closingd: use global tmpctx.

This one is a bit more subtle than others: we can't just free it
inside the read_peer_msg() loop since we hand tmpctx in, so open-code
the two callers and it's clearer.

They're inside the only loops closingd has.

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

closingd/closing.c

@@ -77,22 +77,6 @@ static struct bitcoin_tx *close_tx(const tal_t *ctx,
 	return tx;
 }
 
-/* Handle random messages we might get, returning the first non-handled one. */
-static u8 *closing_read_peer_msg(const tal_t *ctx,
-				 struct crypto_state *cs,
-				 u64 gossip_index,
-				 const struct channel_id *channel)
-{
-	u8 *msg;
-
-	while ((msg = read_peer_msg(ctx, cs, gossip_index, channel,
-				    sync_crypto_write_arg,
-				    status_fail_io,
-				    NULL)) == NULL);
-
-	return msg;
-}
-
 static void do_reconnect(struct crypto_state *cs,
 			 u64 gossip_index,
 			 const struct channel_id *channel_id,
@@ -101,7 +85,6 @@ static void do_reconnect(struct crypto_state *cs,
 {
 	u8 *msg;
 	struct channel_id their_channel_id;
-	const tal_t *tmpctx = tal_tmpctx(NULL);
 	u64 next_local_commitment_number, next_remote_revocation_number;
 
 	/* BOLT #2:
@@ -122,7 +105,11 @@ static void do_reconnect(struct crypto_state *cs,
 		peer_failed_connection_lost();
 
 	/* Wait for them to say something interesting */
-	msg = closing_read_peer_msg(tmpctx, cs, gossip_index, channel_id);
+	while ((msg = read_peer_msg(tmpctx, cs, gossip_index, channel_id,
+				    sync_crypto_write_arg,
+				    status_fail_io,
+				    NULL)) == NULL)
+		clean_tmpctx();
 
 	if (!fromwire_channel_reestablish(msg, &their_channel_id,
 					  &next_local_commitment_number,
@@ -148,7 +135,6 @@ static void do_reconnect(struct crypto_state *cs,
 	/* Since we always transmit closing_signed immediately, if
 	 * we're reconnecting we consider ourselves to have transmitted once,
 	 * and we'll immediately do the retransmit now anyway. */
-	tal_free(tmpctx);
 }
 
 static void send_offer(struct crypto_state *cs,
@@ -166,7 +152,6 @@ static void send_offer(struct crypto_state *cs,
 		       const struct secrets *secrets,
 		       uint64_t fee_to_offer)
 {
-	const tal_t *tmpctx = tal_tmpctx(NULL);
 	struct bitcoin_tx *tx;
 	secp256k1_ecdsa_signature our_sig;
 	u8 *msg;
@@ -203,8 +188,6 @@ static void send_offer(struct crypto_state *cs,
 	msg = towire_closing_signed(tmpctx, channel_id, fee_to_offer, &our_sig);
 	if (!sync_crypto_write(cs, PEER_FD, take(msg)))
 		peer_failed_connection_lost();
-
-	tal_free(tmpctx);
 }
 
 static void tell_master_their_offer(const secp256k1_ecdsa_signature *their_sig,
@@ -238,7 +221,6 @@ static uint64_t receive_offer(struct crypto_state *cs,
 			      uint64_t our_dust_limit,
 			      u64 min_fee_to_accept)
 {
-	const tal_t *tmpctx = tal_tmpctx(NULL);
 	u8 *msg;
 	struct channel_id their_channel_id;
 	u64 received_fee;
@@ -247,7 +229,12 @@ static uint64_t receive_offer(struct crypto_state *cs,
 
 	/* Wait for them to say something interesting */
 	do {
-		msg = closing_read_peer_msg(tmpctx, cs, gossip_index, channel_id);
+		clean_tmpctx();
+
+		msg = read_peer_msg(tmpctx, cs, gossip_index, channel_id,
+				    sync_crypto_write_arg,
+				    status_fail_io,
+				    NULL);
 
 		/* BOLT #2:
 		 *
@@ -256,14 +243,14 @@ static uint64_t receive_offer(struct crypto_state *cs,
 		 */
 		/* This should only happen if we've made no commitments, but
 		 * we don't have to check that: it's their problem. */
-		if (fromwire_peektype(msg) == WIRE_FUNDING_LOCKED)
+		if (msg && fromwire_peektype(msg) == WIRE_FUNDING_LOCKED)
 			msg = tal_free(msg);
 		/* BOLT #2:
 		 *
 		 * ...if the node has sent a previous `shutdown` it MUST
 		 * retransmit it.
 		 */
-		else if (fromwire_peektype(msg) == WIRE_SHUTDOWN)
+		else if (msg && fromwire_peektype(msg) == WIRE_SHUTDOWN)
 			msg = tal_free(msg);
 	} while (!msg);
 
@@ -339,7 +326,6 @@ static uint64_t receive_offer(struct crypto_state *cs,
 		tell_master_their_offer(&their_sig, tx);
 	}
 
-	tal_free(tmpctx);
 	return received_fee;
 }
 
@@ -437,7 +423,7 @@ static u64 adjust_offer(struct crypto_state *cs,
 int main(int argc, char *argv[])
 {
 	struct crypto_state cs;
-	const tal_t *ctx = tal_tmpctx(NULL);
+	const tal_t *ctx = tal(NULL, char);
 	u8 *msg;
 	struct privkey seed;
 	struct pubkey funding_pubkey[NUM_SIDES];
@@ -461,7 +447,7 @@ int main(int argc, char *argv[])
 
 	status_setup_sync(REQ_FD);
 
-	msg = wire_sync_read(ctx, REQ_FD);
+	msg = wire_sync_read(tmpctx, REQ_FD);
 	if (!fromwire_closing_init(ctx, msg,
 				   &cs, &gossip_index, &seed,
 				   &funding_txid, &funding_txout,