Auto merge of #3354 - leto:absurd_fee_bug, r=bitcartel

Fix absurd fee bug reported in #3281, with tests

This was ported from the Hush `absurd_fee_bug` PR: https://github.com/MyHush/hush/pull/136

Tests executed with `./qa/pull-tester/rpc-tests.sh wallet` and pass on Ubuntu 16.04. Some tests were added for previously untested behavior as well.

Closes #3281.

qa/rpc-tests/wallet.py

@@ -463,6 +463,62 @@ class WalletTest (BitcoinTestFramework):
 
         assert_equal("not an integer" in errorString, True);
 
+        myzaddr     = self.nodes[0].z_getnewaddress()
+        recipients  = [ {"address": myzaddr, "amount": Decimal('0.0') } ]
+        errorString = ''
+
+        # Make sure that amount=0 transactions can use the default fee
+        # without triggering "absurd fee" errors
+        try:
+            myopid = self.nodes[0].z_sendmany(myzaddr, recipients)
+            assert(myopid)
+        except JSONRPCException,e:
+            errorString = e.error['message']
+            print errorString
+            assert(False)
+
+        # This fee is larger than the default fee and since amount=0
+        # it should trigger error
+        fee         = Decimal('0.1')
+        recipients  = [ {"address": myzaddr, "amount": Decimal('0.0') } ]
+        minconf     = 1
+        errorString = ''
+
+        try:
+            myopid = self.nodes[0].z_sendmany(myzaddr, recipients, minconf, fee)
+        except JSONRPCException,e:
+            errorString = e.error['message']
+        assert('Small transaction amount' in errorString)
+
+        # This fee is less than default and greater than amount, but still valid
+        fee         = Decimal('0.0000001')
+        recipients  = [ {"address": myzaddr, "amount": Decimal('0.00000001') } ]
+        minconf     = 1
+        errorString = ''
+
+        try:
+            myopid = self.nodes[0].z_sendmany(myzaddr, recipients, minconf, fee)
+            assert(myopid)
+        except JSONRPCException,e:
+            errorString = e.error['message']
+            print errorString
+            assert(False)
+
+        # Make sure amount=0, fee=0 transaction are valid to add to mempool
+        # though miners decide whether to add to a block
+        fee         = Decimal('0.0')
+        minconf     = 1
+        recipients  = [ {"address": myzaddr, "amount": Decimal('0.0') } ]
+        errorString = ''
+
+        try:
+            myopid = self.nodes[0].z_sendmany(myzaddr, recipients, minconf, fee)
+            assert(myopid)
+        except JSONRPCException,e:
+            errorString = e.error['message']
+            print errorString
+            assert(False)
+
 
 if __name__ == '__main__':
     WalletTest ().main ()