esp_tls: Renamed public API to indicate the Plain TCP connection

Also added parameter checks if used from as a public API
and updated the `is_plein_tcp` description that it's possible to connect
directly using plain tcp transport with the new API.

components/esp-tls/esp_tls.c

@@ -267,7 +267,7 @@ static esp_err_t esp_tls_set_socket_non_blocking(int fd, bool non_blocking)
     return ESP_OK;
 }
 
-esp_err_t esp_tls_tcp_connect(const char *host, int hostlen, int port, const esp_tls_cfg_t *cfg, esp_tls_error_handle_t error_handle, int *sockfd)
+static inline esp_err_t tcp_connect(const char *host, int hostlen, int port, const esp_tls_cfg_t *cfg, esp_tls_error_handle_t error_handle, int *sockfd)
 {
     struct sockaddr_storage address;
     int fd;
@@ -371,7 +371,7 @@ static int esp_tls_low_level_conn(const char *hostname, int hostlen, int port, c
             _esp_tls_net_init(tls);
             tls->is_tls = true;
         }
-        if ((esp_ret = esp_tls_tcp_connect(hostname, hostlen, port, cfg, tls->error_handle, &tls->sockfd)) != ESP_OK) {
+        if ((esp_ret = tcp_connect(hostname, hostlen, port, cfg, tls->error_handle, &tls->sockfd)) != ESP_OK) {
             ESP_INT_EVENT_TRACKER_CAPTURE(tls->error_handle, ESP_TLS_ERR_TYPE_ESP, esp_ret);
             return -1;
         }
@@ -440,6 +440,17 @@ static int esp_tls_low_level_conn(const char *hostname, int hostlen, int port, c
     return -1;
 }
 
+/**
+ * @brief Create a new plain TCP connection
+ */
+esp_err_t esp_tls_plain_tcp_connect(const char *host, int hostlen, int port, const esp_tls_cfg_t *cfg, esp_tls_error_handle_t error_handle, int *sockfd)
+{
+    if (sockfd == NULL || error_handle == NULL) {
+        return ESP_ERR_INVALID_ARG;
+    }
+    return tcp_connect(host, hostlen, port, cfg, error_handle, sockfd);
+}
+
 /**
  * @brief      Create a new TLS/SSL connection
  */

components/esp-tls/esp_tls.h

@@ -171,7 +171,10 @@ typedef struct esp_tls_cfg {
 
     void *ds_data;                          /*!< Pointer for digital signature peripheral context */
     bool is_plain_tcp;                      /*!< Use non-TLS connection: When set to true, the esp-tls uses
-                                                 plain TCP transport rather then TLS/SSL connection */
+                                                 plain TCP transport rather then TLS/SSL connection.
+                                                 Note, that it is possible to connect using a plain tcp transport
+                                                 directly with esp_tls_plain_tcp_connect() API */
+
     struct ifreq *if_name;                  /*!< The name of interface for data to go through. Use the default interface without setting */
 } esp_tls_cfg_t;
 
@@ -609,9 +612,10 @@ void esp_tls_server_session_delete(esp_tls_t *tls);
  * @param[out] error_handle ESP-TLS error handle holding potential errors occurred during connection
  * @param[out] sockfd    Socket descriptor if successfully connected on TCP layer
  * @return     ESP_OK   on success
+ *             ESP_ERR_INVALID_ARG if invalid output parameters
  *             ESP-TLS based error codes on failure
  */
-esp_err_t esp_tls_tcp_connect(const char *host, int hostlen, int port, const esp_tls_cfg_t *cfg, esp_tls_error_handle_t error_handle, int *sockfd);
+esp_err_t esp_tls_plain_tcp_connect(const char *host, int hostlen, int port, const esp_tls_cfg_t *cfg, esp_tls_error_handle_t error_handle, int *sockfd);
 
 #ifdef __cplusplus
 }

components/tcp_transport/transport_ssl.c

@@ -134,7 +134,7 @@ static int tcp_connect(esp_transport_handle_t t, const char *host, int port, int
     esp_tls_last_error_t *err_handle = esp_transport_get_error_handle(t);
 
     ssl->cfg.timeout_ms = timeout_ms;
-    esp_err_t err = esp_tls_tcp_connect(host, strlen(host), port, &ssl->cfg, err_handle, &ssl->sockfd);
+    esp_err_t err = esp_tls_plain_tcp_connect(host, strlen(host), port, &ssl->cfg, err_handle, &ssl->sockfd);
     if (err != ESP_OK) {
         ESP_LOGE(TAG, "Failed to open a new connection: %d", err);
         err_handle->last_error = err;