elements: Move from a global is_elements to a global chainparams

We now have a pointer to chainparams, that fails valgrind if we do anything
chain-specific before setting it.

Suggested-by: Rusty Russell <@rustyrussell>

bitcoin/tx.c

@@ -387,7 +387,7 @@ struct bitcoin_tx *bitcoin_tx(const tal_t *ctx,
 	/* If we are constructing an elements transaction we need to
 	 * explicitly add the fee as an extra output. So allocate one more
 	 * than the outputs we need internally. */
-	if (is_elements)
+	if (chainparams->is_elements)
 		output_count += 1;
 
 	wally_tx_init_alloc(WALLY_TX_VERSION_2, 0, input_count, output_count,

channeld/channel_wire.csv

@@ -5,7 +5,7 @@
 
 # Begin!  (passes gossipd-client fd)
 msgtype,channel_init,1000
-msgdata,channel_init,chain_hash,bitcoin_blkid,
+msgdata,channel_init,chainparams,chainparams,
 msgdata,channel_init,funding_txid,bitcoin_txid,
 msgdata,channel_init,funding_txout,u16,
 msgdata,channel_init,funding_satoshi,amount_sat,

channeld/channeld.c

@@ -2944,7 +2944,7 @@ static void init_channel(struct peer *peer)
 
 	msg = wire_sync_read(tmpctx, MASTER_FD);
 	if (!fromwire_channel_init(peer, msg,
-				   &peer->chain_hash,
+				   &chainparams,
 				   &funding_txid, &funding_txout,
 				   &funding,
 				   &minimum_depth,
@@ -3002,7 +3002,9 @@ static void init_channel(struct peer *peer)
 	/* stdin == requests, 3 == peer, 4 = gossip, 5 = gossip_store, 6 = HSM */
 	per_peer_state_set_fds(peer->pps, 3, 4, 5);
 
-	is_elements = chainparams_by_chainhash(&peer->chain_hash)->is_elements;
+	is_elements = chainparams->is_elements;
+	peer->chain_hash = chainparams->genesis_blockhash;
+
 	status_debug("init %s: remote_per_commit = %s, old_remote_per_commit = %s"
 		     " next_idx_local = %"PRIu64
 		     " next_idx_remote = %"PRIu64

closingd/closing_wire.csv

@@ -3,9 +3,8 @@
 #include <common/per_peer_state.h>
 # Begin!  (passes peer fd, gossipd-client fd)
 msgtype,closing_init,2001
-msgdata,closing_init,chain_hash,chain_hash,
+msgdata,closing_init,chainparams,chainparams,
 msgdata,closing_init,pps,per_peer_state,
-msgdata,closing_init,chain_hash,bitcoin_blkid,
 msgdata,closing_init,funding_txid,bitcoin_txid,
 msgdata,closing_init,funding_txout,u16,
 msgdata,closing_init,funding_satoshi,amount_sat,

closingd/closingd.c

@@ -576,8 +576,6 @@ int main(int argc, char *argv[])
 	enum side whose_turn;
 	u8 *channel_reestablish;
 	struct secret last_remote_per_commit_secret;
-	struct bitcoin_blkid chain_hash;
-	const struct chainparams *chainparams;
 
 	subdaemon_setup(argc, argv);
 
@@ -585,7 +583,7 @@ int main(int argc, char *argv[])
 
 	msg = wire_sync_read(tmpctx, REQ_FD);
 	if (!fromwire_closing_init(ctx, msg,
-				   &chain_hash,
+				   &chainparams,
 				   &pps,
 				   &funding_txid, &funding_txout,
 				   &funding,
@@ -611,8 +609,6 @@ int main(int argc, char *argv[])
 
 	/* stdin == requests, 3 == peer, 4 = gossip, 5 = gossip_store, 6 = hsmd */
 	per_peer_state_set_fds(pps, 3, 4, 5);
-	chainparams = chainparams_by_chainhash(&chain_hash);
-	is_elements = chainparams->is_elements;
 
 	status_debug("out = %s/%s",
 		     type_to_string(tmpctx, struct amount_sat, &out[LOCAL]),

common/utils.c

@@ -8,6 +8,8 @@ secp256k1_context *secp256k1_ctx;
 const tal_t *tmpctx;
 bool is_elements = false;
 
+const struct chainparams *chainparams;
+
 char *tal_hexstr(const tal_t *ctx, const void *data, size_t len)
 {
 	char *str = tal_arr(ctx, char, hex_str_size(len));

common/utils.h

@@ -13,6 +13,7 @@ extern secp256k1_context *secp256k1_ctx;
 /* FIXME: Instead of using this as a global, we might want to pass it as
  * context whenever we need it. The global var is just lazy... */
 extern bool is_elements;
+extern const struct chainparams *chainparams;
 
 /* Allocate and fill in a hex-encoded string of this data. */
 char *tal_hexstr(const tal_t *ctx, const void *data, size_t len);

gossipd/gossip_wire.csv

@@ -4,7 +4,7 @@
 
 # Initialize the gossip daemon.
 msgtype,gossipctl_init,3000
-msgdata,gossipctl_init,chain_hash,bitcoin_blkid,
+msgdata,gossipctl_init,chainparams,chainparams,
 msgdata,gossipctl_init,id,node_id,
 msgdata,gossipctl_init,gflen,u16,
 msgdata,gossipctl_init,globalfeatures,u8,gflen

gossipd/gossipd.c

@@ -930,7 +930,7 @@ static struct io_plan *gossip_init(struct io_conn *conn,
 	bool dev_fast_gossip, dev_fast_gossip_prune;
 
 	if (!fromwire_gossipctl_init(daemon, msg,
-				     &daemon->chain_hash,
+				     &chainparams,
 				     &daemon->id, &daemon->globalfeatures,
 				     daemon->rgb,
 				     daemon->alias,
@@ -941,6 +941,7 @@ static struct io_plan *gossip_init(struct io_conn *conn,
 		master_badmsg(WIRE_GOSSIPCTL_INIT, msg);
 	}
 
+	daemon->chain_hash = chainparams->genesis_blockhash;
 	daemon->rstate = new_routing_state(daemon,
 					   chainparams_by_chainhash(&daemon->chain_hash),
 					   &daemon->id,

hsmd/hsm_wire.csv

@@ -9,7 +9,7 @@ msgdata,hsmstatus_client_bad_request,msg,u8,len
 # Start the HSM.
 msgtype,hsm_init,11
 msgdata,hsm_init,bip32_key_version,bip32_key_version,
-msgdata,hsm_init,chain_hash,bitcoin_blkid,
+msgdata,hsm_init,chainparams,chainparams,
 msgdata,hsm_init,dev_force_privkey,?privkey,
 msgdata,hsm_init,dev_force_bip32_seed,?secret,
 msgdata,hsm_init,dev_force_channel_secrets,?secrets,

hsmd/hsmd.c

@@ -580,7 +580,6 @@ static struct io_plan *init_hsm(struct io_conn *conn,
 	struct secret *seed;
 	struct secrets *secrets;
 	struct sha256 *shaseed;
-	struct bitcoin_blkid chain_hash;
 
 	/* This must be lightningd. */
 	assert(is_lightningd(c));
@@ -589,7 +588,7 @@ static struct io_plan *init_hsm(struct io_conn *conn,
 	 * definitions in hsm_client_wire.csv.  The format of those files is
 	 * an extension of the simple comma-separated format output by the
 	 * BOLT tools/extract-formats.py tool. */
-	if (!fromwire_hsm_init(NULL, msg_in, &bip32_key_version, &chain_hash,
+	if (!fromwire_hsm_init(NULL, msg_in, &bip32_key_version, &chainparams,
 			       &privkey, &seed, &secrets, &shaseed))
 		return bad_req(conn, c, msg_in);
 
@@ -602,9 +601,7 @@ static struct io_plan *init_hsm(struct io_conn *conn,
 
 	/* Once we have read the init message we know which params the master
 	 * will use */
-	c->chainparams = chainparams_by_chainhash(&chain_hash);
-	is_elements = c->chainparams->is_elements;
-
+	c->chainparams = chainparams;
 	maybe_create_new_hsm();
 	load_hsm();
 

lightningd/channel_control.c

@@ -421,7 +421,7 @@ void peer_start_channeld(struct channel *channel,
 	}
 
 	initmsg = towire_channel_init(tmpctx,
-				      &get_chainparams(ld)->genesis_blockhash,
+				      chainparams,
 				      &channel->funding_txid,
 				      channel->funding_outnum,
 				      channel->funding,

lightningd/closing_control.c

@@ -273,7 +273,7 @@ void peer_start_closingd(struct channel *channel,
 		return;
 	}
 	initmsg = towire_closing_init(tmpctx,
-				      &get_chainparams(ld)->genesis_blockhash,
+				      chainparams,
 				      pps,
 				      &channel->funding_txid,
 				      channel->funding_outnum,

lightningd/gossip_control.c

@@ -208,7 +208,8 @@ void gossip_init(struct lightningd *ld, int connectd_fd)
 
 	msg = towire_gossipctl_init(
 	    tmpctx,
-	    &get_chainparams(ld)->genesis_blockhash, &ld->id,
+	    chainparams,
+	    &ld->id,
 	    get_offered_globalfeatures(tmpctx),
 	    ld->rgb,
 	    ld->alias,

lightningd/hsm_control.c

@@ -80,8 +80,6 @@ void hsm_init(struct lightningd *ld)
 {
 	u8 *msg;
 	int fds[2];
-	struct bitcoin_blkid chainhash;
-	chainhash = get_chainparams(ld)->genesis_blockhash;
 
 	/* We actually send requests synchronously: only status is async. */
 	if (socketpair(AF_LOCAL, SOCK_STREAM, 0, fds) != 0)
@@ -97,7 +95,7 @@ void hsm_init(struct lightningd *ld)
 	ld->hsm_fd = fds[0];
 	if (!wire_sync_write(ld->hsm_fd, towire_hsm_init(tmpctx,
 							 &ld->topology->bitcoind->chainparams->bip32_key_version,
-							 &chainhash,
+							 chainparams,
 							 IFDEV(ld->dev_force_privkey, NULL),
 							 IFDEV(ld->dev_force_bip32_seed, NULL),
 							 IFDEV(ld->dev_force_channel_secrets, NULL),

lightningd/onchain_control.c

@@ -513,8 +513,7 @@ enum watch_result onchaind_funding_spent(struct channel *channel,
 
 	msg = towire_onchain_init(channel,
 				  &channel->their_shachain.chain,
-				  chainparams->is_elements,
-				  &chainparams->genesis_blockhash,
+				  chainparams,
 				  channel->funding,
 				  &channel->channel_info.old_remote_per_commit,
 				  &channel->channel_info.remote_per_commit,

lightningd/opening_control.c

@@ -937,7 +937,7 @@ void peer_start_openingd(struct peer *peer,
 	uc->minimum_depth = peer->ld->config.anchor_confirms;
 
 	msg = towire_opening_init(NULL,
-				  &get_chainparams(peer->ld)->genesis_blockhash,
+				  chainparams,
 				  &uc->our_config,
 				  max_to_self_delay,
 				  min_effective_htlc_capacity,

lightningd/options.c

@@ -241,7 +241,10 @@ static char *opt_set_network(const char *arg, struct lightningd *ld)
 {
 	assert(arg != NULL);
 
-	ld->topology->bitcoind->chainparams = chainparams_for_network(arg);
+	/* Set the global chainparams instance */
+	chainparams = chainparams_for_network(arg);
+
+	ld->topology->bitcoind->chainparams = chainparams;
 	if (!ld->topology->bitcoind->chainparams)
 		return tal_fmt(NULL, "Unknown network name '%s'", arg);
 	is_elements = ld->topology->bitcoind->chainparams->is_elements;

onchaind/onchain_wire.csv

@@ -7,8 +7,7 @@ msgtype,onchain_init,5001
 msgdata,onchain_init,shachain,shachain,
 # This needs to be set explicitly since the same message also contains a
 # transaction that we need to parse correctly.
-msgdata,onchain_init,is_elements,bool,
-msgdata,onchain_init,chain_hash,bitcoin_blkid,
+msgdata,onchain_init,chainparams,chainparams,
 msgdata,onchain_init,funding_amount_satoshi,amount_sat,
 # Remote per commit point for committed tx.
 msgdata,onchain_init,old_remote_per_commitment_point,pubkey,

onchaind/onchaind.c

@@ -2628,7 +2628,6 @@ int main(int argc, char *argv[])
 	bool *tell_if_missing, *tell_immediately;
 	u32 tx_blockheight;
 	struct pubkey *possible_remote_per_commitment_point;
-	struct bitcoin_blkid chain_hash;
 
 	subdaemon_setup(argc, argv);
 
@@ -2639,8 +2638,7 @@ int main(int argc, char *argv[])
 	msg = wire_sync_read(tmpctx, REQ_FD);
 	if (!fromwire_onchain_init(tmpctx, msg,
 				   &shachain,
-				   &is_elements,
-				   &chain_hash,
+				   &chainparams,
 				   &funding,
 				   &old_remote_per_commit_point,
 				   &remote_per_commit_point,
@@ -2667,7 +2665,7 @@ int main(int argc, char *argv[])
 		master_badmsg(WIRE_ONCHAIN_INIT, msg);
 	}
 
-	tx->chainparams = chainparams_by_chainhash(&chain_hash);
+	tx->chainparams = chainparams;
 
 	status_debug("feerate_per_kw = %u", feerate_per_kw);
 	bitcoin_txid(tx, &txid);

onchaind/test/run-grind_feerate-bug.c

@@ -43,7 +43,7 @@ bool fromwire_onchain_dev_memleak(const void *p UNNEEDED)
 bool fromwire_onchain_htlc(const void *p UNNEEDED, struct htlc_stub *htlc UNNEEDED, bool *tell_if_missing UNNEEDED, bool *tell_immediately UNNEEDED)
 { fprintf(stderr, "fromwire_onchain_htlc called!\n"); abort(); }
 /* Generated stub for fromwire_onchain_init */
-bool fromwire_onchain_init(const tal_t *ctx UNNEEDED, const void *p UNNEEDED, struct shachain *shachain UNNEEDED, bool *is_elements UNNEEDED, struct bitcoin_blkid *chain_hash UNNEEDED, struct amount_sat *funding_amount_satoshi UNNEEDED, struct pubkey *old_remote_per_commitment_point UNNEEDED, struct pubkey *remote_per_commitment_point UNNEEDED, u32 *local_to_self_delay UNNEEDED, u32 *remote_to_self_delay UNNEEDED, u32 *feerate_per_kw UNNEEDED, struct amount_sat *local_dust_limit_satoshi UNNEEDED, struct bitcoin_txid *our_broadcast_txid UNNEEDED, u8 **local_scriptpubkey UNNEEDED, u8 **remote_scriptpubkey UNNEEDED, struct pubkey *ourwallet_pubkey UNNEEDED, enum side *funder UNNEEDED, struct basepoints *local_basepoints UNNEEDED, struct basepoints *remote_basepoints UNNEEDED, struct bitcoin_tx **tx UNNEEDED, u32 *tx_blockheight UNNEEDED, u32 *reasonable_depth UNNEEDED, secp256k1_ecdsa_signature **htlc_signature UNNEEDED, u64 *num_htlcs UNNEEDED, u32 *min_possible_feerate UNNEEDED, u32 *max_possible_feerate UNNEEDED, struct pubkey **possible_remote_per_commit_point UNNEEDED, bool *option_static_remotekey UNNEEDED)
+bool fromwire_onchain_init(const tal_t *ctx UNNEEDED, const void *p UNNEEDED, struct shachain *shachain UNNEEDED, const struct chainparams **chainparams UNNEEDED, struct amount_sat *funding_amount_satoshi UNNEEDED, struct pubkey *old_remote_per_commitment_point UNNEEDED, struct pubkey *remote_per_commitment_point UNNEEDED, u32 *local_to_self_delay UNNEEDED, u32 *remote_to_self_delay UNNEEDED, u32 *feerate_per_kw UNNEEDED, struct amount_sat *local_dust_limit_satoshi UNNEEDED, struct bitcoin_txid *our_broadcast_txid UNNEEDED, u8 **local_scriptpubkey UNNEEDED, u8 **remote_scriptpubkey UNNEEDED, struct pubkey *ourwallet_pubkey UNNEEDED, enum side *funder UNNEEDED, struct basepoints *local_basepoints UNNEEDED, struct basepoints *remote_basepoints UNNEEDED, struct bitcoin_tx **tx UNNEEDED, u32 *tx_blockheight UNNEEDED, u32 *reasonable_depth UNNEEDED, secp256k1_ecdsa_signature **htlc_signature UNNEEDED, u64 *num_htlcs UNNEEDED, u32 *min_possible_feerate UNNEEDED, u32 *max_possible_feerate UNNEEDED, struct pubkey **possible_remote_per_commit_point UNNEEDED, bool *option_static_remotekey UNNEEDED)
 { fprintf(stderr, "fromwire_onchain_init called!\n"); abort(); }
 /* Generated stub for fromwire_onchain_known_preimage */
 bool fromwire_onchain_known_preimage(const void *p UNNEEDED, struct preimage *preimage UNNEEDED)

onchaind/test/run-grind_feerate.c

@@ -47,7 +47,7 @@ bool fromwire_onchain_dev_memleak(const void *p UNNEEDED)
 bool fromwire_onchain_htlc(const void *p UNNEEDED, struct htlc_stub *htlc UNNEEDED, bool *tell_if_missing UNNEEDED, bool *tell_immediately UNNEEDED)
 { fprintf(stderr, "fromwire_onchain_htlc called!\n"); abort(); }
 /* Generated stub for fromwire_onchain_init */
-bool fromwire_onchain_init(const tal_t *ctx UNNEEDED, const void *p UNNEEDED, struct shachain *shachain UNNEEDED, bool *is_elements UNNEEDED, struct bitcoin_blkid *chain_hash UNNEEDED, struct amount_sat *funding_amount_satoshi UNNEEDED, struct pubkey *old_remote_per_commitment_point UNNEEDED, struct pubkey *remote_per_commitment_point UNNEEDED, u32 *local_to_self_delay UNNEEDED, u32 *remote_to_self_delay UNNEEDED, u32 *feerate_per_kw UNNEEDED, struct amount_sat *local_dust_limit_satoshi UNNEEDED, struct bitcoin_txid *our_broadcast_txid UNNEEDED, u8 **local_scriptpubkey UNNEEDED, u8 **remote_scriptpubkey UNNEEDED, struct pubkey *ourwallet_pubkey UNNEEDED, enum side *funder UNNEEDED, struct basepoints *local_basepoints UNNEEDED, struct basepoints *remote_basepoints UNNEEDED, struct bitcoin_tx **tx UNNEEDED, u32 *tx_blockheight UNNEEDED, u32 *reasonable_depth UNNEEDED, secp256k1_ecdsa_signature **htlc_signature UNNEEDED, u64 *num_htlcs UNNEEDED, u32 *min_possible_feerate UNNEEDED, u32 *max_possible_feerate UNNEEDED, struct pubkey **possible_remote_per_commit_point UNNEEDED, bool *option_static_remotekey UNNEEDED)
+bool fromwire_onchain_init(const tal_t *ctx UNNEEDED, const void *p UNNEEDED, struct shachain *shachain UNNEEDED, const struct chainparams **chainparams UNNEEDED, struct amount_sat *funding_amount_satoshi UNNEEDED, struct pubkey *old_remote_per_commitment_point UNNEEDED, struct pubkey *remote_per_commitment_point UNNEEDED, u32 *local_to_self_delay UNNEEDED, u32 *remote_to_self_delay UNNEEDED, u32 *feerate_per_kw UNNEEDED, struct amount_sat *local_dust_limit_satoshi UNNEEDED, struct bitcoin_txid *our_broadcast_txid UNNEEDED, u8 **local_scriptpubkey UNNEEDED, u8 **remote_scriptpubkey UNNEEDED, struct pubkey *ourwallet_pubkey UNNEEDED, enum side *funder UNNEEDED, struct basepoints *local_basepoints UNNEEDED, struct basepoints *remote_basepoints UNNEEDED, struct bitcoin_tx **tx UNNEEDED, u32 *tx_blockheight UNNEEDED, u32 *reasonable_depth UNNEEDED, secp256k1_ecdsa_signature **htlc_signature UNNEEDED, u64 *num_htlcs UNNEEDED, u32 *min_possible_feerate UNNEEDED, u32 *max_possible_feerate UNNEEDED, struct pubkey **possible_remote_per_commit_point UNNEEDED, bool *option_static_remotekey UNNEEDED)
 { fprintf(stderr, "fromwire_onchain_init called!\n"); abort(); }
 /* Generated stub for fromwire_onchain_known_preimage */
 bool fromwire_onchain_known_preimage(const void *p UNNEEDED, struct preimage *preimage UNNEEDED)

openingd/opening_wire.csv

@@ -5,7 +5,7 @@
 
 msgtype,opening_init,6000
 # Which network are we configured for?
-msgdata,opening_init,chain_hash,bitcoin_blkid,
+msgdata,opening_init,chainparams,chainparams,
 # Base configuration we'll offer (channel reserve will vary with amount)
 msgdata,opening_init,our_config,channel_config,
 # Minimum/maximum configuration values we'll accept

openingd/openingd.c

@@ -1410,7 +1410,6 @@ int main(int argc, char *argv[])
 	u8 *msg, *inner;
 	struct pollfd pollfd[3];
 	struct state *state = tal(NULL, struct state);
-	struct bitcoin_blkid chain_hash;
 	struct secret *none;
 
 	subdaemon_setup(argc, argv);
@@ -1422,7 +1421,7 @@ int main(int argc, char *argv[])
 	/*~ The very first thing we read from lightningd is our init msg */
 	msg = wire_sync_read(tmpctx, REQ_FD);
 	if (!fromwire_opening_init(state, msg,
-				   &chain_hash,
+				   &chainparams,
 				   &state->localconf,
 				   &state->max_to_self_delay,
 				   &state->min_effective_htlc_capacity,
@@ -1451,7 +1450,7 @@ int main(int argc, char *argv[])
 	/*~ Even though I only care about bitcoin, there's still testnet and
 	 * regtest modes, so we have a general "parameters for this chain"
 	 * function. */
-	state->chainparams = chainparams_by_chainhash(&chain_hash);
+	state->chainparams = chainparams;
 	is_elements = state->chainparams->is_elements;
 
 	/*~ Initially we're not associated with a channel, but

tools/generate-wire.py

@@ -115,9 +115,12 @@ class Field(object):
         return ', const {} *{}'.format(type_name, self.name)
 
     def arg_desc_from(self):
+        type_name = self.type_obj.type_name()
+        if self.type_obj.is_const_ptr_ptr_type():
+            return ', const {} **{}'.format(type_name, self.name)
+
         if self.len_field_of:
             return ''
-        type_name = self.type_obj.type_name()
         if self.is_array():
             return ', {} {}[{}]'.format(type_name, self.name, self.count)
         ptrs = '*'
@@ -244,6 +247,12 @@ class Type(FieldSet):
         # FIXME: omits 'pad'
     }
 
+    # Types that are const pointer-to-pointers, such as chainparams, i.e.,
+    # they set a reference to some const entry.
+    const_ptr_ptr_types = [
+        'chainparams'
+    ]
+
     @staticmethod
     def true_type(type_name, field_name=None, outer_name=None):
         """ Returns 'true' type of a given type and a flag if
@@ -308,6 +317,9 @@ class Type(FieldSet):
     def is_subtype(self):
         return bool(self.fields)
 
+    def is_const_ptr_ptr_type(self):
+        return self.name in self.const_ptr_ptr_types
+
     def is_truncated(self):
         return self.name in self.truncated_typedefs
 

wire/fromwire.c

@@ -19,6 +19,8 @@
 #define SUPERVERBOSE(...)
 #endif
 
+extern const struct chainparams *chainparams;
+
 /* Sets *cursor to NULL and returns NULL when extraction fails. */
 const void *fromwire_fail(const u8 **cursor, size_t *max)
 {
@@ -389,3 +391,12 @@ struct bitcoin_tx_output *fromwire_bitcoin_tx_output(const tal_t *ctx,
 	fromwire_u8_array(cursor, max, output->script, script_len);
 	return output;
 }
+
+void fromwire_chainparams(const u8 **cursor, size_t *max,
+			  const struct chainparams **chainparams)
+{
+	struct bitcoin_blkid genesis;
+	fromwire_bitcoin_blkid(cursor, max, &genesis);
+	*chainparams = chainparams_by_chainhash(&genesis);
+	is_elements = (*chainparams)->is_elements;
+}

wire/towire.c

@@ -256,3 +256,8 @@ void towire_bitcoin_tx_output(u8 **pptr, const struct bitcoin_tx_output *output)
 	towire_u16(pptr, tal_count(output->script));
 	towire_u8_array(pptr, output->script, tal_count(output->script));
 }
+
+void towire_chainparams(u8 **cursor, const struct chainparams *chainparams)
+{
+	towire_bitcoin_blkid(cursor, &chainparams->genesis_blockhash);
+}

wire/wire.h

@@ -89,6 +89,7 @@ void towire_siphash_seed(u8 **cursor, const struct siphash_seed *seed);
 
 void towire_bip32_key_version(u8 **cursor, const struct bip32_key_version *version);
 void towire_bitcoin_tx_output(u8 **pptr, const struct bitcoin_tx_output *output);
+void towire_chainparams(u8 **cursor, const struct chainparams *chainparams);
 
 const u8 *fromwire(const u8 **cursor, size_t *max, void *copy, size_t n);
 u8 fromwire_u8(const u8 **cursor, size_t *max);
@@ -141,4 +142,8 @@ void fromwire_bip32_key_version(const u8 **cursor, size_t *max,
 				struct bip32_key_version *version);
 struct bitcoin_tx_output *fromwire_bitcoin_tx_output(const tal_t *ctx,
 						     const u8 **cursor, size_t *max);
+
+void fromwire_chainparams(const u8 **cursor, size_t *max,
+			  const struct chainparams **chainparams);
+
 #endif /* LIGHTNING_WIRE_WIRE_H */