Return correct error codes in setban().

The setban() RPC was returning misleading or incorrect error
codes (for example RPC_CLIENT_NODE_ALREADY_ADDED when an invalid IP
address was entered). This commit fixes those error codes:

- RPC_CLIENT_INVALID_IP_OR_SUBNET should be returned if the client
  enters an invalid IP address or subnet.

This commit also updates the test cases to explicitly test the error code.

This commit also adds a testcase for trying to setban on an invalid subnet.

qa/rpc-tests/nodehandling.py

@@ -29,15 +29,13 @@ class NodeHandlingTest (BitcoinTestFramework):
         assert_equal(len(self.nodes[2].listbanned()), 0)
         self.nodes[2].setban("127.0.0.0/24", "add")
         assert_equal(len(self.nodes[2].listbanned()), 1)
-        try:
-            self.nodes[2].setban("127.0.0.1", "add") #throws exception because 127.0.0.1 is within range 127.0.0.0/24
-        except:
-            pass
+        # This will throw an exception because 127.0.0.1 is within range 127.0.0.0/24
+        assert_raises_jsonrpc(-23, "IP/Subnet already banned", self.nodes[2].setban, "127.0.0.1", "add")
+        # This will throw an exception because 127.0.0.1/42 is not a real subnet
+        assert_raises_jsonrpc(-30, "Error: Invalid IP/Subnet", self.nodes[2].setban, "127.0.0.1/42", "add")
         assert_equal(len(self.nodes[2].listbanned()), 1) #still only one banned ip because 127.0.0.1 is within the range of 127.0.0.0/24
-        try:
-            self.nodes[2].setban("127.0.0.1", "remove")
-        except:
-            pass
+        # This will throw an exception because 127.0.0.1 was not added above
+        assert_raises_jsonrpc(-30, "Error: Unban failed", self.nodes[2].setban, "127.0.0.1", "remove")
         assert_equal(len(self.nodes[2].listbanned()), 1)
         self.nodes[2].setban("127.0.0.0/24", "remove")
         assert_equal(len(self.nodes[2].listbanned()), 0)

src/rpc/net.cpp

@@ -506,7 +506,7 @@ UniValue setban(const JSONRPCRequest& request)
         LookupSubNet(request.params[0].get_str().c_str(), subNet);
 
     if (! (isSubnet ? subNet.IsValid() : netAddr.IsValid()) )
-        throw JSONRPCError(RPC_CLIENT_NODE_ALREADY_ADDED, "Error: Invalid IP/Subnet");
+        throw JSONRPCError(RPC_CLIENT_INVALID_IP_OR_SUBNET, "Error: Invalid IP/Subnet");
 
     if (strCommand == "add")
     {
@@ -526,7 +526,7 @@ UniValue setban(const JSONRPCRequest& request)
     else if(strCommand == "remove")
     {
         if (!( isSubnet ? g_connman->Unban(subNet) : g_connman->Unban(netAddr) ))
-            throw JSONRPCError(RPC_MISC_ERROR, "Error: Unban failed");
+            throw JSONRPCError(RPC_CLIENT_INVALID_IP_OR_SUBNET, "Error: Unban failed. Requested address/subnet was not previously banned.");
     }
     return NullUniValue;
 }