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112 lines
3.3 KiB
C
112 lines
3.3 KiB
C
/*
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* Copyright (C) 2022 Otto-von-Guericke-Universität Magdeburg
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*
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* This file is subject to the terms and conditions of the GNU Lesser General
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* Public License v2.1. See the file LICENSE in the top level directory for more
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* details.
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*/
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/**
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* @defgroup sys_string_utils Utility functions that are missing in `string.h`
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* @ingroup sys
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*
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* This header provides utility functions that the standard C libs `string.h`
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* lacks, such as @ref explicit_bzero
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*
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* @{
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*
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* @file
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* @brief Utility functions that are missing in `string.h`
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*
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* @author Marian Buschsieweke <marian.buschsieweke@ovgu.de>
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*/
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#include <errno.h>
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#include <stdint.h>
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/* if explicit_bzero() is provided by standard C lib, it may be defined in
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* either `string.h` or `strings.h`, so just include both here */
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#include <string.h>
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#include <strings.h>
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#include <sys/types.h>
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#include "modules.h"
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#ifndef STRING_UTILS_H
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#define STRING_UTILS_H
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#ifdef __cplusplus
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extern "C" {
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#endif
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/* explicit_bzero is provided if:
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* - glibc is used as C lib (only with board natvie)
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* - newlib is used and __BSD_VISIBILE is set
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* - except for ESP8266, which is using an old version of newlib without it
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* - picolibc is used and __BSD_VISIBLE is set
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*
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* for all other cases, we provide it here
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*/
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#if !defined(CPU_NATIVE) \
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&& !(IS_USED(MODULE_PICOLIBC) && __BSD_VISIBLE) \
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&& !(IS_USED(MODULE_NEWLIB) && __BSD_VISIBLE && !defined(MCU_ESP8266))
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/**
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* @brief Like `memset(dest, 0, n_bytes)`, but secure
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*
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* Unlike `memset(dest, 0, n_bytes)`, this will zero out the memory even in
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* cases the compiler would optimize out the call to `memset()`.
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*
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* @note This is only sensible to use for sensitive data. For non-sensitive
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* data, keep using `memset()` for performance reasons.
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*
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* @param[in,out] dest Memory to clear
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* @param[in] n_bytes Size of memory to clear in bytes
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*/
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static inline void explicit_bzero(void *dest, size_t n_bytes)
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{
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volatile uint8_t *tmp = dest;
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for (size_t i = 0; i < n_bytes; i++) {
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tmp[i] = 0;
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}
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}
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#endif
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/**
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* @brief Copy the string, or as much of it as fits, into the dest buffer.
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*
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* Preferred to `strncpy` since it always returns a valid string, and doesn't
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* unnecessarily force the tail of the destination buffer to be zeroed.
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* If the zeroing is desired, it's likely cleaner to use `strscpy` with an
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* overflow test, then just memset the tail of the dest buffer.
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*
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* @param[out] dest Where to copy the string to
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* @param[in] src Where to copy the string from
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* @param[in] count Size of destination buffer
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*
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* @pre The destination buffer is at least one byte large, as
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* otherwise the terminating zero byte won't fit
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*
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* @return the number of characters copied (not including the trailing zero)
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* @retval -E2BIG the destination buffer wasn't big enough
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*/
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ssize_t strscpy(char *dest, const char *src, size_t count);
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/**
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* @brief Check if the entire buffer is filled with the same byte.
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*
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* @param[in] data The buffer to probe
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* @param[in] c The byte to check of
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* @param[in] len Size of the buffer
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*
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* @return NULL if the entire buffer is filled with @p c
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* @return pointer to the first non-matching byte
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*/
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const void *memchk(const void *data, uint8_t c, size_t len);
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#ifdef __cplusplus
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}
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#endif
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#endif /* STRING_UTILS_H */
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/** @} */
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