From 1fd50dd2cbbe9a7847d8e99d2d802c17122a0be9 Mon Sep 17 00:00:00 2001
From: Euripedes Rocha <rocha.euripedes@espressif.com>
Date: Thu, 14 Oct 2021 11:00:45 -0300
Subject: [PATCH] Adds a config flag to allow an empty client id

This commit covers a use case where the user can select to send an
empty user id.
---
 include/mqtt_client.h |  6 +++++-
 lib/mqtt_msg.c        | 11 ++++++-----
 mqtt_client.c         | 17 +++++++++++------
 3 files changed, 22 insertions(+), 12 deletions(-)

diff --git a/include/mqtt_client.h b/include/mqtt_client.h
index 64cfb77..07feed3 100644
--- a/include/mqtt_client.h
+++ b/include/mqtt_client.h
@@ -176,7 +176,11 @@ typedef struct {
     const char *host;                       /*!< MQTT server domain (ipv4 as string) */
     const char *uri;                        /*!< Complete MQTT broker URI */
     uint32_t port;                          /*!< MQTT server port */
-    const char *client_id;                  /*!< default client id is ``ESP32_%CHIPID%`` where %CHIPID% are last 3 bytes of MAC address in hex format */
+    bool set_null_client_id;                /*!< Selects a NULL client id */
+    const char *client_id;                  /*!< Set client id.
+                                                 Ignored if set_null_client_id == true
+                                                 If NULL set the default client id.
+                                                 Default client id is ``ESP32_%CHIPID%`` where %CHIPID% are last 3 bytes of MAC address in hex format */
     const char *username;                   /*!< MQTT username */
     const char *password;                   /*!< MQTT password */
     const char *lwt_topic;                  /*!< LWT (Last Will and Testament) message topic (NULL by default) */
diff --git a/lib/mqtt_msg.c b/lib/mqtt_msg.c
index e7fb1ab..3a8554c 100644
--- a/lib/mqtt_msg.c
+++ b/lib/mqtt_msg.c
@@ -361,7 +361,7 @@ mqtt_message_t *mqtt_msg_connect(mqtt_connection_t *connection, mqtt_connect_inf
     if (connection->message.length + header_len > connection->buffer_length) {
         return fail_message(connection);
     }
-    char* variable_header = (void *)(connection->buffer + connection->message.length);
+    char *variable_header = (char *)(connection->buffer + connection->message.length);
     connection->message.length += header_len;
 
     int header_idx = 0;
@@ -394,7 +394,9 @@ mqtt_message_t *mqtt_msg_connect(mqtt_connection_t *connection, mqtt_connect_inf
             return fail_message(connection);
         }
     } else {
-        return fail_message(connection);
+        if (append_string(connection, "", 0) < 0) {
+            return fail_message(connection);
+        }
     }
 
     if (info->will_topic != NULL && info->will_topic[0] != '\0') {
@@ -456,7 +458,7 @@ mqtt_message_t *mqtt_msg_publish(mqtt_connection_t *connection, const char *topi
     }
 
     if (data == NULL && data_length > 0) {
-       return fail_message(connection);
+        return fail_message(connection);
     }
 
     if (qos > 0) {
@@ -474,8 +476,7 @@ mqtt_message_t *mqtt_msg_publish(mqtt_connection_t *connection, const char *topi
         connection->message.length = connection->buffer_length;
         connection->message.fragmented_msg_total_length = data_length + connection->message.fragmented_msg_data_offset;
     } else {
-        if (data != NULL)
-        {
+        if (data != NULL) {
             memcpy(connection->buffer + connection->message.length, data, data_length);
             connection->message.length += data_length;
         }
diff --git a/mqtt_client.c b/mqtt_client.c
index 6f8a4ef..3d44241 100644
--- a/mqtt_client.c
+++ b/mqtt_client.c
@@ -395,13 +395,15 @@ esp_err_t esp_mqtt_set_config(esp_mqtt_client_handle_t client, const esp_mqtt_cl
     ESP_MEM_CHECK(TAG, set_if_config(config->username, &client->connect_info.username), goto _mqtt_set_config_failed);
     ESP_MEM_CHECK(TAG, set_if_config(config->password, &client->connect_info.password), goto _mqtt_set_config_failed);
 
-    if (config->client_id) {
-        ESP_MEM_CHECK(TAG, set_if_config(config->client_id, &client->connect_info.client_id), goto _mqtt_set_config_failed);
-    } else if (client->connect_info.client_id == NULL) {
-        client->connect_info.client_id = platform_create_id_string();
+    if (!config->set_null_client_id) {
+        if (config->client_id) {
+            ESP_MEM_CHECK(TAG, set_if_config(config->client_id, &client->connect_info.client_id), goto _mqtt_set_config_failed);
+        } else if (client->connect_info.client_id == NULL) {
+            client->connect_info.client_id = platform_create_id_string();
+        }
+        ESP_MEM_CHECK(TAG, client->connect_info.client_id, goto _mqtt_set_config_failed);
+        ESP_LOGD(TAG, "MQTT client_id=%s", client->connect_info.client_id);
     }
-    ESP_MEM_CHECK(TAG, client->connect_info.client_id, goto _mqtt_set_config_failed);
-    ESP_LOGD(TAG, "MQTT client_id=%s", client->connect_info.client_id);
 
     ESP_MEM_CHECK(TAG, set_if_config(config->uri, &client->config->uri), goto _mqtt_set_config_failed);
     ESP_MEM_CHECK(TAG, set_if_config(config->lwt_topic, &client->connect_info.will_topic), goto _mqtt_set_config_failed);
@@ -427,6 +429,9 @@ esp_err_t esp_mqtt_set_config(esp_mqtt_client_handle_t client, const esp_mqtt_cl
 
     if (config->disable_clean_session == client->connect_info.clean_session) {
         client->connect_info.clean_session = !config->disable_clean_session;
+        if (!client->connect_info.clean_session && config->set_null_client_id) {
+            ESP_LOGE(TAG, "Clean Session flag must be true if client has a null id");
+        }
     }
     if (config->keepalive) {
         client->connect_info.keepalive = config->keepalive;