dialog: don't allow RE-INVITE and OPTIONS pinging at the same time

Enabling both RE-INVITE and OPTIONS pinging for the same endpoint causes
issues with the CSEQ value in:
* ACK (incremented value compared to the corresponding INVITE)
* INVITE and OPTIONS (decreasing values between the requests), in case
  races occur between computing the new CSEQ values and sending the messages.

modules/dialog/dialog.c

@@ -1011,6 +1011,14 @@ static int w_create_dialog(struct sip_msg *req, str *flags_str)
 
 	flags = flags_str? parse_create_dlg_flags(flags_str): 0;
 
+	/* don't allow both Re-INVITE and OPTIONS pinging */
+	if ((flags & (DLG_FLAG_PING_CALLER|DLG_FLAG_REINVITE_PING_CALLER)) ==
+		(DLG_FLAG_PING_CALLER|DLG_FLAG_REINVITE_PING_CALLER))
+		flags &= ~DLG_FLAG_PING_CALLER;
+	if ((flags & (DLG_FLAG_PING_CALLEE|DLG_FLAG_REINVITE_PING_CALLEE)) ==
+		(DLG_FLAG_PING_CALLEE|DLG_FLAG_REINVITE_PING_CALLEE))
+		flags &= ~DLG_FLAG_PING_CALLEE;
+
 	t = d_tmb.t_gett();
 	if (dlg_create_dialog( (t==T_UNDEFINED)?NULL:t, req, flags)!=0)
 		return -1;

modules/dialog/doc/dialog_admin.xml

@@ -1411,6 +1411,11 @@ modparam("dialog", "replicate_profiles_expire", 10)
 			</para></listitem>
 		</itemizedlist>
 		<para>
+		NOTE: both RE-INVITE and OPTIONS pinging cannot be enabled at the same time
+		for a single dialog leg. If both flags ("<emphasis>PR</emphasis>" or
+		"<emphasis>pr</emphasis>") are provided only RE-INVITE pinging will be used.
+		</para>
+		<para>
 		The function returns true if the dialog was successfully created or
 		if the dialog was previously created.
 		</para>