2/2: fixup: add osmo_gsup_peer_id with type enum and union

During code review it was requested to insert an ability to handle different
kinds of peer id, in order to be able to add a Global Title in the future.

Add this, but only in the publicly visible API. For osmo-hlr internal code, I
intend to push implementing this into the future, when a different peer
identification actually gets introduced.

This way we don't need to implement it now in all osmo-hlr code paths (save
time now), but still make all API users aware that this type may be extended in
the future.

Change-Id: Ide9dcdca283ab989240cfc6e53e9211862a199c5
diff --git a/include/osmocom/gsupclient/gsup_peer_id.h b/include/osmocom/gsupclient/gsup_peer_id.h
new file mode 100644
index 0000000..f67671b
--- /dev/null
+++ b/include/osmocom/gsupclient/gsup_peer_id.h
@@ -0,0 +1,64 @@
+/* Copyright 2019 by sysmocom s.f.m.c. GmbH <info@sysmocom.de>
+ *
+ * All Rights Reserved
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 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 General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+#include <unistd.h>
+#include <stdint.h>
+#include <osmocom/core/utils.h>
+
+/*! IPA Name: Arbitrary length blob, not necessarily zero-terminated.
+ * In osmo-hlr, struct hlr_subscriber is mostly used as static reference and cannot serve as talloc context, which is
+ * why this is also implemented as a fixed-maximum-size buffer instead of a talloc'd arbitrary sized buffer.
+ * NOTE: The length of val may be extended in the future if it becomes necessary.
+ * At the time of writing, this holds IPA unit name strings of very limited length.
+ */
+struct osmo_ipa_name {
+	size_t len;
+	uint8_t val[128];
+};
+
+bool osmo_ipa_name_is_empty(struct osmo_ipa_name *ipa_name);
+int osmo_ipa_name_set(struct osmo_ipa_name *ipa_name, const uint8_t *val, size_t len);
+int osmo_ipa_name_set_str(struct osmo_ipa_name *ipa_name, const char *str_fmt, ...);
+int osmo_ipa_name_cmp(const struct osmo_ipa_name *a, const struct osmo_ipa_name *b);
+const char *osmo_ipa_name_to_str(const struct osmo_ipa_name *ipa_name);
+
+enum osmo_gsup_peer_id_type {
+	OSMO_GSUP_PEER_ID_EMPTY=0,
+	OSMO_GSUP_PEER_ID_IPA_NAME,
+	/* OSMO_GSUP_PEER_ID_GLOBAL_TITLE, <-- currently not implemented, but likely future possibility */
+};
+
+extern const struct value_string osmo_gsup_peer_id_type_names[];
+static inline const char *osmo_gsup_peer_id_type_name(enum osmo_gsup_peer_id_type val)
+{ return get_value_string(osmo_gsup_peer_id_type_names, val); }
+
+struct osmo_gsup_peer_id {
+	enum osmo_gsup_peer_id_type type;
+	union {
+		struct osmo_ipa_name ipa_name;
+	};
+};
+
+bool osmo_gsup_peer_id_is_empty(struct osmo_gsup_peer_id *gsup_peer_id);
+int osmo_gsup_peer_id_set(struct osmo_gsup_peer_id *gsup_peer_id, enum osmo_gsup_peer_id_type type,
+			  const uint8_t *val, size_t len);
+int osmo_gsup_peer_id_set_str(struct osmo_gsup_peer_id *gsup_peer_id, enum osmo_gsup_peer_id_type type,
+			      const char *str_fmt, ...);
+int osmo_gsup_peer_id_cmp(const struct osmo_gsup_peer_id *a, const struct osmo_gsup_peer_id *b);
+const char *osmo_gsup_peer_id_to_str(const struct osmo_gsup_peer_id *gsup_peer_id);