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spa/util: add spa_scnprintf to use over snprintf

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Wraps the glibc snprintf/vsnprintf calls, but aborts if given a negative size
and zero-terminates the buffer on error.

The returned value is clipped to size - 1 which avoids issues like the one
fixed in c851349f17.
This commit is contained in:
Peter Hutterer 2021-05-30 20:21:00 +10:00
parent 5a054cfc9e
commit 47c173c83f
2 changed files with 107 additions and 0 deletions
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45
spa/include/spa/utils/string.h
View file

@ -29,6 +29,7 @@
extern "C" {
#endif
#include <stdarg.h>
#include <stdbool.h>
#include <errno.h>
@ -178,6 +179,50 @@ static inline bool spa_atob(const char *str)
return spa_streq(str, "true") || spa_streq(str, "1");
}
/**
* "Safe" version of vsnprintf. Exactly the same as vsnprintf but the
* returned value is clipped to `size - 1` and a negative or zero size
* will abort() the program.
*
* \return The number of bytes printed, capped to `size-1`, or a negative
* number on error.
*/
SPA_PRINTF_FUNC(3, 0)
static inline int spa_vscnprintf(char *buffer, size_t size, const char *format, va_list args)
{
int r;
spa_assert((ssize_t)size > 0);
r = vsnprintf(buffer, size, format, args);
if (SPA_UNLIKELY(r < 0))
buffer[0] = '\0';
if (SPA_LIKELY(r < (ssize_t)size))
return r;
return size - 1;
}
/**
* "Safe" version of snprintf. Exactly the same as snprintf but the
* returned value is clipped to `size - 1` and a negative or zero size
* will abort() the program.
*
* \return The number of bytes printed, capped to `size-1`, or a negative
* number on error.
*/
SPA_PRINTF_FUNC(3, 4)
static inline int spa_scnprintf(char *buffer, size_t size, const char *format, ...)
{
int r;
va_list args;
va_start(args, format);
r = spa_vscnprintf(buffer, size, format, args);
va_end(args);
return r;
}
/**
* Convert \a str to a float and store the result in \a val.
*

62
spa/tests/test-utils.c
View file

@ -23,6 +23,8 @@
*/
#include <locale.h>
#include <unistd.h>
#include <sys/wait.h>
#include <spa/utils/defs.h>
#include <spa/utils/result.h>
@ -752,6 +754,65 @@ static void test_ansi(void)
SPA_ANSI_ITALIC, SPA_ANSI_BOLD_YELLOW, SPA_ANSI_RESET);
}
static void test_snprintf(void)
{
char dest[8];
pid_t pid;
int len;
/* Basic printf */
spa_assert(spa_scnprintf(dest, sizeof(dest), "foo%d%s", 10, "2") == 6);
spa_assert(spa_streq(dest, "foo102"));
/* Print a few strings, make sure dest is truncated and return value
* is the length of the returned string */
spa_assert(spa_scnprintf(dest, sizeof(dest), "1234567") == 7);
spa_assert(spa_streq(dest, "1234567"));
spa_assert(spa_scnprintf(dest, sizeof(dest), "12345678") == 7);
spa_assert(spa_streq(dest, "1234567"));
spa_assert(spa_scnprintf(dest, sizeof(dest), "123456789") == 7);
spa_assert(spa_streq(dest, "1234567"));
/* Same as above, but with printf %s expansion */
spa_assert(spa_scnprintf(dest, sizeof(dest), "%s", "1234567") == 7);
spa_assert(spa_streq(dest, "1234567"));
spa_assert(spa_scnprintf(dest, sizeof(dest), "%s", "12345678") == 7);
spa_assert(spa_streq(dest, "1234567"));
spa_assert(spa_scnprintf(dest, sizeof(dest), "%s", "123456789") == 7);
spa_assert(spa_streq(dest, "1234567"));
spa_assert(spa_scnprintf(dest, 2, "1234567") == 1);
spa_assert(spa_streq(dest, "1"));
spa_assert(spa_scnprintf(dest, 1, "1234567") == 0);
spa_assert(spa_streq(dest, ""));
/* Check for abort on negative/zero size */
for (int i = -2; i <= 0; i++) {
pid = fork();
if (pid == 0) {
close(STDOUT_FILENO);
close(STDERR_FILENO);
spa_assert(spa_scnprintf(dest, (size_t)i, "1234"));
exit(0);
} else {
int r;
int status;
r = waitpid(pid, &status, 0);
spa_assert(r == pid);
spa_assert(WIFSIGNALED(status));
spa_assert(WTERMSIG(status) == SIGABRT);
}
}
/* The "append until buffer is full" use-case */
len = 0;
while ((size_t)len < sizeof(dest) - 1)
len += spa_scnprintf(dest + len, sizeof(dest) - len, "123");
/* and once more for good measure, this should print 0 characters */
len = spa_scnprintf(dest + len, sizeof(dest) - len, "abc");
spa_assert(len == 0);
spa_assert(spa_streq(dest, "1231231"));
}
int main(int argc, char *argv[])
{
setlocale(LC_NUMERIC, "C"); /* For decimal number parsing */
@ -768,6 +829,7 @@ int main(int argc, char *argv[])
test_strtof();
test_strtod();
test_streq();
test_snprintf();
test_atob();
test_ansi();
return 0;