feat(esp_https_ota): Support partial downloading of OTA over single connection

This commit added support to download OTA with partial download feature
over single HTTP connection if server supports persistent connection.

components/esp_http_client/esp_http_client.c

@@ -185,7 +185,7 @@ static const char *HTTP_METHOD_MAPPING[] = {
     "REPORT"
 };
 
-static esp_err_t esp_http_client_request_send(esp_http_client_handle_t client, int write_len);
+esp_err_t esp_http_client_request_send(esp_http_client_handle_t client, int write_len);
 static esp_err_t esp_http_client_connect(esp_http_client_handle_t client);
 static esp_err_t esp_http_client_send_post_data(esp_http_client_handle_t client);
 
@@ -701,8 +701,12 @@ error:
 }
 #endif
 
-static esp_err_t esp_http_client_prepare(esp_http_client_handle_t client)
+esp_err_t esp_http_client_prepare(esp_http_client_handle_t client)
 {
+    if (client == NULL) {
+        return ESP_FAIL;
+    }
+
     esp_err_t ret = ESP_OK;
     client->process_again = 0;
     client->response->data_process = 0;
@@ -1711,8 +1715,12 @@ static int http_client_prepare_first_line(esp_http_client_handle_t client, int w
     return first_line_len;
 }
 
-static esp_err_t esp_http_client_request_send(esp_http_client_handle_t client, int write_len)
+esp_err_t esp_http_client_request_send(esp_http_client_handle_t client, int write_len)
 {
+    if (client == NULL) {
+        return ESP_FAIL;
+    }
+
     int first_line_len = 0;
     if (!client->first_line_prepared) {
         if ((first_line_len = http_client_prepare_first_line(client, write_len)) < 0) {
@@ -2065,3 +2073,15 @@ esp_http_state_t esp_http_client_get_state(esp_http_client_handle_t client)
     }
     return client->state;
 }
+
+bool esp_http_client_is_persistent_connection(esp_http_client_handle_t client)
+{
+    if (client == NULL) {
+        return false;
+    }
+
+    if (http_should_keep_alive(client->parser)) {
+        return true;
+    }
+    return false;
+}

components/esp_http_client/include/esp_http_client.h

@@ -343,6 +343,33 @@ esp_http_client_handle_t esp_http_client_init(const esp_http_client_config_t *co
  */
 esp_err_t esp_http_client_perform(esp_http_client_handle_t client);
 
+/**
+ * @brief      Prepare HTTP client for a new request
+ *             This function initializes the client state and prepares authentication if needed.
+ *             It should be called before sending a request.
+ *
+ * @param[in]  client  The esp_http_client handle
+ *
+ * @return
+ *  - ESP_OK on successful
+ *  - ESP_FAIL on error
+ */
+esp_err_t esp_http_client_prepare(esp_http_client_handle_t client);
+
+/**
+ * @brief      Send HTTP request headers and data
+ *             This function sends the HTTP request line, headers, and any post data to the server.
+ *
+ * @param[in]  client     The esp_http_client handle
+ * @param[in]  write_len  Length of data to write (for POST/PUT requests)
+ *
+ * @return
+ *  - ESP_OK on successful
+ *  - ESP_FAIL on error
+ *  - ESP_ERR_HTTP_WRITE_DATA if write operation fails
+ */
+esp_err_t esp_http_client_request_send(esp_http_client_handle_t client, int write_len);
+
 /**
  * @brief       Cancel an ongoing HTTP request. This API closes the current socket and opens a new socket with the same esp_http_client context.
  *
@@ -866,6 +893,15 @@ esp_err_t esp_http_client_get_chunk_length(esp_http_client_handle_t client, int
  */
 esp_http_state_t esp_http_client_get_state(esp_http_client_handle_t client);
 
+/**
+ * @brief      Check if persistent connection is supported by the server
+ *
+ * @param[in]  client  The HTTP client handle
+ *
+ * @return     true if persistent connection is supported, false otherwise
+ */
+bool esp_http_client_is_persistent_connection(esp_http_client_handle_t client);
+
 #ifdef __cplusplus
 }
 #endif

components/esp_https_ota/src/esp_https_ota.c

@@ -165,7 +165,22 @@ static esp_err_t _http_connect(esp_https_ota_t *https_ota_handle)
          * is enabled
          */
         int post_len = esp_http_client_get_post_field(https_ota_handle->http_client, &post_data);
-        err = esp_http_client_open(https_ota_handle->http_client, post_len);
+
+#if CONFIG_ESP_HTTPS_OTA_ENABLE_PARTIAL_DOWNLOAD
+        // If support_persistent_connection is enabled and this is a subsequent request, skip connection
+        if (esp_http_client_is_persistent_connection(https_ota_handle->http_client) && https_ota_handle->state == ESP_HTTPS_OTA_IN_PROGRESS) {
+            ESP_LOGD(TAG, "Using existing connection for partial download");
+            err = esp_http_client_prepare(https_ota_handle->http_client);
+            if (err != ESP_OK) {
+                ESP_LOGE(TAG, "Failed to reset HTTP client response state: %s", esp_err_to_name(err));
+                return err;
+            }
+            err = esp_http_client_request_send(https_ota_handle->http_client, post_len);
+        } else
+#endif
+        {
+            err = esp_http_client_open(https_ota_handle->http_client, post_len);
+        }
         if (err != ESP_OK) {
             ESP_LOGE(TAG, "Failed to open HTTP connection: %s", esp_err_to_name(err));
             return err;
@@ -827,7 +842,10 @@ esp_err_t esp_https_ota_perform(esp_https_ota_handle_t https_ota_handle)
 #if CONFIG_ESP_HTTPS_OTA_ENABLE_PARTIAL_DOWNLOAD
     if (handle->partial_http_download) {
         if (handle->state == ESP_HTTPS_OTA_IN_PROGRESS && handle->image_length > handle->binary_file_len) {
-            esp_http_client_close(handle->http_client);
+            // Only close connection if support_persistent_connection is not enabled
+            if (!esp_http_client_is_persistent_connection(handle->http_client)) {
+                esp_http_client_close(handle->http_client);
+            }
             char *header_val = NULL;
             int header_size = 0;
 #if CONFIG_ESP_HTTPS_OTA_DECRYPT_CB