--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/libsip/uas_basic.c	Tue Sep 06 20:29:44 2022 -0800
@@ -0,0 +1,88 @@
+/*
+ * Here we implement some essential UAS functions.
+ */
+
+#include <ctype.h>
+#include <string.h>
+#include <strings.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include "parse.h"
+#include "uas_basic.h"
+#include "out_msg.h"
+
+extern char *get_single_header();
+
+uas_get_basic_headers(msg, ess)
+	struct sip_pkt_rx *msg;
+	struct uas_parse_hdrs *ess;
+{
+	char *hval, *cp;
+	int dup_flag = 0;
+
+	hval = get_single_header(msg, "Call-ID", "i", &dup_flag);
+	if (!hval || dup_flag) {
+		ess->error_field = "Call-ID";
+		return(-1);
+	}
+	ess->call_id = hval;
+	hval = get_single_header(msg, "CSeq", (char *) 0, &dup_flag);
+	if (!hval || dup_flag) {
+bad_cseq:	ess->error_field = "CSeq";
+		return(-1);
+	}
+	if (!isdigit(*hval))
+		goto bad_cseq;
+	ess->cseq_num = strtoul(hval, &cp, 10);
+	if (*cp) {
+		if (!isspace(*cp))
+			goto bad_cseq;
+		while (isspace(*cp))
+			cp++;
+		if (strcmp(cp, msg->req_method))
+			goto bad_cseq;
+	}
+	hval = get_single_header(msg, "From", "f", &dup_flag);
+	if (!hval || dup_flag) {
+		ess->error_field = "From";
+		return(-1);
+	}
+	ess->from = hval;
+	hval = get_single_header(msg, "To", "t", &dup_flag);
+	if (!hval || dup_flag) {
+		ess->error_field = "To";
+		return(-1);
+	}
+	ess->to = hval;
+	hval = get_single_header(msg, "Via", "v", &dup_flag);
+	if (!hval || dup_flag) {
+		ess->error_field = "Via";
+		return(-1);
+	}
+	ess->via = hval;
+	return(0);
+}
+
+add_resp_basic_headers(msg, ess, req_method)
+	struct sip_msg_out *msg;
+	struct uas_parse_hdrs *ess;
+	char *req_method;
+{
+	char cseq_str[80];
+	int rc;
+
+	rc = out_msg_add_header(msg, "From", ess->from);
+	if (rc < 0)
+		return rc;
+	rc = out_msg_add_header(msg, "To", ess->to);
+	if (rc < 0)
+		return rc;
+	rc = out_msg_add_header(msg, "Call-ID", ess->call_id);
+	if (rc < 0)
+		return rc;
+	sprintf(cseq_str, "%u %.64s", ess->cseq_num, req_method);
+	rc = out_msg_add_header(msg, "CSeq", cseq_str);
+	if (rc < 0)
+		return rc;
+	return out_msg_add_header(msg, "Via", ess->via);
+}