implement sending "path control" (onioned control) message

TODO: handle at transit hop, handle at terminal hop, create and handle responses

llarp/path/path.cpp

@@ -107,8 +107,33 @@ namespace llarp::path
   Path::send_path_control_message(
       std::string method, std::string body, std::function<void(oxen::quic::message m)> func)
   {
+    oxenc::bt_dict_producer btdp;
+    btdp.append("METHOD", method);
+    btdp.append("BODY", body);
+    auto payload = std::move(btdp).str();
+    auto* payload_ptr = reinterpret_cast<unsigned char*>(payload.data());
+
+    // TODO: old impl padded messages if smaller than a certain size; do we still want to?
+
+    auto crypto = CryptoManager::instance();
+
+    TunnelNonce nonce;
+    outer_nonce.Randomize();
+    for (const auto& hop : hops)
+    {
+      // do a round of chacha for each hop and mutate the nonce with that hop's nonce
+      CryptoManager::instance()->xchacha20(payload_ptr, hop.shared, nonce);
+      nonce ^= hop.nonceXOR;
+    }
+
+    oxenc::bt_dict_producer outer_dict;
+    outer_dict.append("PATHID", TXID().ToView());
+    outer_dict.append("NONCE", nonce.ToView());
+    outer_dict.append("PAYLOAD", payload);
+
+
     return router.send_control_message(
-        upstream(), std::move(method), std::move(body), std::move(func));
+        upstream(), "path_control", std::move(outer_dict.str()), std::move(func));
   }
 
   bool