1 files changed, 18 insertions, 0 deletions

diff --git a/src/main_gui.cpp b/src/main_gui.cpp
index 842b0d5..edc772d 100644
--- a/src/main_gui.cpp
+++ b/src/main_gui.cpp
@@ -58,6 +58,7 @@ static void PrintUsage()
     printf("  /connectbtf=PEER_BTF_ADDRESS\n");
     printf("  /rvrelay=HOST:PORT\n");
     printf("  /announcerelay=HOST:PORT\n");
+    printf("  /port=N                  (P2P listen port, default 8433)\n");
     printf("\n");
     printf("Each option also accepts '-' instead of '/'.\n");
 }
@@ -113,6 +114,23 @@ static void ParseStartupArguments(int argc, char* argv[])
     string announceRelay = argval2(argc, argv, "/announcerelay", "-announcerelay");
     if (!announceRelay.empty())
         strBtfAnnounceRelay = announceRelay;
+
+    // net.cpp has claimed nListenPort was "tunable via /port" since it was
+    // written, but nothing ever read the option. Without it a second node
+    // cannot start on a machine that already runs one -- which is exactly what
+    // testing peer exchange needs.
+    string strPort = argval2(argc, argv, "/port", "-port");
+    if (!strPort.empty())
+    {
+        int nPort = atoi(strPort.c_str());
+        if (nPort <= 0 || nPort > 65535)
+            fprintf(stderr, "Ignoring /port=%s: not a port number\n", strPort.c_str());
+        else
+        {
+            nListenPort = htons((unsigned short)nPort);
+            addrLocalHost.port = nListenPort;  // or we advertise a port we never bound
+        }
+    }
 }
 
 int main(int argc, char* argv[])