Merge pull request #18621 from benpicco/strscpy

sys/string_utils: add strscpy()

makefiles/defaultmodules_regular.inc.mk

@@ -6,7 +6,7 @@
 DEFAULT_MODULE += board board_common_init \
                   cpu \
                   core core_init core_lib core_msg core_panic core_thread \
-                  sys
+                  sys libc
 
 # Include potentially added default modules by the board
 -include $(BOARDDIR)/Makefile.default

sys/Kconfig

@@ -37,6 +37,7 @@ rsource "fs/Kconfig"
 rsource "hashes/Kconfig"
 rsource "iolist/Kconfig"
 rsource "isrpipe/Kconfig"
+rsource "libc/Kconfig"
 
 menu "Libc"
 

sys/include/string_utils.h

@@ -22,11 +22,13 @@
  * @author      Marian Buschsieweke <marian.buschsieweke@ovgu.de>
  */
 
+#include <errno.h>
+#include <stdint.h>
 /* if explicit_bzero() is provided by standard C lib, it may be defined in
  * either `string.h` or `strings.h`, so just include both here */
-#include <stdint.h>
 #include <string.h>
 #include <strings.h>
+#include <sys/types.h>
 
 #include "kernel_defines.h"
 
@@ -45,7 +47,7 @@ extern "C" {
  *
  * for all other cases, we provide it here
  */
-#if !defined(BOARD_NATIVE) \
+#if !defined(CPU_NATIVE) \
     && !(IS_USED(MODULE_PICOLIBC) && __BSD_VISIBLE) \
     && !(IS_USED(MODULE_NEWLIB) && __BSD_VISIBLE && !defined(MCU_ESP8266))
 
@@ -70,6 +72,26 @@ static inline void explicit_bzero(void *dest, size_t n_bytes)
 }
 #endif
 
+/**
+ * @brief Copy the string, or as much of it as fits, into the dest buffer.
+ *
+ * Preferred to `strncpy` since it always returns a valid string, and doesn't
+ * unnecessarily force the tail of the destination buffer to be zeroed.
+ * If the zeroing is desired, it's likely cleaner to use `strscpy` with an
+ * overflow test, then just memset the tail of the dest buffer.
+ *
+ * @param[out] dest     Where to copy the string to
+ * @param[in]   src     Where to copy the string from
+ * @param[in] count     Size of destination buffer
+ *
+ * @pre       The destination buffer is at least one byte large, as
+ *            otherwise the terminating zero byte won't fit
+ *
+ * @return the number of characters copied (not including the trailing zero)
+ * @retval  -E2BIG      the destination buffer wasn't big enough
+ */
+ssize_t strscpy(char *dest, const char *src, size_t count);
+
 #ifdef __cplusplus
 }
 #endif

sys/libc/Kconfig

@@ -0,0 +1,11 @@
+# Copyright (c) 2021 HAW Hamburg
+#
+# This file is subject to the terms and conditions of the GNU Lesser
+# General Public License v2.1. See the file LICENSE in the top level
+# directory for more details.
+#
+
+config MODULE_LIBC
+    bool "C Library helper functions"
+    default y
+    depends on TEST_KCONFIG

sys/libc/Makefile

@@ -0,0 +1 @@
+include $(RIOTBASE)/Makefile.base

sys/libc/string.c

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2022 ML!PA Consulting GmbH
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @{
+ *
+ * @file
+ *
+ * @author      Benjamin Valentin <benjamin.valentin@ml-pa.com>
+ */
+
+#include <errno.h>
+#include "string_utils.h"
+
+ssize_t strscpy(char *dest, const char *src, size_t count)
+{
+    const char *start = dest;
+
+    if (!count) {
+        return -E2BIG;
+    }
+
+    while (--count && *src) {
+        *dest++ = *src++;
+    }
+
+    *dest = 0;
+
+    if (*src == 0) {
+        return dest - start;
+    } else {
+        return -E2BIG;
+    }
+}
+/** @} */

tests/unittests/tests-libc/Makefile

@@ -0,0 +1 @@
+include $(RIOTBASE)/Makefile.base

tests/unittests/tests-libc/tests-libc.c

@@ -0,0 +1,46 @@
+/*
+ * Copyright (C) 2019 ML!PA Consulting GmbH
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+#include <stdint.h>
+#include <string.h>
+#include "string_utils.h"
+
+#include "tests-libc.h"
+
+static void test_libc_strscpy(void)
+{
+    char buffer[8];
+
+    TEST_ASSERT_EQUAL_INT(strscpy(buffer, "Hello", sizeof(buffer)), 5);
+    TEST_ASSERT_EQUAL_INT(strcmp(buffer, "Hello"), 0);
+    TEST_ASSERT_EQUAL_INT(strscpy(buffer, "012345678", sizeof(buffer)), -E2BIG);
+    TEST_ASSERT_EQUAL_INT(strcmp(buffer, "0123456"), 0);
+    memset(buffer, 0, sizeof(buffer));
+    TEST_ASSERT_EQUAL_INT(strscpy(buffer, "01234567", sizeof(buffer)), -E2BIG);
+    TEST_ASSERT_EQUAL_INT(strcmp(buffer, "0123456"), 0);
+    memset(buffer, 0, sizeof(buffer));
+    TEST_ASSERT_EQUAL_INT(strscpy(buffer, "0123456", sizeof(buffer)), 7);
+    TEST_ASSERT_EQUAL_INT(strcmp(buffer, "0123456"), 0);
+    TEST_ASSERT_EQUAL_INT(strscpy(buffer, "empty", 0), -E2BIG);
+}
+
+Test *tests_libc_tests(void)
+{
+    EMB_UNIT_TESTFIXTURES(fixtures) {
+        new_TestFixture(test_libc_strscpy),
+    };
+
+    EMB_UNIT_TESTCALLER(libc_tests, NULL, NULL, fixtures);
+
+    return (Test *)&libc_tests;
+}
+
+void tests_libc(void)
+{
+    TESTS_RUN(tests_libc_tests());
+}

tests/unittests/tests-libc/tests-libc.h

@@ -0,0 +1,44 @@
+/*
+ * Copyright (C) 2022 ML!PA Consulting GmbH
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @addtogroup  unittests
+ * @{
+ *
+ * @file
+ * @brief       Unittests for the ``libc`` module
+ *
+ * @author      Benjamin Valentin <benjamin.valentin@ml-pa.com>
+ */
+#ifndef TESTS_LIBC_H
+#define TESTS_LIBC_H
+
+#include "embUnit.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief   The entry point of this test suite.
+ */
+void tests_libc(void);
+
+/**
+ * @brief   Generates tests for libc
+ *
+ * @return  embUnit tests if successful, NULL if not.
+ */
+Test *tests_libc_tests(void);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* TESTS_LIBC_H */
+/** @} */