strace/xstring.h

#ifndef STRACE_XSTRING_H
#define STRACE_XSTRING_H

#include <stdarg.h>
#include <stdio.h>

#include "error_prints.h"
#include "gcc_compat.h"

/**
 * Print to static buffer and die on (really unexpected) errors and overflows.
 * Shouldn't be used directly; please refer to helper macros xsnprintf and
 * xsprint instead.
 *
 * @param str    String buffer to print into.
 * @param size   Size of the string buffer in bytes.
 * @param func   Function name from which this function is called.
 * @param argstr Stringified arguments (including format argument).
 * @param format Format string.
 * @param ...    Format arguments.
 * @return       Number of characters printed, excluding terminating null byte
 *               (the same as s(n)printf).
 */
static inline int ATTRIBUTE_FORMAT((printf, 5, 6))
xsnprintf_(char *str, size_t size, const char *func, const char *argstr,
	   const char *format, ...)
{
	int ret;
	va_list ap;

	va_start(ap, format);
	ret = vsnprintf(str, size, format, ap);
	va_end(ap);

	if (ret < 0 || (unsigned int) ret >= size)
		error_msg_and_die("%s: got unexpected return value %d for "
				  "snprintf(buf, %zu, %s)",
				  func, ret, size, argstr);

	return ret;
}

/**
 * snprintf that dies on (really unexpected) errors and overflows.
 *
 * @param str_  String buffer to print into.
 * @param size_ Size of the string buffer in bytes.
 * @param fmt_  Format string.
 * @param ...   Format arguments.
 */
#define xsnprintf(str_, size_, fmt_, ...) \
	xsnprintf_((str_), (size_), __func__, #fmt_ ", " #__VA_ARGS__, \
		   (fmt_), __VA_ARGS__)

/**
 * Print to a character array buffer and die on (really unexpected) errors and
 * overflows.  Buffer size is obtained with sizeof().
 *
 * @param str_  Character array buffer to print into.
 * @param fmt_  Format string.
 * @param ...   Format arguments.
 */
#define xsprintf(str_, fmt_, ...) \
	xsnprintf((str_), sizeof(str_) + MUST_BE_ARRAY(str_), (fmt_), \
		  __VA_ARGS__)

static inline size_t
get_pos_diff_(char *str, size_t size, char *pos, const char *func,
	   const char *call)
{
	if ((str + size) < str)
		error_msg_and_die("%s: string size overflow (%p+%zu) in %s",
				  func, str, size, call);

	if (pos > (str + size))
		error_msg_and_die("%s: got position (%p) beyond string "
				  "(%p+%zu) in %s",
				  func, pos, str, size, call);

	if (pos < str)
		error_msg_and_die("%s: got position %p before string %p in %s",
				  func, pos, str, call);

	return pos - str;
}

/**
 * Helper function for constructing string in a character array by appending
 * new formatted parts.  Returns new position.  Fails on error or buffer
 * overflow, in line with the rest of x* functions.  Obtains buffer size via
 * sizeof(str_).
 *
 * @param str_  Character array buffer to print into.
 * @param pos_  Current position.
 * @param fmt_  Format string.
 * @param ...   Format arguments.
 * @return      New position.
 */
#define xappendstr(str_, pos_, fmt_, ...) \
	(xsnprintf((pos_), sizeof(str_) + MUST_BE_ARRAY(str_) - \
		   get_pos_diff_((str_), sizeof(str_), (pos_), __func__, \
				 "xappendstr(" #str_ ", " #pos_ ", " #fmt_ ", " \
				 #__VA_ARGS__ ")"), \
		   (fmt_), ##__VA_ARGS__) + (pos_))

#endif /* !STRACE_XSTRING_H */