locktime: nice abstractions for absolute and relative locktimes.

I got confused navigating these, especially since Alpha and Bitcoin
have diverged (BIP68 was proposed after Elements Alpha).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

Makefile

@@ -39,6 +39,7 @@ TEST_PROGRAMS :=				\
 BITCOIN_OBJS :=					\
 	bitcoin/address.o			\
 	bitcoin/base58.o			\
+	bitcoin/locktime.o			\
 	bitcoin/pubkey.o			\
 	bitcoin/script.o			\
 	bitcoin/shadouble.o			\

bitcoin/locktime.c

@@ -0,0 +1,101 @@
+#include "bitcoin/locktime.h"
+#include <assert.h>
+
+/* Alpha uses simple locktimes a-la the tx locktime field; BIP68 uses
+ * a bitmask */
+#define SECONDS_POINT 500000000
+
+#define BIP68_SECONDS_FLAG (1<<22)
+#define BIP68_LOCKTIME_MASK (0x0000FFFF)
+#define BIP68_SECONDS_SHIFT 9
+
+static bool abs_seconds_to_locktime(u32 seconds, u32 *locktime)
+{
+	*locktime = seconds;
+	if (*locktime < SECONDS_POINT)
+		return false;
+	return true;
+}
+
+static bool abs_blocks_to_locktime(u32 blocks, u32 *locktime)
+{
+	*locktime = blocks;
+	if (*locktime >= SECONDS_POINT)
+		return false;
+	return true;
+}
+
+static bool abs_is_seconds(u32 locktime)
+{
+	return locktime >= SECONDS_POINT;
+}
+
+bool seconds_to_rel_locktime(u32 seconds, struct rel_locktime *rel)
+{
+#ifdef HAS_BIP68
+	if ((seconds >> BIP68_SECONDS_SHIFT) > BIP68_LOCKTIME_MASK)
+		return false;
+	rel->locktime = BIP68_SECONDS_FLAG | (seconds >> BIP68_SECONDS_SHIFT);
+	return true;
+#else
+	/* Make abs-style time by adding SECONDS_POINT. */
+	return abs_seconds_to_locktime(seconds + SECONDS_POINT, &rel->locktime);
+#endif
+}
+
+bool blocks_to_rel_locktime(u32 blocks, struct rel_locktime *rel)
+{
+#ifdef HAS_BIP68
+	if (blocks > BIP68_LOCKTIME_MASK)
+		return false;
+#endif
+	rel->locktime = blocks;
+	return true;
+}
+
+bool rel_locktime_is_seconds(const struct rel_locktime *rel)
+{
+#ifdef HAS_BIP68
+	return rel->locktime & BIP68_SECONDS_FLAG;
+#else
+	return abs_is_seconds(rel->locktime);
+#endif
+}
+
+u32 rel_locktime_to_seconds(const struct rel_locktime *rel)
+{
+	assert(rel_locktime_is_seconds(rel));
+#ifdef HAS_BIP68
+	return rel->locktime & BIP68_LOCKTIME_MASK;
+#else
+	return rel->locktime - SECONDS_POINT;
+#endif
+}
+
+u32 bitcoin_nsequence(const struct rel_locktime *rel)
+{
+#ifdef HAS_BIP68
+	/* Can't set disable bit, or other bits except low 16 and bit 22 */
+	assert(!(rel->locktime & ~(BIP68_SECONDS_FLAG|BIP68_LOCKTIME_MASK)));
+	return rel->locktime;
+#else
+	/* Alpha uses the original proposal: simply invert the bits. */
+	return ~rel->locktime;
+#endif
+}
+
+bool seconds_to_abs_locktime(u32 seconds, struct abs_locktime *abs)
+{
+	return abs_seconds_to_locktime(seconds, &abs->locktime);
+}
+	
+bool blocks_to_abs_locktime(u32 blocks, struct abs_locktime *abs)
+{
+	return abs_blocks_to_locktime(blocks, &abs->locktime);
+}
+
+bool abs_locktime_is_seconds(const struct abs_locktime *abs)
+{
+	return abs_is_seconds(abs->locktime);
+}
+

bitcoin/locktime.h

@@ -0,0 +1,27 @@
+#ifndef LIGHTNING_BITCOIN_LOCKTIME_H
+#define LIGHTNING_BITCOIN_LOCKTIME_H
+#include <ccan/short_types/short_types.h>
+#include <stdbool.h>
+
+/* As used by nSequence and OP_CHECKSEQUENCEVERIFY (BIP68) */
+struct rel_locktime {
+	u32 locktime;
+};
+
+bool seconds_to_rel_locktime(u32 seconds, struct rel_locktime *rel);
+bool blocks_to_rel_locktime(u32 blocks, struct rel_locktime *rel);
+bool rel_locktime_is_seconds(const struct rel_locktime *rel);
+u32 rel_locktime_to_seconds(const struct rel_locktime *rel);
+
+u32 bitcoin_nsequence(const struct rel_locktime *rel);
+
+/* As used by nLocktime and OP_CHECKLOCKTIMEVERIFY (BIP65) */
+struct abs_locktime {
+	u32 locktime;
+};
+
+bool seconds_to_abs_locktime(u32 seconds, struct abs_locktime *abs);
+bool blocks_to_abs_locktime(u32 blocks, struct abs_locktime *abs);
+bool abs_locktime_is_seconds(const struct abs_locktime *abs);
+
+#endif /* LIGHTNING_BITCOIN_LOCKTIME_H */

bitcoin/script.c

@@ -3,6 +3,7 @@
 #include <ccan/endian/endian.h>
 #include <assert.h>
 #include "address.h"
+#include "locktime.h"
 #include "pubkey.h"
 #include "script.h"
 #include "signature.h"
@@ -179,8 +180,8 @@ u8 *scriptpubkey_p2sh(const tal_t *ctx, const u8 *redeemscript)
 u8 *scriptpubkey_htlc_send(const tal_t *ctx,
 			   const struct pubkey *ourkey,
 			   const struct pubkey *theirkey,
-			   uint32_t htlc_abstimeout,
+			   const struct abs_locktime *htlc_abstimeout,
-			   uint32_t locktime,
+			   const struct rel_locktime *locktime,
 			   const struct sha256 *commit_revoke,
 			   const struct sha256 *rhash)
 {
@@ -210,9 +211,9 @@ u8 *scriptpubkey_htlc_send(const tal_t *ctx,
 	add_op(&script, OP_ELSE);
 
 	/* If HTLC times out, they can collect after a delay. */
-	add_number(&script, htlc_abstimeout);
+	add_number(&script, htlc_abstimeout->locktime);
 	add_op(&script, OP_CHECKLOCKTIMEVERIFY);
-	add_number(&script, locktime);
+	add_number(&script, locktime->locktime);
 	add_op(&script, OP_CHECKSEQUENCEVERIFY);
 	add_op(&script, OP_2DROP);
 	add_push_key(&script, ourkey);
@@ -227,8 +228,8 @@ u8 *scriptpubkey_htlc_send(const tal_t *ctx,
 u8 *scriptpubkey_htlc_recv(const tal_t *ctx,
 			   const struct pubkey *ourkey,
 			   const struct pubkey *theirkey,
-			   uint32_t htlc_abstimeout,
+			   const struct abs_locktime *htlc_abstimeout,
-			   uint32_t locktime,
+			   const struct rel_locktime *locktime,
 			   const struct sha256 *commit_revoke,
 			   const struct sha256 *rhash)
 {
@@ -247,7 +248,7 @@ u8 *scriptpubkey_htlc_recv(const tal_t *ctx,
 	add_op(&script, OP_EQUAL);
 	add_op(&script, OP_IF);
 
-	add_number(&script, locktime);
+	add_number(&script, locktime->locktime);
 	add_op(&script, OP_CHECKSEQUENCEVERIFY);
 	/* Drop extra hash as well as locktime. */
 	add_op(&script, OP_2DROP);
@@ -264,7 +265,7 @@ u8 *scriptpubkey_htlc_recv(const tal_t *ctx,
 	add_op(&script, OP_NOTIF);
 
 	/* Otherwise, they must wait for HTLC timeout. */
-	add_number(&script, htlc_abstimeout);
+	add_number(&script, htlc_abstimeout->locktime);
 	add_op(&script, OP_CHECKLOCKTIMEVERIFY);
 	add_op(&script, OP_DROP);
 	add_op(&script, OP_ENDIF);
@@ -361,7 +362,7 @@ bool is_p2sh(const u8 *script, size_t script_len)
  * it after delay. */
 u8 *bitcoin_redeem_secret_or_delay(const tal_t *ctx,
 				   const struct pubkey *delayed_key,
-				   u32 locktime,
+				   const struct rel_locktime *locktime,
 				   const struct pubkey *key_if_secret_known,
 				   const struct sha256 *hash_of_secret)
 {
@@ -382,7 +383,7 @@ u8 *bitcoin_redeem_secret_or_delay(const tal_t *ctx,
 	add_op(&script, OP_ELSE);
 
 	/* Other can collect after a delay. */
-	add_number(&script, locktime);
+	add_number(&script, locktime->locktime);
 	add_op(&script, OP_CHECKSEQUENCEVERIFY);
 	add_op(&script, OP_DROP);
 	add_push_key(&script, delayed_key);

bitcoin/script.h

@@ -7,6 +7,8 @@
 struct bitcoin_address;
 struct pubkey;
 struct sha256;
+struct rel_locktime;
+struct abs_locktime;
 
 /* A bitcoin signature includes one byte for the type. */
 struct bitcoin_signature {
@@ -26,7 +28,7 @@ u8 *bitcoin_redeem_single(const tal_t *ctx, const struct pubkey *key);
  * it after delay. */
 u8 *bitcoin_redeem_secret_or_delay(const tal_t *ctx,
 				   const struct pubkey *delayed_key,
-				   u32 locktime,
+				   const struct rel_locktime *locktime,
 				   const struct pubkey *key_if_secret_known,
 				   const struct sha256 *hash_of_secret);
 
@@ -41,8 +43,8 @@ u8 *scriptsig_pay_to_pubkeyhash(const tal_t *ctx,
 u8 *scriptpubkey_htlc_send(const tal_t *ctx,
 			   const struct pubkey *ourkey,
 			   const struct pubkey *theirkey,
-			   uint32_t htlc_abstimeout,
+			   const struct abs_locktime *htlc_abstimeout,
-			   uint32_t locktime,
+			   const struct rel_locktime *locktime,
 			   const struct sha256 *commit_revoke,
 			   const struct sha256 *rhash);
 
@@ -50,8 +52,8 @@ u8 *scriptpubkey_htlc_send(const tal_t *ctx,
 u8 *scriptpubkey_htlc_recv(const tal_t *ctx,
 			   const struct pubkey *ourkey,
 			   const struct pubkey *theirkey,
-			   uint32_t htlc_abstimeout,
+			   const struct abs_locktime *htlc_abstimeout,
-			   uint32_t locktime,
+			   const struct rel_locktime *locktime,
 			   const struct sha256 *commit_revoke,
 			   const struct sha256 *rhash);
 

bitcoin/tx.c

@@ -546,17 +546,3 @@ bool bitcoin_tx_write(int fd, const struct bitcoin_tx *tx)
 	tal_free(tx_arr);
 	return ok;
 }
-
-u32 bitcoin_nsequence(u32 locktime)
-{
-#ifdef HAS_BIP68
-	/* FIXME: return fail to caller. */
-	/* Can't set disable bit, or other bits except low 16 and bit 22 */
-	assert(!(locktime & ~((1 << 22) | 0xFFFF)));
-	return locktime;
-#else
-	/* Alpha uses the original proposal: simply invert the bits. */
-	return ~locktime;
-#endif
-}
-		

bitcoin/tx.h

@@ -66,6 +66,4 @@ bool bitcoin_txid_from_hex(const char *hexstr, size_t hexstr_len,
 bool bitcoin_txid_to_hex(const struct sha256_double *txid,
 			 char *hexstr, size_t hexstr_len);
 
-/* Get sequence number for a given locktime. */
-u32 bitcoin_nsequence(u32 locktime);
 #endif /* LIGHTNING_BITCOIN_TX_H */

commit_tx.c

@@ -1,3 +1,4 @@
+#include "bitcoin/locktime.h"
 #include "bitcoin/pubkey.h"
 #include "bitcoin/script.h"
 #include "bitcoin/shadouble.h"
@@ -14,16 +15,16 @@ static bool add_htlc(struct bitcoin_tx *tx, size_t n,
 		     const struct pubkey *ourkey,
 		     const struct pubkey *theirkey,
 		     const struct sha256 *rhash,
-		     u32 locktime,
+		     const struct rel_locktime *locktime,
 		     u8 *(*scriptpubkeyfn)(const tal_t *,
 					   const struct pubkey *,
 					   const struct pubkey *,
-					   uint32_t,
+					   const struct abs_locktime *,
-					   uint32_t,
+					   const struct rel_locktime *,
 					   const struct sha256 *,
 					   const struct sha256 *))
 {
-	uint32_t htlc_abstime;
+	struct abs_locktime htlc_abstime;
 	struct sha256 htlc_rhash;
 
 	assert(!tx->output[n].script);
@@ -35,7 +36,7 @@ static bool add_htlc(struct bitcoin_tx *tx, size_t n,
 	proto_to_sha256(h->r_hash, &htlc_rhash);
 	tx->output[n].script = scriptpubkey_p2sh(tx,
 				 scriptpubkeyfn(tx, ourkey, theirkey,
-						htlc_abstime, locktime, rhash,
+						&htlc_abstime, locktime, rhash,
 						&htlc_rhash));
 	tx->output[n].script_length = tal_count(tx->output[n].script);
 	tx->output[n].amount = h->amount_msat / 1000;
@@ -52,7 +53,7 @@ struct bitcoin_tx *create_commit_tx(const tal_t *ctx,
 	struct bitcoin_tx *tx;
 	const u8 *redeemscript;
 	struct pubkey ourkey, theirkey;
-	u32 locktime;
+	struct rel_locktime locktime;
 	size_t i, num;
 	uint64_t total;
 
@@ -76,7 +77,7 @@ struct bitcoin_tx *create_commit_tx(const tal_t *ctx,
 
 	/* First output is a P2SH to a complex redeem script (usu. for me) */
 	redeemscript = bitcoin_redeem_secret_or_delay(tx, &ourkey,
-						      locktime,
+						      &locktime,
 						      &theirkey,
 						      rhash);
 	tx->output[0].script = scriptpubkey_p2sh(tx, redeemscript);
@@ -97,14 +98,14 @@ struct bitcoin_tx *create_commit_tx(const tal_t *ctx,
 	/* HTLCs we've sent. */
 	for (i = 0; i < tal_count(cstate->a.htlcs); i++) {
 		if (!add_htlc(tx, num, cstate->a.htlcs[i], &ourkey, &theirkey,
-			      rhash, locktime, scriptpubkey_htlc_send))
+			      rhash, &locktime, scriptpubkey_htlc_send))
 			return tal_free(tx);
 		total += tx->output[num++].amount;
 	}
 	/* HTLCs we've received. */
 	for (i = 0; i < tal_count(cstate->b.htlcs); i++) {
 		if (!add_htlc(tx, num, cstate->b.htlcs[i], &ourkey, &theirkey,
-			      rhash, locktime, scriptpubkey_htlc_recv))
+			      rhash, &locktime, scriptpubkey_htlc_recv))
 			return tal_free(tx);
 		total += tx->output[num++].amount;
 	}

protobuf_convert.c

@@ -1,4 +1,5 @@
 #include <ccan/crypto/sha256/sha256.h>
+#include "bitcoin/locktime.h"
 #include "bitcoin/pubkey.h"
 #include "bitcoin/signature.h"
 #include "protobuf_convert.h"
@@ -105,54 +106,26 @@ void proto_to_sha256(const Sha256Hash *pb, struct sha256 *hash)
 	memcpy(hash->u.u8 + 24, &pb->d, 8);
 }
 
-static bool proto_to_locktime(const Locktime *l, uint32_t off,
+bool proto_to_rel_locktime(const Locktime *l, struct rel_locktime *locktime)
-			      uint32_t *locktime)
 {
 	switch (l->locktime_case) {
 	case LOCKTIME__LOCKTIME_SECONDS:
-		*locktime = off + l->seconds;
+		return seconds_to_rel_locktime(l->seconds, locktime);
-		/* Check for wrap, or too low value */
-		if (*locktime < 500000000)
-			return false;
-		break;
 	case LOCKTIME__LOCKTIME_BLOCKS:
-		if (l->blocks >= 500000000)
+		return blocks_to_rel_locktime(l->blocks, locktime);
-			return false;
-		*locktime = l->blocks;
-		break;
 	default:
 		return false;
 	}
-	return true;
 }
 
-bool proto_to_rel_locktime(const Locktime *l, uint32_t *locktime)
+bool proto_to_abs_locktime(const Locktime *l, struct abs_locktime *locktime)
 {
-	/* Original proposal from Elements Alpha was simply locktime. */
-#ifdef HAS_BIP68
 	switch (l->locktime_case) {
 	case LOCKTIME__LOCKTIME_SECONDS:
-		*locktime = (1 << 22) | (l->seconds / 512);
+		return seconds_to_abs_locktime(l->seconds, locktime);
-		if (l->seconds / 512 > 0xFFFF)
-			return false;
-		break;
 	case LOCKTIME__LOCKTIME_BLOCKS:
-		*locktime = l->blocks;
+		return blocks_to_abs_locktime(l->blocks, locktime);
-		if (l->blocks > 0xFFFF)
-			return false;
-		break;
 	default:
 		return false;
 	}
-	/* No other bits should be set. */
-	assert((*locktime & ~((1 << 22) | 0xFFFF)) == 0);
-	return true;
-#else
-	return proto_to_locktime(l, 500000000, locktime);
-#endif
-}
-
-bool proto_to_abs_locktime(const Locktime *l, uint32_t *locktime)
-{
-	return proto_to_locktime(l, 0, locktime);
 }

protobuf_convert.h

@@ -19,6 +19,8 @@ struct sha256;
 Sha256Hash *sha256_to_proto(const tal_t *ctx, const struct sha256 *hash);
 void proto_to_sha256(const Sha256Hash *pb, struct sha256 *hash);
 
-bool proto_to_rel_locktime(const Locktime *l, uint32_t *locktime);
+struct rel_locktime;
-bool proto_to_abs_locktime(const Locktime *l, uint32_t *locktime);
+struct abs_locktime;
+bool proto_to_rel_locktime(const Locktime *l, struct rel_locktime *locktime);
+bool proto_to_abs_locktime(const Locktime *l, struct abs_locktime *locktime);
 #endif /* LIGHTNING_PROTOBUF_CONVERT_H */

test-cli/create-commit-spend-tx.c

@@ -21,6 +21,7 @@
 #include "test-cli/gather_updates.h"
 #include "funding.h"
 #include "version.h"
+#include "bitcoin/locktime.h"
 #include <unistd.h>
 
 int main(int argc, char *argv[])
@@ -37,7 +38,7 @@ int main(int argc, char *argv[])
 	struct sha256 rhash;
 	size_t p2sh_out;
 	u64 fee = 10000;
-	u32 locktime;
+	struct rel_locktime locktime;
 
 	err_set_progname(argv[0]);
 
@@ -87,7 +88,7 @@ int main(int argc, char *argv[])
 		       NULL, &rhash, NULL, NULL);
 
 	/* Create redeem script */
-	redeemscript = bitcoin_redeem_secret_or_delay(ctx, &pubkey1, locktime,
+	redeemscript = bitcoin_redeem_secret_or_delay(ctx, &pubkey1, &locktime,
 						      &pubkey2, &rhash);
 
 	/* Now, create transaction to spend it. */
@@ -98,7 +99,7 @@ int main(int argc, char *argv[])
 	tx->input[0].input_amount = commit->output[p2sh_out].amount;
 	tx->fee = fee;
 
-	tx->input[0].sequence_number = bitcoin_nsequence(locktime);
+	tx->input[0].sequence_number = bitcoin_nsequence(&locktime);
 
 	if (commit->output[p2sh_out].amount <= fee)
 		errx(1, "Amount of %llu won't exceed fee",

test-cli/create-htlc-spend-tx.c

@@ -16,6 +16,7 @@
 #include "bitcoin/privkey.h"
 #include "protobuf_convert.h"
 #include "find_p2sh_out.h"
+#include "bitcoin/locktime.h"
 #include "version.h"
 #include <unistd.h>
 
@@ -31,7 +32,8 @@ int main(int argc, char *argv[])
 	struct bitcoin_signature sig;
 	struct privkey privkey;
 	bool testnet;
-	u32 locktime, htlc_abstimeout;
+	struct rel_locktime locktime;
+	struct abs_locktime htlc_abstimeout;
 	char *rvalue = NULL, *preimage = NULL;
 	bool received, own_commit_tx;
 	Pkt *pkt;
@@ -114,13 +116,13 @@ int main(int argc, char *argv[])
 
 	if (received) {
 		redeemscript = scriptpubkey_htlc_recv(ctx, &pubkey1, &pubkey2,
-						      htlc_abstimeout,
+						      &htlc_abstimeout,
-						      locktime, &revoke_hash,
+						      &locktime, &revoke_hash,
 						      &htlc_rhash);
 	} else {
 		redeemscript = scriptpubkey_htlc_send(ctx, &pubkey1, &pubkey2,
-						      htlc_abstimeout,
+						      &htlc_abstimeout,
-						      locktime, &revoke_hash,
+						      &locktime, &revoke_hash,
 						      &htlc_rhash);
 	}
 
@@ -163,14 +165,14 @@ int main(int argc, char *argv[])
 
 	if (!secret_len) {
 		/* We must be relying on HTLC timeout. */
-		tx->lock_time = htlc_abstimeout;
+		tx->lock_time = htlc_abstimeout.locktime;
 		/* Locktime only applies if an input has seq != ffffffff... */
 		tx->input[0].sequence_number = 0;
 	}
 
 	/* If it's our own commit tx, we also need delay. */
 	if (own_commit_tx)
-		tx->input[0].sequence_number = bitcoin_nsequence(locktime);
+		tx->input[0].sequence_number = bitcoin_nsequence(&locktime);
 
 	/* Leave 10,000 satoshi as fee (if we can!). */
 	tx->fee = 10000;

test-cli/create-steal-tx.c

@@ -15,6 +15,7 @@
 #include "bitcoin/privkey.h"
 #include "protobuf_convert.h"
 #include "version.h"
+#include "bitcoin/locktime.h"
 #include <unistd.h>
 
 int main(int argc, char *argv[])
@@ -30,7 +31,7 @@ int main(int argc, char *argv[])
 	struct bitcoin_signature sig;
 	struct privkey privkey;
 	bool testnet;
-	u32 locktime_seconds;
+	struct rel_locktime locktime;
 
 	err_set_progname(argv[0]);
 
@@ -68,7 +69,7 @@ int main(int argc, char *argv[])
 
 	o1 = pkt_from_file(argv[4], PKT__PKT_OPEN)->open;
 	o2 = pkt_from_file(argv[5], PKT__PKT_OPEN)->open;
-	if (!proto_to_rel_locktime(o1->delay, &locktime_seconds))
+	if (!proto_to_rel_locktime(o1->delay, &locktime))
 		errx(1, "Invalid locktime in o2");
 
 	if (!pubkey_from_hexstr(argv[6], &outpubkey))
@@ -85,7 +86,7 @@ int main(int argc, char *argv[])
 	/* Now, which commit output?  Match redeem script. */
 	sha256(&revoke_hash, &revoke_preimage, sizeof(revoke_preimage));
 	redeemscript = bitcoin_redeem_secret_or_delay(ctx, &pubkey2,
-						      locktime_seconds,
+						      &locktime,
 						      &pubkey1, &revoke_hash);
 	p2sh = scriptpubkey_p2sh(ctx, redeemscript);