feat(httpd): avoid useless string copy by introducing httpd_req_get_url_query_str_ptr()

components/esp_http_server/include/esp_http_server.h

@@ -1021,6 +1021,36 @@ size_t httpd_req_get_url_query_len(httpd_req_t *r);
  */
 esp_err_t httpd_req_get_url_query_str(httpd_req_t *r, char *buf, size_t buf_len);
 
+/**
+ * @brief   Similar to httpd_req_get_url_query_str() but avoids the string copy
+ *
+ * @note
+ *  - This API is meant to be used with std::string_view or similar
+ *  - Presently, the user can fetch the full URL query string, but decoding
+ *    will have to be performed by the user. Request headers can be read using
+ *    httpd_req_get_hdr_value_str() to know the 'Content-Type' (eg. Content-Type:
+ *    application/x-www-form-urlencoded) and then the appropriate decoding
+ *    algorithm needs to be applied.
+ *  - This API is supposed to be called only from the context of
+ *    a URI handler where httpd_req_t* request pointer is valid
+ *  - The byte range between buf and buf_len should only be used withing
+ *    the URI handler and not after since it will lead to use after free
+ *    errors
+ *
+ * @param[in]  r         The request being responded to
+ * @param[out] buf       Pointer to a pointer that should be updated to the begin of
+ *                       the buffer
+ * @param[out] buf_len   Pointer of length of output buffer
+ *
+ * @return
+ *  - ESP_OK : Query is found in the request URL and copied to buffer
+ *  - ESP_FAIL                   : uri is empty
+ *  - ESP_ERR_NOT_FOUND          : Query not found
+ *  - ESP_ERR_INVALID_ARG        : Null arguments
+ *  - ESP_ERR_HTTPD_INVALID_REQ  : Invalid HTTP request pointer
+ */
+esp_err_t httpd_req_get_url_query_str_ptr(httpd_req_t *r, const char **buf, size_t *buf_len);
+
 /**
  * @brief   Helper function to get a URL query tag from a query
  *          string of the type param1=val1&param2=val2

components/esp_http_server/src/httpd_parse.c

@@ -1014,6 +1014,36 @@ esp_err_t httpd_req_get_url_query_str(httpd_req_t *r, char *buf, size_t buf_len)
     return ESP_ERR_NOT_FOUND;
 }
 
+esp_err_t httpd_req_get_url_query_str_ptr(httpd_req_t *r, const char **buf, size_t *buf_len)
+{
+    if (r == NULL || buf == NULL) {
+        return ESP_ERR_INVALID_ARG;
+    }
+
+    if (!httpd_valid_req(r)) {
+        return ESP_ERR_HTTPD_INVALID_REQ;
+    }
+
+    if (r->uri[0] == '\0') {
+        ESP_LOGD(TAG, "uri is empty");
+        return ESP_FAIL;
+    }
+
+    struct httpd_req_aux   *ra  = r->aux;
+    struct http_parser_url *res = &ra->url_parse_res;
+
+    /* Check if query field is present in the URL */
+    if (res->field_set & (1 << UF_QUERY)) {
+        *buf = r->uri + res->field_data[UF_QUERY].off;
+
+        /* Query data length does not include terminating null */
+        *buf_len = res->field_data[UF_QUERY].len;
+
+        return ESP_OK;
+    }
+    return ESP_ERR_NOT_FOUND;
+}
+
 /* Get the length of the value string of a header request field */
 size_t httpd_req_get_hdr_value_len(httpd_req_t *r, const char *field)
 {