Remember .btf peers that answered, and dial them first on start (#25)

* net: remember .btf peers that answered, and dial them first on start

Discovery depends entirely on the Nostr relays. A node that has been up
for hours knows exactly which peers respond, and throws all of it away on
exit; the next start reaches for the relays again and walks the same
descriptor list, of which roughly 96% is dead. That is what makes a
restart take minutes before the first tunnel opens -- measured today at
about seven.

Every peer that completes a tunnel is now written to btfpeers.json with
its meeting node and encryption key, which is everything needed to redial
it. On start a thread tries those before the relays have answered
anything, stopping once eight are connected. Entries older than a week
are dropped, and the file holds at most fifty.

Cache only: nothing here changes how a first-ever run bootstraps, and a
missing or corrupt file just falls through to relay discovery.

* net: exchange signed .btf descriptors between peers

Discovery has depended entirely on the Nostr relays. Two connected nodes never
told each other who else existed, so a relay outage left a running network
unable to grow, and a node that found one stale peer had no way to learn there
was anything better. The old `addr` gossip went out with the IRC seed.

Peers now trade signed descriptors over a new "btfpeers" message: our own
first, then peers that actually answered us. The receiver checks each Schnorr
signature against the key the `.btf` address decodes to, so the sender is
trusted for nothing -- forging an entry needs somebody else's secret key. That
leaves flooding with self-generated keys, which the per-message caps and the
"peers that answered" ordering are there to blunt.

Unknown commands are ignored (main.cpp), so nodes without this just drop the
message; nothing here is a protocol break.

The cache from the peer-cache change now keeps each peer's descriptor verbatim
alongside the parsed fields, because that signature is what makes a peer
relayable. Entries without one -- resolved through Nostr, or written before
this -- stay dialable, just not passed on. A dial never clears a descriptor
already on file.

* main_gui: implement /port, which net.cpp already documented

net.cpp has said nListenPort is "tunable via /port" since it was written, but
nothing ever parsed the option. Two nodes could not share a machine, which is
exactly what testing peer exchange needs. Sets addrLocalHost.port too, so we
do not advertise a port we never bound.

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[])