find_p2sh_out: extract helper.

Really only for our silly little utils.

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

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;
+}