--- a/sip-manual-out/Makefile	Sat Oct 08 23:01:32 2022 -0800
+++ b/sip-manual-out/Makefile	Sat Oct 08 23:52:08 2022 -0800
@@ -1,8 +1,8 @@
 CC=	gcc
 CFLAGS=	-O2
 PROG=	sip-manual-out
-OBJS=	bye_in.o disc_cmd.o dummy_rtp.o main.o readconf.o sip_log.o sip_udp.o \
-	uac.o uas.o
+OBJS=	bye_in.o disc_cmd.o dummy_rtp.o main.o readconf.o reinvite.o sip_log.o \
+	sip_udp.o uac.o uas.o
 LIBS=	../libsip/libsip.a ../libutil/libutil.a
 INSTBIN=/usr/local/bin
 

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/sip-manual-out/reinvite.c	Sat Oct 08 23:52:08 2022 -0800
@@ -0,0 +1,70 @@
+/*
+ * Here we handle incoming INVITE requests in the UAS role: even though
+ * we are strictly outbound, BulkVS servers will send us periodic
+ * re-INVITEs as keepalives, and we have to play along.
+ */
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netinet/in.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <strings.h>
+#include "../libsip/parse.h"
+#include "../libsip/uas_basic.h"
+#include "../libsip/out_msg.h"
+
+extern char call_id[];
+
+static void
+invite_correct_call(req, ess, sin)
+	struct sip_pkt_rx *req;
+	struct uas_parse_hdrs *ess;
+	struct sockaddr_in *sin;
+{
+	struct sip_msg_out resp;
+	int rc;
+
+	printf("Received re-INVITE for our call, responding with 200\n");
+	start_response_out_msg(&resp, "200 OK");
+	rc = add_resp_basic_headers(&resp, ess, req->req_method);
+	if (rc < 0) {
+		fprintf(stderr, "sending 200 response: msg length exceeded\n");
+		return;
+	}
+	out_msg_finish(&resp);
+	sip_tx_packet(&resp, sin);
+}
+
+static void
+invite_unknown_call(req, ess, sin)
+	struct sip_pkt_rx *req;
+	struct uas_parse_hdrs *ess;
+	struct sockaddr_in *sin;
+{
+	struct sip_msg_out resp;
+	int rc;
+
+	printf("Received INVITE for unknown call, responding with 405\n");
+	start_response_out_msg(&resp, "405 This gateway is outbound only");
+	rc = add_resp_basic_headers(&resp, ess, req->req_method);
+	if (rc < 0) {
+		fprintf(stderr, "sending 405 response: msg length exceeded\n");
+		return;
+	}
+	out_msg_finish(&resp);
+	sip_tx_packet(&resp, sin);
+}
+
+void
+handle_invite_req(req, ess, sin)
+	struct sip_pkt_rx *req;
+	struct uas_parse_hdrs *ess;
+	struct sockaddr_in *sin;
+{
+	if (!strcmp(ess->call_id, call_id))
+		invite_correct_call(req, ess, sin);
+	else
+		invite_unknown_call(req, ess, sin);
+}

--- a/sip-manual-out/uas.c	Sat Oct 08 23:01:32 2022 -0800
+++ b/sip-manual-out/uas.c	Sat Oct 08 23:52:08 2022 -0800
@@ -30,7 +30,7 @@
 			"sending 501 error: response length exceeded\n");
 		return;
 	}
-	rc = out_msg_add_header(&resp, "Allow", "BYE");
+	rc = out_msg_add_header(&resp, "Allow", "INVITE,ACK,BYE");
 	if (rc < 0)
 		goto too_long;
 	out_msg_finish(&resp);
@@ -52,10 +52,12 @@
 		return;
 	}
 	/* dispatch by method */
-	if (!strcmp(msg->req_method, "BYE"))
+	if (!strcmp(msg->req_method, "INVITE"))
+		handle_invite_req(msg, &ess, sin);
+	else if (!strcmp(msg->req_method, "ACK"))
+		printf("Received ACK request, swallowing it\n");
+	else if (!strcmp(msg->req_method, "BYE"))
 		handle_bye_req(msg, &ess, sin);
-	else if (!strcmp(msg->req_method, "ACK"))
-		printf("Received unexpected ACK, swallowing it\n");
 	else
 		unsupported_method(msg, &ess, sin);
 }