Fix TCP-only channel linking when UDP is compiled out

aether/channels/ethernet_channel.cpp

@@ -65,6 +65,12 @@ ex::sender auto TransportConnect(std::unique_ptr<ByteIStream>&& stream) {
                     ex::set_error_t(int)>(
       [&, s{std::move(stream)},
        link_sub{Subscription{}}](auto& ctx) mutable noexcept {
+        if (!s) {
+          // Protocol compiled out (AE_SUPPORT_* = 0) — factory returns null.
+          ex::set_error(std::move(ctx.receiver), 1);
+          return;
+        }
+
         auto handle_link_state = [&]() noexcept {
           link_sub.Reset();
           switch (s->stream_info().link_state) {

aether/channels/wifi_channel.cpp

@@ -85,6 +85,12 @@ ex::sender auto TransportConnect(std::unique_ptr<ByteIStream>&& stream) {
                     ex::set_error_t(int)>(
       [s{std::move(stream)},
        link_sub{Subscription{}}](auto& ctx) mutable noexcept {
+        if (!s) {
+          // Protocol compiled out (AE_SUPPORT_* = 0) — factory returns null.
+          ex::set_error(std::move(ctx.receiver), 1);
+          return;
+        }
+
         auto handle_link_state = [&]() noexcept {
           link_sub.Reset();  // ensure subscribed only to one event
           auto link_state = s->stream_info().link_state;

aether/server_connections/server_connection.cpp

@@ -21,7 +21,9 @@
 
 #include "aether/aether.h"
 #include "aether/channels/channel.h"
+#include "aether/config.h"
 #include "aether/server.h"
+#include "aether/types/address.h"
 
 #include "aether/tele.h"
 
@@ -94,7 +96,25 @@ void ServerConnection::InitChannels() {
   for (auto c : server->channels) {
     // channel must be loaded before use
     assert(c.is_valid() && "Channel is not loaded");
-    channels.emplace_back(c.Load());
+    auto channel = c.Load();
+    // Skip channels whose transport was compiled out (e.g. UDP-only state
+    // loaded into a TCP-only build). Factory returns nullptr for those and
+    // the connection would never link.
+    if (auto endpoint = channel->endpoint()) {
+#if !AE_SUPPORT_TCP
+      if (endpoint->protocol == Protocol::kTcp) {
+        AE_TELED_DEBUG("Skip unsupported TCP channel {}", *endpoint);
+        continue;
+      }
+#endif
+#if !AE_SUPPORT_UDP
+      if (endpoint->protocol == Protocol::kUdp) {
+        AE_TELED_DEBUG("Skip unsupported UDP channel {}", *endpoint);
+        continue;
+      }
+#endif
+    }
+    channels.emplace_back(std::move(channel));
   }
   // sort channels by the fastest
   std::sort(std::begin(channels), std::end(channels),

examples/a_b_message_exchange/CMakeLists.txt

@@ -26,6 +26,11 @@ if(NOT CM_PLATFORM)
 else()
   idf_build_get_property(CM_PLATFORM CM_PLATFORM)
   if(CM_PLATFORM STREQUAL "ESP32")
+    # TCP-only ping-pong config unless the build already selected one.
+    if("${USER_CONFIG}" STREQUAL "")
+      set(USER_CONFIG "${CMAKE_CURRENT_SOURCE_DIR}/user_config.h"
+          CACHE PATH "Path to user provided configuration header file" FORCE)
+    endif()
     idf_component_register(
       SRCS main.cpp a_b_message_exchange.cpp
       INCLUDE_DIRS ${CMAKE_CURRENT_SOURCE_DIR} ../common

examples/a_b_message_exchange/user_config.h

@@ -0,0 +1,75 @@
+/*
+ * Copyright 2026 Aethernet Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef EXAMPLES_A_B_MESSAGE_EXCHANGE_USER_CONFIG_H_
+#define EXAMPLES_A_B_MESSAGE_EXCHANGE_USER_CONFIG_H_
+
+#include "aether/config_consts.h"
+
+/**
+ * \brief For full config list and default values \see aether/config.h
+ *
+ * Desktop ping-pong (ab-message-exchange): force TCP-only cloud/server
+ * channels. Without this, connectionless UDP channels sort first and are
+ * preferred over TCP.
+ */
+
+#define AE_CRYPTO_ASYNC AE_HYDRO_CRYPTO_PK
+#define AE_CRYPTO_SYNC AE_HYDRO_CRYPTO_SK
+#define AE_SIGNATURE AE_HYDRO_SIGNATURE
+#define AE_KDF AE_HYDRO_KDF
+
+#define AE_SUPPORT_UDP 0
+#define AE_SUPPORT_TCP 1
+
+#if !ESP_PLATFORM
+#  define AE_SUPPORT_WIFIS 0
+#endif
+
+#define AE_TELE_ENABLED 1
+#define AE_TELE_LOG_CONSOLE 1
+#define AE_TELE_COMPILATION_INFO 1
+#define AE_TELE_LOG_TO_STATISTICS 1
+#define AE_STATISTICS_MAX_SIZE 1024
+
+#define AE_TELE_METRICS_MODULES_EXCLUDE \
+  { AE_LOG_MODULE }
+#define AE_TELE_METRICS_DURATION_EXCLUDE \
+  { AE_LOG_MODULE }
+
+#define AE_TELE_LOG_MODULES AE_ALL
+#define AE_TELE_DEBUG_MODULES AE_ALL
+#define AE_TELE_INFO_MODULES AE_ALL
+#define AE_TELE_WARN_MODULES AE_ALL
+#define AE_TELE_ERROR_MODULES AE_ALL
+
+#define AE_TELE_LOG_TIME_POINT AE_ALL
+#define AE_TELE_LOG_LOCATION \
+  { AE_LOG_MODULE }
+#define AE_TELE_LOG_NAME_EXCLUDE \
+  { AE_LOG_MODULE }
+#define AE_TELE_LOG_LEVEL_MODULE AE_ALL
+#define AE_TELE_LOG_BLOB AE_ALL
+
+#if AE_DISTILLATION || AE_FILTRATION
+#  define AE_SUPPORT_REGISTRATION 1
+#  define AE_SUPPORT_CLOUD_DNS 1
+#else
+#  define AE_SUPPORT_REGISTRATION 0
+#  define AE_SUPPORT_CLOUD_DNS 0
+#endif
+
+#endif  // EXAMPLES_A_B_MESSAGE_EXCHANGE_USER_CONFIG_H_