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implement intelligent matching of AMR fmtp 

Change-Id: I5a1e11e762a0ac511085377aeeb0a371fd2940f5
This commit is contained in:
Neels Hofmeyr 2024-01-30 05:52:49 +01:00
parent 314cc11a45
commit 00f8fcbc86
2 changed files with 50 additions and 0 deletions
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49
src/libmsc/sdp_msg.c
View File

@ -22,6 +22,7 @@
*/
#include <string.h>
#include <ctype.h>
#include <errno.h>
#include <osmocom/core/utils.h>
@ -37,6 +38,49 @@ bool sdp_audio_codec_is_set(const struct sdp_audio_codec *a)
return a && a->subtype_name[0];
}
static void strip_whitespace(char *str)
{
char *i = str;
char *o = str;
for (; *i; i++, o++) {
while (isspace(*i))
i++;
*o = *i;
if (!*i)
break;
}
}
static bool amr_fmtp_match(const char *a, const char *b)
{
char a_modeset[32] = {};
char b_modeset[32] = {};
/* octet-align=1. Omission means octet-align=0 */
if (osmo_sdp_fmtp_amr_is_octet_aligned(a) != osmo_sdp_fmtp_amr_is_octet_aligned(b))
return false;
/* mode-set=0,1,2,3,4,5,6,7. Omission of 'mode-set' means, match any and all codec modes. So if either a or b
* have no 'mode-set', it's a match. If both have one, they must be identical to match. We expect the
* mode-set string to be in ascending order. */
if (osmo_sdp_fmtp_get_val(a_modeset, sizeof(a_modeset), a, "mode-set")
&& osmo_sdp_fmtp_get_val(b_modeset, sizeof(b_modeset), b, "mode-set")) {
/* Strip whitespace: We don't know what remote SDP peers may throw at us. There could be whitespace
* around the separators like 'mode-set=2,3 ; octet-align=1', which may show up here as whitespace in
* the value string as "2,3 ", which would mismatch "2,3". */
strip_whitespace(a_modeset);
strip_whitespace(b_modeset);
if (strcmp(a_modeset, b_modeset))
return false;
}
/* TODO: treat other AMR traits, see RFC4867 8.1. Maybe generically match all values that are present?
* So far we have not seen any peer use other values than octet-align and mode-set. */
/* No mismatch found, it's a match */
return true;
}
/* Compare name, rate and fmtp, returning typical cmp result: 0 on match, and -1 / 1 on mismatch.
* If cmp_fmtp is false, do *not* compare the fmtp string; if true, compare fmtp 1:1 as strings.
* If cmp_payload_type is false, do *not* compare the payload_type number.
@ -60,6 +104,11 @@ int sdp_audio_codec_cmp(const struct sdp_audio_codec *a, const struct sdp_audio_
return cmp;
if (cmp_fmtp) {
cmp = strncmp(a->fmtp, b->fmtp, sizeof(a->fmtp));
/* In case of AMR, allow logical matching; we only need to do that if the strings differ. */
if (cmp
&& !strcmp("AMR", a->subtype_name)
&& amr_fmtp_match(a->fmtp, b->fmtp))
cmp = 0;
if (cmp)
return cmp;
}

1
tests/sdp_msg/Makefile.am
View File

@ -17,6 +17,7 @@ AM_LDFLAGS = \
LDADD = \
$(top_builddir)/src/libmsc/libmsc.a \
$(LIBOSMOCORE_LIBS) \
$(LIBOSMOMGCPCLIENT_LIBS) \
$(NULL)
EXTRA_DIST = \