Create bitcoin_tx helper.

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

anchor.c

@@ -10,32 +10,30 @@ struct bitcoin_tx *anchor_tx_create(const tal_t *ctx,
 				    const OpenChannel *o2,
 				    size_t **inmapp, size_t **outmapp)
 {
-	uint64_t i;
-	struct bitcoin_tx *tx = tal(ctx, struct bitcoin_tx);
+	uint64_t i, n_out;
+	struct bitcoin_tx *tx;
 	u8 *redeemscript;
 	size_t *inmap, *outmap;
 
-	/* Use lesser of two versions. */
+	if (add_overflows_size_t(o1->anchor->n_inputs, o2->anchor->n_inputs))
+		return tal_free(tx);
+
+	n_out = 1 + !!o1->anchor->change + !!o2->anchor->change;
+	tx = bitcoin_tx(ctx, o1->anchor->n_inputs+o2->anchor->n_inputs, n_out);
+
+	/* Override version to use lesser of two versions. */
 	if (o1->tx_version < o2->tx_version)
 		tx->version = o1->tx_version;
 	else
 		tx->version = o2->tx_version;
-
-	if (add_overflows_size_t(o1->anchor->n_inputs, o2->anchor->n_inputs))
-		return tal_free(tx);
-	tx->input_count = o1->anchor->n_inputs + o2->anchor->n_inputs;
-
-	tx->input = tal_arr(tx, struct bitcoin_tx_input, tx->input_count);
+	
 	/* Populate inputs. */
 	for (i = 0; i < o1->anchor->n_inputs; i++) {
 		BitcoinInput *pb = o1->anchor->inputs[i];
 		struct bitcoin_tx_input *in = &tx->input[i];
 		proto_to_sha256(pb->txid, &in->txid.sha);
 		in->index = pb->output;
-		in->sequence_number = 0xFFFFFFFF;
 		/* Leave inputs as stubs for now, for signing. */
-		in->script_length = 0;
-		in->script = NULL;
 	}
 	for (i = 0; i < o2->anchor->n_inputs; i++) {
 		BitcoinInput *pb = o2->anchor->inputs[i];
@@ -43,17 +41,10 @@ struct bitcoin_tx *anchor_tx_create(const tal_t *ctx,
 			= &tx->input[o1->anchor->n_inputs + i];
 		proto_to_sha256(pb->txid, &in->txid.sha);
 		in->index = pb->output;
-		in->sequence_number = 0xFFFFFFFF;
 		/* Leave inputs as stubs for now, for signing. */
-		in->script_length = 0;
-		in->script = NULL;
 	}
 
 	/* Populate outputs. */
-	tx->output_count = 1;
-	/* Allocate for worst case. */
-	tx->output = tal_arr(tx, struct bitcoin_tx_output, 3);
-
 	if (add_overflows_u64(o1->anchor->total, o2->anchor->total))
 		return tal_free(tx);
 
@@ -65,19 +56,21 @@ struct bitcoin_tx *anchor_tx_create(const tal_t *ctx,
 	tx->output[0].script_length = tal_count(tx->output[0].script);
 
 	/* Add change transactions (if any) */
+	n_out = 1;
 	if (o1->anchor->change) {
-		struct bitcoin_tx_output *out = &tx->output[tx->output_count++];
+		struct bitcoin_tx_output *out = &tx->output[n_out++];
 		out->amount = o1->anchor->change->amount;
 		out->script_length = o1->anchor->change->script.len;
 		out->script = o1->anchor->change->script.data;
 	}
 	if (o2->anchor->change) {
-		struct bitcoin_tx_output *out = &tx->output[tx->output_count++];
+		struct bitcoin_tx_output *out = &tx->output[n_out++];
 		out->amount = o2->anchor->change->amount;
 		out->script_length = o2->anchor->change->script.len;
 		out->script = o2->anchor->change->script.data;
 	}
-
+	assert(n_out == tx->output_count);
+	
 	if (inmapp)
 		inmap = *inmapp = tal_arr(ctx, size_t, tx->input_count);
 	else

bitcoin_tx.c

@@ -1,5 +1,6 @@
 #include "bitcoin_tx.h"
 #include <ccan/crypto/sha256/sha256.h>
+#include <assert.h>
 
 static void sha256_varint(struct sha256_ctx *ctx, varint_t v)
 {
@@ -62,3 +63,24 @@ void sha256_tx(struct sha256_ctx *ctx, const struct bitcoin_tx *tx)
 		sha256_tx_output(ctx, &tx->output[i]);
 	sha256_le32(ctx, tx->lock_time);
 }
+
+struct bitcoin_tx *bitcoin_tx(const tal_t *ctx, varint_t input_count,
+			      varint_t output_count)
+{
+	struct bitcoin_tx *tx = tal(ctx, struct bitcoin_tx);
+	size_t i;
+
+	tx->version = BITCOIN_TX_VERSION;
+	tx->output_count = output_count;
+	tx->output = tal_arrz(tx, struct bitcoin_tx_output, output_count);
+	tx->input_count = input_count;
+	tx->input = tal_arrz(tx, struct bitcoin_tx_input, input_count);
+	for (i = 0; i < tx->input_count; i++) {
+		/* We assume NULL is a zero bitmap */
+		assert(tx->input[i].script == NULL);
+		tx->input[i].sequence_number = 0xFFFFFFFF;
+	}
+	tx->lock_time = 0xFFFFFFFF;
+
+	return tx;
+}

bitcoin_tx.h

@@ -1,6 +1,7 @@
 #ifndef LIGHTNING_BITCOIN_TX_H
 #define LIGHTNING_BITCOIN_TX_H
 #include <ccan/short_types/short_types.h>
+#include <ccan/tal/tal.h>
 #include "shadouble.h"
 
 #define BITCOIN_TX_VERSION 1
@@ -35,4 +36,9 @@ struct bitcoin_tx_input {
  * signature. */
 void sha256_tx(struct sha256_ctx *shactx, const struct bitcoin_tx *tx);
 
+/* Allocate a tx: you just need to fill in inputs and outputs (they're
+ * zeroed with inputs' sequence_number set to FFFFFFFF) */
+struct bitcoin_tx *bitcoin_tx(const tal_t *ctx, varint_t input_count,
+			      varint_t output_count);
+
 #endif /* LIGHTNING_BITCOIN_TX_H */