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add OSMO_STRBUF_PRINTF() 

We are using macros like this or different workarounds in libmsc. In the course
of implementing inter-MSC handover, I am encountering yet another such
situation of appending multiple strings to a limited char buffer. Standardize.

Add a unit test to utils_test.c.

Change-Id: I2497514e26c5e7a5d88985fc7e58343be1a027b2
This commit is contained in:
Neels Hofmeyr 2019-02-11 20:32:06 +01:00 committed by Neels Hofmeyr
parent 8667f7a815
commit 2cbe25f484
3 changed files with 188 additions and 0 deletions
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85
include/osmocom/core/utils.h
View File

@ -145,4 +145,89 @@ uint32_t osmo_isqrt32(uint32_t x);
const char osmo_luhn(const char* in, int in_len);
/*! State for OSMO_STRBUF_APPEND() and OSMO_STRBUF_PRINTF(). See there for examples. */
struct osmo_strbuf {
/*! Point to the start of a string buffer. */
char *buf;
/*! Total sizeof() the buffer buf points at. */
size_t len;
/*! Current writing position in buf (end of the string written so far). */
char *pos;
/*! After all OSMO_STRBUF_APPEND operations, reflects the total number of characters that would be written had
* buf been large enough. Like snprintf()'s return value, this does not include the terminating nul character.
* Hence, to allocate an adequately sized buffer, add 1 to this number. */
size_t chars_needed;
};
/*! Append a string to a buffer, as printed by an snprintf()-like function and with similar bounds checking.
* Make sure to never write past the end of the buffer, and collect the total size that would be needed.
*
* // an example function implementation to append: write N spaces.
* int print_spaces(char *dst, size_t dst_len, int n)
* {
* int i;
* if (n < 0)
* return -EINVAL;
* for (i = 0; i < n && i < dst_len; i++)
* dst[i] = ' ';
* if (dst_len)
* dst[OSMO_MIN(dst_len - 1, n)] = '\0';
* // return the n that we would have liked to write if space were available:
* return n;
* }
*
* // append above spaces as well as an snprintf()
* void strbuf_example()
* {
* char buf[23];
* struct osmo_strbuf sb = { .buf = buf, .len = sizeof(buf) };
*
* OSMO_STRBUF_APPEND(sb, print_spaces, 5);
* OSMO_STRBUF_APPEND(sb, snprintf, "The answer is %d but what is the question?", 42);
* OSMO_STRBUF_APPEND(sb, print_spaces, 423423);
*
* printf("%s\n", buf);
* printf("would have needed %zu bytes\n", sb.chars_needed);
* }
*
* \param[inout] STRBUF A struct osmo_strbuf instance.
* \param[in] func A function with a signature of int func(char *dst, size_t dst_len [, args]) with semantics like
* snprintf().
* \param[in] args Arguments passed to func, if any.
*/
#define OSMO_STRBUF_APPEND(STRBUF, func, args...) do { \
if (!(STRBUF).pos) \
(STRBUF).pos = (STRBUF).buf; \
size_t remain = (STRBUF).buf ? (STRBUF).len - ((STRBUF).pos - (STRBUF).buf) : 0; \
int l = func((STRBUF).pos, remain, ##args); \
if (l < 0 || l > remain) \
(STRBUF).pos = (STRBUF).buf + (STRBUF).len; \
else \
(STRBUF).pos += l; \
if (l > 0) \
(STRBUF).chars_needed += l; \
} while(0)
/*! Shortcut for OSMO_STRBUF_APPEND() invocation using snprintf().
*
* int strbuf_example2(char *buf, size_t buflen)
* {
* int i;
* struct osmo_strbuf sb = { .buf = buf, .len = buflen };
*
* OSMO_STRBUF_PRINTF(sb, "T minus");
* for (i = 10; i; i--)
* OSMO_STRBUF_PRINTF(sb, " %d", i);
* OSMO_STRBUF_PRINTF(sb, " ... Lift off!");
*
* return sb.chars_needed;
* }
*
* \param[inout] STRBUF A struct osmo_strbuf instance.
* \param[in] fmt Format string passed to snprintf.
* \param[in] args Additional arguments passed to snprintf, if any.
*/
#define OSMO_STRBUF_PRINTF(STRBUF, fmt, args...) \
OSMO_STRBUF_APPEND(STRBUF, snprintf, fmt, ##args)
/*! @} */

86
tests/utils/utils_test.c
View File

@ -33,6 +33,7 @@
#include <netinet/in.h>
#include <arpa/inet.h>
#include <errno.h>
#include <limits.h>
static void hexdump_test(void)
{
@ -936,6 +937,90 @@ static void osmo_str_tolowupper_test()
OSMO_ASSERT(ok);
}
/* Copy of the examples from OSMO_STRBUF_APPEND() */
int print_spaces(char *dst, size_t dst_len, int argument)
{
int i;
if (argument < 0)
return -EINVAL;
for (i = 0; i < argument && i < dst_len; i++)
dst[i] = ' ';
if (dst_len)
dst[OSMO_MIN(dst_len - 1, argument)] = '\0';
return argument;
}
void strbuf_example(char *buf, size_t buflen)
{
struct osmo_strbuf sb = { .buf = buf, .len = buflen };
OSMO_STRBUF_APPEND(sb, print_spaces, 5);
OSMO_STRBUF_APPEND(sb, snprintf, "The answer is %d but what is the question?", 42);
OSMO_STRBUF_APPEND(sb, print_spaces, 423423);
printf("%s\n", buf);
printf("would have needed %zu bytes\n", sb.chars_needed);
}
/* Copy of the examples from OSMO_STRBUF_PRINTF() */
int strbuf_example2(char *buf, size_t buflen)
{
int i;
struct osmo_strbuf sb = { .buf = buf, .len = buflen };
OSMO_STRBUF_PRINTF(sb, "T minus");
for (i = 10; i; i--)
OSMO_STRBUF_PRINTF(sb, " %d", i);
OSMO_STRBUF_PRINTF(sb, " ... Lift off!");
return sb.chars_needed;
}
int strbuf_cascade(char *buf, size_t buflen)
{
struct osmo_strbuf sb = { .buf = buf, .len = buflen };
OSMO_STRBUF_APPEND(sb, strbuf_example2);
OSMO_STRBUF_PRINTF(sb, " -- ");
OSMO_STRBUF_APPEND(sb, strbuf_example2);
OSMO_STRBUF_PRINTF(sb, " -- ");
OSMO_STRBUF_APPEND(sb, strbuf_example2);
return sb.chars_needed;
}
void strbuf_test()
{
char buf[256];
int rc;
printf("\n%s\n", __func__);
printf("OSMO_STRBUF_APPEND():\n");
strbuf_example(buf, 23);
printf("\nOSMO_STRBUF_PRINTF():\n");
rc = strbuf_example2(buf, 23);
printf("1: (need %d chars, had size=23) %s\n", rc, buf);
rc = strbuf_example2(buf, rc);
printf("2: (need %d chars, had size=%d) %s\n", rc, rc, buf);
rc = strbuf_example2(buf, rc + 1);
printf("3: (need %d chars, had size=%d+1) %s\n", rc, rc, buf);
rc = strbuf_example2(buf, 0);
snprintf(buf, sizeof(buf), "0x2b 0x2b 0x2b...");
printf("4: (need %d chars, had size=0) %s\n", rc, buf);
rc = strbuf_example2(NULL, 99);
printf("5: (need %d chars, had NULL buffer)\n", rc);
printf("\ncascade:\n");
rc = strbuf_cascade(buf, sizeof(buf));
printf("(need %d chars)\n%s\n", rc, buf);
rc = strbuf_cascade(buf, 63);
printf("(need %d chars, had size=63) %s\n", rc, buf);
}
int main(int argc, char **argv)
{
@ -954,5 +1039,6 @@ int main(int argc, char **argv)
isqrt_test();
osmo_sockaddr_to_str_and_uint_test();
osmo_str_tolowupper_test();
strbuf_test();
return 0;
}

17
tests/utils/utils_test.ok
View File

@ -325,3 +325,20 @@ osmo_str_toupper_buf(28, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!@
= 62, "ABCDEFGHIJKLMNOPQRSTUVWXYZA"
osmo_str_toupper_buf(28, "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ!@#$%^&*()", in-place)
= 27, "ABCDEFGHIJKLMNOPQRSTUVWXYZA"
strbuf_test
OSMO_STRBUF_APPEND():
The answer is 42
would have needed 423470 bytes
OSMO_STRBUF_PRINTF():
1: (need 42 chars, had size=23) T minus 10 9 8 7 6 5 4
2: (need 42 chars, had size=42) T minus 10 9 8 7 6 5 4 3 2 1 ... Lift off
3: (need 42 chars, had size=42+1) T minus 10 9 8 7 6 5 4 3 2 1 ... Lift off!
4: (need 42 chars, had size=0) 0x2b 0x2b 0x2b...
5: (need 42 chars, had NULL buffer)
cascade:
(need 134 chars)
T minus 10 9 8 7 6 5 4 3 2 1 ... Lift off! -- T minus 10 9 8 7 6 5 4 3 2 1 ... Lift off! -- T minus 10 9 8 7 6 5 4 3 2 1 ... Lift off!
(need 134 chars, had size=63) T minus 10 9 8 7 6 5 4 3 2 1 ... Lift off! -- T minus 10 9 8 7