Fix crash with empty keypool for getauxblock.

Fix namecoin#25.  This implements the
upstream fix done in Bitcoin's bitcoin/bitcoin#6567
also for getauxblock.

qa/rpc-tests/keypool.py

@@ -16,6 +16,7 @@
 import traceback
 
 from test_framework.util import *
+from test_framework import auxpow
 
 
 def check_array_result(object_array, to_match, expected):
@@ -89,6 +90,42 @@ def run_test(nodes, tmpdir):
     except JSONRPCException,e:
         assert(e.error['code']==-12)
 
+    # test draining with getauxblock
+    test_auxpow(nodes)
+
+def test_auxpow(nodes):
+    """
+    Test behaviour of getauxpow.  Calling getauxpow should reserve
+    a key from the pool, but it should be released again if the
+    created block is not actually used.  On the other hand, if the
+    auxpow is submitted and turned into a block, the keypool should
+    be drained.
+    """
+
+    nodes[0].walletpassphrase('test', 12000)
+    nodes[0].keypoolrefill(1)
+    nodes[0].walletlock()
+    assert_equal (nodes[0].getwalletinfo()['keypoolsize'], 2)
+
+    nodes[0].getauxblock()
+    assert_equal (nodes[0].getwalletinfo()['keypoolsize'], 2)
+    nodes[0].generate(1)
+    assert_equal (nodes[0].getwalletinfo()['keypoolsize'], 1)
+    auxblock = nodes[0].getauxblock()
+    assert_equal (nodes[0].getwalletinfo()['keypoolsize'], 1)
+
+    target = auxpow.reverseHex(auxblock['_target'])
+    solved = auxpow.computeAuxpow(auxblock['hash'], target, True)
+    res = nodes[0].getauxblock(auxblock['hash'], solved)
+    assert res
+    assert_equal(nodes[0].getwalletinfo()['keypoolsize'], 0)
+
+    try:
+        nodes[0].getauxblock()
+        raise AssertionError('Keypool should be exhausted by getauxblock')
+    except JSONRPCException,e:
+        assert(e.error['code']==-12)
+
 def main():
     import optparse
 

src/rpcmining.cpp

@@ -762,6 +762,10 @@ UniValue getauxblock(const UniValue& params, bool fHelp)
     boost::shared_ptr<CReserveScript> coinbaseScript;
     GetMainSignals().ScriptForMining(coinbaseScript);
 
+    // If the keypool is exhausted, no script is returned at all.  Catch this.
+    if (!coinbaseScript)
+        throw JSONRPCError(RPC_WALLET_KEYPOOL_RAN_OUT, "Error: Keypool ran out, please call keypoolrefill first");
+
     //throw an error if no script was provided
     if (!coinbaseScript->reserveScript.size())
         throw JSONRPCError(RPC_INTERNAL_ERROR, "No coinbase script available (mining requires a wallet)");