lightningd / openingd: remove limits if we negotiate option_support_large_channel.

Note that now we check capacity once we've figured out which peer, which
broke a test (we returned "unknown peer" instead of "capacity exceeded"),
so we rework that too.

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

lightningd/opening_control.c

@@ -1146,12 +1146,6 @@ static struct command_result *json_fund_channel_start(struct command *cmd,
 		   NULL))
 		return command_param_failed();
 
-	if (amount_sat_greater(*amount, chainparams->max_funding))
-		return command_fail(cmd, FUND_MAX_EXCEEDED,
-				    "Amount exceeded %s",
-				    type_to_string(tmpctx, struct amount_sat,
-						   &chainparams->max_funding));
-
 	if (push_msat && amount_msat_greater_sat(*push_msat, *amount))
 		return command_fail(cmd, FUND_CANNOT_AFFORD,
 				    "Requested to push_msat of %s is greater than "
@@ -1199,6 +1193,20 @@ static struct command_result *json_fund_channel_start(struct command *cmd,
 		return command_fail(cmd, LIGHTNINGD, "Already funding channel");
 	}
 
+	/* BOLT #2:
+	 *  - if both nodes advertised `option_support_large_channel`:
+	 *    - MAY set `funding_satoshis` greater than or equal to 2^24 satoshi.
+	 *  - otherwise:
+	 *    - MUST set `funding_satoshis` to less than 2^24 satoshi.
+	 */
+	if (!feature_negotiated(cmd->ld->feature_set,
+				peer->features, OPT_LARGE_CHANNELS)
+	    && amount_sat_greater(*amount, chainparams->max_funding))
+		return command_fail(cmd, FUND_MAX_EXCEEDED,
+				    "Amount exceeded %s",
+				    type_to_string(tmpctx, struct amount_sat,
+						   &chainparams->max_funding));
+
 	fc->push = push_msat ? *push_msat : AMOUNT_MSAT(0);
 	fc->channel_flags = OUR_CHANNEL_FLAGS;
 	if (!*announce_channel) {
@@ -1207,7 +1215,6 @@ static struct command_result *json_fund_channel_start(struct command *cmd,
 			type_to_string(fc, struct node_id, id));
 	}
 
-	assert(!amount_sat_greater(*amount, chainparams->max_funding));
 	peer->uncommitted_channel->fc = tal_steal(peer->uncommitted_channel, fc);
 	fc->uc = peer->uncommitted_channel;
 

openingd/openingd.c

@@ -487,9 +487,13 @@ static bool setup_channel_funder(struct state *state)
 	 *
 	 * The sending node:
 	 *...
-	 *   - MUST set `funding_satoshis` to less than 2^24 satoshi.
+	 *  - if both nodes advertised `option_support_large_channel`:
+	 *    - MAY set `funding_satoshis` greater than or equal to 2^24 satoshi.
+	 *  - otherwise:
+	 *    - MUST set `funding_satoshis` to less than 2^24 satoshi.
 	 */
-	if (amount_sat_greater(state->funding, chainparams->max_funding)) {
+	if (!feature_negotiated(state->fset, state->features, OPT_LARGE_CHANNELS)
+	    && amount_sat_greater(state->funding, chainparams->max_funding)) {
 		status_failed(STATUS_FAIL_MASTER_IO,
 			      "funding_satoshis must be < %s, not %s",
 			      type_to_string(tmpctx, struct amount_sat,
@@ -969,11 +973,15 @@ static u8 *fundee_channel(struct state *state, const u8 *open_channel_msg)
 		return NULL;
 	}
 
-	/* BOLT #2 FIXME:
+	/* BOLT #2:
 	 *
-	 * The receiving node ... MUST fail the channel if `funding-satoshis`
-	 * is greater than or equal to 2^24 */
-	if (amount_sat_greater(state->funding, chainparams->max_funding)) {
+	 * The receiving node MUST fail the channel if:
+	 *...
+	 * - `funding_satoshis` is greater than or equal to 2^24 and the receiver does not support
+	 *   `option_support_large_channel`. */
+	/* We choose to require *negotiation*, not just support! */
+	if (!feature_negotiated(state->fset, state->features, OPT_LARGE_CHANNELS)
+	    && amount_sat_greater(state->funding, chainparams->max_funding)) {
 		negotiation_failed(state, false,
 				   "funding_satoshis %s too large",
 				   type_to_string(tmpctx, struct amount_sat,

tests/test_connection.py

@@ -888,10 +888,6 @@ def test_funding_external_wallet_corners(node_factory, bitcoind):
     amount = 2**24
     l1.fundwallet(amount + 10000000)
 
-    # Fail to open (too large)
-    with pytest.raises(RpcError, match=r'Amount exceeded 16777215'):
-        l1.rpc.fundchannel_start(l2.info['id'], amount)
-
     amount = amount - 1
     fake_txid = '929764844a8f9938b669a60a1d51a11c9e2613c7eb4776e4126f1f20c0a685c3'
     fake_txout = 0
@@ -907,6 +903,10 @@ def test_funding_external_wallet_corners(node_factory, bitcoind):
     with pytest.raises(RpcError, match=r'No channel funding in progress.'):
         l1.rpc.fundchannel_complete(l2.info['id'], fake_txid, fake_txout)
 
+    # Fail to open (too large)
+    with pytest.raises(RpcError, match=r'Amount exceeded 16777215'):
+        l1.rpc.fundchannel_start(l2.info['id'], amount + 1)
+
     l1.rpc.fundchannel_start(l2.info['id'], amount)
     with pytest.raises(RpcError, match=r'Already funding channel'):
         l1.rpc.fundchannel(l2.info['id'], amount)