add IPv6 support in proxy

src/AsyncUtils.hh

@@ -224,6 +224,14 @@ inline asio::ip::tcp::endpoint make_endpoint_ipv4(uint32_t addr, uint16_t port)
   return asio::ip::tcp::endpoint(asio::ip::address_v4(addr), port);
 }
 
+inline asio::ip::tcp::endpoint make_endpoint_ipv6(const void* addr, uint16_t port) {
+  std::array<uint8_t, 0x10> bytes;
+  for (size_t z = 0; z < 0x10; z++) {
+    bytes[z] = reinterpret_cast<const uint8_t*>(addr)[z];
+  }
+  return asio::ip::tcp::endpoint(asio::ip::address_v6(bytes), port);
+}
+
 inline std::string str_for_endpoint(const asio::ip::tcp::endpoint& ep) {
   return ep.address().to_string() + std::format(":{}", ep.port());
 }

src/CommandFormats.hh

@@ -807,6 +807,20 @@ struct C_WriteFileConfirmation_V3_BB_13_A7 {
 using S_Reconnect_19 = S_ReconnectT<le_uint16_t>;
 check_struct_size(S_Reconnect_19, 8);
 
+// Sylverant implements an IPv6 version of this command, but it's not obvious
+// why. IPv6 technically did exist as a draft standard at the time of PSO's
+// development, but it wasn't widely used until over a decade later. IPv6
+// support is not implemented in any version of the PSO client that I've seen,
+// but we implement Sylverant's version of this command anyway because newserv
+// may connect to Sylverant via IPv6 when using the proxy. Sylverant sends the
+// value 6 in header.flag in this case, presumably to indicate the protocol.
+
+struct S_ReconnectIPv6_Extension_19 {
+  parray<uint8_t, 0x10> address;
+  le_uint16_t port = 0;
+  le_uint16_t unused = 0;
+} __packed_ws__(S_ReconnectIPv6_Extension_19, 0x14);
+
 // Because PSO PC and some versions of PSO DC/GC use the same port but different
 // protocols, we use a specially-crafted 19 command to send them to two
 // different ports depending on the client version. I first saw this technique

src/ProxyCommands.cc

@@ -779,6 +779,9 @@ static asio::awaitable<HandlerResult> S_19_U_14(shared_ptr<Client> c, Channel::M
   if (is_patch(c->version())) {
     auto& cmd = msg.check_size_t<S_Reconnect_Patch_14>();
     new_ep = make_endpoint_ipv4(cmd.address, cmd.port);
+  } else if (msg.flag == 6 && msg.data.size() >= sizeof(S_ReconnectIPv6_Extension_19)) {
+    auto& cmd = msg.check_size_t<S_ReconnectIPv6_Extension_19>(0xFFFF);
+    new_ep = make_endpoint_ipv6(cmd.address.data(), cmd.port);
   } else {
     // This weird maximum size is here to properly handle the version-split
     // command that some servers (including newserv) use on port 9100