shachain: shachain_get_secret helper.

This is a wrapper around shachain_get_hash, which converts the
commit_num to an index and returns a 'struct secret' rather than a
'struct sha256' (which is really an internal detail).

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

common/derive_basepoints.c

@@ -228,3 +228,16 @@ void fromwire_basepoints(const u8 **ptr, size_t *max,
 	fromwire_pubkey(ptr, max, &b->htlc);
 	fromwire_pubkey(ptr, max, &b->delayed_payment);
 }
+
+bool shachain_get_secret(const struct shachain *shachain,
+			 u64 commit_num,
+			 struct secret *preimage)
+{
+	struct sha256 sha;
+
+	if (!shachain_get_hash(shachain, shachain_index(commit_num), &sha))
+		return false;
+	BUILD_ASSERT(sizeof(*preimage) == sizeof(sha));
+	memcpy(preimage, &sha, sizeof(*preimage));
+	return true;
+}

common/derive_basepoints.h

@@ -145,6 +145,10 @@ static inline u64 revocations_received(const struct shachain *shachain)
 	return (1ULL << SHACHAIN_BITS) - (shachain_next_index(shachain) + 1);
 }
 
+bool shachain_get_secret(const struct shachain *shachain,
+			 u64 commit_num,
+			 struct secret *preimage);
+
 void towire_basepoints(u8 **pptr, const struct basepoints *b);
 void fromwire_basepoints(const u8 **ptr, size_t *max,
 			 struct basepoints *b);

onchaind/onchain.c

@@ -1698,7 +1698,7 @@ static void steal_htlc(struct tracked_output *out)
 static void handle_their_cheat(const struct bitcoin_tx *tx,
 			       const struct bitcoin_txid *txid,
 			       u32 tx_blockheight,
-			       const struct sha256 *revocation_preimage,
+			       const struct secret *revocation_preimage,
 			       const struct basepoints basepoints[NUM_SIDES],
 			       const struct htlc_stub *htlcs,
 			       const bool *tell_if_missing,
@@ -2223,7 +2223,7 @@ int main(int argc, char *argv[])
 		 *    party crashed, for instance. One side publishes its
 		 *    *latest commitment transaction*.
 		 */
-		struct sha256 revocation_preimage;
+		struct secret revocation_preimage;
 		commit_num = unmask_commit_number(tx, funder,
 						  &basepoints[LOCAL].payment,
 						  &basepoints[REMOTE].payment);
@@ -2246,9 +2246,8 @@ int main(int argc, char *argv[])
 		 * *outdated commitment transaction* (presumably, a prior
 		 * version, which is more in its favor).
 		 */
-		else if (shachain_get_hash(&shachain,
-					   shachain_index(commit_num),
-					   &revocation_preimage)) {
+		else if (shachain_get_secret(&shachain, commit_num,
+					     &revocation_preimage)) {
 			handle_their_cheat(tx, &txid,
 					   tx_blockheight,
 					   &revocation_preimage,

onchaind/test/run-grind_feerate.c

@@ -81,6 +81,11 @@ void master_badmsg(u32 type_expected UNNEEDED, const u8 *msg)
 /* Generated stub for peer_billboard */
 void peer_billboard(bool perm UNNEEDED, const char *fmt UNNEEDED, ...)
 { fprintf(stderr, "peer_billboard called!\n"); abort(); }
+/* Generated stub for shachain_get_secret */
+bool shachain_get_secret(const struct shachain *shachain UNNEEDED,
+			 u64 commit_num UNNEEDED,
+			 struct secret *preimage UNNEEDED)
+{ fprintf(stderr, "shachain_get_secret called!\n"); abort(); }
 /* Generated stub for status_failed */
 void status_failed(enum status_failreason code UNNEEDED,
 		   const char *fmt UNNEEDED, ...)