Add missing free functions to C API

This patch adds two missing free functions, NK_free_config and
NK_free_password_safe_slot_status, to enable memory-safe use of the C
API.

Fixes #173.

3 files changed, 24 insertions, 2 deletions

diff --git a/NK_C_API.cc b/NK_C_API.cc
index 1d3fa3a..0b7f5f7 100644
--- a/NK_C_API.cc
+++ b/NK_C_API.cc
@@ -226,6 +226,10 @@ extern "C" {
 		});
 	}
 
+        NK_C_API void NK_free_config(uint8_t* config) {
+                delete[] config;
+        }
+
 
 	NK_C_API enum NK_device_model NK_get_device_model() {
 		auto m = NitrokeyManager::instance();
@@ -448,6 +452,10 @@ extern "C" {
 
 	}
 
+        NK_C_API void NK_free_password_safe_slot_status(uint8_t* status) {
+                delete[] status;
+        }
+
 	NK_C_API uint8_t NK_get_user_retry_count() {
 		auto m = NitrokeyManager::instance();
 		return get_with_result([&]() {
diff --git a/NK_C_API.h b/NK_C_API.h
index d5c54a3..c4cb448 100644
--- a/NK_C_API.h
+++ b/NK_C_API.h
@@ -451,6 +451,7 @@ extern "C" {
 
 	/**
 	 * Get currently set config - status of function Numlock/Capslock/Scrollock OTP sending and is enabled PIN protected OTP
+         * The return value must be freed using NK_free_config.
 	 * @see NK_write_config
 	 * @return  uint8_t general_config[5]:
 	 *            uint8_t numlock;
@@ -462,6 +463,12 @@ extern "C" {
 	 */
 	NK_C_API uint8_t* NK_read_config();
 
+        /**
+         * Free a value returned by NK_read_config.  May be called with a NULL
+         * argument.
+         */
+        NK_C_API void NK_free_config(uint8_t* config);
+
 	//OTP
 
 	/**
@@ -634,10 +641,17 @@ extern "C" {
 
 	/**
 	 * Get password safe slots' status
+         * The return value must be freed using NK_free_password_safe_slot_status.
 	 * @return uint8_t[16] slot statuses - each byte represents one slot with 0 (not programmed) and 1 (programmed)
 	 */
 	NK_C_API uint8_t * NK_get_password_safe_slot_status();
 
+        /**
+         * Free a value returned by NK_get_password_safe_slot_status.  May be
+         * called with a NULL argument.
+         */
+        NK_C_API void NK_free_password_safe_slot_status(uint8_t* status);
+
 	/**
 	 * Get password safe slot name
 	 * @param slot_number password safe slot number, slot_number<16
diff --git a/unittest/test_memory.c b/unittest/test_memory.c
index 34ea7d5..20b11b2 100644
--- a/unittest/test_memory.c
+++ b/unittest/test_memory.c
@@ -44,7 +44,7 @@ int main() {
 	uint8_t *config = NK_read_config();
 	if (config == NULL)
 		return 1;
-	free(config);
+	NK_free_config(config);
 
 	result = NK_enable_password_safe("123456");
 	if (result != 0)
@@ -54,7 +54,7 @@ int main() {
 	if (slot_status == NULL) {
 		return 1;
 	}
-	free(slot_status);
+	NK_free_password_safe_slot_status(slot_status);
 
 	NK_logout();