commit_tx: expose more internal functions.

without having to build it, which is needed for limit enforcement.

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

Author: rustyrussell

lightningd/commit_tx.c

@@ -73,13 +73,11 @@ u64 htlc_success_fee(u64 feerate_per_kw)
 	return feerate_per_kw * 673 / 1000;
 }
 
-static const struct htlc **untrimmed(const tal_t *ctx,
-				     const struct htlc **htlcs,
-				     enum side side,
-				     u64 htlc_fee, u64 dust_limit_satoshis)
+static bool trim(const struct htlc *htlc,
+		 u64 feerate_per_kw, u64 dust_limit_satoshis,
+		 enum side side)
 {
-	const struct htlc **arr;
-	size_t i, n;
+	u64 htlc_fee;
 
 	/* BOLT #3:
 	 *
@@ -88,29 +86,36 @@ static const struct htlc **untrimmed(const tal_t *ctx,
 	 * owner, the commitment transaction MUST NOT contain that output,
 	 * otherwise it MUST be generated as specified in [Offered HTLC
 	 * Outputs](#offered-htlc-outputs).
+	 */
+	if (htlc_owner(htlc) == side)
+		htlc_fee = htlc_timeout_fee(feerate_per_kw);
+	/* BOLT #3:
 	 *
 	 * For every received HTLC, if the HTLC amount minus the HTLC-success
 	 * fee would be less than `dust-limit-satoshis` set by the transaction
 	 * owner, the commitment transaction MUST NOT contain that output,
 	 * otherwise it MUST be generated as specified in [Received HTLC
 	 * Outputs](#received-htlc-outputs).
 	 */
-	arr = tal_arr(ctx, const struct htlc *, tal_count(htlcs));
-	for (i = n = 0; i < tal_count(htlcs); i++) {
-		if (htlc_owner(htlcs[i]) != side)
-			continue;
-		if (htlcs[i]->msatoshi / 1000 < dust_limit_satoshis + htlc_fee)
-			continue;
-		arr[n++] = htlcs[i];
-	}
+	else
+		htlc_fee = htlc_success_fee(feerate_per_kw);
 
-	assert(n <= tal_count(arr));
-	tal_resize(&arr, n);
+	return htlc->msatoshi / 1000 < dust_limit_satoshis + htlc_fee;
+}
 
-	return arr;
+size_t commit_tx_num_untrimmed(const struct htlc **htlcs,
+			       u64 feerate_per_kw, u64 dust_limit_satoshis,
+			       enum side side)
+{
+	size_t i, n;
+
+	for (i = n = 0; i < tal_count(htlcs); i++)
+		n += !trim(htlcs[i], feerate_per_kw, dust_limit_satoshis, side);
+
+	return n;
 }
 
-static u64 commit_tx_base_fee(u64 feerate_per_kw, size_t num_untrimmed_htlcs)
+u64 commit_tx_base_fee(u64 feerate_per_kw, size_t num_untrimmed_htlcs)
 {
 	u64 weight;
 
@@ -139,6 +144,38 @@ static u64 commit_tx_base_fee(u64 feerate_per_kw, size_t num_untrimmed_htlcs)
 	return feerate_per_kw * weight / 1000;
 }
 
+static void add_offered_htlc_out(struct bitcoin_tx *tx, size_t n,
+				 const struct htlc *htlc,
+				 const struct pubkey *selfkey,
+				 const struct pubkey *otherkey)
+{
+	u8 *wscript = bitcoin_wscript_htlc_offer(tx,
+						 selfkey, otherkey,
+						 &htlc->rhash);
+	tx->output[n].amount = htlc->msatoshi / 1000;
+	tx->output[n].script = scriptpubkey_p2wsh(tx, wscript);
+	SUPERVERBOSE("# HTLC offered amount %"PRIu64" wscript %s\n",
+		     tx->output[n].amount, tal_hex(wscript, wscript));
+	tal_free(wscript);
+}
+
+static void add_received_htlc_out(struct bitcoin_tx *tx, size_t n,
+				  const struct htlc *htlc,
+				  const struct pubkey *selfkey,
+				  const struct pubkey *otherkey)
+{
+	u8 *wscript = bitcoin_wscript_htlc_receive(tx,
+						   &htlc->expiry,
+						   selfkey, otherkey,
+						   &htlc->rhash);
+	tx->output[n].amount = htlc->msatoshi / 1000;
+	tx->output[n].script = scriptpubkey_p2wsh(tx->output, wscript);
+	SUPERVERBOSE("# HTLC received amount %"PRIu64" wscript %s\n",
+		     tx->output[n].amount,
+		     tal_hex(wscript, wscript));
+	tal_free(wscript);
+}
+
 struct bitcoin_tx *commit_tx(const tal_t *ctx,
 			     const struct sha256_double *funding_txid,
 			     unsigned int funding_txout,
@@ -159,10 +196,9 @@ struct bitcoin_tx *commit_tx(const tal_t *ctx,
 			     enum side side)
 {
 	const tal_t *tmpctx = tal_tmpctx(ctx);
-	const struct htlc **offered, **received;
 	u64 base_fee_msat;
 	struct bitcoin_tx *tx;
-	size_t i, n;
+	size_t i, n, untrimmed;
 
 	assert(self_pay_msat + other_pay_msat <= funding_satoshis * 1000);
 
@@ -171,22 +207,16 @@ struct bitcoin_tx *commit_tx(const tal_t *ctx,
 	 * 1. Calculate which committed HTLCs need to be trimmed (see
 	 * [Trimmed Outputs](#trimmed-outputs)).
 	 */
-	offered = untrimmed(tmpctx, htlcs, side,
-			    htlc_timeout_fee(feerate_per_kw),
-			    dust_limit_satoshis);
-	received = untrimmed(tmpctx, htlcs, !side,
-			     htlc_success_fee(feerate_per_kw),
-			     dust_limit_satoshis);
+	untrimmed = commit_tx_num_untrimmed(htlcs,
+					    feerate_per_kw,
+					    dust_limit_satoshis, side);
 
 	/* BOLT #3:
 	 *
 	 * 2. Calculate the base [commitment transaction
 	 * fee](#fee-calculation).
 	 */
-	base_fee_msat = commit_tx_base_fee(feerate_per_kw,
-					   tal_count(offered)
-					   + tal_count(received))
-		* 1000;
+	base_fee_msat = commit_tx_base_fee(feerate_per_kw, untrimmed) * 1000;
 
 	SUPERVERBOSE("# base commitment transaction fee = %"PRIu64"\n",
 		     base_fee_msat / 1000);
@@ -200,45 +230,41 @@ struct bitcoin_tx *commit_tx(const tal_t *ctx,
 		     &self_pay_msat, &other_pay_msat);
 
 	/* Worst-case sizing: both to-local and to-remote outputs. */
-	tx = bitcoin_tx(ctx, 1, tal_count(offered) + tal_count(received) + 2);
+	tx = bitcoin_tx(ctx, 1, untrimmed + 2);
 
 	/* We keep track of which outputs have which HTLCs */
 	*htlcmap = tal_arr(tx, const struct htlc *, tal_count(tx->output));
 
+	/* This could be done in a single loop, but we follow the BOLT
+	 * literally to make comments in test vectors clearer. */
+
+	n = 0;
 	/* BOLT #3:
 	 *
-	 * 3. For every offered HTLC, if it is not trimmed, add an [offered
-	 *    HTLC output](#offered-htlc-outputs).
+	 * 3. For every offered HTLC, if it is not trimmed, add an
+	 *    [offered HTLC output](#offered-htlc-outputs).
 	 */
-	n = 0;
-	for (i = 0; i < tal_count(offered); i++, n++) {
-		u8 *wscript = bitcoin_wscript_htlc_offer(tmpctx,
-							 selfkey, otherkey,
-							 &offered[i]->rhash);
-		tx->output[n].amount = offered[i]->msatoshi / 1000;
-		tx->output[n].script = scriptpubkey_p2wsh(tx, wscript);
-		(*htlcmap)[n] = offered[i];
-		SUPERVERBOSE("# HTLC offered amount %"PRIu64" wscript %s\n",
-			     tx->output[n].amount,
-			     tal_hex(tmpctx, wscript));
+	for (i = 0; i < tal_count(htlcs); i++) {
+		if (htlc_owner(htlcs[i]) != side)
+			continue;
+		if (trim(htlcs[i], feerate_per_kw, dust_limit_satoshis, side))
+			continue;
+		add_offered_htlc_out(tx, n, htlcs[i], selfkey, otherkey);
+		(*htlcmap)[n++] = htlcs[i];
 	}
 
 	/* BOLT #3:
 	 *
-	 * 4. For every received HTLC, if it is not trimmed, add an [received
-	 *    HTLC output](#received-htlc-outputs).
+	 * 4. For every received HTLC, if it is not trimmed, add an
+	 *    [received HTLC output](#received-htlc-outputs).
 	 */
-	for (i = 0; i < tal_count(received); i++, n++) {
-		u8 *wscript = bitcoin_wscript_htlc_receive(tmpctx,
-							   &received[i]->expiry,
-							   selfkey, otherkey,
-							   &received[i]->rhash);
-		tx->output[n].amount = received[i]->msatoshi / 1000;
-		tx->output[n].script = scriptpubkey_p2wsh(tx, wscript);
-		(*htlcmap)[n] = received[i];
-		SUPERVERBOSE("# HTLC received amount %"PRIu64" wscript %s\n",
-			     tx->output[n].amount,
-			     tal_hex(tmpctx, wscript));
+	for (i = 0; i < tal_count(htlcs); i++) {
+		if (htlc_owner(htlcs[i]) == side)
+			continue;
+		if (trim(htlcs[i], feerate_per_kw, dust_limit_satoshis, side))
+			continue;
+		add_received_htlc_out(tx, n, htlcs[i],selfkey, otherkey);
+		(*htlcmap)[n++] = htlcs[i];
 	}
 
 	/* BOLT #3:

lightningd/commit_tx.h

@@ -20,6 +20,23 @@ u64 commit_number_obscurer(const struct pubkey *opener_payment_basepoint,
 u64 htlc_success_fee(u64 feerate_per_kw);
 u64 htlc_timeout_fee(u64 feerate_per_kw);
 
+/**
+ * commit_tx_num_untrimmed: how many of these htlc outputs will commit tx have?
+ * @htlcs: tal_arr of HTLCs
+ * @feerate_per_kw: feerate to use
+ * @dust_limit_satoshis: dust limit below which to trim outputs.
+ * @side: from which side's point of view
+ *
+ * We need @side because HTLC fees are different for offered and
+ * received HTLCs.
+ */
+size_t commit_tx_num_untrimmed(const struct htlc **htlcs,
+			       u64 feerate_per_kw, u64 dust_limit_satoshis,
+			       enum side side);
+
+/* Helper to calculate the base fee if we add this extra htlc */
+u64 commit_tx_base_fee(u64 feerate_per_kw, size_t num_untrimmed_htlcs);
+
 /**
  * commit_tx: create (unsigned) commitment tx to spend the funding tx output
  * @ctx: context to allocate transaction and @htlc_map from.

lightningd/test/Makefile

@@ -10,7 +10,7 @@ update-mocks: $(LIGHTNINGD_TEST_SRC:%=update-mocks/%)
 
 $(LIGHTNINGD_TEST_PROGRAMS): $(CCAN_OBJS) $(CORE_OBJS) $(CORE_TX_OBJS) $(BITCOIN_OBJS) $(WIRE_OBJS) $(LIBBASE58_OBJS) $(LIGHTNINGD_OLD_LIB_OBJS) utils.o libsecp256k1.a libsodium.a
 
-$(LIGHTNINGD_TEST_OBJS): $(LIGHTNINGD_HEADERS)
+$(LIGHTNINGD_TEST_OBJS): $(LIGHTNINGD_HEADERS) $(LIGHTNINGD_SRC) $(LIGHTNINGD_LIB_SRC)
 
 lightningd/tests: $(LIGHTNINGD_TEST_PROGRAMS:%=unittest/%)