feat: Add support for percent-encoding in password and it's corresponding test

Add support of percent-encoded characters when passing the username and password in URI

Closes https://github.com/espressif/esp-mqtt/issues/294

lib/mqtt_utils/CMakeLists.txt

@@ -0,0 +1,8 @@
+set(srcs mqtt_utils.c)
+
+add_library(mqtt_utils_lib ${srcs})
+target_include_directories(mqtt_utils_lib PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include)
+target_include_directories(mqtt_utils_lib PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/../include)
+idf_component_get_property(log log COMPONENT_LIB)
+target_link_libraries(mqtt_utils_lib PRIVATE ${log})
+add_library(idf::mqtt::utils ALIAS mqtt_utils_lib)

lib/mqtt_utils/include/mqtt_utils.h

@@ -0,0 +1,17 @@
+/*
+ * SPDX-FileCopyrightText: 2025 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#pragma once
+
+#ifdef __cplusplus
+extern "C" {
+#endif // #ifdef __cplusplus
+
+char *mqtt_create_string(const char *ptr, int len);
+int esp_mqtt_decode_percent_encoded_string(char *uri);
+
+#ifdef __cplusplus
+}
+#endif // #ifdef __cplusplus

lib/mqtt_utils/mqtt_utils.c

@@ -0,0 +1,54 @@
+/*
+ * SPDX-FileCopyrightText: 2025-2026 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+#include <string.h>
+#include <ctype.h>
+#include <stdlib.h>
+#include "include/mqtt_utils.h"
+
+char *mqtt_create_string(const char *ptr, int len)
+{
+    if (len <= 0) {
+        return NULL;
+    }
+
+    char *ret = calloc(1, len + 1);
+
+    if (ret == NULL) {
+        return NULL;
+    }
+
+    memcpy(ret, ptr, len);
+    return ret;
+}
+
+int esp_mqtt_decode_percent_encoded_string(char *uri)
+{
+    if (uri == NULL) {
+        return -1;
+    }
+
+    char *write_ptr = uri;
+    size_t uri_len = strlen(uri);
+
+    for (intptr_t i = 0; i < uri_len; i++, write_ptr++) {
+        if (uri[i] == '%') {
+            if (!(isxdigit((unsigned char) uri[i + 1]) && isxdigit((unsigned char) uri[i + 2]))) {
+                // having non [0-9a-fA-F] characters after % is illegal in URI
+                return -1;
+            }
+
+            char hexvalue[3] = {0, 0, 0};
+            memcpy(hexvalue, uri + i + 1, 2);
+            *write_ptr = (char) strtol(hexvalue, NULL, 16);
+            i += 2;
+        } else {
+            *write_ptr = uri[i];
+        }
+    }
+
+    *write_ptr = '\0';
+    return (int)(write_ptr - uri);
+}