find_p2sh_out: extract helper.

Really only for our silly little utils.

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

Makefile

@@ -5,7 +5,7 @@ PROTOCC:=protoc-c
 
 PROGRAMS := open-channel open-anchor-scriptsigs leak-anchor-sigs open-commit-sig check-commit-sig check-anchor-scriptsigs get-anchor-depth create-steal-tx create-commit-spend-tx close-channel create-close-tx
 
-HELPER_OBJS := base58.o lightning.pb-c.o shadouble.o pkt.o bitcoin_script.o permute_tx.o signature.o bitcoin_tx.o bitcoin_address.o anchor.o commit_tx.o pubkey.o opt_bits.o close_tx.o
+HELPER_OBJS := base58.o lightning.pb-c.o shadouble.o pkt.o bitcoin_script.o permute_tx.o signature.o bitcoin_tx.o bitcoin_address.o anchor.o commit_tx.o pubkey.o opt_bits.o close_tx.o find_p2sh_out.o
 
 CCAN_OBJS := ccan-crypto-sha256.o ccan-crypto-shachain.o ccan-err.o ccan-tal.o ccan-tal-str.o ccan-take.o ccan-list.o ccan-str.o ccan-opt-helpers.o ccan-opt.o ccan-opt-parse.o ccan-opt-usage.o ccan-read_write_all.o ccan-str-hex.o ccan-tal-grab_file.o ccan-noerr.o
 

close-channel.c

@@ -18,6 +18,7 @@
 #include "signature.h"
 #include "pubkey.h"
 #include "close_tx.h"
+#include "find_p2sh_out.h"
 #include <openssl/ec.h>
 #include <unistd.h>
 
@@ -32,8 +33,7 @@ int main(int argc, char *argv[])
 	EC_KEY *privkey;
 	bool testnet, complete = false;
 	struct pubkey pubkey1, pubkey2;
-	u8 *redeemscript, *p2sh;
+	u8 *redeemscript;
-	size_t i;
 
 	err_set_progname(argv[0]);
 
@@ -74,20 +74,9 @@ int main(int argc, char *argv[])
 	/* This is what the anchor pays to; figure out whick output. */
 	redeemscript = bitcoin_redeem_2of2(ctx, &pubkey1, &pubkey2);
 
-	/* This is the scriptPubKey commit tx will have */
-	p2sh = scriptpubkey_p2sh(ctx, redeemscript);
-
-	for (i = 0; i < anchor->output_count; i++) {
-		if (anchor->output[i].script_length != tal_count(p2sh))
-			continue;
-		if (memcmp(anchor->output[i].script, p2sh, tal_count(p2sh)) == 0)
-			break;
-	}
-	if (i == anchor->output_count)
-		errx(1, "No matching output in %s", argv[1]);
-
 	/* Now create the close tx to spend 2/2 output of anchor. */
-	close_tx = create_close_tx(ctx, o1, o2, &anchor_txid, i);
+	close_tx = create_close_tx(ctx, o1, o2, &anchor_txid,
+				   find_p2sh_out(anchor, redeemscript));
 
 	/* Sign it for them. */
 	sign_tx_input(ctx, close_tx, 0, redeemscript, tal_count(redeemscript),

create-close-tx.c

@@ -17,6 +17,7 @@
 #include "signature.h"
 #include "pubkey.h"
 #include "close_tx.h"
+#include "find_p2sh_out.h"
 #include <openssl/ec.h>
 #include <unistd.h>
 
@@ -28,11 +29,10 @@ int main(int argc, char *argv[])
 	struct sha256_double anchor_txid;
 	struct bitcoin_signature sig1, sig2;
 	struct pubkey pubkey1, pubkey2;
-	u8 *redeemscript, *p2sh, *tx_arr;
+	u8 *redeemscript, *tx_arr;
 	char *tx_hex;
 	CloseChannel *close;
 	CloseChannelComplete *closecomplete;
-	size_t i;
 
 	err_set_progname(argv[0]);
 
@@ -64,20 +64,9 @@ int main(int argc, char *argv[])
 	/* This is what the anchor pays to; figure out which output. */
 	redeemscript = bitcoin_redeem_2of2(ctx, &pubkey1, &pubkey2);
 
-	/* This is the scriptPubKey commit tx will have */
-	p2sh = scriptpubkey_p2sh(ctx, redeemscript);
-
-	for (i = 0; i < anchor->output_count; i++) {
-		if (anchor->output[i].script_length != tal_count(p2sh))
-			continue;
-		if (memcmp(anchor->output[i].script, p2sh, tal_count(p2sh)) == 0)
-			break;
-	}
-	if (i == anchor->output_count)
-		errx(1, "No matching output in %s", argv[1]);
-
 	/* Now create the close tx to spend 2/2 output of anchor. */
-	close_tx = create_close_tx(ctx, o1, o2, &anchor_txid, i);
+	close_tx = create_close_tx(ctx, o1, o2, &anchor_txid,
+				   find_p2sh_out(anchor, redeemscript));
 
 	/* Signatures well-formed? */
 	sig1.stype = sig2.stype = SIGHASH_ALL;

create-commit-spend-tx.c

@@ -20,6 +20,7 @@
 #include "pubkey.h"
 #include "bitcoin_address.h"
 #include "opt_bits.h"
+#include "find_p2sh_out.h"
 #include <openssl/ec.h>
 #include <unistd.h>
 
@@ -32,10 +33,10 @@ int main(int argc, char *argv[])
 	EC_KEY *privkey;
 	bool testnet;
 	struct pubkey pubkey1, pubkey2, outpubkey;
-	u8 *redeemscript, *p2sh, *tx_arr;
+	u8 *redeemscript, *tx_arr;
 	char *tx_hex;
 	struct sha256 rhash;
-	size_t i;
+	size_t p2sh_out;
 	u64 fee = 10000;
 
 	err_set_progname(argv[0]);
@@ -87,29 +88,17 @@ int main(int argc, char *argv[])
 						o2->locktime_seconds,
 						&pubkey2, &rhash);
 
-	/* This is the scriptPubKey commit tx will have */
-	p2sh = scriptpubkey_p2sh(ctx, redeemscript);
-
-	/* Which output of commit tx are we spending? */
-	for (i = 0; i < commit->output_count; i++) {
-		if (commit->output[i].script_length != tal_count(p2sh))
-			continue;
-		if (memcmp(commit->output[i].script, p2sh, tal_count(p2sh)) == 0)
-			break;
-	}
-	if (i == commit->output_count)
-		errx(1, "No matching output in %s", argv[1]);
-
 	/* Now, create transaction to spend it. */
 	tx = bitcoin_tx(ctx, 1, 1);
 	bitcoin_txid(commit, &tx->input[0].txid);
-	tx->input[0].index = i;
+	p2sh_out = find_p2sh_out(commit, redeemscript);
+	tx->input[0].index = p2sh_out;
 
-	if (commit->output[i].amount <= fee)
+	if (commit->output[p2sh_out].amount <= fee)
 		errx(1, "Amount of %llu won't exceed fee",
-		     (unsigned long long)commit->output[i].amount);
+		     (unsigned long long)commit->output[p2sh_out].amount);
 
-	tx->output[0].amount = commit->output[i].amount - fee;
+	tx->output[0].amount = commit->output[p2sh_out].amount - fee;
 	tx->output[0].script = scriptpubkey_p2sh(tx,
 						 bitcoin_redeem_single(tx, &outpubkey));
 	tx->output[0].script_length = cpu_to_le32(tal_count(tx->output[0].script));

find_p2sh_out.c

@@ -0,0 +1,24 @@
+#include "find_p2sh_out.h"
+#include "bitcoin_tx.h"
+#include "bitcoin_script.h"
+#include <string.h>
+#include <ccan/err/err.h>
+#include <ccan/tal/tal.h>
+
+u32 find_p2sh_out(const struct bitcoin_tx *tx, u8 *redeemscript)
+{
+	/* This is the scriptPubKey commit tx will have */
+	u8 *p2sh = scriptpubkey_p2sh(NULL, redeemscript);
+	u32 i;
+
+	for (i = 0; i < tx->output_count; i++) {
+		if (tx->output[i].script_length != tal_count(p2sh))
+			continue;
+		if (memcmp(tx->output[i].script, p2sh, tal_count(p2sh)) == 0)
+			break;
+	}
+	if (i == tx->output_count)
+		errx(1, "No matching output in tx");
+	tal_free(p2sh);
+	return i;
+}

find_p2sh_out.h

@@ -0,0 +1,11 @@
+#ifndef LIGHTNING_FIND_P2SH_OUT_H
+#define LIGHTNING_FIND_P2SH_OUT_H
+#include <ccan/short_types/short_types.h>
+
+struct bitcoin_tx;
+
+/* Normally we'd simply remember which output of the anchor or commit
+ * tx is the one which pays to this script.  But for these examples,
+ * we have to figure it out by recreating the output and matching. */
+u32 find_p2sh_out(const struct bitcoin_tx *tx, u8 *redeemscript);
+#endif /* LIGHTNING_FIND_P2SH_OUT_H */