying the port
+// which is about to be found in use.  All of them must still follow the fallback.
+void testconflictifaces(const char* addr1, const char* addr2)
+{
+    testDiag("%s(\"%s\", \"%s\")", __func__, addr1, addr2);
+
+    evsocket otherserver(AF_INET, SOCK_STREAM, 0);
+    otherserver.bind(SockAddr::any(AF_INET));
+    otherserver.listen(4);
+
+    server::Config::defs_t defs;
+    defs["EPICS_PVAS_SERVER_PORT"] = SB()<<otherserver.sockname().port();
+    defs["EPICS_PVAS_BROADCAST_PORT"] = "0"; // choose randomly
+    defs["EPICS_PVAS_INTF_ADDR_LIST"] = SB()<<addr1<<' '<<addr2;
+
+    server::Config iconf;
+    iconf.applyDefs(defs);
+
+    auto serv(iconf.build());
+    auto fconf(serv.config());
+    testShow()<<"Server Config\n"<<fconf;
+
+    testNotEq(0u, fconf.udp_port);
+    testNotEq(iconf.tcp_port, fconf.tcp_port);
+}
+
 } // namespace
 
 MAIN(testwild)
 {
-    testPlan(18);
+    testPlan(20);
     testSetup();
     logger_config_env();
     SockAttach attach;
@@ -98,8 +126,10 @@ MAIN(testwild)
     }
     if(evsocket::ipstack==evsocket::Linsock) {
         testconflict("127.0.0.1");
+        // 127.0.0.0/8 is entirely local, so a second loopback address is available.
+        testconflictifaces("127.0.0.1", "127.0.0.2");
     } else {
-        testSkip(2, "Can bind both 0.0.0.0 and 127.0.0.1 to the same port");
+        testSkip(4, "Can bind both 0.0.0.0 and 127.0.0.1 to the same port, and have one loopback address");
     }
     testconflict("0.0.0.0");
     if(canIPv6) {