libosmo-gtlv: add C code generator for IE structs and arrays

Defining a protocol of message types with lists of IEs bears a lot of
repetitive, copy-paste-error-prone writing out of data structures.
Add a third layer to libosmo-gtlv, which allows helpful code generation.

By non-repetitive data structures that briefly describe the protocol's
messages and IEs, generate possibly repetitive IE list arrays and
decoded-struct definitions automatically, avoiding grunt work errors.

I tried C macros for this at first, but it became too convoluted.
Generating C code that can be read and grepped makes things easier.

A usage example is found in tests/libosmo-gtlv/test_gtlv_gen/.

Related: SYS#5599
Change-Id: Ifb3ea54d2797ce060b95834aa117725ec2d6c4cf

7 files changed, 850 insertions, 0 deletions

diff --git a/tests/libosmo-gtlv/Makefile.am b/tests/libosmo-gtlv/Makefile.am
index 6d85334..392a73e 100644
--- a/tests/libosmo-gtlv/Makefile.am
+++ b/tests/libosmo-gtlv/Makefile.am
@@ -1,3 +1,7 @@
+SUBDIRS = \
+	test_gtlv_gen \
+	$(NULL)
+
 AM_CPPFLAGS = \
 	$(all_includes) \
 	-I$(top_srcdir)/include \
@@ -40,3 +44,4 @@ gtlv_dec_enc_test_LDADD = \
 update_exp:
 	$(builddir)/gtlv_test >$(srcdir)/gtlv_test.ok
 	$(builddir)/gtlv_dec_enc_test >$(srcdir)/gtlv_dec_enc_test.ok
+	$(MAKE) -C test_gtlv_gen update_exp
diff --git a/tests/libosmo-gtlv/test_gtlv_gen/Makefile.am b/tests/libosmo-gtlv/test_gtlv_gen/Makefile.am
new file mode 100644
index 0000000..0d27292
--- /dev/null
+++ b/tests/libosmo-gtlv/test_gtlv_gen/Makefile.am
@@ -0,0 +1,60 @@
+AM_CPPFLAGS = \
+	$(all_includes) \
+	-I$(top_srcdir)/include \
+	-I$(bulddir) \
+	$(NULL)
+
+AM_CFLAGS = \
+	-Wall \
+	$(LIBOSMOCORE_CFLAGS) \
+	$(NULL)
+
+noinst_PROGRAMS = \
+	gen__myproto_ies_auto \
+	gtlv_gen_test \
+	$(NULL)
+
+EXTRA_DIST = \
+	myproto_ies_custom.h \
+	gtlv_gen_test.ok \
+	$(NULL)
+
+BUILT_SOURCES = \
+	myproto_ies_auto.h \
+	myproto_ies_auto.c \
+	$(NULL)
+
+CLEANFILES = \
+	myproto_ies_auto.h \
+	myproto_ies_auto.c \
+	$(NULL)
+
+gen__myproto_ies_auto_SOURCES = \
+	gen__myproto_ies_auto.c \
+	myproto_ies_custom.c \
+	$(NULL)
+
+gen__myproto_ies_auto_LDADD = \
+	$(top_builddir)/src/libosmo-gtlv/libosmo-gtlv.a \
+	$(LIBOSMOCORE_LIBS) \
+	$(NULL)
+
+myproto_ies_auto.h: $(builddir)/gen__myproto_ies_auto
+	$(builddir)/gen__myproto_ies_auto h > $(builddir)/myproto_ies_auto.h
+myproto_ies_auto.c: $(builddir)/gen__myproto_ies_auto
+	$(builddir)/gen__myproto_ies_auto c > $(builddir)/myproto_ies_auto.c
+
+gtlv_gen_test_SOURCES = \
+	gtlv_gen_test.c \
+	myproto_ies_custom.c \
+	myproto_ies_auto.c \
+	$(NULL)
+
+gtlv_gen_test_LDADD = \
+	$(top_builddir)/src/libosmo-gtlv/libosmo-gtlv.a \
+	$(LIBOSMOCORE_LIBS) \
+	$(NULL)
+
+.PHONY: update_exp
+update_exp:
+	$(builddir)/gtlv_gen_test >$(srcdir)/gtlv_gen_test.ok
diff --git a/tests/libosmo-gtlv/test_gtlv_gen/gen__myproto_ies_auto.c b/tests/libosmo-gtlv/test_gtlv_gen/gen__myproto_ies_auto.c
new file mode 100644
index 0000000..75d657d
--- /dev/null
+++ b/tests/libosmo-gtlv/test_gtlv_gen/gen__myproto_ies_auto.c
@@ -0,0 +1,114 @@
+/*
+ * (C) 2021-2022 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved.
+ *
+ * Author: Neels Janosch Hofmeyr <nhofmeyr@sysmocom.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ *  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/>.
+ *
+ */
+
+#include <stdbool.h>
+#include <stdio.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/core/linuxlist.h>
+#include <osmocom/core/talloc.h>
+#include <osmocom/gtlv/gtlv_gen.h>
+
+#define O OSMO_GTLV_GEN_O
+#define M OSMO_GTLV_GEN_M
+#define O_MULTI OSMO_GTLV_GEN_O_MULTI
+#define M_MULTI OSMO_GTLV_GEN_M_MULTI
+
+#define ALL_FROM_NAME osmo_gtlv_gen_ie_auto
+
+/* An IE where the type is not a 'struct myproto_ie_${name}'. */
+static const struct osmo_gtlv_gen_ie number = {
+	.decoded_type =	"int", /* add 'int foo;' to the struct */
+	.dec_enc = "u16", /* use myproto_dec_u16() and myproto_enc_u16() for the TLV value part */
+	.spec_ref = "an int coded as uint16_t",
+};
+
+static const struct osmo_gtlv_gen_ie_o ies_in_moo_nest[] = {
+	/* Mandatory member xxx.foo of the type defined in 'number' above. */
+	M(number, "foo"),
+	/* Mandatory member xxx.bar of type 'struct myproto_ie_bar', using myproto_ie_dec_bar(), myproto_ie_enc_bar(),
+	 * myproto_ie_enc_to_str_bar(), all defined in myproto_ies_custom.h/c. */
+	M(ALL_FROM_NAME, "bar"),
+	M(ALL_FROM_NAME, "baz"),
+	{}
+};
+
+static const struct osmo_gtlv_gen_ie huge_number = {
+	.decoded_type =	"uint64_t",
+	.dec_enc = "u64",
+};
+
+static const struct osmo_gtlv_gen_ie moo_nest = {
+	.tag_name = "moo_nest",
+	.nested_ies = ies_in_moo_nest,
+};
+
+static const struct osmo_gtlv_gen_ie_o ies_in_goo_nest[] = {
+	O(huge_number, "val"),
+	M(moo_nest, "nest"),
+	{}
+};
+
+static const struct osmo_gtlv_gen_ie goo_nest = {
+	.tag_name = "goo_nest",
+	.nested_ies = ies_in_goo_nest,
+};
+
+static const struct osmo_gtlv_gen_ie_o ies_in_moo_msg[] = {
+	M(number, "foo"),
+	M(ALL_FROM_NAME, "bar"),
+	O(ALL_FROM_NAME, "baz"),
+	O_MULTI(32, number, "repeat_int"),
+	O_MULTI(32, ALL_FROM_NAME, "repeat_struct"),
+	O(moo_nest, "nest"),
+	{}
+};
+
+static const struct osmo_gtlv_gen_ie_o ies_in_goo_msg[] = {
+	M(number, "foo"),
+	O(ALL_FROM_NAME, "bar"),
+	O_MULTI(8, goo_nest, "nest"),
+	{}
+};
+
+static const struct osmo_gtlv_gen_msg msg_defs[] = {
+	{ "moo", ies_in_moo_msg },
+	{ "goo", ies_in_goo_msg },
+	{}
+};
+
+int main(int argc, const char **argv)
+{
+	struct osmo_gtlv_gen_cfg cfg = {
+		.proto_name = "myproto",
+		.message_type_enum = "enum myproto_msg_type",
+		.message_type_prefix = "MYPROTO_MSGT_",
+		.tag_enum = "enum myproto_iei",
+		.tag_prefix = "MYPROTO_IEI_",
+		.decoded_type_prefix = "struct myproto_ie_",
+		.h_header = "#include \"myproto_ies_custom.h\"",
+		.c_header = "#include <myproto_ies_auto.h>",
+		.msg_defs = msg_defs,
+		.add_enc_to_str = true,
+	};
+	return osmo_gtlv_gen_main(&cfg, argc, argv);
+}
diff --git a/tests/libosmo-gtlv/test_gtlv_gen/gtlv_gen_test.c b/tests/libosmo-gtlv/test_gtlv_gen/gtlv_gen_test.c
new file mode 100644
index 0000000..ef5372c
--- /dev/null
+++ b/tests/libosmo-gtlv/test_gtlv_gen/gtlv_gen_test.c
@@ -0,0 +1,261 @@
+/*
+ * (C) 2021-2022 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved.
+ *
+ * Author: Neels Janosch Hofmeyr <nhofmeyr@sysmocom.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ *  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/>.
+ *
+ */
+
+#include <stdio.h>
+#include <errno.h>
+
+#include <osmocom/core/application.h>
+#include <osmocom/core/utils.h>
+#include <osmocom/core/msgb.h>
+
+#include <osmocom/gtlv/gtlv.h>
+
+#include <myproto_ies_auto.h>
+
+struct myproto_msg {
+	enum myproto_msg_type type;
+	union myproto_ies ies;
+};
+
+static void err_cb(void *data, void *decoded_struct, const char *file, int line, const char *fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	//printf("ERR: %s:%d ", file, line);
+	printf("ERR: ");
+	vprintf(fmt, args);
+	va_end(args);
+}
+
+static int myproto_msg_enc(struct msgb *dst, const struct myproto_msg *msg, const struct osmo_gtlv_cfg *cfg)
+{
+	struct osmo_gtlv_put gtlv = {
+		.cfg = cfg,
+		.dst = dst,
+	};
+
+	msgb_put_u8(gtlv.dst, msg->type);
+	return myproto_ies_encode(&gtlv, (void *)&msg->ies, msg->type, err_cb, NULL, myproto_iei_names);
+}
+
+static int myproto_msg_dec(struct myproto_msg *msg, const uint8_t *data, size_t data_len,
+			   const struct osmo_gtlv_cfg *cfg, bool ordered)
+{
+	struct osmo_gtlv_load gtlv;
+	if (data_len < 1)
+		return -EINVAL;
+	msg->type = data[0];
+	gtlv = (struct osmo_gtlv_load){
+		.cfg = cfg,
+		.src = { data + 1, data_len - 1 },
+	};
+	return myproto_ies_decode(&msg->ies, &gtlv, ordered, msg->type, err_cb, NULL, myproto_iei_names);
+}
+
+void *ctx;
+
+struct myproto_msg tests[] = {
+	{
+		MYPROTO_MSGT_MOO,
+		{
+			.moo = {
+				.foo = 23,
+				.bar = { "twentythree" },
+			},
+		},
+	},
+	{
+		MYPROTO_MSGT_MOO,
+		{
+			.moo = {
+				.foo = 23,
+				.bar = { "twentythree" },
+
+				.baz_present = true,
+				.baz = {
+					.v_int = 2323,
+					.v_bool = true,
+				},
+			},
+		},
+	},
+	{
+		MYPROTO_MSGT_MOO,
+		{
+			.moo = {
+				.foo = 23,
+				.bar = { "twentythree" },
+
+				.baz_present = true,
+				.baz = {
+					.v_int = 2323,
+					.v_bool = true,
+				},
+
+				.repeat_int_count = 3,
+				.repeat_int = { 1, 2, 0x7fff },
+			},
+		},
+	},
+	{
+		MYPROTO_MSGT_MOO,
+		{
+			.moo = {
+				.foo = 23,
+				.bar = { "twentythree" },
+
+				.baz_present = true,
+				.baz = {
+					.v_int = 2323,
+					.v_bool = true,
+				},
+
+				.repeat_int_count = 3,
+				.repeat_int = { 1, 2, 0x7fff },
+
+				.repeat_struct_count = 2,
+				.repeat_struct = {
+					{
+						.v_int = 1001,
+						.v_bool = true,
+						.v_enum = R_A,
+					},
+					{
+						.v_int = 1002,
+						.v_bool = false,
+						.v_enum = R_B,
+					},
+				},
+
+				.nest_present = true,
+				.nest = {
+					.foo = 42,
+					.bar = { "fortytwo" },
+					.baz = {
+						.v_int = 4242,
+						.v_bool = false,
+					},
+				},
+			},
+		},
+	},
+	{
+		MYPROTO_MSGT_GOO,
+		{
+			.goo = {
+				.foo = 17,
+
+				.bar_present = true,
+				.bar = { "gooei" },
+
+				.nest_count = 2,
+				.nest = {
+					{
+						.val_present = true,
+						.val = 0x0123456789abcdef,
+						.nest = {
+							.foo = 11,
+							.bar = { "eleven" },
+							.baz = {
+								.v_int = 1111,
+								.v_bool = true,
+							},
+						},
+					},
+					{
+						.val_present = false,
+						.nest = {
+							.foo = 12,
+							.bar = { "twelve" },
+							.baz = {
+								.v_int = 1212,
+								.v_bool = false,
+							},
+						},
+					},
+				},
+			},
+		},
+	},
+};
+
+int myproto_msg_to_str_buf(char *buf, size_t buflen, const struct myproto_msg *m)
+{
+	struct osmo_strbuf sb = { .buf = buf, .len = buflen };
+	OSMO_STRBUF_PRINTF(sb, "%s={", get_value_string(myproto_msg_type_names, m->type));
+	OSMO_STRBUF_APPEND(sb, osmo_gtlvs_encode_to_str_buf, &m->ies, 0, myproto_get_msg_coding(m->type),
+			   myproto_iei_names);
+	OSMO_STRBUF_PRINTF(sb, " }");
+	return sb.chars_needed;
+
+}
+
+char *myproto_msg_to_str(const struct myproto_msg *m)
+{
+	OSMO_NAME_C_IMPL(ctx, 256, "ERROR", myproto_msg_to_str_buf, m)
+}
+
+void test_enc_dec(const char *label, const struct osmo_gtlv_cfg *cfg, bool ordered)
+{
+	int i;
+	for (i = 0; i < ARRAY_SIZE(tests); i++) {
+		int rc;
+		const struct myproto_msg *orig = &tests[i];
+		struct myproto_msg parsed = {};
+		struct msgb *msg;
+
+		printf("\n=== start %s %s[%d]\n", label, __func__, i);
+		printf("encoded: %s\n", myproto_msg_to_str(orig));
+
+		msg = msgb_alloc(1024, __func__);
+		rc = myproto_msg_enc(msg, orig, cfg);
+		printf("myproto_msg_enc() rc = %d\n", rc);
+		printf("%s.\n", osmo_hexdump(msg->data, msg->len));
+
+		rc = myproto_msg_dec(&parsed, msg->data, msg->len, cfg, ordered);
+		printf("myproto_msg_dec() rc = %d\n", rc);
+		printf("decoded: %s\n", myproto_msg_to_str(&parsed));
+		if (strcmp(myproto_msg_to_str(orig), myproto_msg_to_str(&parsed))) {
+			printf(" ERROR: parsed != orig\n");
+			exit(1);
+		}
+
+		msgb_free(msg);
+		printf("=== end %s %s[%d]\n", label, __func__, i);
+	}
+}
+
+int main()
+{
+	ctx = talloc_named_const(NULL, 0, "test_gen_tlv");
+	msgb_talloc_ctx_init(ctx, 0);
+
+	test_enc_dec("t8l8v ordered", &osmo_t8l8v_cfg, true);
+	test_enc_dec("t8l8v unordered", &osmo_t8l8v_cfg, false);
+
+	test_enc_dec("t16l16v ordered", &osmo_t16l16v_cfg, true);
+	test_enc_dec("t16l16v unordered", &osmo_t16l16v_cfg, false);
+
+	talloc_free(ctx);
+	return 0;
+}
diff --git a/tests/libosmo-gtlv/test_gtlv_gen/gtlv_gen_test.ok b/tests/libosmo-gtlv/test_gtlv_gen/gtlv_gen_test.ok
new file mode 100644
index 0000000..e178831
--- /dev/null
+++ b/tests/libosmo-gtlv/test_gtlv_gen/gtlv_gen_test.ok
@@ -0,0 +1,160 @@
+
+=== start t8l8v ordered test_enc_dec[0]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" }
+myproto_msg_enc() rc = 0
+01 01 02 00 17 02 0b 74 77 65 6e 74 79 74 68 72 65 65 .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" }
+=== end t8l8v ordered test_enc_dec[0]
+
+=== start t8l8v ordered test_enc_dec[1]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} }
+myproto_msg_enc() rc = 0
+01 01 02 00 17 02 0b 74 77 65 6e 74 79 74 68 72 65 65 03 02 89 13 .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} }
+=== end t8l8v ordered test_enc_dec[1]
+
+=== start t8l8v ordered test_enc_dec[2]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } }
+myproto_msg_enc() rc = 0
+01 01 02 00 17 02 0b 74 77 65 6e 74 79 74 68 72 65 65 03 02 89 13 04 02 00 01 04 02 00 02 04 02 7f ff .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } }
+=== end t8l8v ordered test_enc_dec[2]
+
+=== start t8l8v ordered test_enc_dec[3]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } 'REPEAT_STRUCT'={ {1001,true,R_A}, {1002,false,R_B} } 'MOO_NEST'={ 'FOO'=42 'BAR'="fortytwo" 'BAZ'={4242,false} } }
+myproto_msg_enc() rc = 0
+01 01 02 00 17 02 0b 74 77 65 6e 74 79 74 68 72 65 65 03 02 89 13 04 02 00 01 04 02 00 02 04 02 7f ff 05 03 03 e9 80 05 03 03 ea 01 06 12 01 02 00 2a 02 08 66 6f 72 74 79 74 77 6f 03 02 10 92 .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } 'REPEAT_STRUCT'={ {1001,true,R_A}, {1002,false,R_B} } 'MOO_NEST'={ 'FOO'=42 'BAR'="fortytwo" 'BAZ'={4242,false} } }
+=== end t8l8v ordered test_enc_dec[3]
+
+=== start t8l8v ordered test_enc_dec[4]
+encoded: GOO={ 'FOO'=17 'BAR'="gooei" 'GOO_NEST'={ { 'VAL'=0x123456789abcdef 'MOO_NEST'={ 'FOO'=11 'BAR'="eleven" 'BAZ'={1111,true} } }, { 'MOO_NEST'={ 'FOO'=12 'BAR'="twelve" 'BAZ'={1212,false} } } } }
+myproto_msg_enc() rc = 0
+07 01 02 00 11 02 05 67 6f 6f 65 69 08 1c 07 08 01 23 45 67 89 ab cd ef 06 10 01 02 00 0b 02 06 65 6c 65 76 65 6e 03 02 84 57 08 12 06 10 01 02 00 0c 02 06 74 77 65 6c 76 65 03 02 04 bc .
+myproto_msg_dec() rc = 0
+decoded: GOO={ 'FOO'=17 'BAR'="gooei" 'GOO_NEST'={ { 'VAL'=0x123456789abcdef 'MOO_NEST'={ 'FOO'=11 'BAR'="eleven" 'BAZ'={1111,true} } }, { 'MOO_NEST'={ 'FOO'=12 'BAR'="twelve" 'BAZ'={1212,false} } } } }
+=== end t8l8v ordered test_enc_dec[4]
+
+=== start t8l8v unordered test_enc_dec[0]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" }
+myproto_msg_enc() rc = 0
+01 01 02 00 17 02 0b 74 77 65 6e 74 79 74 68 72 65 65 .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" }
+=== end t8l8v unordered test_enc_dec[0]
+
+=== start t8l8v unordered test_enc_dec[1]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} }
+myproto_msg_enc() rc = 0
+01 01 02 00 17 02 0b 74 77 65 6e 74 79 74 68 72 65 65 03 02 89 13 .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} }
+=== end t8l8v unordered test_enc_dec[1]
+
+=== start t8l8v unordered test_enc_dec[2]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } }
+myproto_msg_enc() rc = 0
+01 01 02 00 17 02 0b 74 77 65 6e 74 79 74 68 72 65 65 03 02 89 13 04 02 00 01 04 02 00 02 04 02 7f ff .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } }
+=== end t8l8v unordered test_enc_dec[2]
+
+=== start t8l8v unordered test_enc_dec[3]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } 'REPEAT_STRUCT'={ {1001,true,R_A}, {1002,false,R_B} } 'MOO_NEST'={ 'FOO'=42 'BAR'="fortytwo" 'BAZ'={4242,false} } }
+myproto_msg_enc() rc = 0
+01 01 02 00 17 02 0b 74 77 65 6e 74 79 74 68 72 65 65 03 02 89 13 04 02 00 01 04 02 00 02 04 02 7f ff 05 03 03 e9 80 05 03 03 ea 01 06 12 01 02 00 2a 02 08 66 6f 72 74 79 74 77 6f 03 02 10 92 .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } 'REPEAT_STRUCT'={ {1001,true,R_A}, {1002,false,R_B} } 'MOO_NEST'={ 'FOO'=42 'BAR'="fortytwo" 'BAZ'={4242,false} } }
+=== end t8l8v unordered test_enc_dec[3]
+
+=== start t8l8v unordered test_enc_dec[4]
+encoded: GOO={ 'FOO'=17 'BAR'="gooei" 'GOO_NEST'={ { 'VAL'=0x123456789abcdef 'MOO_NEST'={ 'FOO'=11 'BAR'="eleven" 'BAZ'={1111,true} } }, { 'MOO_NEST'={ 'FOO'=12 'BAR'="twelve" 'BAZ'={1212,false} } } } }
+myproto_msg_enc() rc = 0
+07 01 02 00 11 02 05 67 6f 6f 65 69 08 1c 07 08 01 23 45 67 89 ab cd ef 06 10 01 02 00 0b 02 06 65 6c 65 76 65 6e 03 02 84 57 08 12 06 10 01 02 00 0c 02 06 74 77 65 6c 76 65 03 02 04 bc .
+myproto_msg_dec() rc = 0
+decoded: GOO={ 'FOO'=17 'BAR'="gooei" 'GOO_NEST'={ { 'VAL'=0x123456789abcdef 'MOO_NEST'={ 'FOO'=11 'BAR'="eleven" 'BAZ'={1111,true} } }, { 'MOO_NEST'={ 'FOO'=12 'BAR'="twelve" 'BAZ'={1212,false} } } } }
+=== end t8l8v unordered test_enc_dec[4]
+
+=== start t16l16v ordered test_enc_dec[0]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" }
+myproto_msg_enc() rc = 0
+01 00 01 00 02 00 17 00 02 00 0b 74 77 65 6e 74 79 74 68 72 65 65 .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" }
+=== end t16l16v ordered test_enc_dec[0]
+
+=== start t16l16v ordered test_enc_dec[1]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} }
+myproto_msg_enc() rc = 0
+01 00 01 00 02 00 17 00 02 00 0b 74 77 65 6e 74 79 74 68 72 65 65 00 03 00 02 89 13 .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} }
+=== end t16l16v ordered test_enc_dec[1]
+
+=== start t16l16v ordered test_enc_dec[2]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } }
+myproto_msg_enc() rc = 0
+01 00 01 00 02 00 17 00 02 00 0b 74 77 65 6e 74 79 74 68 72 65 65 00 03 00 02 89 13 00 04 00 02 00 01 00 04 00 02 00 02 00 04 00 02 7f ff .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } }
+=== end t16l16v ordered test_enc_dec[2]
+
+=== start t16l16v ordered test_enc_dec[3]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } 'REPEAT_STRUCT'={ {1001,true,R_A}, {1002,false,R_B} } 'MOO_NEST'={ 'FOO'=42 'BAR'="fortytwo" 'BAZ'={4242,false} } }
+myproto_msg_enc() rc = 0
+01 00 01 00 02 00 17 00 02 00 0b 74 77 65 6e 74 79 74 68 72 65 65 00 03 00 02 89 13 00 04 00 02 00 01 00 04 00 02 00 02 00 04 00 02 7f ff 00 05 00 03 03 e9 80 00 05 00 03 03 ea 01 00 06 00 18 00 01 00 02 00 2a 00 02 00 08 66 6f 72 74 79 74 77 6f 00 03 00 02 10 92 .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } 'REPEAT_STRUCT'={ {1001,true,R_A}, {1002,false,R_B} } 'MOO_NEST'={ 'FOO'=42 'BAR'="fortytwo" 'BAZ'={4242,false} } }
+=== end t16l16v ordered test_enc_dec[3]
+
+=== start t16l16v ordered test_enc_dec[4]
+encoded: GOO={ 'FOO'=17 'BAR'="gooei" 'GOO_NEST'={ { 'VAL'=0x123456789abcdef 'MOO_NEST'={ 'FOO'=11 'BAR'="eleven" 'BAZ'={1111,true} } }, { 'MOO_NEST'={ 'FOO'=12 'BAR'="twelve" 'BAZ'={1212,false} } } } }
+myproto_msg_enc() rc = 0
+07 00 01 00 02 00 11 00 02 00 05 67 6f 6f 65 69 00 08 00 26 00 07 00 08 01 23 45 67 89 ab cd ef 00 06 00 16 00 01 00 02 00 0b 00 02 00 06 65 6c 65 76 65 6e 00 03 00 02 84 57 00 08 00 1a 00 06 00 16 00 01 00 02 00 0c 00 02 00 06 74 77 65 6c 76 65 00 03 00 02 04 bc .
+myproto_msg_dec() rc = 0
+decoded: GOO={ 'FOO'=17 'BAR'="gooei" 'GOO_NEST'={ { 'VAL'=0x123456789abcdef 'MOO_NEST'={ 'FOO'=11 'BAR'="eleven" 'BAZ'={1111,true} } }, { 'MOO_NEST'={ 'FOO'=12 'BAR'="twelve" 'BAZ'={1212,false} } } } }
+=== end t16l16v ordered test_enc_dec[4]
+
+=== start t16l16v unordered test_enc_dec[0]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" }
+myproto_msg_enc() rc = 0
+01 00 01 00 02 00 17 00 02 00 0b 74 77 65 6e 74 79 74 68 72 65 65 .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" }
+=== end t16l16v unordered test_enc_dec[0]
+
+=== start t16l16v unordered test_enc_dec[1]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} }
+myproto_msg_enc() rc = 0
+01 00 01 00 02 00 17 00 02 00 0b 74 77 65 6e 74 79 74 68 72 65 65 00 03 00 02 89 13 .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} }
+=== end t16l16v unordered test_enc_dec[1]
+
+=== start t16l16v unordered test_enc_dec[2]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } }
+myproto_msg_enc() rc = 0
+01 00 01 00 02 00 17 00 02 00 0b 74 77 65 6e 74 79 74 68 72 65 65 00 03 00 02 89 13 00 04 00 02 00 01 00 04 00 02 00 02 00 04 00 02 7f ff .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } }
+=== end t16l16v unordered test_enc_dec[2]
+
+=== start t16l16v unordered test_enc_dec[3]
+encoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } 'REPEAT_STRUCT'={ {1001,true,R_A}, {1002,false,R_B} } 'MOO_NEST'={ 'FOO'=42 'BAR'="fortytwo" 'BAZ'={4242,false} } }
+myproto_msg_enc() rc = 0
+01 00 01 00 02 00 17 00 02 00 0b 74 77 65 6e 74 79 74 68 72 65 65 00 03 00 02 89 13 00 04 00 02 00 01 00 04 00 02 00 02 00 04 00 02 7f ff 00 05 00 03 03 e9 80 00 05 00 03 03 ea 01 00 06 00 18 00 01 00 02 00 2a 00 02 00 08 66 6f 72 74 79 74 77 6f 00 03 00 02 10 92 .
+myproto_msg_dec() rc = 0
+decoded: MOO={ 'FOO'=23 'BAR'="twentythree" 'BAZ'={2323,true} 'REPEAT_INT'={ 1, 2, 32767 } 'REPEAT_STRUCT'={ {1001,true,R_A}, {1002,false,R_B} } 'MOO_NEST'={ 'FOO'=42 'BAR'="fortytwo" 'BAZ'={4242,false} } }
+=== end t16l16v unordered test_enc_dec[3]
+
+=== start t16l16v unordered test_enc_dec[4]
+encoded: GOO={ 'FOO'=17 'BAR'="gooei" 'GOO_NEST'={ { 'VAL'=0x123456789abcdef 'MOO_NEST'={ 'FOO'=11 'BAR'="eleven" 'BAZ'={1111,true} } }, { 'MOO_NEST'={ 'FOO'=12 'BAR'="twelve" 'BAZ'={1212,false} } } } }
+myproto_msg_enc() rc = 0
+07 00 01 00 02 00 11 00 02 00 05 67 6f 6f 65 69 00 08 00 26 00 07 00 08 01 23 45 67 89 ab cd ef 00 06 00 16 00 01 00 02 00 0b 00 02 00 06 65 6c 65 76 65 6e 00 03 00 02 84 57 00 08 00 1a 00 06 00 16 00 01 00 02 00 0c 00 02 00 06 74 77 65 6c 76 65 00 03 00 02 04 bc .
+myproto_msg_dec() rc = 0
+decoded: GOO={ 'FOO'=17 'BAR'="gooei" 'GOO_NEST'={ { 'VAL'=0x123456789abcdef 'MOO_NEST'={ 'FOO'=11 'BAR'="eleven" 'BAZ'={1111,true} } }, { 'MOO_NEST'={ 'FOO'=12 'BAR'="twelve" 'BAZ'={1212,false} } } } }
+=== end t16l16v unordered test_enc_dec[4]
diff --git a/tests/libosmo-gtlv/test_gtlv_gen/myproto_ies_custom.c b/tests/libosmo-gtlv/test_gtlv_gen/myproto_ies_custom.c
new file mode 100644
index 0000000..8548165
--- /dev/null
+++ b/tests/libosmo-gtlv/test_gtlv_gen/myproto_ies_custom.c
@@ -0,0 +1,180 @@
+/* Example for defining custom IES for gtlv_gen. */
+/*
+ * (C) 2021-2022 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved.
+ *
+ * Author: Neels Janosch Hofmeyr <nhofmeyr@sysmocom.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ *  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/>.
+ *
+ */
+
+#include <errno.h>
+#include <inttypes.h>
+
+#include <osmocom/core/bits.h>
+#include <osmocom/core/msgb.h>
+#include <osmocom/gtlv/gtlv.h>
+
+#include <myproto_ies_custom.h>
+
+int myproto_dec_u16(void *decoded_struct, void *decode_to, const struct osmo_gtlv_load *gtlv)
+{
+	int *foo = decode_to;
+	if (gtlv->len != 2)
+		return -EINVAL;
+	*foo = osmo_load16be(gtlv->val);
+	return 0;
+}
+
+int myproto_enc_u16(struct osmo_gtlv_put *gtlv, void *decoded_struct, void *encode_from)
+{
+	int *foo = encode_from;
+	if (*foo > INT16_MAX)
+		return -EINVAL;
+	msgb_put_u16(gtlv->dst, *foo);
+	return 0;
+}
+
+int myproto_enc_to_str_u16(char *buf, size_t buflen, void *encode_from)
+{
+	int *foo = encode_from;
+	return snprintf(buf, buflen, "%d", *foo);
+}
+
+int myproto_dec_u64(void *decoded_struct, void *decode_to, const struct osmo_gtlv_load *gtlv)
+{
+	uint64_t *val = decode_to;
+	if (gtlv->len != sizeof(uint64_t))
+		return -EINVAL;
+	*val = osmo_load64be(gtlv->val);
+	return 0;
+}
+
+int myproto_enc_u64(struct osmo_gtlv_put *gtlv, void *decoded_struct, void *encode_from)
+{
+	uint64_t *val = encode_from;
+	osmo_store64be(*val, msgb_put(gtlv->dst, sizeof(*val)));
+	return 0;
+}
+
+int myproto_enc_to_str_u64(char *buf, size_t buflen, void *encode_from)
+{
+	uint64_t *val = encode_from;
+	return snprintf(buf, buflen, "0x%"PRIx64, *val);
+}
+
+int myproto_dec_bar(void *decoded_struct, void *decode_to, const struct osmo_gtlv_load *gtlv)
+{
+	struct myproto_ie_bar *bar = decode_to;
+	if (gtlv->len > sizeof(bar->str) - 1)
+		return -EINVAL;
+	osmo_strlcpy(bar->str, (const char *)gtlv->val, OSMO_MIN(gtlv->len + 1, sizeof(bar->str)));
+	return 0;
+}
+
+int myproto_enc_bar(struct osmo_gtlv_put *gtlv, void *decoded_struct, void *encode_from)
+{
+	struct myproto_ie_bar *bar = encode_from;
+	int len = strnlen(bar->str, sizeof(bar->str));
+	memcpy(msgb_put(gtlv->dst, len), bar, len);
+	return 0;
+}
+
+int myproto_enc_to_str_bar(char *buf, size_t buflen, void *encode_from)
+{
+	struct myproto_ie_bar *bar = encode_from;
+	return osmo_quote_str_buf3(buf, buflen, bar->str, -1);
+}
+
+int myproto_dec_baz(void *decoded_struct, void *decode_to, const struct osmo_gtlv_load *gtlv)
+{
+	struct myproto_ie_baz *baz = decode_to;
+	uint16_t l;
+	if (gtlv->len != 2)
+		return -EINVAL;
+	l = osmo_load16be(gtlv->val);
+	baz->v_int = l & 0x7fff;
+	baz->v_bool = (l & 0x8000) ? true : false;
+	return 0;
+}
+
+int myproto_enc_baz(struct osmo_gtlv_put *gtlv, void *decoded_struct, void *encode_from)
+{
+	struct myproto_ie_baz *baz = encode_from;
+	if (baz->v_int > 0x7fff)
+		return -EINVAL;
+	msgb_put_u16(gtlv->dst, (baz->v_bool ? 0x8000 : 0) + (baz->v_int & 0x7fff));
+	return 0;
+}
+
+int myproto_enc_to_str_baz(char *buf, size_t buflen, void *encode_from)
+{
+	struct myproto_ie_baz *baz = encode_from;
+	return snprintf(buf, buflen, "{%d,%s}", baz->v_int, baz->v_bool ? "true" : "false");
+}
+
+int myproto_dec_repeat_struct(void *decoded_struct, void *decode_to, const struct osmo_gtlv_load *gtlv)
+{
+	struct myproto_ie_repeat_struct *repeat_struct = decode_to;
+	if (gtlv->len != 3)
+		return -EINVAL;
+	repeat_struct->v_int = osmo_load16be(gtlv->val);
+	repeat_struct->v_bool = gtlv->val[2] & 0x80;
+	repeat_struct->v_enum = gtlv->val[2] & 0x7f;
+	return 0;
+}
+
+int myproto_enc_repeat_struct(struct osmo_gtlv_put *gtlv, void *decoded_struct, void *encode_from)
+{
+	struct myproto_ie_repeat_struct *repeat_struct = encode_from;
+	msgb_put_u16(gtlv->dst, repeat_struct->v_int);
+	msgb_put_u8(gtlv->dst, (repeat_struct->v_bool ? 0x80 : 0) + (repeat_struct->v_enum & 0x7f));
+	return 0;
+}
+
+int myproto_enc_to_str_repeat_struct(char *buf, size_t buflen, void *encode_from)
+{
+	struct myproto_ie_repeat_struct *repeat_struct = encode_from;
+	return snprintf(buf, buflen, "{%d,%s,%s}",
+			repeat_struct->v_int, repeat_struct->v_bool ?  "true" : "false",
+			get_value_string(myproto_repeat_enum_names, repeat_struct->v_enum));
+}
+
+const struct value_string myproto_msg_type_names[] = {
+	{ MYPROTO_MSGT_MOO, "MOO" },
+	{ MYPROTO_MSGT_GOO, "GOO" },
+	{}
+};
+
+const struct value_string myproto_iei_names[] = {
+	{ MYPROTO_IEI_FOO, "FOO" },
+	{ MYPROTO_IEI_BAR, "BAR" },
+	{ MYPROTO_IEI_BAZ, "BAZ" },
+	{ MYPROTO_IEI_REPEAT_INT, "REPEAT_INT" },
+	{ MYPROTO_IEI_REPEAT_STRUCT, "REPEAT_STRUCT" },
+	{ MYPROTO_IEI_MOO_NEST, "MOO_NEST" },
+	{ MYPROTO_IEI_VAL, "VAL" },
+	{ MYPROTO_IEI_GOO_NEST, "GOO_NEST" },
+	{}
+};
+
+const struct value_string myproto_repeat_enum_names[] = {
+	OSMO_VALUE_STRING(R_A),
+	OSMO_VALUE_STRING(R_B),
+	OSMO_VALUE_STRING(R_C),
+	{}
+};
diff --git a/tests/libosmo-gtlv/test_gtlv_gen/myproto_ies_custom.h b/tests/libosmo-gtlv/test_gtlv_gen/myproto_ies_custom.h
new file mode 100644
index 0000000..56039af
--- /dev/null
+++ b/tests/libosmo-gtlv/test_gtlv_gen/myproto_ies_custom.h
@@ -0,0 +1,70 @@
+/* Definitions for decoded message IEs, to be used by the auto-generated myproto_ies_auto.c. */
+/*
+ * (C) 2021-2022 by sysmocom - s.f.m.c. GmbH <info@sysmocom.de>
+ * All Rights Reserved.
+ *
+ * Author: Neels Janosch Hofmeyr <nhofmeyr@sysmocom.de>
+ *
+ * SPDX-License-Identifier: GPL-2.0+
+ *
+ *  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 <osmocom/core/utils.h>
+
+enum myproto_msg_type {
+	MYPROTO_MSGT_MOO = 1,
+	MYPROTO_MSGT_GOO = 7,
+};
+
+extern const struct value_string myproto_msg_type_names[];
+
+enum myproto_iei {
+	MYPROTO_IEI_FOO = 1,
+	MYPROTO_IEI_BAR,
+	MYPROTO_IEI_BAZ,
+	MYPROTO_IEI_REPEAT_INT,
+	MYPROTO_IEI_REPEAT_STRUCT,
+	MYPROTO_IEI_MOO_NEST,
+	MYPROTO_IEI_VAL,
+	MYPROTO_IEI_GOO_NEST,
+};
+
+extern const struct value_string myproto_iei_names[];
+
+struct myproto_ie_bar {
+	char str[23];
+};
+
+struct myproto_ie_baz {
+	int v_int;
+	bool v_bool;
+};
+
+enum myproto_repeat_enum {
+	R_A,
+	R_B,
+	R_C,
+};
+
+extern const struct value_string myproto_repeat_enum_names[];
+
+struct myproto_ie_repeat_struct {
+	int v_int;
+	bool v_bool;
+	enum myproto_repeat_enum v_enum;
+};