withdraw: fix incorrect error when we have an empty wallet.

This also highlights the danger of searching the logs: that error
appeared previously in the logs, so we didn't notice that the actual
withdraw call gave a different error.

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

CHANGELOG.md

@@ -46,6 +46,8 @@ changes.
 - JSON RPC: `getroute` `fuzzpercent` and `pay` `maxfeepercent` can now be > 100.
 - JSON RPC: `riskfactor` in `pay` and `getroute` no longer always treated as 1.
 - JSON-RPC: `listpeers` was always reporting 0 for all stats.
+- JSON RPC: `withdraw all` says `Cannot afford transaction` if you have
+             absolutely no funds, rather than `Output 0 satoshis would be dust`.
 - Protocol: don't send gossip about closed channels.
 - Protocol: fix occasional deadlock when both peers flood with gossip.
 - Protocol: fix occasional long delay on sending `reply_short_channel_ids_end`.

common/wallet_tx.c

@@ -14,7 +14,7 @@ void wtx_init(struct command *cmd, struct wallet_tx * wtx)
 
 static bool check_amount(const struct wallet_tx *tx, u64 amount)
 {
-	if (!tx->utxos) {
+	if (tal_count(tx->utxos) == 0) {
 		command_fail(tx->cmd, FUND_CANNOT_AFFORD,
 			     "Cannot afford transaction");
 		return false;

tests/test_misc.py

@@ -370,6 +370,8 @@ def test_withdraw(node_factory, bitcoind):
         l1.rpc.withdraw(waddr, 'not an amount')
     with pytest.raises(RpcError):
         l1.rpc.withdraw(waddr, -amount)
+    with pytest.raises(RpcError, match=r'Cannot afford transaction'):
+        l1.rpc.withdraw(waddr, amount * 100)
 
     out = l1.rpc.withdraw(waddr, 2 * amount)
 
@@ -462,9 +464,8 @@ def test_withdraw(node_factory, bitcoind):
     assert l1.db_query('SELECT COUNT(*) as c FROM outputs WHERE status=0')[0]['c'] == 0
 
     # This should fail, can't even afford fee.
-    with pytest.raises(RpcError):
+    with pytest.raises(RpcError, match=r'Cannot afford transaction'):
         l1.rpc.withdraw(waddr, 'all')
-    l1.daemon.wait_for_log('Cannot afford transaction')
 
 
 def test_addfunds_from_block(node_factory, bitcoind):