Auto merge of #1431 - bitcartel:master_1373_taddr_coinbase_error, r=bitcartel

Return a more informative error message when trying to spend coinbase; select non-coinbase inputs when sending to a transparent output if needed

For #1373 and #1519

Code change:
- Extra parameter added to AvailableCoins to include or exclude Coinbase coins.  Default value of parameter is 'true' as current behaviour is to include Coinbase coins.
- SelectCoins, used for sending taddr->taddr, will now exclude Coinbase coins.

Unit test:
Tried to write a test to focus on the extra parameter added to AvailableCoins but could not.

Empirical testing on Testnet:
Current behaviour is that upstream RPC commands sendfrom and sendtoaddress try to spend coinbase coins returned by AvailableCoins.  So the user will see:

```
./zcash-cli sendtoaddress mrEGRmGJhmwAa4MQjzGd86ry63vrvovu9b 1000.0
error: {"code":-6,"message":"Insufficient funds"}

./zcash-cli sendtoaddress mrEGRmGJhmwAa4MQjzGd86ry63vrvovu9b 0.00003000
error: {"code":-4,"message":"Error: The transaction was rejected! This might happen if some of the coins in your wallet were already spent, such as if you used a copy of wallet.dat and coins were spent in the copy but not marked as spent here."}

./zcash-cli sendfrom "" mrEGRmGJhmwAa4MQjzGd86ry63vrvovu9b 0.00003000
error: {"code":-4,"message":"Error: The transaction was rejected! This might happen if some of the coins in your wallet were already spent, such as if you used a copy of wallet.dat and coins were spent in the copy but not marked as spent here."}
```

After fix is applied:

```
./zcash-cli sendtoaddress mrEGRmGJhmwAa4MQjzGd86ry63vrvovu9b 1000.0
error: {"code":-6,"message":"Insufficient funds"}

./zcash-cli sendtoaddress mrEGRmGJhmwAa4MQjzGd86ry63vrvovu9b 0.00003000
error: {"code":-4,"message":"Coinbase funds can only be sent to a zaddr"}
```

When non-coinbase UTXOs exist, they will now be selected and used:

```
./zcash-cli z_sendmany tnPJZHeVxegCg91utaquBRPEDBGjozfz9iLDHt7zvphFbZdspNgkTVLCGjDcadQBKNyUwKs8pNjDXuEZKrE1aNLpFwHgz4t '[{"address":"mx5fTRhLZwbYE7ZqhAPueZgQGSnwTbdvKU", "amount":0.01}]'

./zcash-cli sendtoaddress mrEGRmGJhmwAa4MQjzGd86ry63vrvovu9b 1000.0
error: {"code":-6,"message":"Insufficient funds"}

./zcash-cli sendtoaddress mrEGRmGJhmwAa4MQjzGd86ry63vrvovu9b 0.00003000
9818e543ac2f689d4ce8b52087607d73fecd771d45d316a1d9db092f0485aff2

./zcash-cli sendfrom "" mrEGRmGJhmwAa4MQjzGd86ry63vrvovu9b 0.00003000
899f2894823f51f15fc73b5e0871ac943edbe0ff88e1635f86906087b72caf30
```

qa/pull-tester/rpc-tests.sh

@@ -11,6 +11,7 @@ export BITCOIND=${REAL_BITCOIND}
 #Run the tests
 
 testScripts=(
+    'wallet_protectcoinbase.py'
     'wallet.py'
     'wallet_nullifiers.py'
     'listtransactions.py'

qa/rpc-tests/wallet_protectcoinbase.py

@@ -0,0 +1,126 @@
+#!/usr/bin/env python2
+# Copyright (c) 2016 The Zcash developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import *
+from time import *
+
+class Wallet2Test (BitcoinTestFramework):
+
+    def setup_chain(self):
+        print("Initializing test directory "+self.options.tmpdir)
+        initialize_chain_clean(self.options.tmpdir, 4)
+
+    # Start nodes with -regtestprotectcoinbase to set fCoinbaseMustBeProtected to true.
+    def setup_network(self, split=False):
+        self.nodes = start_nodes(3, self.options.tmpdir, extra_args=[['-regtestprotectcoinbase']] * 3 )
+        connect_nodes_bi(self.nodes,0,1)
+        connect_nodes_bi(self.nodes,1,2)
+        connect_nodes_bi(self.nodes,0,2)
+        self.is_network_split=False
+        self.sync_all()
+
+    def wait_for_operationd_success(self, myopid):
+        print('waiting for async operation {}'.format(myopid))
+        opids = []
+        opids.append(myopid)
+        timeout = 120
+        status = None
+        for x in xrange(1, timeout):
+            results = self.nodes[0].z_getoperationresult(opids)
+            if len(results)==0:
+                sleep(1)
+            else:
+                status = results[0]["status"]
+                break
+        print('...returned status: {}'.format(status))
+        assert_equal("success", status)
+
+    def run_test (self):
+        print "Mining blocks..."
+
+        self.nodes[0].generate(4)
+
+        walletinfo = self.nodes[0].getwalletinfo()
+        assert_equal(walletinfo['immature_balance'], 40)
+        assert_equal(walletinfo['balance'], 0)
+
+        self.sync_all()
+        self.nodes[1].generate(101)
+        self.sync_all()
+
+        assert_equal(self.nodes[0].getbalance(), 40)
+        assert_equal(self.nodes[1].getbalance(), 10)
+        assert_equal(self.nodes[2].getbalance(), 0)
+
+        # Send will fail because we are enforcing the consensus rule that
+        # coinbase utxos can only be sent to a zaddr.
+        errorString = ""
+        try:
+            self.nodes[0].sendtoaddress(self.nodes[2].getnewaddress(), 1.0)
+        except JSONRPCException,e:
+            errorString = e.error['message']
+        assert_equal("Coinbase funds can only be sent to a zaddr" in errorString, True)
+
+        # send node 0 taddr to node 0 zaddr
+        mytaddr = self.nodes[0].getnewaddress()
+        myzaddr = self.nodes[0].z_getnewaddress()
+        recipients = []
+        recipients.append({"address":myzaddr, "amount":20.0})
+        myopid = self.nodes[0].z_sendmany(mytaddr, recipients)
+        self.wait_for_operationd_success(myopid)
+        self.nodes[1].generate(1)
+        self.sync_all()
+
+        # check balances (the z_sendmany consumes 3 coinbase utxos)
+        resp = self.nodes[0].z_gettotalbalance()
+        assert_equal(Decimal(resp["transparent"]), Decimal('10.0'))
+        assert_equal(Decimal(resp["private"]), Decimal('29.9999'))
+        assert_equal(Decimal(resp["total"]), Decimal('39.9999'))
+
+        # convert note to transparent funds
+        recipients = []
+        recipients.append({"address":mytaddr, "amount":20.0})
+        myopid = self.nodes[0].z_sendmany(myzaddr, recipients)
+        self.wait_for_operationd_success(myopid)
+        self.nodes[1].generate(1)
+        self.sync_all()
+
+        # check balances
+        resp = self.nodes[0].z_gettotalbalance()
+        assert_equal(Decimal(resp["transparent"]), Decimal('30.0'))
+        assert_equal(Decimal(resp["private"]), Decimal('9.9998'))
+        assert_equal(Decimal(resp["total"]), Decimal('39.9998'))
+
+        # Send will fail because send amount is too big, even when including coinbase utxos
+        errorString = ""
+        try:
+            self.nodes[0].sendtoaddress(self.nodes[2].getnewaddress(), 99999.0)
+        except JSONRPCException,e:
+            errorString = e.error['message']
+        assert_equal("Insufficient funds" in errorString, True)
+
+        # Send will fail because of insufficient funds unless sender uses coinbase utxos
+        try:
+            self.nodes[0].sendtoaddress(self.nodes[2].getnewaddress(), 21.0)
+        except JSONRPCException,e:
+            errorString = e.error['message']
+        assert_equal("Insufficient funds, coinbase funds can only be spent after they have been sent to a zaddr" in errorString, True)
+
+        # Send will succeed because the balance of non-coinbase utxos is 20.0
+        try:
+            self.nodes[0].sendtoaddress(self.nodes[2].getnewaddress(), 19.0)
+        except JSONRPCException:
+            assert(False)
+
+        self.nodes[1].generate(10)
+        self.sync_all()
+
+        # check balance
+        assert_equal(self.nodes[2].getbalance(), Decimal('19'))
+
+if __name__ == '__main__':
+    Wallet2Test ().main ()