From 6de7db4765334096a3ac39149cf5016e8ba12c8d Mon Sep 17 00:00:00 2001
From: James Osborne <incentive@circlewithadot.net>
Date: Fri, 15 May 2026 15:06:32 -0400
Subject: [PATCH] Add IP stack port remapping

---
 src/IPStackSimulator.cc | 21 ++++++++++++++++++---
 src/ServerState.cc      | 17 +++++++++++++++++
 src/ServerState.hh      |  1 +
 3 files changed, 36 insertions(+), 3 deletions(-)

diff --git a/src/IPStackSimulator.cc b/src/IPStackSimulator.cc
index 492f849e..0cd1793e 100644
--- a/src/IPStackSimulator.cc
+++ b/src/IPStackSimulator.cc
@@ -1356,9 +1356,24 @@ asio::awaitable<void> IPStackSimulator::open_server_connection(
   string conn_str = this->str_for_tcp_connection(c, conn);
 
   // Figure out which logical port the connection should go to
-  auto port_config_it = this->state->number_to_port_config.find(conn->server_port);
+  uint16_t effective_server_port = conn->server_port;
+  auto remap_it = this->state->ip_stack_port_remap.find(effective_server_port);
+  if (remap_it != this->state->ip_stack_port_remap.end()) {
+    this->log.info_f(
+        "Remapping IP stack TCP destination port {} to {} for connection {}",
+        effective_server_port,
+        remap_it->second,
+        conn_str);
+    effective_server_port = remap_it->second;
+  }
+
+  auto port_config_it = this->state->number_to_port_config.find(effective_server_port);
   if (port_config_it == this->state->number_to_port_config.end()) {
-    this->log.error_f("TCP connection {} is to undefined port {}", conn_str, conn->server_port);
+    this->log.error_f(
+        "TCP connection {} is to undefined port {} after remap from {}",
+        conn_str,
+        effective_server_port,
+        conn->server_port);
     co_await this->close_tcp_connection(c, conn);
     co_return;
   }
@@ -1371,7 +1386,7 @@ asio::awaitable<void> IPStackSimulator::open_server_connection(
     co_await this->close_tcp_connection(c, conn);
     co_return;
   } else {
-    this->state->game_server->connect_channel(conn->server_channel, conn->server_port, port_config->behavior);
+    this->state->game_server->connect_channel(conn->server_channel, effective_server_port, port_config->behavior);
     this->log.info_f("Connected TCP connection {} to game server", conn_str);
   }
 }
diff --git a/src/ServerState.cc b/src/ServerState.cc
index 71052f2d..0069aa7f 100644
--- a/src/ServerState.cc
+++ b/src/ServerState.cc
@@ -737,6 +737,23 @@ void ServerState::load_config_early() {
     }
 
     this->set_port_configuration(parse_port_configuration(this->config_json->at("PortConfiguration")));
+
+    this->ip_stack_port_remap.clear();
+    try {
+      for (const auto& item : this->config_json->at("IPStackPortRemap").as_dict()) {
+        uint64_t from_port = stoull(item.first, nullptr, 0);
+        uint64_t to_port = item.second->as_int();
+
+        if (from_port > 0xFFFF || to_port > 0xFFFF) {
+          throw runtime_error("IPStackPortRemap port number is out of range");
+        }
+
+        this->ip_stack_port_remap.emplace(
+            static_cast<uint16_t>(from_port),
+            static_cast<uint16_t>(to_port));
+      }
+    } catch (const out_of_range&) {
+    }
     try {
       auto spec = this->parse_port_spec(this->config_json->at("DNSServerPort"));
       this->dns_server_addr = std::move(spec.first);
diff --git a/src/ServerState.hh b/src/ServerState.hh
index 78c5a4c7..f2540f04 100644
--- a/src/ServerState.hh
+++ b/src/ServerState.hh
@@ -112,6 +112,7 @@ struct ServerState : public std::enable_shared_from_this<ServerState> {
   std::string name;
   std::unordered_map<std::string, std::shared_ptr<PortConfiguration>> name_to_port_config;
   std::unordered_map<uint16_t, std::shared_ptr<PortConfiguration>> number_to_port_config;
+  std::unordered_map<uint16_t, uint16_t> ip_stack_port_remap;
   std::string username;
   std::string dns_server_addr;
   uint16_t dns_server_port = 0;