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

2 files changed, 167 insertions, 0 deletions

diff --git a/include/osmocom/gtlv/Makefile.am b/include/osmocom/gtlv/Makefile.am
index a7c10a6..fc0cff2 100644
--- a/include/osmocom/gtlv/Makefile.am
+++ b/include/osmocom/gtlv/Makefile.am
@@ -1,6 +1,7 @@
 tlv_HEADERS = \
 	gtlv.h \
 	gtlv_dec_enc.h \
+	gtlv_gen.h \
 	$(NULL)
 
 tlvdir = $(includedir)/osmocom/gtlv
diff --git a/include/osmocom/gtlv/gtlv_gen.h b/include/osmocom/gtlv/gtlv_gen.h
new file mode 100644
index 0000000..a2f088b
--- /dev/null
+++ b/include/osmocom/gtlv/gtlv_gen.h
@@ -0,0 +1,166 @@
+/* Write h and c source files for TLV protocol definitions, based on very sparse TLV definitions.
+ * For a usage example see tests/libosmo-gtlv/test_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/>.
+ *
+ */
+
+#pragma once
+
+#include <stdbool.h>
+
+struct osmo_gtlv_gen_ie;
+
+/* O means optional, M means mandatory.
+ * If all of the IE struct, tag name and functions can be derived from the name, just pass osmo_gtlv_gen_ie_auto as
+ * TLV_GEN_IE. */
+#define OSMO_GTLV_GEN_O(TLV_GEN_IE, MEMB_NAME) { MEMB_NAME, .optional = true, .ie = &(TLV_GEN_IE) }
+#define OSMO_GTLV_GEN_M(TLV_GEN_IE, MEMB_NAME) { MEMB_NAME, .ie = &(TLV_GEN_IE) }
+#define OSMO_GTLV_GEN_O_MULTI(MAX, TLV_GEN_IE, MEMB_NAME) { MEMB_NAME, .multi = MAX, .ie = &(TLV_GEN_IE) }
+#define OSMO_GTLV_GEN_M_MULTI(MAX, MAND_COUNT, TLV_GEN_IE, MEMB_NAME) \
+	{ MEMB_NAME, .multi = MAX, .multi_mandatory = MAND_COUNT, .ie = &(TLV_GEN_IE) }
+
+/*! osmo_gtlv_gen_ie with all members == NULL, so that all are derived from the member name. */
+extern const struct osmo_gtlv_gen_ie osmo_gtlv_gen_ie_auto;
+
+/*! Modifier for Mandatory/Optional/Multiple around an osmo_gtlv_gen_ie. */
+struct osmo_gtlv_gen_ie_o {
+	/*! The C name of the member in a decoded struct, to be of the type defined by .ie.
+	 * All parts of .ie, if NULL, are derived from this name.
+	 *
+	 * For example, simply this
+	 *
+	 *   struct osmo_gtlv_gen_ie_o foo[] = {
+	 *       OSMO_GTLV_GEN_O("bar", NULL),
+	 *   };
+	 *
+	 * Generates
+	 *
+	 *   struct myproto_msg_foo {
+	 *       struct myproto_ie_bar bar;
+	 *   }
+	 *
+	 * and an osmo_gtlv_coding entry of
+	 *
+	 * { MYPROTO_IEI_BAR,
+	 *   .memb_ofs = offsetof(struct myproto_msg_foo, bar),
+	 *   .dec_func = myproto_dec_bar,
+	 *   .enc_func = myproto_enc_bar,
+	 *   .enc_to_str_func = myproto_enc_to_str_bar,
+	 * }
+	 *
+	 * See also osmo_gtlv_gen_cfg.add_enc_to_str.
+	 */
+	const char *name;
+
+	/*! Whether to add a bool foo_present, and to skip encoding/decoding if false.
+	 * Only useful for non-multi IEs (compare OSMO_GTLV_GEN_O_MULTI() vs OSMO_GTLV_GEN_M_MULTI()). */
+	bool optional;
+
+	/*! If non-NULL, the member is an array: foo[123] with an unsigned int foo_count.
+	 * Set to the maximum number of array elements; for foo[123] set .multi = 123. */
+	unsigned int multi;
+	/*! Number of mandatory occurences of the IE, only has an effect if .multi > 0. */
+	unsigned int multi_mandatory;
+
+	/*! IE decoding / encoding instructions. If NULL, the entire IE definition is derived from .name.
+	 * 'MYPROTO_IEI_NAME', 'myproto_dec_name()', 'myproto_enc_name()', 'myproto_enc_to_str_name()'.
+	 * Your myproto_ies_custom.h needs to define an enum value MYPROTO_IEI_NAME and*/
+	const struct osmo_gtlv_gen_ie *ie;
+};
+
+/*! Define decoding and encoding of a single IE, i.e. one full TLV. */
+struct osmo_gtlv_gen_ie {
+	/*! like "uint32_t" or "struct foo".
+	 * If NULL, use "struct myproto_ie_<name>" instead, where <name> comes from the osmo_gtlv_gen_ie_o.
+	 * When there are nested IEs, the struct definition is auto-generated, deriving the struct members from the
+	 * nested_ies list.
+	 * When there are no nested IEs, the type needs to be defined manually by a myproto_ies_custom.h. */
+	const char *decoded_type;
+
+	/*! C name of this tag value, e.g. "MYPROTO_IEI_FOO". If NULL, take "MYPROTO_IEI_"+upper(name) instead. */
+	const char *tag_name;
+
+	/*! Name suffix of the dec/enc functions. "foo" -> myproto_dec_foo(), myproto_enc_foo(),
+	 * myproto_enc_to_str_foo().
+	 * These functions need to be implemented manually in a myproto_ies_custom.c.
+	 * When osmo_gtlv_gen_cfg.add_enc_to_str is false, the myproto_enc_to_str_foo() is not required. */
+	const char *dec_enc;
+
+	/*! List of inner IEs terminated by {}. If non-NULL, this is a "Grouped IE" with an inner TLV structure inside
+	 * this IE's V part. */
+	const struct osmo_gtlv_gen_ie_o *nested_ies;
+
+	/*! To place a spec comment in the generated code. */
+	const char *spec_ref;
+};
+
+/*! General TLV decoding and encoding definitions applying to all IEs (and nested IEs). */
+struct osmo_gtlv_gen_cfg {
+	/*! Name of the protocol for use in C type or function names, like "myproto". */
+	const char *proto_name;
+
+	/*! When placing comments to spec references, prefix with this. For example, "3GPP TS 12.345 ". */
+	const char *spec_ref_prefix;
+
+	/*! The type to pass a message discriminator as, like 'enum myproto_message_types' */
+	const char *message_type_enum;
+	/*! To reference a message type discriminator like MYPROTO_MSGT_FOO, this would be "MYPROTO_MSGT_". */
+	const char *message_type_prefix;
+
+	/*! Type to use to represent tag IEI in decoded form.
+	 * For example "enum foo_msg_iei". */
+	const char *tag_enum;
+	/*! The tag IEI enum value is uppercase(tag_prefix + (iedef->tag_name or iedef->name)).
+	 * For example, with tag_prefix = "OSMO_FOO_IEI_", we would generate code like
+	 * enum osmo_foo_iei tag = OSMO_FOO_IEI_BAR; */
+	const char *tag_prefix;
+
+	/*! When an osmo_gtlv_gen_ie provides no decoded_type string, it is derived from .name and this prefix is
+	 * added. For example, with decoded_type_prefix = "struct foo_ie_", the decoded_type defaults to
+	 * struct foo_ie_bar for an IE definition with name = "bar". */
+	const char *decoded_type_prefix;
+
+	/*! To include user defined headers, set to something like "#include <osmocom/foo/foo_tlv_devs.h". This is put at
+	 * the head of the generated .h file. */
+	const char *h_header;
+
+	/*! To include user defined headers, set to something like "#include <osmocom/foo/foo_msg.h". This is put at
+	 * the head of the generated .c file. */
+	const char *c_header;
+
+	/*! Array of message IE definitions, indexed by message type. */
+	const struct osmo_gtlv_gen_msg *msg_defs;
+
+	/*! Whether to add to_str functions. When true, every automatically derived IE (that has no nested IEs) needs to
+	 * have a myproto_enc_to_str_foo() defined by a myproto_ies_custom.c. When false, osmo_gtlvs_encode_to_str_buf()
+	 * will print '?' instead of the IE contents. */
+	bool add_enc_to_str;
+};
+
+/*! For generating the outer union that composes a protocol's PDU variants, an entry of the list of message names and
+ * IEs in each message. */
+struct osmo_gtlv_gen_msg {
+	const char *name;
+	const struct osmo_gtlv_gen_ie_o *ies;
+};
+
+int osmo_gtlv_gen_main(const struct osmo_gtlv_gen_cfg *cfg, int argc, const char **argv);