TLV: Add one-shot TLV encoder

So far, the TLV code contained two types of functions
* tlp_parse() to parse all TLVs according to definition into tlvp_parsed
* various helper functions to encode individual TLVs during message
  generation

This patch implements the inverse of tlv_parse(): tlv_encode(), which
takes a full 'struct tlv_pared' and encodes all IEs found in it.  The
order of IEs is in numerically ascending order of the tag.

As many protocols have different IE/TLV ordering requirements, let's add
a tlv_encode_ordered() function where the caller can specify the TLV
ordering during the one-shot encode.

Change-Id: I761a30bf20355a9f80a4a8e0c60b0b0f78515efe

5 files changed, 155 insertions, 0 deletions

diff --git a/include/osmocom/gsm/tlv.h b/include/osmocom/gsm/tlv.h
index d0c95522..bb0e8fc9 100644
--- a/include/osmocom/gsm/tlv.h
+++ b/include/osmocom/gsm/tlv.h
@@ -457,6 +457,12 @@ int tlv_parse2(struct tlv_parsed *dec, int dec_multiples,
 /* take a master (src) tlv def and fill up all empty slots in 'dst' */
 void tlv_def_patch(struct tlv_definition *dst, const struct tlv_definition *src);
 
+int tlv_encode_one(struct msgb *msg, enum tlv_type type, uint8_t tag,
+		   unsigned int len, const uint8_t *val);
+int tlv_encode(struct msgb *msg, const struct tlv_definition *def, const struct tlv_parsed *tp);
+int tlv_encode_ordered(struct msgb *msg, const struct tlv_definition *def, const struct tlv_parsed *tp,
+			const uint8_t *tag_order, unsigned int tag_order_len);
+
 #define TLVP_PRESENT(x, y)	((x)->lv[y].val)
 #define TLVP_LEN(x, y)		(x)->lv[y].len
 #define TLVP_VAL(x, y)		(x)->lv[y].val
diff --git a/src/gsm/libosmogsm.map b/src/gsm/libosmogsm.map
index 0f4a0db1..299504e8 100644
--- a/src/gsm/libosmogsm.map
+++ b/src/gsm/libosmogsm.map
@@ -537,6 +537,9 @@ tlv_dump;
 tlv_parse;
 tlv_parse2;
 tlv_parse_one;
+tlv_encode;
+tlv_encode_ordered;
+tlv_encode_one;
 tvlv_att_def;
 vtvlv_gan_att_def;
 
diff --git a/src/gsm/tlv_parser.c b/src/gsm/tlv_parser.c
index 6e089f7f..159b42bd 100644
--- a/src/gsm/tlv_parser.c
+++ b/src/gsm/tlv_parser.c
@@ -120,6 +120,103 @@ int osmo_tlvp_merge(struct tlv_parsed *dst, const struct tlv_parsed *src)
 	return 0;
 }
 
+
+/*! Encode a single TLV into given message buffer
+ *  \param[inout] msg Caller-allocated message buffer with sufficient tailroom
+ *  \param[in] type TLV type/format to use during encode
+ *  \param[in] tag Tag of TLV to be encoded
+ *  \parma[in] len Length of TLV to be encoded
+ *  \param[in] val Value part of TLV to be encoded
+ *  \returns 0 on success; negative in case of error */
+int tlv_encode_one(struct msgb *msg, enum tlv_type type, uint8_t tag,
+		   unsigned int len, const uint8_t *val)
+{
+	switch (type) {
+	case TLV_TYPE_NONE:
+		break;
+	case TLV_TYPE_FIXED:
+		msgb_tv_fixed_put(msg, tag, len, val);
+		break;
+	case TLV_TYPE_T:
+		msgb_v_put(msg, tag);
+		break;
+	case TLV_TYPE_TV:
+		msgb_tv_put(msg, tag, val[0]);
+		break;
+	case TLV_TYPE_TLV:
+		msgb_tlv_put(msg, tag, len, val);
+		break;
+	case TLV_TYPE_TL16V:
+		msgb_tl16v_put(msg, tag, len, val);
+		break;
+	case TLV_TYPE_TvLV:
+		msgb_tvlv_put(msg, tag, len, val);
+		break;
+	case TLV_TYPE_SINGLE_TV:
+		msgb_v_put(msg, (tag << 4) | (val[0] & 0xf));
+		break;
+	case TLV_TYPE_vTvLV_GAN:
+		msgb_vtvlv_gan_put(msg, tag, len, val);
+		break;
+	default:
+		return -EINVAL;
+	}
+	return 0;
+}
+
+/*! Encode a set of decoded TLVs according to a given definition into a message buffer
+ *  \param[inout] msg Caller-allocated message buffer with sufficient tailroom
+ *  \param[in] def structure defining the valid TLV tags / configurations
+ *  \param[in] tp decoded values to be encoded
+ *  \returns number of bytes consumed in msg; negative in case of error */
+int tlv_encode(struct msgb *msg, const struct tlv_definition *def, const struct tlv_parsed *tp)
+{
+	unsigned int tailroom_before = msgb_tailroom(msg);
+	unsigned int i;
+	int rc;
+
+	for (i = 0; i < ARRAY_SIZE(tp->lv); i++) {
+		/* skip entries in the array that aren't used/filled */
+		if (!TLVP_PRESENT(tp, i))
+			continue;
+
+		rc = tlv_encode_one(msg, def->def[i].type, i, TLVP_LEN(tp, i), TLVP_VAL(tp, i));
+		if (rc < 0)
+			return rc;
+	}
+
+	return tailroom_before - msgb_tailroom(msg);
+}
+
+/*! Encode a set of decoded TLVs according to a given definition and IE order into a message buffer
+ *  \param[inout] msg Caller-allocated message buffer with sufficient tailroom
+ *  \param[in] def structure defining the valid TLV tags / configurations
+ *  \param[in] tp decoded values to be encoded
+ *  \param[in] tag_order array of tags determining the IE encoding order
+ *  \param[in] tag_order_len length of tag_order
+ *  \returns number of bytes consumed in msg; negative in case of error */
+int tlv_encode_ordered(struct msgb *msg, const struct tlv_definition *def, const struct tlv_parsed *tp,
+			const uint8_t *tag_order, unsigned int tag_order_len)
+{
+
+	unsigned int tailroom_before = msgb_tailroom(msg);
+	unsigned int i;
+	int rc;
+
+	for (i = 0; i < tag_order_len; i++) {
+		uint8_t tag = tag_order[i];
+
+		/* skip entries in the array that aren't used/filled */
+		if (!TLVP_PRESENT(tp, tag))
+			continue;
+
+		rc = tlv_encode_one(msg, def->def[tag].type, tag, TLVP_LEN(tp, tag), TLVP_VAL(tp, tag));
+		if (rc < 0)
+			return rc;
+	}
+	return tailroom_before - msgb_tailroom(msg);
+}
+
 /*! Parse a single TLV encoded IE
  *  \param[out] o_tag the tag of the IE that was found
  *  \param[out] o_len length of the IE that was found
diff --git a/tests/tlv/tlv_test.c b/tests/tlv/tlv_test.c
index e2065b00..925d7628 100644
--- a/tests/tlv/tlv_test.c
+++ b/tests/tlv/tlv_test.c
@@ -1,4 +1,6 @@
+#include <osmocom/core/msgb.h>
 #include <osmocom/gsm/tlv.h>
+#include <osmocom/gsm/gsm0808.h>
 
 static void check_tlv_parse(uint8_t **data, size_t *data_len,
 			    uint8_t exp_tag, size_t exp_len, const uint8_t *exp_val)
@@ -286,12 +288,57 @@ static void test_tlv_repeated_ie()
 	OSMO_ASSERT(dec3[2].lv[tag].val == &test_data[2 + 3 + 3]);
 }
 
+static void test_tlv_encoder()
+{
+	const uint8_t enc_ies[] = {
+		0x17, 0x14,	0x06, 0x2b, 0x12, 0x2b, 0x0b, 0x40, 0x2b, 0xb7, 0x05, 0xd0, 0x63, 0x82, 0x95, 0x03, 0x05, 0x40,
+				0x07, 0x08, 0x43, 0x90,
+		0x2c,		0x04,
+		0x40,		0x42,
+	};
+	const uint8_t ie_order[] = { 0x2c, 0x40, 0x17 };
+	const uint8_t enc_ies_reordered[] = {
+		0x2c,		0x04,
+		0x40,		0x42,
+		0x17, 0x14,	0x06, 0x2b, 0x12, 0x2b, 0x0b, 0x40, 0x2b, 0xb7, 0x05, 0xd0, 0x63, 0x82, 0x95, 0x03, 0x05, 0x40,
+				0x07, 0x08, 0x43, 0x90,
+	};
+	struct tlv_parsed tp;
+	struct msgb *msg = msgb_alloc(1024, __func__);
+	int rc;
+
+	printf("Testing TLV encoder by decoding + re-encoding binary\n");
+
+	OSMO_ASSERT(msg);
+
+	/* decode BSSAP IEs specified above */
+	rc = osmo_bssap_tlv_parse(&tp, enc_ies, ARRAY_SIZE(enc_ies));
+	OSMO_ASSERT(rc == 3);
+
+	/* re-encode it */
+	rc = tlv_encode(msg, gsm0808_att_tlvdef(), &tp);
+	OSMO_ASSERT(rc == ARRAY_SIZE(enc_ies));
+	OSMO_ASSERT(!memcmp(msgb_data(msg), enc_ies, ARRAY_SIZE(enc_ies)));
+
+	msgb_reset(msg);
+
+	printf("Testing TLV encoder with IE ordering\n");
+
+	/* re-encodei in different order */
+	rc = tlv_encode_ordered(msg, gsm0808_att_tlvdef(), &tp, ie_order, ARRAY_SIZE(ie_order));
+	OSMO_ASSERT(rc == ARRAY_SIZE(enc_ies));
+	OSMO_ASSERT(!memcmp(msgb_data(msg), enc_ies_reordered, ARRAY_SIZE(enc_ies_reordered)));
+
+	msgb_free(msg);
+}
+
 int main(int argc, char **argv)
 {
 	//osmo_init_logging2(ctx, &info);
 
 	test_tlv_shift_functions();
 	test_tlv_repeated_ie();
+	test_tlv_encoder();
 
 	printf("Done.\n");
 	return EXIT_SUCCESS;
diff --git a/tests/tlv/tlv_test.ok b/tests/tlv/tlv_test.ok
index de159bfb..f3f0fd41 100644
--- a/tests/tlv/tlv_test.ok
+++ b/tests/tlv/tlv_test.ok
@@ -1,2 +1,4 @@
 Test shift functions
+Testing TLV encoder by decoding + re-encoding binary
+Testing TLV encoder with IE ordering
 Done.