Added wallet related error codes

New codes: FUND_MAX_EXCEEDED, FUND_CANNOT_AFFORD, FUND_DUST_LIMIT_UNMET.

The error message "Cannot afford fee" was not exactly correct because
it would also occur if the amount requested could not be afforded.  So
I changed it to the more generic "Cannot afford transaction".

Other things:

* Fixed off-by-one satoshi in fundchannel manpage.
* Changed 'arror' to 'error' because we are not pirates.

common/wallet_tx.c

@@ -12,6 +12,21 @@ void wtx_init(struct command *cmd, struct wallet_tx * wtx)
 	wtx->all_funds = false;
 }
 
+static bool check_amount(const struct wallet_tx *tx)
+{
+	if (!tx->utxos) {
+		command_fail(tx->cmd, FUND_CANNOT_AFFORD,
+			     "Cannot afford funding transaction");
+		return false;
+	}
+	if (tx->amount < 546) {
+		command_fail(tx->cmd, FUND_DUST_LIMIT_UNMET,
+			     "Dust limit unmet");
+		return false;
+	}
+	return true;
+}
+
 bool wtx_select_utxos(struct wallet_tx * tx, u32 fee_rate_per_kw,
 	              size_t out_len)
 {
@@ -21,23 +36,18 @@ bool wtx_select_utxos(struct wallet_tx * tx, u32 fee_rate_per_kw,
 					      fee_rate_per_kw, out_len,
 					      &tx->amount,
 					      &fee_estimate);
-		if (!tx->utxos || tx->amount < 546) {
-			command_fail(tx->cmd, LIGHTNINGD,
-				     "Cannot afford fee %"PRIu64,
-				     fee_estimate);
+		if (!check_amount(tx))
 			return false;
-		}
+
 		tx->change = 0;
 	} else {
 		tx->utxos = wallet_select_coins(tx->cmd, tx->cmd->ld->wallet,
 						tx->amount,
 						fee_rate_per_kw, out_len,
 						&fee_estimate, &tx->change);
-		if (!tx->utxos || tx->amount < 546) {
-			command_fail(tx->cmd, LIGHTNINGD,
-				     "Cannot afford funding transaction");
+		if (!check_amount(tx))
 			return false;
-		}
+
 		if (tx->change < 546) {
 			tx->change = 0;
 			tx->change_key_index = 0;

doc/lightning-fundchannel.7.txt

@@ -24,7 +24,7 @@ for the channel.
 
 'satoshi' is the amount in satoshis taken from the internal wallet to fund the channel.
 The string 'all' can be used to specify all available funds.
-This value must be greater than the dust limit, currently set to 546.
+This value cannot be less than the dust limit, currently set to 546.
 And it must be less than 1<<24 (approximately 0.16778 BTC).
 
 RETURN VALUE
@@ -35,14 +35,11 @@ On failure, an error is reported and the channel is not funded.
 
 The following error codes may occur:
 
-* -1. Catchall nonspecific arror.
-
-The above error may include a descriptive message indicating:
-
-* The 'id' is invalid.
-* There are not enough funds in the internal wallet to create the transaction.
-* The maximum allowed funding amount is exceeded.
-* 'satoshi' is less than the dust limit.
+* -1. Catchall nonspecific error.
+* 300. The maximum allowed funding amount is exceeded.
+* 301. There are not enough funds in the internal wallet (including fees) to
+       create the transaction.
+* 302. The dust limit is not met.
 
 Failure may also occur if *lightningd* and the peer cannot agree on channel
 parameters (funding limits, channel reserves, fees, etc.).

doc/lightning-withdraw.7.txt

@@ -33,11 +33,14 @@ be returned.
 'tx' represents the raw bitcoin, fully signed, transaction
 and 'txid' represent the bitcoin transaction id.
 
-ERRORS
-------
-If an incorrect address is supplied or the 'satoshi' 
-parameter exceeds the amount in the internal wallet 
-an error message will be returned. 
+On failure, an error is reported and the channel is not funded.
+
+The following error codes may occur:
+
+* -1. Catchall nonspecific error.
+* 301. There are not enough funds in the internal wallet (including fees) to
+       create the transaction.
+* 302. The dust limit is not met.
 
 AUTHOR
 ------

lightningd/jsonrpc_errors.h

@@ -29,6 +29,11 @@
 #define PAY_UNSPECIFIED_ERROR		209
 #define PAY_STOPPED_RETRYING		210
 
+/* `fundchannel` or `withdraw` errors */
+#define FUND_MAX_EXCEEDED               300
+#define FUND_CANNOT_AFFORD              301
+#define FUND_DUST_LIMIT_UNMET           302
+
 /* Errors from `invoice` command */
 #define INVOICE_LABEL_ALREADY_EXISTS	900
 #define INVOICE_PREIMAGE_ALREADY_EXISTS	901

lightningd/opening_control.c

@@ -922,7 +922,7 @@ static void json_fund_channel(struct command *cmd,
 		return;
 
 	if (fc->wtx.amount > MAX_FUNDING_SATOSHI) {
-		command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+		command_fail(cmd, FUND_MAX_EXCEEDED,
 			     "Funding satoshi must be <= %d",
 			     MAX_FUNDING_SATOSHI);
 		return;

tests/test_lightningd.py

@@ -3915,7 +3915,7 @@ class LightningDTests(BaseLightningDTests):
 
         # This should fail, can't even afford fee.
         self.assertRaises(ValueError, l1.rpc.withdraw, waddr, 'all')
-        l1.daemon.wait_for_log('Cannot afford fee')
+        l1.daemon.wait_for_log('Cannot afford funding transaction')
 
     def test_funding_change(self):
         """Add some funds, fund a channel, and make sure we remember the change