Perform case insensitive comparisons for T.38 attributes

RFC5347 section 2.5.2 states the following:
...
The attribute "T38MaxBitRate" was once incorrectly registered with
IANA as "T38maxBitRate" (lower-case "m"). In accordance with T.38
examples and common implementation practice, the form "T38MaxBitRate"
SHOULD be generated by implementations conforming to this package.
In general, it is RECOMMENDED that implementations of this package
accept lowercase, uppercase, and mixed upper/lowercase encodings of
all the T.38 attributes.
...

Asterisk currently does not perform case insensitive matching on the T.38
attributes. This causes the T38MaxBitRate attribute to be negotiated at
2400 baud instead of 14400 (or whatever value you actually wanted).

This patch makes it so that when we compare T.38 attributes, we do so in a case
insensitive fashion.

Note that while the issue reporter did not directly write the patch, they
contributed to it (and would have provided one themselves if the license had
gone through a tad faster), and hence get attribution for it.

Review: https://reviewboard.asterisk.org/r/2298/

(closes issue ASTERISK-20897)
Reported by: Eric Hill
Tested by: Eric Hill
patches:
  -- uploaded by Eric Hill
........

Merged revisions 380458 from http://svn.asterisk.org/svn/asterisk/branches/1.8
........

Merged revisions 380465 from http://svn.asterisk.org/svn/asterisk/branches/11


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@380479 65c4cc65-6c06-0410-ace0-fbb531ad65f3

1 files changed, 23 insertions, 12 deletions

diff --git a/channels/chan_sip.c b/channels/chan_sip.c
index 6f046b58c..b547edb23 100644
--- a/channels/chan_sip.c
+++ b/channels/chan_sip.c
@@ -11228,15 +11228,26 @@ static int process_sdp_a_image(const char *a, struct sip_pvt *p)
 	int found = FALSE;
 	char s[256];
 	unsigned int x;
+	char *attrib = ast_strdupa(a);
+	char *pos;
 
 	if (initialize_udptl(p)) {
 		return found;
 	}
 
-	if ((sscanf(a, "T38FaxMaxBuffer:%30u", &x) == 1)) {
+	/* Due to a typo in an IANA registration of one of the T.38 attributes,
+	 * RFC5347 section 2.5.2 recommends that all T.38 attributes be parsed in
+	 * a case insensitive manner. Hence, the importance of proof reading (and
+	 * code reviews).
+	 */
+	for (pos = attrib; *pos; ++pos) {
+		*pos = tolower(*pos);
+	}
+
+	if ((sscanf(attrib, "t38faxmaxbuffer:%30u", &x) == 1)) {
 		ast_debug(3, "MaxBufferSize:%d\n", x);
 		found = TRUE;
-	} else if ((sscanf(a, "T38MaxBitRate:%30u", &x) == 1) || (sscanf(a, "T38FaxMaxRate:%30u", &x) == 1)) {
+	} else if ((sscanf(attrib, "t38maxbitrate:%30u", &x) == 1) || (sscanf(attrib, "t38faxmaxrate:%30u", &x) == 1)) {
 		ast_debug(3, "T38MaxBitRate: %d\n", x);
 		switch (x) {
 		case 14400:
@@ -11259,11 +11270,11 @@ static int process_sdp_a_image(const char *a, struct sip_pvt *p)
 			break;
 		}
 		found = TRUE;
-	} else if ((sscanf(a, "T38FaxVersion:%30u", &x) == 1)) {
+	} else if ((sscanf(attrib, "t38faxversion:%30u", &x) == 1)) {
 		ast_debug(3, "FaxVersion: %u\n", x);
 		p->t38.their_parms.version = x;
 		found = TRUE;
-	} else if ((sscanf(a, "T38FaxMaxDatagram:%30u", &x) == 1) || (sscanf(a, "T38MaxDatagram:%30u", &x) == 1)) {
+	} else if ((sscanf(attrib, "t38faxmaxdatagram:%30u", &x) == 1) || (sscanf(attrib, "t38maxdatagram:%30u", &x) == 1)) {
 		/* override the supplied value if the configuration requests it */
 		if (((signed int) p->t38_maxdatagram >= 0) && ((unsigned int) p->t38_maxdatagram > x)) {
 			ast_debug(1, "Overriding T38FaxMaxDatagram '%d' with '%d'\n", x, p->t38_maxdatagram);
@@ -11272,8 +11283,8 @@ static int process_sdp_a_image(const char *a, struct sip_pvt *p)
 		ast_debug(3, "FaxMaxDatagram: %u\n", x);
 		ast_udptl_set_far_max_datagram(p->udptl, x);
 		found = TRUE;
-	} else if ((strncmp(a, "T38FaxFillBitRemoval", 20) == 0)) {
-		if (sscanf(a, "T38FaxFillBitRemoval:%30u", &x) == 1) {
+	} else if ((strncmp(attrib, "t38faxfillbitremoval", sizeof("t38faxfillbitremoval") - 1) == 0)) {
+		if (sscanf(attrib, "t38faxfillbitremoval:%30u", &x) == 1) {
 			ast_debug(3, "FillBitRemoval: %d\n", x);
 			if (x == 1) {
 				p->t38.their_parms.fill_bit_removal = TRUE;
@@ -11283,8 +11294,8 @@ static int process_sdp_a_image(const char *a, struct sip_pvt *p)
 			p->t38.their_parms.fill_bit_removal = TRUE;
 		}
 		found = TRUE;
-	} else if ((strncmp(a, "T38FaxTranscodingMMR", 20) == 0)) {
-		if (sscanf(a, "T38FaxTranscodingMMR:%30u", &x) == 1) {
+	} else if ((strncmp(attrib, "t38faxtranscodingmmr", sizeof("t38faxtranscodingmmr") - 1) == 0)) {
+		if (sscanf(attrib, "t38faxtranscodingmmr:%30u", &x) == 1) {
 			ast_debug(3, "Transcoding MMR: %d\n", x);
 			if (x == 1) {
 				p->t38.their_parms.transcoding_mmr = TRUE;
@@ -11294,8 +11305,8 @@ static int process_sdp_a_image(const char *a, struct sip_pvt *p)
 			p->t38.their_parms.transcoding_mmr = TRUE;
 		}
 		found = TRUE;
-	} else if ((strncmp(a, "T38FaxTranscodingJBIG", 21) == 0)) {
-		if (sscanf(a, "T38FaxTranscodingJBIG:%30u", &x) == 1) {
+	} else if ((strncmp(attrib, "t38faxtranscodingjbig", sizeof("t38faxtranscodingjbig") - 1) == 0)) {
+		if (sscanf(attrib, "t38faxtranscodingjbig:%30u", &x) == 1) {
 			ast_debug(3, "Transcoding JBIG: %d\n", x);
 			if (x == 1) {
 				p->t38.their_parms.transcoding_jbig = TRUE;
@@ -11305,14 +11316,14 @@ static int process_sdp_a_image(const char *a, struct sip_pvt *p)
 			p->t38.their_parms.transcoding_jbig = TRUE;
 		}
 		found = TRUE;
-	} else if ((sscanf(a, "T38FaxRateManagement:%255s", s) == 1)) {
+	} else if ((sscanf(attrib, "t38faxratemanagement:%255s", s) == 1)) {
 		ast_debug(3, "RateManagement: %s\n", s);
 		if (!strcasecmp(s, "localTCF"))
 			p->t38.their_parms.rate_management = AST_T38_RATE_MANAGEMENT_LOCAL_TCF;
 		else if (!strcasecmp(s, "transferredTCF"))
 			p->t38.their_parms.rate_management = AST_T38_RATE_MANAGEMENT_TRANSFERRED_TCF;
 		found = TRUE;
-	} else if ((sscanf(a, "T38FaxUdpEC:%255s", s) == 1)) {
+	} else if ((sscanf(attrib, "t38faxudpec:%255s", s) == 1)) {
 		ast_debug(3, "UDP EC: %s\n", s);
 		if (!strcasecmp(s, "t38UDPRedundancy")) {
 			ast_udptl_set_error_correction_scheme(p->udptl, UDPTL_ERROR_CORRECTION_REDUNDANCY);