peer: give more sensible error if anchor is too large.

Currently we get the odd message "Own anchor has insufficient funds".

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

daemon/channel.c

@@ -120,6 +120,12 @@ static bool change_funding(uint64_t anchor_satoshis,
 	return true;
 }
 
+bool anchor_too_large(uint64_t anchor_satoshis)
+{
+	/* Anchor must fit in 32 bit. */
+	return anchor_satoshis >= (1ULL << 32) / 1000;
+}
+
 struct channel_state *initial_cstate(const tal_t *ctx,
 				      uint64_t anchor_satoshis,
 				      uint64_t fee_rate,
@@ -134,8 +140,7 @@ struct channel_state *initial_cstate(const tal_t *ctx,
 	cstate->num_nondust = 0;
 
 	/* Anchor must fit in 32 bit. */
-	if (anchor_satoshis >= (1ULL << 32) / 1000)
-		return tal_free(cstate);
+	assert(!anchor_too_large(anchor_satoshis));
 
 	fee_msat = calculate_fee_msat(0, fee_rate);
 	if (fee_msat > anchor_satoshis * 1000)

daemon/channel.h

@@ -133,6 +133,12 @@ bool force_fee(struct channel_state *cstate, uint64_t fee);
  */
 uint64_t fee_by_feerate(size_t txsize, uint64_t fee_rate);
 
+/**
+ * anchor_too_large: does anchor amount fit in 32-bits of millisatoshi.
+ * @anchor_satoshis: amount in satoshis
+ */
+bool anchor_too_large(uint64_t anchor_satoshis);
+
 /* Routines to db to force HTLC changes out-of-order which may wrap. */
 void force_add_htlc(struct channel_state *cstate, const struct htlc *htlc);
 void force_fail_htlc(struct channel_state *cstate, const struct htlc *htlc);

daemon/packets.c

@@ -343,6 +343,9 @@ Pkt *accept_pkt_anchor(struct peer *peer, const Pkt *pkt)
 	assert(peer->local.offer_anchor == CMD_OPEN_WITHOUT_ANCHOR);
 	assert(peer->remote.offer_anchor == CMD_OPEN_WITH_ANCHOR);
 
+	if (anchor_too_large(a->amount))
+		return pkt_err(peer, "Anchor millisatoshis exceeds 32 bits");
+	
 	proto_to_sha256(a->txid, &peer->anchor.txid.sha);
 	peer->anchor.index = a->output_index;
 	peer->anchor.satoshis = a->amount;

daemon/peer.c

@@ -2862,6 +2862,11 @@ static void json_connect(struct command *cmd,
 
 	connect->input->index = output;
 	connect->input->amount = tx->output[output].amount;
+	if (anchor_too_large(connect->input->amount)) {
+		command_fail(cmd, "Amount %"PRIu64" is too large",
+			     connect->input->amount);
+		return;
+	}
 	if (!dns_resolve_and_connect(cmd->dstate, connect->name, connect->port,
 				     peer_connected_out, peer_failed, connect)) {
 		command_fail(cmd, "DNS failed");