--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/.hgignore	Tue Aug 01 17:14:37 2023 -0800
@@ -0,0 +1,5 @@
+syntax: regexp
+
+\.[oa]$
+
+^euse-demo/osmo-euse-demo$

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/README	Tue Aug 01 17:14:37 2023 -0800
@@ -0,0 +1,5 @@
+This Hg code repository is Mother Mychaela's little playground for experimenting
+with Osmocom libraries.  The objective is to find out: is it possible to link
+with Osmocom libraries, and thus avail ourselves of their awesome power,
+*without* immersing ourselves in the cesspool of autotools?  I (Mother Mychaela)
+and autotools do not mix!

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/euse-demo/Makefile	Tue Aug 01 17:14:37 2023 -0800
@@ -0,0 +1,13 @@
+CC=	gcc
+CFLAGS=	-O2 -pthread -I/opt/osmocni2/include -I/usr/include/samba-4.0
+PROG=	osmo-euse-demo
+OBJS=	osmo-euse-demo.o
+OSMOLIB=-L/opt/osmocni2/lib -losmo-gsup-client -losmogsm -losmocore -ltalloc
+
+all:	${PROG}
+
+${PROG}:	${OBJS}
+	${CC} -o $@ ${OBJS} ${OSMOLIB}
+
+clean:
+	rm -f *.o ${PROG}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/euse-demo/osmo-euse-demo.c	Tue Aug 01 17:14:37 2023 -0800
@@ -0,0 +1,242 @@
+/* osmo-demo-euse: An External USSD Entity (EUSE) for demo purpose */
+
+/* (C) 2018 by Harald Welte <laforge@gnumonks.org>
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Affero General Public License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+/*
+ * This program illustrates how to implement an external USSD application using
+ * the existing osmocom libraries, particularly libosmocore, libosmogsm and libosmo-gsup-client.
+ *
+ * It will receive any MS-originated USSD message that is routed to it via the HLR, and
+ * simply respond it quoted in the following string: 'You sent "foobar"' (assuming the original
+ * message was 'foobar').
+ */
+
+#include <string.h>
+#include <stdio.h>
+#include <errno.h>
+#include <signal.h>
+
+#include <osmocom/core/msgb.h>
+#include <osmocom/core/select.h>
+#include <osmocom/core/application.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/core/logging.h>
+
+#include <osmocom/gsm/gsup.h>
+#include <osmocom/gsm/gsm0480.h>
+#include <osmocom/gsm/protocol/gsm_04_80.h>
+
+#include <osmocom/gsupclient/gsup_client.h>
+
+/* logging categories */
+enum {
+	DMAIN,
+};
+
+static struct osmo_gsup_client *g_gc;
+
+/*! send a SS/USSD response to a given imsi/session.
+ *  \param[in] gsupc GSUP client connection through which to send
+ *  \param[in] imsi IMSI of the subscriber
+ *  \param[in] session_id Unique identifier of SS session for which this response is
+ *  \param[in] gsup_msg_type GSUP message type (OSMO_GSUP_MSGT_PROC_SS_{REQUEST,RESULT,ERROR})
+ *  \param[in] final Is this the final result (true=END) or an intermediate result (false=CONTINUE)
+ *  \param[in] msg Optional binary/BER encoded SS date (for FACILITY IE). Can be NULL. Freed in
+ *  		   this function call.
+ */
+static int euse_tx_ss(struct osmo_gsup_client *gsupc, const char *imsi, uint32_t session_id,
+		      enum osmo_gsup_message_type gsup_msg_type, bool final, struct msgb *ss_msg)
+{
+	struct osmo_gsup_message resp = {0};
+	struct msgb *resp_msg;
+
+	switch (gsup_msg_type) {
+	case OSMO_GSUP_MSGT_PROC_SS_REQUEST:
+	case OSMO_GSUP_MSGT_PROC_SS_RESULT:
+	case OSMO_GSUP_MSGT_PROC_SS_ERROR:
+		break;
+	default:
+		msgb_free(ss_msg);
+		return -EINVAL;
+	}
+
+	resp.message_type = gsup_msg_type;
+	OSMO_STRLCPY_ARRAY(resp.imsi, imsi);
+	if (final)
+		resp.session_state = OSMO_GSUP_SESSION_STATE_END;
+	else
+		resp.session_state = OSMO_GSUP_SESSION_STATE_CONTINUE;
+	resp.session_id = session_id;
+	if (ss_msg) {
+		resp.ss_info = msgb_data(ss_msg);
+		resp.ss_info_len = msgb_length(ss_msg);
+	}
+
+	resp_msg = gsm0480_msgb_alloc_name(__func__);
+	OSMO_ASSERT(resp_msg);
+	osmo_gsup_encode(resp_msg, &resp);
+	msgb_free(ss_msg);
+	return osmo_gsup_client_send(gsupc, resp_msg);
+}
+
+/*! send a SS/USSD reject to a given IMSI/session.
+ * \param[in] gsupc		GSUP client connection through which to send
+ * \param[in] imsi		IMSI of the subscriber
+ * \param[in] session_id	Unique identifier of SS session for which this response is
+ * \param[in] invoke_id		InvokeID of the request
+ * \param[in] problem_tag	Problem code tag (table 3.13)
+ * \param[in] problem_code	Problem code (table 3.14-3.17)
+ */
+static int euse_tx_ussd_reject(struct osmo_gsup_client *gsupc, const char *imsi, uint32_t session_id,
+				int invoke_id, uint8_t problem_tag, uint8_t problem_code)
+{
+	struct msgb *msg = gsm0480_gen_reject(invoke_id, problem_tag, problem_code);
+	LOGP(DMAIN, LOGL_NOTICE, "Tx %s/0x%08x: Reject(%d, 0x%02x, 0x%02x)\n", imsi, session_id,
+		invoke_id, problem_tag, problem_code);
+	OSMO_ASSERT(msg);
+	return euse_tx_ss(gsupc, imsi, session_id, OSMO_GSUP_MSGT_PROC_SS_RESULT, true, msg);
+}
+
+/*! send a SS/USSD response in 7-bit GSM default alphabet o a given imsi/session.
+ * \param[in] gsupc		GSUP client connection through which to send
+ * \param[in] imsi		IMSI of the subscriber
+ * \param[in] session_id	Unique identifier of SS session for which this response is
+ * \param[in] final		Is this the final result (true=END) or an intermediate result
+ * 				(false=CONTINUE)
+ * \param[in] invoke_id		InvokeID of the request
+ */
+static int euse_tx_ussd_resp_7bit(struct osmo_gsup_client *gsupc, const char *imsi, uint32_t session_id,
+				  bool final, uint8_t invoke_id, const char *text)
+{
+	struct msgb *ss_msg;
+
+	/* encode response; remove L3 header */
+	ss_msg = gsm0480_gen_ussd_resp_7bit(invoke_id, text);
+	LOGP(DMAIN, LOGL_DEBUG, "Tx %s/0x%08x: USSD Result(%d, %s, '%s')\n", imsi, session_id,
+		invoke_id, final ? "END" : "CONTINUE", text);
+	OSMO_ASSERT(ss_msg);
+	return euse_tx_ss(gsupc, imsi, session_id, OSMO_GSUP_MSGT_PROC_SS_RESULT, final, ss_msg);
+}
+
+static int euse_rx_proc_ss_req(struct osmo_gsup_client *gsupc, const struct osmo_gsup_message *gsup)
+{
+	char buf[GSM0480_USSD_7BIT_STRING_LEN+1];
+	struct ss_request req = {0};
+
+	if (gsup->ss_info && gsup->ss_info_len) {
+		if (gsm0480_parse_facility_ie(gsup->ss_info, gsup->ss_info_len, &req)) {
+			return euse_tx_ussd_reject(gsupc, gsup->imsi, gsup->session_id, -1,
+						   GSM_0480_PROBLEM_CODE_TAG_GENERAL,
+						   GSM_0480_GEN_PROB_CODE_BAD_STRUCTURE);
+		}
+	}
+
+	LOGP(DMAIN, LOGL_INFO, "Rx %s/0x%08x: USSD SessionState=%s, OpCode=%s, '%s'\n", gsup->imsi,
+		gsup->session_id, osmo_gsup_session_state_name(gsup->session_state),
+		gsm0480_op_code_name(req.opcode), req.ussd_text);
+
+	/* we only handle single-request-response USSD in this demo */
+	if (gsup->session_state != OSMO_GSUP_SESSION_STATE_BEGIN) {
+		return euse_tx_ussd_reject(gsupc, gsup->imsi, gsup->session_id, req.invoke_id,
+					   GSM_0480_PROBLEM_CODE_TAG_GENERAL,
+					   GSM_0480_GEN_PROB_CODE_UNRECOGNISED);
+	}
+
+	snprintf(buf, sizeof(buf), "You sent \"%s\"", req.ussd_text);
+	return euse_tx_ussd_resp_7bit(gsupc, gsup->imsi, gsup->session_id, true, req.invoke_id, buf);
+}
+
+static int gsupc_read_cb(struct osmo_gsup_client *gsupc, struct msgb *msg)
+{
+	struct osmo_gsup_message gsup_msg = {0};
+	int rc;
+
+	rc = osmo_gsup_decode(msgb_l2(msg), msgb_l2len(msg), &gsup_msg);
+	if (rc < 0) {
+		LOGP(DMAIN, LOGL_ERROR, "Error decoding GSUP: %s\n", msgb_hexdump(msg));
+		return rc;
+	}
+	DEBUGP(DMAIN, "Rx GSUP %s: %s\n", osmo_gsup_message_type_name(gsup_msg.message_type),
+		msgb_hexdump(msg));
+
+	switch (gsup_msg.message_type) {
+	case OSMO_GSUP_MSGT_PROC_SS_REQUEST:
+	case OSMO_GSUP_MSGT_PROC_SS_RESULT:
+		euse_rx_proc_ss_req(gsupc, &gsup_msg);
+		break;
+	case OSMO_GSUP_MSGT_PROC_SS_ERROR:
+		break;
+	default:
+		LOGP(DMAIN, LOGL_DEBUG, "Unhandled GSUP message type %s\n",
+			osmo_gsup_message_type_name(gsup_msg.message_type));
+		break;
+	}
+
+	msgb_free(msg);
+	return 0;
+}
+
+
+static struct log_info_cat default_categories[] = {
+	[DMAIN] = {
+		.name = "DMAIN",
+		.description = "Main Program",
+		.enabled = 1, .loglevel = LOGL_DEBUG,
+	},
+};
+
+static const struct log_info gsup_log_info = {
+	.cat = default_categories,
+	.num_cat = ARRAY_SIZE(default_categories),
+};
+
+static void print_usage(void)
+{
+	printf("Usage: osmo-euse-demo [hlr-ip [hlr-gsup-port]]\n");
+}
+
+int main(int argc, char **argv)
+{
+	char *server_host = "127.0.0.1";
+	uint16_t server_port = OSMO_GSUP_PORT;
+	void *ctx = talloc_named_const(NULL, 0, "demo-euse");
+
+	osmo_init_logging2(ctx, &gsup_log_info);
+
+	printf("argc=%d\n", argc);
+
+	if (argc > 1) {
+		if (!strcmp(argv[1], "--help") || !strcmp(argv[1], "-h")) {
+			print_usage();
+			exit(0);
+		} else
+			server_host = argv[1];
+	}
+	if (argc > 2)
+		server_port = atoi(argv[2]);
+
+	g_gc = osmo_gsup_client_create(ctx, "EUSE-foobar", server_host, server_port, gsupc_read_cb, NULL);
+
+	while (1) {
+		osmo_select_main(0);
+	}
+
+	exit(0);
+}
+