Track transaction packages in CTxMemPoolEntry

Associate with each CTxMemPoolEntry all the size/fees of descendant
mempool transactions.  Sort mempool by max(feerate of entry, feerate
of descendants).  Update statistics on-the-fly as transactions enter
or leave the mempool.

Also add ancestor and descendant limiting, so that transactions can
be rejected if the number or size of unconfirmed ancestors exceeds
a target, or if adding a transaction would cause some other mempool
entry to have too many (or too large) a set of unconfirmed in-
mempool descendants.

qa/pull-tester/rpc-tests.sh

@@ -57,6 +57,7 @@ testScriptsExt=(
     'invalidblockrequest.py'
 #    'forknotify.py'
     'p2p-acceptblock.py'
+    'mempool_packages.py'
 );
 
 #if [ "x$ENABLE_ZMQ" = "x1" ]; then

qa/rpc-tests/mempool_packages.py

@@ -0,0 +1,107 @@
+#!/usr/bin/env python2
+# Copyright (c) 2014-2015 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+# Test descendant package tracking code
+
+from test_framework.test_framework import BitcoinTestFramework
+from test_framework.util import *
+
+def satoshi_round(amount):
+    return  Decimal(amount).quantize(Decimal('0.00000001'), rounding=ROUND_DOWN)
+
+class MempoolPackagesTest(BitcoinTestFramework):
+
+    def setup_network(self):
+        self.nodes = []
+        self.nodes.append(start_node(0, self.options.tmpdir, ["-maxorphantx=1000", "-relaypriority=0"]))
+        self.is_network_split = False
+        self.sync_all()
+
+    # Build a transaction that spends parent_txid:vout
+    # Return amount sent
+    def chain_transaction(self, parent_txid, vout, value, fee, num_outputs):
+        send_value = satoshi_round((value - fee)/num_outputs)
+        inputs = [ {'txid' : parent_txid, 'vout' : vout} ]
+        outputs = {}
+        for i in xrange(num_outputs):
+            outputs[self.nodes[0].getnewaddress()] = send_value
+        rawtx = self.nodes[0].createrawtransaction(inputs, outputs)
+        signedtx = self.nodes[0].signrawtransaction(rawtx)
+        txid = self.nodes[0].sendrawtransaction(signedtx['hex'])
+        fulltx = self.nodes[0].getrawtransaction(txid, 1)
+        assert(len(fulltx['vout']) == num_outputs) # make sure we didn't generate a change output
+        return (txid, send_value)
+
+    def run_test(self):
+        ''' Mine some blocks and have them mature. '''
+        self.nodes[0].generate(101)
+        utxo = self.nodes[0].listunspent(10)
+        txid = utxo[0]['txid']
+        vout = utxo[0]['vout']
+        value = utxo[0]['amount']
+
+        fee = Decimal("0.0001")
+        # 100 transactions off a confirmed tx should be fine
+        chain = []
+        for i in xrange(100):
+            (txid, sent_value) = self.chain_transaction(txid, 0, value, fee, 1)
+            value = sent_value
+            chain.append(txid)
+
+        # Check mempool has 100 transactions in it, and descendant
+        # count and fees should look correct
+        mempool = self.nodes[0].getrawmempool(True)
+        assert_equal(len(mempool), 100)
+        descendant_count = 1
+        descendant_fees = 0
+        descendant_size = 0
+        SATOSHIS = 100000000
+
+        for x in reversed(chain):
+            assert_equal(mempool[x]['descendantcount'], descendant_count)
+            descendant_fees += mempool[x]['fee']
+            assert_equal(mempool[x]['descendantfees'], SATOSHIS*descendant_fees)
+            descendant_size += mempool[x]['size']
+            assert_equal(mempool[x]['descendantsize'], descendant_size)
+            descendant_count += 1
+
+        # Adding one more transaction on to the chain should fail.
+        try:
+            self.chain_transaction(txid, vout, value, fee, 1)
+        except JSONRPCException as e:
+            print "too-long-ancestor-chain successfully rejected"
+
+        # TODO: test ancestor size limits
+
+        # Now test descendant chain limits
+        txid = utxo[1]['txid']
+        value = utxo[1]['amount']
+        vout = utxo[1]['vout']
+
+        transaction_package = []
+        # First create one parent tx with 10 children
+        (txid, sent_value) = self.chain_transaction(txid, vout, value, fee, 10)
+        parent_transaction = txid
+        for i in xrange(10):
+            transaction_package.append({'txid': txid, 'vout': i, 'amount': sent_value})
+
+        for i in xrange(1000):
+            utxo = transaction_package.pop(0)
+            try:
+                (txid, sent_value) = self.chain_transaction(utxo['txid'], utxo['vout'], utxo['amount'], fee, 10)
+                for j in xrange(10):
+                    transaction_package.append({'txid': txid, 'vout': j, 'amount': sent_value})
+                if i == 998:
+                    mempool = self.nodes[0].getrawmempool(True)
+                    assert_equal(mempool[parent_transaction]['descendantcount'], 1000)
+            except JSONRPCException as e:
+                print e.error['message']
+                assert_equal(i, 999)
+                print "tx that would create too large descendant package successfully rejected"
+
+        # TODO: test descendant size limits
+
+if __name__ == '__main__':
+    MempoolPackagesTest().main()