--- /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);
+}