fix(async_handler): Async handler example scratch buffer fix

1. In httpd_req_async_handler_begin, the httpd_req_aux is locally malloced
and data is  done memcpy to local httpd_req_aux from request'ss httpd_req_aux for
async request use-case, this causes scartch pointer from these two structs
pointing to same memory address.
2. In current workflow, the request's sratch buffer is freed in httpd_parse.c
httpd_req_cleanup api. Therefore if the user try to fetch the data (like headers)
from the scratch buffer, data will be not available.
3. Each request should have the deep copy of the scratch buffer. To retrive
the data later.

Closes #15587

Author: hrushikesh430

components/esp_http_server/src/httpd_txrx.c

@@ -647,6 +647,18 @@ esp_err_t httpd_req_async_handler_begin(httpd_req_t *r, httpd_req_t **out)
     struct httpd_req_aux *async_aux = (struct httpd_req_aux *) async->aux;
     struct httpd_req_aux *r_aux = (struct httpd_req_aux *) r->aux;
 
+    if (r_aux->scratch) {
+        async_aux->scratch = malloc(r_aux->scratch_cur_size);
+        if (async_aux->scratch == NULL) {
+            free(async_aux);
+            free(async);
+            return ESP_ERR_NO_MEM;
+        }
+        memcpy(async_aux->scratch, r_aux->scratch, r_aux->scratch_cur_size);
+    } else {
+        async_aux->scratch = NULL;
+    }
+
     async_aux->resp_hdrs = calloc(hd->config.max_resp_headers, sizeof(struct resp_hdr));
     if (async_aux->resp_hdrs == NULL) {
         free(async_aux);

examples/protocols/http_server/async_handlers/main/main.c

@@ -95,7 +95,42 @@ static esp_err_t queue_request(httpd_req_t *req, httpd_req_handler_t handler)
 /* handle long request (on async thread) */
 static esp_err_t long_async(httpd_req_t *req)
 {
-    ESP_LOGI(TAG, "running: /long");
+    char*  buf;
+    size_t buf_len;
+
+    /* Get URI */
+    ESP_LOGI(TAG, "Request URI: %s", req->uri);
+
+    /* Get header value string length and allocate memory for length + 1,
+     * extra byte for null termination */
+    buf_len = httpd_req_get_hdr_value_len(req, "Host") + 1;
+    if (buf_len > 1) {
+        buf = malloc(buf_len);
+        if (buf == NULL) {
+            ESP_LOGE(TAG, "Failed to allocate memory for headers");
+            return ESP_FAIL;
+        }
+        /* Copy null terminated value string into buffer */
+        if (httpd_req_get_hdr_value_str(req, "Host", buf, buf_len) == ESP_OK) {
+            ESP_LOGI(TAG, "Found header => Host: %s", buf);
+        }
+        free(buf);
+    }
+    /* Get query string length and allocate memory for length + 1,
+     * extra byte for null termination */
+    buf_len = httpd_req_get_url_query_len(req) + 1;
+    if (buf_len > 1) {
+        buf = malloc(buf_len);
+        if (buf == NULL) {
+            ESP_LOGE(TAG, "Failed to allocate memory for query string");
+            return ESP_FAIL;
+        }
+        /* Copy null terminated query string into buffer */
+        if (httpd_req_get_url_query_str(req, buf, buf_len) == ESP_OK) {
+            ESP_LOGI(TAG, "Found query string => %s", buf);
+        }
+        free(buf);
+    }
 
     // track the number of long requests
     static uint8_t req_count = 0;