7e213cfb50
[v]stpeprintf() are similar to [v]snprintf(3), but they allow chaining. [v]snprintf(3) are very dangerous for catenating strings, since the obvious ways to do it invoke Undefined Behavior, and the ways that avoid UB are very error-prone. Cc: Iker Pedrosa <ipedrosa@redhat.com> Signed-off-by: Alejandro Colomar <alx@kernel.org>
120 lines
2.6 KiB
C
120 lines
2.6 KiB
C
/*
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* SPDX-FileCopyrightText: 2022 - 2023, Alejandro Colomar <alx@kernel.org>
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*
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* SPDX-License-Identifier: BSD-3-Clause
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*/
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#ifndef SHADOW_INCLUDE_LIB_STPEPRINTF_H_
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#define SHADOW_INCLUDE_LIB_STPEPRINTF_H_
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#include <config.h>
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#if !defined(HAVE_STPEPRINTF)
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#include <stdarg.h>
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#include <stddef.h>
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#include <stdio.h>
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#include "defines.h"
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format_attr(printf, 3, 4)
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inline char *stpeprintf(char *dst, char *end, const char *restrict fmt, ...);
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format_attr(printf, 3, 0)
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inline char *vstpeprintf(char *dst, char *end, const char *restrict fmt,
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va_list ap);
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/*
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* SYNOPSIS
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* [[gnu::format(printf, 3, 4)]]
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* char *_Nullable stpeprintf(char *_Nullable dst, char end[0],
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* const char *restrict fmt, ...);
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*
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* [[gnu::format(printf, 3, 0)]]
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* char *_Nullable vstpeprintf(char *_Nullable dst, char end[0],
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* const char *restrict fmt, va_list ap);
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*
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*
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* ARGUMENTS
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* dst Destination buffer where to write a string.
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*
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* end Pointer to one after the last element of the buffer
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* pointed to by `dst`. Usually, it should be calculated
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* as `dst + NITEMS(dst)`.
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*
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* fmt Format string
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*
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* ...
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* ap Variadic argument list
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*
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* DESCRIPTION
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* These functions are very similar to [v]snprintf(3).
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*
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* The destination buffer is limited by a pointer to its end --one
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* after its last element-- instead of a size. This allows
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* chaining calls to it safely, unlike [v]snprintf(3), which is
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* difficult to chain without invoking Undefined Behavior.
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*
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* RETURN VALUE
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* dst + strlen(dst)
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* • On success, these functions return a pointer to the
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* terminating NUL byte.
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*
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* end
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* • If this call truncated the resulting string.
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* • If `dst == end` (a previous chained call to these
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* functions truncated).
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* NULL
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* • If this function failed (see ERRORS).
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* • If `dst == NULL` (a previous chained call to these
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* functions failed).
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*
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* ERRORS
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* These functions may fail for the same reasons as vsnprintf(3).
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*/
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inline char *
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stpeprintf(char *dst, char *end, const char *restrict fmt, ...)
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{
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char *p;
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va_list ap;
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va_start(ap, fmt);
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p = vstpeprintf(dst, end, fmt, ap);
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va_end(ap);
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return p;
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}
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inline char *
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vstpeprintf(char *dst, char *end, const char *restrict fmt, va_list ap)
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{
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int len;
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ptrdiff_t size;
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if (dst == end)
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return end;
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if (dst == NULL)
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return NULL;
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size = end - dst;
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len = vsnprintf(dst, size, fmt, ap);
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if (len == -1)
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return NULL;
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if (len >= size)
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return end;
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return dst + len;
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}
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#endif // !HAVE_STPEPRINTF
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#endif // include guard
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