feat(mosq): Add example with two brokers synced on P2P

Broker-less two chip example which virtual private IoT
networks on MQTT protocol.

.github/workflows/mosq__build.yml

@@ -17,7 +17,8 @@ jobs:
     runs-on: ubuntu-22.04
     container: espressif/idf:${{ matrix.idf_ver }}
     env:
-      TEST_DIR: components/mosquitto/examples/broker
+      TEST_DIR: components/mosquitto/examples
+      TARGET_TEST: broker
       TARGET_TEST_DIR: build_esp32_default
     steps:
       - name: Checkout esp-protocols
@@ -29,14 +30,15 @@ jobs:
         run: |
           . ${IDF_PATH}/export.sh
           pip install idf-component-manager idf-build-apps --upgrade
-          python ci/build_apps.py ${TEST_DIR}
-          cd ${TEST_DIR}
+          python ci/build_apps.py -c ${TEST_DIR} -m components/mosquitto/.build-test-rules.yml
+          # upload only the target test artifacts
+          cd ${TEST_DIR}/${TARGET_TEST}
           ${GITHUB_WORKSPACE}/ci/clean_build_artifacts.sh `pwd`/${TARGET_TEST_DIR}
           zip -qur artifacts.zip ${TARGET_TEST_DIR}
       - uses: actions/upload-artifact@v4
         with:
           name: mosq_target_esp32_${{ matrix.idf_ver }}
-          path: ${{ env.TEST_DIR }}/artifacts.zip
+          path: ${{ env.TEST_DIR }}/${{ env.TARGET_TEST }}/artifacts.zip
           if-no-files-found: error
 
   test_mosq:

ci/check_copyright_ignore.txt

@@ -0,0 +1 @@
+components/mosquitto/examples/serverless_mqtt/components/libjuice/port/juice_random.c

components/mosquitto/.build-test-rules.yml

@@ -0,0 +1,3 @@
+components/mosquitto/examples/serverless_mqtt:
+  disable:
+    - if: IDF_TARGET not in ["esp32", "esp32s3", "esp32c3"]

components/mosquitto/examples/serverless_mqtt/CMakeLists.txt

@@ -0,0 +1,6 @@
+# The following five lines of boilerplate have to be in your project's
+# CMakeLists in this exact order for cmake to work correctly
+cmake_minimum_required(VERSION 3.16)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(serverless_mqtt)

components/mosquitto/examples/serverless_mqtt/README.md

@@ -0,0 +1,53 @@
+# Brokerless MQTT Example
+
+MQTT served by (two) mosquitto's running on two ESP chips.
+
+* Leverages MQTT connectivity between two private networks without cloud premisses.
+* Creates two local MQTT servers (on ESP32x's) which are being synchronized over peer to peer connection (established via ICE protocol, by [libjuice](https://github.com/paullouisageneau/libjuice)).
+
+## How it works
+
+This example needs two ESP32 chipsets, that will create two separate Wi-Fi networks (IoT networks) used for IoT devices.
+Each IoT network is served by an MQTT server (using mosquitto component).
+This example will also synchronize these two MQTT brokers, as if there was only one IoT network with one broker.
+This example creates a peer to peer connection between two chipsets to keep them synchronize. This connection utilizes libjuice (which implements a simplified ICE-UDP) to traverse NATs, which enabling direct connection between two private networks behind NATs.
+
+* Diagram
+
+![demo](serverless.png)
+
+Here's a step-by-step procedure of establishing this remote connection:
+1) Initialize and start Wi-Fi AP (for IoT networks) and Wi-Fi station (for internet connection)
+2) Start mosquitto broker on IoT network
+3) Start libjuice to gather connection candidates
+4) Synchronize using a public MQTT broker and exchange ICE descriptors
+5) Establish ICE UDP connection between the two ESP32 chipsets
+6) Start forwarding mqtt messages
+   - Each remote datagram (received from ICE-UDP channel) is re-published to the local MQTT server
+   - Each local MQTT message (received from mosquitto on_message callback) is sent in ICE-UDP datagram
+
+## How to use this example
+
+You need two ESP32 devices that support Wi-Fi station and Wi-Fi software access point.
+
+* Configure Wi-Fi credentials for both devices on both interfaces
+  * These devices would be deployed in distinct Wi-Fi environments, so the Wi-Fi station credentials would likely be different.
+  * They also create their own IoT network (on the soft-AP interface) Wi-Fi, so the AP credentials would likely be the same, suggesting the IoT networks will be keep synchronized (even though these are two distict Wi-Fi networks).
+* Choose `CONFIG_EXAMPLE_SERVERLESS_ROLE_PEER1` for one device and `CONFIG_EXAMPLE_SERVERLESS_ROLE_PEER2` for another. It's not important which device is PEER1, since the code is symmetric, but these two devices need to have different role.
+* Optionally: You can use `idf.py` `-D` and `-B` flag to keep separate build directories and sdkconfigs for these two roles
+```
+idf.py -B build1 -DSDKCONFIG=build1/sdkconfig menuconfig build flash monitor
+```
+* Flash and run the two devices and wait for them to connect and synchronize.
+* Now you can test MQTT connectivity, for example:
+  * Join PEER1 device's AP and connect to the MQTT broker with one or more clients, subscribing to one or more topics.
+  * Join PEER2 device's AP and connect to the MQTT broker with one or more clients, subscribing to one or more topics.
+  * Whenever you publish to a topic, all subscribed clients should receive the message, no matter which Wi-Fi network they're connected to.
+
+## Warning
+
+This example uses libjuice as a dependency:
+
+* libjuice (UDP Interactive Connectivity Establishment): https://github.com/paullouisageneau/libjuice
+
+which is distributed under Mozilla Public License v2.0.

components/mosquitto/examples/serverless_mqtt/components/libjuice/CMakeLists.txt

@@ -0,0 +1,44 @@
+set(LIBJUICE_VERSION "73785387eafe15c02b6a210edb10f722474e8e14")
+set(LIBJUICE_URL "https://github.com/paullouisageneau/libjuice/archive/${LIBJUICE_VERSION}.zip")
+
+set(libjuice_dir ${CMAKE_BINARY_DIR}/libjuice/libjuice-${LIBJUICE_VERSION})
+
+# Fetch the library
+if(NOT EXISTS ${libjuice_dir})
+        message(STATUS "Downloading libjuice ${LIBJUICE_VERSION}...")
+        file(DOWNLOAD ${LIBJUICE_URL} ${CMAKE_BINARY_DIR}/libjuice.zip SHOW_PROGRESS)
+        execute_process(COMMAND unzip -o ${CMAKE_BINARY_DIR}/libjuice.zip -d ${CMAKE_BINARY_DIR}/libjuice
+                WORKING_DIRECTORY ${CMAKE_BINARY_DIR})
+endif()
+
+set(JUICE_SOURCES   ${libjuice_dir}/src/addr.c
+                    ${libjuice_dir}/src/agent.c
+                    ${libjuice_dir}/src/base64.c
+                    ${libjuice_dir}/src/conn.c
+                    ${libjuice_dir}/src/conn_mux.c
+                    ${libjuice_dir}/src/conn_poll.c
+                    ${libjuice_dir}/src/conn_thread.c
+                    ${libjuice_dir}/src/const_time.c
+                    ${libjuice_dir}/src/crc32.c
+                    ${libjuice_dir}/src/hash.c
+                    ${libjuice_dir}/src/ice.c
+                    ${libjuice_dir}/src/juice.c
+                    ${libjuice_dir}/src/log.c
+                    ${libjuice_dir}/src/server.c
+                    ${libjuice_dir}/src/stun.c
+                    ${libjuice_dir}/src/timestamp.c
+                    ${libjuice_dir}/src/turn.c
+                    ${libjuice_dir}/src/udp.c
+# Use hmac from mbedtls and random numbers from esp_random:
+#                    ${libjuice_dir}/src/hmac.c
+#                    ${libjuice_dir}/src/random.c
+        )
+
+idf_component_register(SRCS     port/juice_random.c
+                                ${JUICE_SOURCES}
+                       INCLUDE_DIRS "include"  "${libjuice_dir}/include" "${libjuice_dir}/include/juice"
+                       REQUIRES esp_netif
+                       PRIV_REQUIRES sock_utils)
+
+target_compile_options(${COMPONENT_LIB} PRIVATE "-Wno-format")
+set_source_files_properties(${libjuice_dir}/src/udp.c PROPERTIES COMPILE_FLAGS -Wno-unused-variable)

components/mosquitto/examples/serverless_mqtt/components/libjuice/include/ifaddrs.h

@@ -0,0 +1,13 @@
+/*
+ * SPDX-FileCopyrightText: 2024 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Unlicense OR CC0-1.0
+ */
+#pragma once
+
+// Purpose of this header is to replace udp_sendto() to avoid name conflict with lwip
+// added here since ifaddrs.h is included from juice_udp sources
+#define udp_sendto juice_udp_sendto
+
+// other than that, let's just include the ifaddrs (from sock_utils)
+#include_next "ifaddrs.h"

components/mosquitto/examples/serverless_mqtt/components/libjuice/port/juice_random.c

@@ -0,0 +1,40 @@
+/**
+ * Copyright (c) 2020 Paul-Louis Ageneau
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+#include "esp_random.h"
+
+void juice_random(void *buf, size_t size)
+{
+    esp_fill_random(buf, size);
+}
+
+void juice_random_str64(char *buf, size_t size)
+{
+    static const char chars64[] =
+        "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
+    size_t i = 0;
+    for (i = 0; i + 1 < size; ++i) {
+        uint8_t byte = 0;
+        juice_random(&byte, 1);
+        buf[i] = chars64[byte & 0x3F];
+    }
+    buf[i] = '\0';
+}
+
+uint32_t juice_rand32(void)
+{
+    uint32_t r = 0;
+    juice_random(&r, sizeof(r));
+    return r;
+}
+
+uint64_t juice_rand64(void)
+{
+    uint64_t r = 0;
+    juice_random(&r, sizeof(r));
+    return r;
+}

components/mosquitto/examples/serverless_mqtt/main/CMakeLists.txt

@@ -0,0 +1,4 @@
+idf_component_register(SRCS "serverless_mqtt.c"
+                            "wifi_connect.c"
+                    INCLUDE_DIRS "."
+                    REQUIRES libjuice nvs_flash mqtt json esp_wifi)

components/mosquitto/examples/serverless_mqtt/main/Kconfig.projbuild

@@ -0,0 +1,85 @@
+menu "Example Configuration"
+
+    menu "AP Configuration"
+        comment "AP Configuration"
+
+        config EXAMPLE_AP_SSID
+            string "Wi-Fi SSID"
+            default "myssid"
+            help
+                Set the SSID of Wi-Fi ap interface.
+
+        config EXAMPLE_AP_PASSWORD
+            string "Wi-Fi Password"
+            default "12345678"
+            help
+                Set the password of Wi-Fi ap interface.
+
+    endmenu
+
+    menu "STA Configuration"
+        comment "STA Configuration"
+
+        config EXAMPLE_STA_SSID
+            string "WiFi Station SSID"
+            default "mystationssid"
+            help
+                SSID for the example's sta to connect to.
+
+        config EXAMPLE_STA_PASSWORD
+            string "WiFi Station Password"
+            default "mystationpassword"
+            help
+                WiFi station password for the example to use.
+    endmenu
+
+    config EXAMPLE_MQTT_BROKER_URI
+        string "MQTT Broker URL"
+        default "mqtt://mqtt.eclipseprojects.io"
+        help
+            URL of the mqtt broker use for synchronisation and exchanging
+            ICE connect info (description and candidates).
+
+    config EXAMPLE_MQTT_SYNC_TOPIC
+        string "MQTT topic for synchronisation"
+        default "/topic/serverless_mqtt"
+        help
+            MQTT topic used fo synchronisation.
+
+    config EXAMPLE_STUN_SERVER
+        string "Hostname of STUN server"
+        default "stun.l.google.com"
+        help
+            STUN server hostname.
+
+    config EXAMPLE_MQTT_CLIENT_STACK_SIZE
+        int "Stack size for mqtt client"
+        default 16384
+        help
+            Set stack size for the mqtt client.
+            Need more stack, since calling juice API from the handler.
+
+    config EXAMPLE_MQTT_BROKER_PORT
+        int "port for the mosquitto to listen to"
+        default 1883
+        help
+            This is a port which the local mosquitto uses.
+
+    choice EXAMPLE_SERVERLESS_ROLE
+        prompt "Choose your role"
+        default EXAMPLE_SERVERLESS_ROLE_PEER1
+        help
+            Choose either peer1 or peer2.
+            It's not very important which device is peer1
+            (peer-1 sends sync messages, peer2 listens for them)
+            It is important that we have two peers,
+            one with peer1 config, another one with peer2 config
+
+        config EXAMPLE_SERVERLESS_ROLE_PEER1
+            bool "peer1"
+
+        config EXAMPLE_SERVERLESS_ROLE_PEER2
+            bool "peer2"
+    endchoice
+
+endmenu

components/mosquitto/examples/serverless_mqtt/main/idf_component.yml

@@ -0,0 +1,5 @@
+## IDF Component Manager Manifest File
+dependencies:
+  espressif/mosquitto:
+    override_path: ../../..
+  espressif/sock_utils: "*"

components/mosquitto/examples/serverless_mqtt/main/serverless_mqtt.c

@@ -0,0 +1,374 @@
+/*
+ * SPDX-FileCopyrightText: 2024 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Unlicense OR CC0-1.0
+ */
+#include <stdio.h>
+#include "freertos/FreeRTOS.h"
+#include "freertos/event_groups.h"
+#include "mqtt_client.h"
+#include "esp_wifi.h"
+#include "esp_log.h"
+#include "esp_random.h"
+#include "esp_check.h"
+#include "esp_sleep.h"
+#include "mosq_broker.h"
+#include "juice/juice.h"
+#include "cJSON.h"
+
+#if defined(CONFIG_EXAMPLE_SERVERLESS_ROLE_PEER1)
+#define OUR_PEER "1"
+#define THEIR_PEER "2"
+#elif defined(CONFIG_EXAMPLE_SERVERLESS_ROLE_PEER2)
+#define OUR_PEER "2"
+#define THEIR_PEER "1"
+#endif
+
+#define PEER_SYNC0 BIT(0)
+#define PEER_SYNC1 BIT(1)
+#define PEER_SYNC2 BIT(2)
+#define PEER_FAIL  BIT(3)
+#define PEER_GATHER_DONE  BIT(4)
+#define PEER_DESC_PUBLISHED  BIT(5)
+#define PEER_CONNECTED  BIT(6)
+
+#define SYNC_BITS (PEER_SYNC1 | PEER_SYNC2 | PEER_FAIL)
+
+#define PUBLISH_SYNC_TOPIC CONFIG_EXAMPLE_MQTT_SYNC_TOPIC OUR_PEER
+#define SUBSCRIBE_SYNC_TOPIC CONFIG_EXAMPLE_MQTT_SYNC_TOPIC THEIR_PEER
+#define MAX_BUFFER_SIZE JUICE_MAX_SDP_STRING_LEN
+
+typedef struct message_wrap {
+    uint16_t topic_len;
+    uint16_t data_len;
+    char data[];
+} __attribute__((packed)) message_wrap_t;
+
+static const char *TAG = "serverless_mqtt" OUR_PEER;
+static char s_buffer[MAX_BUFFER_SIZE];
+static EventGroupHandle_t s_state = NULL;
+static juice_agent_t *s_agent = NULL;
+static cJSON *s_peer_desc_json = NULL;
+static char *s_peer_desc = NULL;
+static esp_mqtt_client_handle_t s_local_mqtt = NULL;
+
+char *wifi_get_ipv4(wifi_interface_t interface);
+esp_err_t wifi_connect(void);
+static esp_err_t sync_peers(void);
+static esp_err_t create_candidates(void);
+static esp_err_t create_local_client(void);
+static esp_err_t create_local_broker(void);
+
+void app_main(void)
+{
+    __attribute__((__unused__)) esp_err_t ret;
+    ESP_GOTO_ON_ERROR(wifi_connect(), err, TAG, "Failed to initialize WiFi");
+    ESP_GOTO_ON_ERROR(create_local_broker(), err, TAG, "Failed to create local broker");
+    ESP_GOTO_ON_ERROR(create_candidates(), err, TAG, "Failed to create juice candidates");
+    ESP_GOTO_ON_ERROR(sync_peers(), err, TAG, "Failed to sync with the other peer");
+    EventBits_t bits = xEventGroupWaitBits(s_state, PEER_FAIL | PEER_CONNECTED, pdFALSE, pdFALSE, pdMS_TO_TICKS(90000));
+    if (bits & PEER_CONNECTED) {
+        ESP_LOGI(TAG, "Peer is connected!");
+        ESP_GOTO_ON_ERROR(create_local_client(), err, TAG, "Failed to create forwarding mqtt client");
+        ESP_LOGI(TAG, "Everything is ready, exiting main task");
+        return;
+    }
+err:
+    ESP_LOGE(TAG, "Non recoverable error, going to sleep for some time (random, max 20s)");
+    esp_deep_sleep(1000000LL * (esp_random() % 20));
+}
+
+static void mqtt_event_handler(void *handler_args, esp_event_base_t base, int32_t event_id, void *event_data)
+{
+    esp_mqtt_event_handle_t event = event_data;
+    esp_mqtt_client_handle_t client = event->client;
+    switch ((esp_mqtt_event_id_t)event_id) {
+    case MQTT_EVENT_CONNECTED:
+        ESP_LOGI(TAG, "MQTT_EVENT_CONNECTED");
+        if (esp_mqtt_client_subscribe(client, SUBSCRIBE_SYNC_TOPIC, 1) < 0) {
+            ESP_LOGE(TAG, "Failed to subscribe to the sync topic");
+        }
+        xEventGroupSetBits(s_state, PEER_SYNC0);
+        break;
+    case MQTT_EVENT_DISCONNECTED:
+        ESP_LOGI(TAG, "MQTT_EVENT_DISCONNECTED");
+        xEventGroupSetBits(s_state, PEER_FAIL);
+        break;
+
+    case MQTT_EVENT_DATA:
+        ESP_LOGI(TAG, "MQTT_EVENT_DATA");
+        printf("TOPIC=%.*s\r\n", event->topic_len, event->topic);
+        printf("DATA=%.*s\r\n", event->data_len, event->data);
+        if (s_state == NULL || memcmp(event->topic, SUBSCRIBE_SYNC_TOPIC, event->topic_len) != 0) {
+            break;
+        }
+        EventBits_t bits = xEventGroupGetBits(s_state);
+        if (event->data_len > 1 && s_agent) {
+            cJSON *root = cJSON_Parse(event->data);
+            if (root == NULL) {
+                break;
+            }
+            cJSON *desc = cJSON_GetObjectItem(root, "desc");
+            if (desc == NULL) {
+                cJSON_Delete(root);
+                break;
+            }
+            printf("desc->valuestring:%s\n", desc->valuestring);
+            juice_set_remote_description(s_agent, desc->valuestring);
+            char cand_name[] = "cand0";
+            while (true) {
+                cJSON *cand = cJSON_GetObjectItem(root, cand_name);
+                if (cand == NULL) {
+                    break;
+                }
+                printf("%s: cand->valuestring:%s\n", cand_name, cand->valuestring);
+                juice_add_remote_candidate(s_agent, cand->valuestring);
+                cand_name[4]++;
+            }
+            cJSON_Delete(root);
+            xEventGroupSetBits(s_state, PEER_DESC_PUBLISHED); // this will complete the sync process
+            // and destroy the mqtt client
+        }
+#ifdef CONFIG_EXAMPLE_SERVERLESS_ROLE_PEER1
+        if (event->data_len == 1 && event->data[0] == '1' && (bits & PEER_SYNC2) == 0) {
+            if (esp_mqtt_client_publish(client, PUBLISH_SYNC_TOPIC, "2", 1, 1, 0) >= 0) {
+                xEventGroupSetBits(s_state, PEER_SYNC2);
+            } else {
+                xEventGroupSetBits(s_state, PEER_FAIL);
+            }
+        }
+#else
+        if (event->data_len == 1 && event->data[0] == '0' && (bits & PEER_SYNC1) == 0) {
+            if (esp_mqtt_client_publish(client, PUBLISH_SYNC_TOPIC, "1", 1, 1, 0) >= 0) {
+                xEventGroupSetBits(s_state, PEER_SYNC1);
+            }  else {
+                xEventGroupSetBits(s_state, PEER_FAIL);
+            }
+        } else if (event->data_len == 1 && event->data[0] == '2' && (bits & PEER_SYNC2) == 0) {
+            xEventGroupSetBits(s_state, PEER_SYNC2);
+        }
+#endif
+        break;
+    case MQTT_EVENT_ERROR:
+        ESP_LOGI(TAG, "MQTT_EVENT_ERROR");
+        xEventGroupSetBits(s_state, PEER_FAIL);
+        break;
+    default:
+        ESP_LOGI(TAG, "Other event id:%d", event->event_id);
+        break;
+    }
+}
+
+static esp_err_t sync_peers(void)
+{
+    esp_err_t ret = ESP_OK;
+    esp_mqtt_client_config_t mqtt_cfg = {
+        .broker.address.uri = CONFIG_EXAMPLE_MQTT_BROKER_URI,
+        .task.stack_size = CONFIG_EXAMPLE_MQTT_CLIENT_STACK_SIZE,
+    };
+    esp_mqtt_client_handle_t client = esp_mqtt_client_init(&mqtt_cfg);
+    ESP_GOTO_ON_FALSE(client, ESP_ERR_NO_MEM, err, TAG, "Failed to create mqtt client");
+    ESP_GOTO_ON_ERROR(esp_mqtt_client_register_event(client, ESP_EVENT_ANY_ID, mqtt_event_handler, NULL),
+                      err, TAG, "Failed to register mqtt event handler");
+    ESP_GOTO_ON_ERROR(esp_mqtt_client_start(client), err, TAG, "Failed to start mqtt client");
+    ESP_GOTO_ON_FALSE(xEventGroupWaitBits(s_state, PEER_SYNC0, pdTRUE, pdTRUE, pdMS_TO_TICKS(10000)),
+                      ESP_FAIL, err, TAG, "Failed to connect to the sync broker");
+    ESP_LOGI(TAG, "Waiting for the other peer...");
+    const int max_sync_retry = 60;
+    int retry = 0;
+    while (true) {
+        EventBits_t bits = xEventGroupWaitBits(s_state, SYNC_BITS, pdTRUE, pdFALSE, pdMS_TO_TICKS(1000));
+        if (bits & PEER_SYNC2) {
+            break;
+        }
+        if (bits & PEER_SYNC1) {
+            continue;
+        }
+        ESP_GOTO_ON_FALSE((bits & PEER_FAIL) == 0, ESP_FAIL, err, TAG, "Failed to sync with the other peer");
+        ESP_GOTO_ON_FALSE(retry++ < max_sync_retry, ESP_FAIL, err, TAG, "Failed to sync after %d seconds", retry);
+#ifdef CONFIG_EXAMPLE_SERVERLESS_ROLE_PEER1
+        ESP_RETURN_ON_FALSE(esp_mqtt_client_publish(client, PUBLISH_SYNC_TOPIC, "0", 1, 1, 0) >= 0,
+                            ESP_FAIL, TAG, "Failed to publish mqtt message");
+#endif
+    }
+    ESP_LOGI(TAG, "Sync done");
+    ESP_RETURN_ON_FALSE(esp_mqtt_client_publish(client, PUBLISH_SYNC_TOPIC, s_peer_desc, 0, 1, 0) >= 0,
+                        ESP_FAIL, TAG, "Failed to publish peer's description");
+    ESP_LOGI(TAG, "Waiting for the other peer description and candidates...");
+    ESP_GOTO_ON_FALSE(xEventGroupWaitBits(s_state, PEER_DESC_PUBLISHED, pdTRUE, pdTRUE, pdMS_TO_TICKS(10000)),
+                      ESP_FAIL, err, TAG, "Timeout in waiting for the other peer candidates");
+err:
+    free(s_peer_desc);
+    esp_mqtt_client_destroy(client);
+    return ret;
+}
+
+static void juice_state(juice_agent_t *agent, juice_state_t state, void *user_ptr)
+{
+    ESP_LOGI(TAG, "JUICE state change: %s", juice_state_to_string(state));
+    if (state == JUICE_STATE_CONNECTED) {
+        xEventGroupSetBits(s_state, PEER_CONNECTED);
+    } else if (state == JUICE_STATE_FAILED || state == JUICE_STATE_DISCONNECTED) {
+        esp_restart();
+    }
+}
+
+static void juice_candidate(juice_agent_t *agent, const char *sdp, void *user_ptr)
+{
+    static uint8_t cand_nr = 0;
+    if (s_peer_desc_json && cand_nr < 10) { // supporting only 10 candidates
+        char cand_name[] = "cand0";
+        cand_name[4] += cand_nr++;
+        cJSON_AddStringToObject(s_peer_desc_json, cand_name, sdp);
+    }
+}
+
+static void juice_gathering_done(juice_agent_t *agent, void *user_ptr)
+{
+    ESP_LOGI(TAG, "Gathering done");
+    if (s_state) {
+        xEventGroupSetBits(s_state, PEER_GATHER_DONE);
+    }
+}
+
+#define ALIGN(size) (((size) + 3U) & ~(3U))
+
+static void juice_recv(juice_agent_t *agent, const char *data, size_t size, void *user_ptr)
+{
+    if (s_local_mqtt) {
+        message_wrap_t *message = (message_wrap_t *)data;
+        int topic_len = message->topic_len;
+        int payload_len = message->data_len;
+        int topic_len_aligned = ALIGN(topic_len);
+        char *topic = message->data;
+        char *payload = message->data + topic_len_aligned;
+        if (topic_len + topic_len_aligned + 4 > size) {
+            ESP_LOGE(TAG, "Received invalid message");
+            return;
+        }
+        ESP_LOGI(TAG, "forwarding remote message: topic:%s", topic);
+        ESP_LOGI(TAG, "forwarding remote message: payload:%.*s", payload_len, payload);
+        esp_mqtt_client_publish(s_local_mqtt, topic, payload, payload_len, 0, 0);
+    }
+}
+
+static esp_err_t create_candidates(void)
+{
+    ESP_RETURN_ON_FALSE(s_state = xEventGroupCreate(), ESP_ERR_NO_MEM, TAG, "Failed to create state event group");
+    s_peer_desc_json = cJSON_CreateObject();
+    esp_err_t ret = ESP_OK;
+    juice_set_log_level(JUICE_LOG_LEVEL_INFO);
+    juice_config_t config = { .stun_server_host = CONFIG_EXAMPLE_STUN_SERVER,
+                              .bind_address = wifi_get_ipv4(WIFI_IF_STA),
+                              .stun_server_port = 19302,
+                              .cb_state_changed = juice_state,
+                              .cb_candidate = juice_candidate,
+                              .cb_gathering_done = juice_gathering_done,
+                              .cb_recv = juice_recv,
+                            };
+
+    s_agent = juice_create(&config);
+    ESP_RETURN_ON_FALSE(s_agent, ESP_FAIL, TAG, "Failed to create juice agent");
+    ESP_GOTO_ON_FALSE(juice_get_local_description(s_agent, s_buffer, MAX_BUFFER_SIZE) == JUICE_ERR_SUCCESS,
+                      ESP_FAIL, err, TAG, "Failed to get local description");
+    ESP_LOGI(TAG, "desc: %s", s_buffer);
+    cJSON_AddStringToObject(s_peer_desc_json, "desc", s_buffer);
+
+    ESP_GOTO_ON_FALSE(juice_gather_candidates(s_agent) == JUICE_ERR_SUCCESS,
+                      ESP_FAIL, err, TAG, "Failed to start gathering candidates");
+    ESP_GOTO_ON_FALSE(xEventGroupWaitBits(s_state, PEER_GATHER_DONE, pdTRUE, pdTRUE, pdMS_TO_TICKS(30000)),
+                      ESP_FAIL, err, TAG, "Failed to connect to the sync broker");
+    s_peer_desc = cJSON_Print(s_peer_desc_json);
+    ESP_LOGI(TAG, "desc: %s", s_peer_desc);
+    cJSON_Delete(s_peer_desc_json);
+    return ESP_OK;
+
+err:
+    juice_destroy(s_agent);
+    s_agent = NULL;
+    cJSON_Delete(s_peer_desc_json);
+    s_peer_desc_json = NULL;
+    return ret;
+}
+
+static void local_handler(void *args, esp_event_base_t base, int32_t id, void *data)
+{
+    switch (id) {
+    case MQTT_EVENT_CONNECTED:
+        ESP_LOGI(TAG, "local client connected");
+        break;
+    case MQTT_EVENT_DISCONNECTED:
+        ESP_LOGI(TAG, "local client disconnected");
+        break;
+
+    case MQTT_EVENT_ERROR:
+        ESP_LOGI(TAG, "local client error");
+        break;
+    default:
+        ESP_LOGI(TAG, "local client event id:%d", (int)id);
+        break;
+    }
+}
+
+static esp_err_t create_local_client(void)
+{
+    esp_err_t ret = ESP_OK;
+    esp_mqtt_client_config_t mqtt_cfg = {
+        .broker.address.transport = MQTT_TRANSPORT_OVER_TCP,
+        .broker.address.hostname = wifi_get_ipv4(WIFI_IF_AP),
+        .broker.address.port = CONFIG_EXAMPLE_MQTT_BROKER_PORT,
+        .task.stack_size = CONFIG_EXAMPLE_MQTT_CLIENT_STACK_SIZE,
+        .credentials.client_id = "local_mqtt"
+    };
+    s_local_mqtt = esp_mqtt_client_init(&mqtt_cfg);
+    ESP_GOTO_ON_FALSE(s_local_mqtt, ESP_ERR_NO_MEM, err, TAG, "Failed to create mqtt client");
+    ESP_GOTO_ON_ERROR(esp_mqtt_client_register_event(s_local_mqtt, ESP_EVENT_ANY_ID, local_handler, NULL),
+                      err, TAG, "Failed to register mqtt event handler");
+    ESP_GOTO_ON_ERROR(esp_mqtt_client_start(s_local_mqtt), err, TAG, "Failed to start mqtt client");
+
+    return ESP_OK;
+err:
+    esp_mqtt_client_destroy(s_local_mqtt);
+    s_local_mqtt = NULL;
+    return ret;
+}
+
+static void handle_message(char *client, char *topic, char *payload, int len, int qos, int retain)
+{
+    if (client && strcmp(client, "local_mqtt") == 0 ) {
+        // This is our little local client -- do not forward
+        return;
+    }
+    ESP_LOGI(TAG, "handle_message topic:%s", topic);
+    ESP_LOGI(TAG, "handle_message data:%.*s", len, payload);
+    ESP_LOGI(TAG, "handle_message qos=%d, retain=%d", qos, retain);
+    if (s_local_mqtt && s_agent) {
+        int topic_len = strlen(topic) + 1; // null term
+        int topic_len_aligned = ALIGN(topic_len);
+        int total_msg_len = 2 + 2 /* msg_wrap header */ + topic_len_aligned + len;
+        if (total_msg_len > MAX_BUFFER_SIZE) {
+            ESP_LOGE(TAG, "Fail to forward, message too long");
+            return;
+        }
+        message_wrap_t *message = (message_wrap_t *)s_buffer;
+        message->topic_len = topic_len;
+        message->data_len = len;
+
+        memcpy(s_buffer + 4, topic, topic_len);
+        memcpy(s_buffer + 4 + topic_len_aligned, payload, len);
+        juice_send(s_agent, s_buffer, total_msg_len);
+    }
+}
+
+static void broker_task(void *ctx)
+{
+    struct mosq_broker_config config = { .host = wifi_get_ipv4(WIFI_IF_AP), .port = CONFIG_EXAMPLE_MQTT_BROKER_PORT, .handle_message_cb = handle_message };
+    mosq_broker_run(&config);
+    vTaskDelete(NULL);
+}
+
+static esp_err_t create_local_broker(void)
+{
+    return xTaskCreate(broker_task, "mqtt_broker_task", 1024 * 32, NULL, 5, NULL) == pdTRUE ?
+           ESP_OK : ESP_FAIL;
+}

components/mosquitto/examples/serverless_mqtt/main/wifi_connect.c

@@ -0,0 +1,122 @@
+/*
+ * SPDX-FileCopyrightText: 2024 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Unlicense OR CC0-1.0
+ */
+#include "nvs_flash.h"
+#include "esp_event.h"
+#include "esp_netif.h"
+#include "esp_check.h"
+#include "esp_wifi.h"
+#include "esp_mac.h"
+
+#define WIFI_CONNECTED_BIT BIT0
+#define WIFI_FAIL_BIT      BIT1
+
+static const char *TAG = "serverless_wifi";
+static EventGroupHandle_t s_wifi_events;
+static int s_retry_num = 0;
+static const int s_max_retry = 30;
+
+static void wifi_event_handler(void *arg, esp_event_base_t event_base,
+                               int32_t event_id, void *event_data)
+{
+    if (event_id == WIFI_EVENT_AP_STACONNECTED) {
+        wifi_event_ap_staconnected_t *event = (wifi_event_ap_staconnected_t *) event_data;
+        ESP_LOGI(TAG, "station "MACSTR" join, AID=%d",
+                 MAC2STR(event->mac), event->aid);
+    } else if (event_id == WIFI_EVENT_AP_STADISCONNECTED) {
+        wifi_event_ap_stadisconnected_t *event = (wifi_event_ap_stadisconnected_t *) event_data;
+        ESP_LOGI(TAG, "station "MACSTR" leave, AID=%d",
+                 MAC2STR(event->mac), event->aid);
+    } else if (event_base == WIFI_EVENT && event_id == WIFI_EVENT_STA_START) {
+        esp_wifi_connect();
+    } else if (event_base == WIFI_EVENT && event_id == WIFI_EVENT_STA_DISCONNECTED) {
+        if (s_retry_num < s_max_retry) {
+            esp_wifi_connect();
+            s_retry_num++;
+            ESP_LOGI(TAG, "retry to connect to the AP");
+        } else {
+            xEventGroupSetBits(s_wifi_events, WIFI_FAIL_BIT);
+        }
+        ESP_LOGI(TAG, "Connect to the AP fail");
+    } else if (event_base == IP_EVENT && event_id == IP_EVENT_STA_GOT_IP) {
+        ip_event_got_ip_t *event = (ip_event_got_ip_t *) event_data;
+        ESP_LOGI(TAG, "Got ip:" IPSTR, IP2STR(&event->ip_info.ip));
+        s_retry_num = 0;
+        xEventGroupSetBits(s_wifi_events, WIFI_CONNECTED_BIT);
+    }
+}
+
+esp_err_t wifi_connect(void)
+{
+    esp_err_t ret = ESP_OK;
+    ESP_GOTO_ON_FALSE(s_wifi_events = xEventGroupCreate(), ESP_ERR_NO_MEM, err, TAG, "Failed to create wifi_events");
+    ESP_GOTO_ON_ERROR(nvs_flash_init(), err, TAG, "Failed to init nvs flash");
+    ESP_GOTO_ON_ERROR(esp_netif_init(), err, TAG, "Failed to init esp_netif");
+    ESP_GOTO_ON_ERROR(esp_event_loop_create_default(), err, TAG, "Failed to create default event loop");
+    ESP_GOTO_ON_ERROR(esp_event_handler_register(WIFI_EVENT, ESP_EVENT_ANY_ID, wifi_event_handler, NULL),
+                      err, TAG, "Failed to register WiFi event handler");
+    ESP_GOTO_ON_ERROR(esp_event_handler_register(IP_EVENT, IP_EVENT_STA_GOT_IP, wifi_event_handler, NULL),
+                      err, TAG, "Failed to register IP event handler");
+
+    // Initialize WiFi
+    wifi_init_config_t cfg = WIFI_INIT_CONFIG_DEFAULT();
+    ESP_GOTO_ON_ERROR(esp_wifi_init(&cfg), err, TAG, "Failed to initialize WiFi");
+    ESP_GOTO_ON_ERROR(esp_wifi_set_mode(WIFI_MODE_APSTA), err, TAG, "Failed to set STA+AP mode");
+
+    // Initialize AP
+    esp_netif_t *ap = esp_netif_create_default_wifi_ap();
+    ESP_GOTO_ON_FALSE(ap, ESP_FAIL, err, TAG, "Failed to create AP network interface");
+    wifi_config_t wifi_ap_config = {
+        .ap = {
+            .ssid = CONFIG_EXAMPLE_AP_SSID,
+            .password = CONFIG_EXAMPLE_AP_PASSWORD,
+            .authmode = WIFI_AUTH_WPA2_PSK,
+            .max_connection = 4,
+        },
+    };
+    ESP_GOTO_ON_ERROR(esp_wifi_set_config(WIFI_IF_AP, &wifi_ap_config), err, TAG, "Failed to set AP config");
+
+
+    // Initialize STA
+    esp_netif_t *sta = esp_netif_create_default_wifi_sta();
+    ESP_GOTO_ON_FALSE(sta, ESP_FAIL, err, TAG, "Failed to create WiFi station network interface");
+    wifi_config_t wifi_sta_config = {
+        .sta = {
+            .ssid = CONFIG_EXAMPLE_STA_SSID,
+            .password = CONFIG_EXAMPLE_STA_PASSWORD,
+        },
+    };
+    ESP_GOTO_ON_ERROR(esp_wifi_set_config(WIFI_IF_STA, &wifi_sta_config), err, TAG, "Failed to set STA config");
+
+    // Start WiFi
+    ESP_GOTO_ON_ERROR(esp_wifi_start(), err, TAG, "Failed to start WiFi");
+
+    // Wait for connection
+    EventBits_t bits = xEventGroupWaitBits(s_wifi_events, WIFI_CONNECTED_BIT | WIFI_FAIL_BIT,
+                                           pdFALSE, pdFALSE, pdMS_TO_TICKS(30000));
+    ESP_GOTO_ON_FALSE((bits & WIFI_CONNECTED_BIT) == WIFI_CONNECTED_BIT, ESP_FAIL, err,
+                      TAG, "Failed to obtain IP address from WiFi station");
+    return ESP_OK;
+err:
+    esp_wifi_stop();
+    esp_wifi_deinit();
+    nvs_flash_deinit();
+    esp_netif_deinit();
+    esp_event_loop_delete_default();
+    return ret;
+
+}
+
+_Thread_local char s_ipv4_addr[4 * 4]; // 4 octets + '.'/term
+
+char *wifi_get_ipv4(wifi_interface_t interface)
+{
+    esp_netif_t *netif = esp_netif_get_handle_from_ifkey(interface == WIFI_IF_AP ? "WIFI_AP_DEF" : "WIFI_STA_DEF");
+    ESP_RETURN_ON_FALSE(netif, NULL, TAG, "Failed to find default Wi-Fi netif");
+    esp_netif_ip_info_t ip_info;
+    ESP_RETURN_ON_FALSE(esp_netif_get_ip_info(netif, &ip_info) == ESP_OK, NULL, TAG, "Failed to get IP from netif");
+    ESP_RETURN_ON_FALSE(esp_ip4addr_ntoa(&ip_info.ip, s_ipv4_addr, sizeof(s_ipv4_addr)) != NULL, NULL, TAG, "Failed to convert IP");
+    return s_ipv4_addr;
+}

components/mosquitto/examples/serverless_mqtt/sdkconfig.defaults

@@ -0,0 +1,3 @@
+CONFIG_PARTITION_TABLE_SINGLE_APP_LARGE=y
+CONFIG_ESP_MAIN_TASK_STACK_SIZE=16384
+CONFIG_PTHREAD_TASK_STACK_SIZE_DEFAULT=32768