registrars: Allow accepting Re-REGISTERs with equal CSeq

New module setting for both registrar and mid-registrar which controls
the policy on handling same Call-ID REGISTERs, with the same CSeq.

    modparam: allow_dup_cseq
    default:  false (100% backwards-compatible)

Ultimately, this boils down to a trade-off between interoperability and
RFC strictness.  More info in the modparam documentation.

(cherry picked from commit dda9010)
(cherry picked from commit f47c2f4)

Author: liviuchircu

lib/reg/common.c

@@ -28,6 +28,7 @@ int max_username_len = USERNAME_MAX_SIZE;
 int max_domain_len   = DOMAIN_MAX_SIZE;
 int max_aor_len      = MAX_AOR_LEN;
 int max_contact_len  = CONTACT_MAX_SIZE;
+int allow_dup_cseq   = 0;
 
 int reg_init_globals(void)
 {
@@ -38,6 +39,7 @@ int reg_init_globals(void)
 
 	realm_prefix.len = strlen(realm_prefix.s);
 	rcv_param.len = strlen(rcv_param.s);
+	allow_dup_cseq = !!allow_dup_cseq;
 
 	if (expires_max_deviation < 0) {
 		expires_max_deviation = -expires_max_deviation;

lib/reg/common.h

@@ -52,6 +52,7 @@ extern int max_contacts;
 extern int max_username_len;
 extern int max_domain_len;
 extern int max_aor_len;
+extern int allow_dup_cseq;
 extern int max_contact_len;
 
 #define reg_modparams \
@@ -60,6 +61,7 @@ extern int max_contact_len;
 	{"max_domain_len",        INT_PARAM, &max_domain_len}, \
 	{"max_aor_len",           INT_PARAM, &max_aor_len}, \
 	{"max_contact_len",       INT_PARAM, &max_contact_len}, \
+	{"allow_dup_cseq",        INT_PARAM, &allow_dup_cseq}, \
 	{"expires_max_deviation", INT_PARAM, &expires_max_deviation}
 
 /* common registrar init code */
@@ -91,4 +93,6 @@ static inline time_t randomize_expires(unsigned int expires_ts)
 	return ret;
 }
 
+#define REG_CSEQ_ADJUST(_cs) ((_cs) + allow_dup_cseq)
+
 #endif /* __LIB_REG_COMMON_H__ */

lib/reg/doc/reg_modparams.xml

@@ -1,5 +1,30 @@
 <!-- Common registrar modparams-->
 
+	<section id="param_allow_dup_cseq" xreflabel="allow_dup_cseq">
+		<title><varname>allow_dup_cseq</varname> (boolean)</title>
+		<para>
+		Some SIP stacks will re-REGISTER using the same Call-ID and CSeq values.
+		While rejecting such requests is consistent with RFC 3261 § 10.3.7, enabling
+		this parameter instructs the &reg_module; to accept them instead,
+		improving interoperability.
+		</para>
+		<para>
+		<emphasis>
+			Default value is <emphasis>false</emphasis> (duplicate CSeq is rejected).
+		</emphasis>
+		</para>
+		<example>
+		<title>Setting the <varname>allow_dup_cseq</varname> parameter</title>
+		<programlisting format="linespecific">
+...
+# loose RFC 3261 compliance: allow REGISTER requests with duplicate CSeq
+modparam("&reg_module;", "allow_dup_cseq", true)
+...
+		</programlisting>
+		</example>
+	</section>
+
+
 	<section id="param_expires_max_deviation" xreflabel="expires_max_deviation">
 		<title><varname>expires_max_deviation</varname> (integer)</title>
 		<para>

modules/mid_registrar/save.c

@@ -2214,7 +2214,7 @@ static int process_contacts_by_ct(struct sip_msg *msg, urecord_t *urec,
 			return 1;
 		}
 
-		ret = ul.get_ucontact(urec, &ct->uri, ci->callid, ci->cseq,
+		ret = ul.get_ucontact(urec, &ct->uri, ci->callid, REG_CSEQ_ADJUST(ci->cseq),
 			&_sctx->cmatch, &c);
 		if (ret == -1) {
 			LM_ERR("invalid cseq for aor <%.*s>\n",urec->aor.len,urec->aor.s);
@@ -2400,7 +2400,8 @@ static int process_contacts_by_aor(struct sip_msg *req, urecord_t *urec,
 			e = e_out;
 		}
 
-		ret = ul.get_ucontact(urec, &ct->uri, ci->callid, ci->cseq,
+
+		ret = ul.get_ucontact(urec, &ct->uri, ci->callid, REG_CSEQ_ADJUST(ci->cseq),
 			&_sctx->cmatch, &c);
 		if (ret == -1) {
 			LM_ERR("invalid cseq for aor <%.*s>\n",urec->aor.len,urec->aor.s);

modules/registrar/save.c

@@ -399,7 +399,7 @@ static inline int update_contacts(struct sip_msg* _m, urecord_t* _r,
 		calc_contact_expires(_m, _c->expires, &e, _sctx);
 
 		/* search for the contact*/
-		ret = ul.get_ucontact( _r, &_c->uri, ci->callid, ci->cseq,
+		ret = ul.get_ucontact( _r, &_c->uri, ci->callid, REG_CSEQ_ADJUST(ci->cseq),
 			&_sctx->cmatch, &c);
 		if (ret==-1) {
 			LM_ERR("invalid cseq for aor <%.*s>\n",_r->aor.len,_r->aor.s);