From 4837682b4dc51f5b3ab86d8aeef482b2b6c25105 Mon Sep 17 00:00:00 2001
From: Jianping Wu <jianping.wu@gmail.com>
Date: Mon, 17 Sep 2018 17:06:47 -0700
Subject: [PATCH] WIP: started implementing namespace, key and value.

---
 .gitignore               |   2 +
 src/keva/common.h        |   0
 src/keva/main.cpp        | 760 +++++++++++++++++++++++++++++++++++++++
 src/keva/main.h          | 324 +++++++++++++++++
 src/script/keva.h        |   0
 src/wallet/rpckeva.cpp   | 137 +++++++
 src/wallet/rpcwallet.cpp |   5 +
 7 files changed, 1228 insertions(+)
 create mode 100644 src/keva/common.h
 create mode 100644 src/keva/main.cpp
 create mode 100644 src/keva/main.h
 create mode 100644 src/script/keva.h
 create mode 100644 src/wallet/rpckeva.cpp

diff --git a/.gitignore b/.gitignore
index 0823df294..61641ef5f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -115,3 +115,5 @@ test/cache/*
 
 libbitcoinconsensus.pc
 contrib/devtools/split-debug.sh
+
+*/.vscode/*
diff --git a/src/keva/common.h b/src/keva/common.h
new file mode 100644
index 000000000..e69de29bb
diff --git a/src/keva/main.cpp b/src/keva/main.cpp
new file mode 100644
index 000000000..1052d13b6
--- /dev/null
+++ b/src/keva/main.cpp
@@ -0,0 +1,760 @@
+// Copyright (c) 2018 Jianping Wu
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <keva/main.h>
+
+#include <chainparams.h>
+#include <coins.h>
+#include <consensus/validation.h>
+#include <hash.h>
+#include <dbwrapper.h>
+#include <script/interpreter.h>
+#include <script/keva.h>
+#include <txmempool.h>
+#include <undo.h>
+#include <util.h>
+#include <utilstrencodings.h>
+#include <validation.h>
+
+
+/* ************************************************************************** */
+/* CNameData.  */
+
+bool
+CNameData::isExpired () const
+{
+  return isExpired (chainActive.Height ());
+}
+
+bool
+CNameData::isExpired (unsigned h) const
+{
+  return ::isExpired (nHeight, h);
+}
+
+/* ************************************************************************** */
+/* CNameTxUndo.  */
+
+void
+CNameTxUndo::fromOldState (const valtype& nm, const CCoinsView& view)
+{
+  name = nm;
+  isNew = !view.GetName (name, oldData);
+}
+
+void
+CNameTxUndo::apply (CCoinsViewCache& view) const
+{
+  if (isNew)
+    view.DeleteName (name);
+  else
+    view.SetName (name, oldData, true);
+}
+
+/* ************************************************************************** */
+/* CKevaMemPool.  */
+
+uint256
+CKevaMemPool::getTxForName (const valtype& name) const
+{
+  NameTxMap::const_iterator mi;
+
+  mi = mapNameRegs.find (name);
+  if (mi != mapNameRegs.end ())
+    {
+      assert (mapNameUpdates.count (name) == 0);
+      return mi->second;
+    }
+
+  mi = mapNameUpdates.find (name);
+  if (mi != mapNameUpdates.end ())
+    {
+      assert (mapNameRegs.count (name) == 0);
+      return mi->second;
+    }
+
+  return uint256 ();
+}
+
+void
+CKevaMemPool::addUnchecked (const uint256& hash, const CTxMemPoolEntry& entry)
+{
+  AssertLockHeld (pool.cs);
+
+  if (entry.isNameNew ())
+    {
+      const valtype& newHash = entry.getNameNewHash ();
+      const NameTxMap::const_iterator mit = mapNameNews.find (newHash);
+      if (mit != mapNameNews.end ())
+        assert (mit->second == hash);
+      else
+        mapNameNews.insert (std::make_pair (newHash, hash));
+    }
+
+  if (entry.isNameRegistration ())
+    {
+      const valtype& name = entry.getName ();
+      assert (mapNameRegs.count (name) == 0);
+      mapNameRegs.insert (std::make_pair (name, hash));
+    }
+
+  if (entry.isNameUpdate ())
+    {
+      const valtype& name = entry.getName ();
+      assert (mapNameUpdates.count (name) == 0);
+      mapNameUpdates.insert (std::make_pair (name, hash));
+    }
+}
+
+void
+CKevaMemPool::remove (const CTxMemPoolEntry& entry)
+{
+  AssertLockHeld (pool.cs);
+
+  if (entry.isNameRegistration ())
+    {
+      const NameTxMap::iterator mit = mapNameRegs.find (entry.getName ());
+      assert (mit != mapNameRegs.end ());
+      mapNameRegs.erase (mit);
+    }
+  if (entry.isNameUpdate ())
+    {
+      const NameTxMap::iterator mit = mapNameUpdates.find (entry.getName ());
+      assert (mit != mapNameUpdates.end ());
+      mapNameUpdates.erase (mit);
+    }
+}
+
+void
+CKevaMemPool::removeConflicts (const CTransaction& tx)
+{
+  AssertLockHeld (pool.cs);
+
+  if (!tx.IsNamecoin ())
+    return;
+
+  for (const auto& txout : tx.vout)
+    {
+      const CNameScript nameOp(txout.scriptPubKey);
+      if (nameOp.isNameOp () && nameOp.getNameOp () == OP_NAME_FIRSTUPDATE)
+        {
+          const valtype& name = nameOp.getOpName ();
+          const NameTxMap::const_iterator mit = mapNameRegs.find (name);
+          if (mit != mapNameRegs.end ())
+            {
+              const CTxMemPool::txiter mit2 = pool.mapTx.find (mit->second);
+              assert (mit2 != pool.mapTx.end ());
+              pool.removeRecursive (mit2->GetTx (),
+                                    MemPoolRemovalReason::NAME_CONFLICT);
+            }
+        }
+    }
+}
+
+void
+CKevaMemPool::removeUnexpireConflicts (const std::set<valtype>& unexpired)
+{
+  AssertLockHeld (pool.cs);
+
+  for (const auto& name : unexpired)
+    {
+      LogPrint (BCLog::NAMES, "unexpired: %s, mempool: %u\n",
+                ValtypeToString (name).c_str (), mapNameRegs.count (name));
+
+      const NameTxMap::const_iterator mit = mapNameRegs.find (name);
+      if (mit != mapNameRegs.end ())
+        {
+          const CTxMemPool::txiter mit2 = pool.mapTx.find (mit->second);
+          assert (mit2 != pool.mapTx.end ());
+          pool.removeRecursive (mit2->GetTx (),
+                                MemPoolRemovalReason::NAME_CONFLICT);
+        }
+    }
+}
+
+void
+CKevaMemPool::removeExpireConflicts (const std::set<valtype>& expired)
+{
+  AssertLockHeld (pool.cs);
+
+  for (const auto& name : expired)
+    {
+      LogPrint (BCLog::NAMES, "expired: %s, mempool: %u\n",
+                ValtypeToString (name).c_str (), mapNameUpdates.count (name));
+
+      const NameTxMap::const_iterator mit = mapNameUpdates.find (name);
+      if (mit != mapNameUpdates.end ())
+        {
+          const CTxMemPool::txiter mit2 = pool.mapTx.find (mit->second);
+          assert (mit2 != pool.mapTx.end ());
+          pool.removeRecursive (mit2->GetTx (),
+                                MemPoolRemovalReason::NAME_CONFLICT);
+        }
+    }
+}
+
+void
+CKevaMemPool::check (const CCoinsView& coins) const
+{
+  AssertLockHeld (pool.cs);
+
+  const uint256 blockHash = coins.GetBestBlock ();
+  int nHeight;
+  if (blockHash.IsNull())
+    nHeight = 0;
+  else
+    nHeight = mapBlockIndex.find (blockHash)->second->nHeight;
+
+  std::set<valtype> nameRegs;
+  std::set<valtype> nameUpdates;
+  for (const auto& entry : pool.mapTx)
+    {
+      const uint256 txHash = entry.GetTx ().GetHash ();
+      if (entry.isNameNew ())
+        {
+          const valtype& newHash = entry.getNameNewHash ();
+          const NameTxMap::const_iterator mit = mapNameNews.find (newHash);
+
+          assert (mit != mapNameNews.end ());
+          assert (mit->second == txHash);
+        }
+
+      if (entry.isNameRegistration ())
+        {
+          const valtype& name = entry.getName ();
+
+          const NameTxMap::const_iterator mit = mapNameRegs.find (name);
+          assert (mit != mapNameRegs.end ());
+          assert (mit->second == txHash);
+
+          assert (nameRegs.count (name) == 0);
+          nameRegs.insert (name);
+
+          /* The old name should be expired already.  Note that we use
+             nHeight+1 for the check, because that's the height at which
+             the mempool tx will actually be mined.  */
+          CNameData data;
+          if (coins.GetName (name, data))
+            assert (data.isExpired (nHeight + 1));
+        }
+
+      if (entry.isNameUpdate ())
+        {
+          const valtype& name = entry.getName ();
+
+          const NameTxMap::const_iterator mit = mapNameUpdates.find (name);
+          assert (mit != mapNameUpdates.end ());
+          assert (mit->second == txHash);
+
+          assert (nameUpdates.count (name) == 0);
+          nameUpdates.insert (name);
+
+          /* As above, use nHeight+1 for the expiration check.  */
+          CNameData data;
+          if (!coins.GetName (name, data))
+            assert (false);
+          assert (!data.isExpired (nHeight + 1));
+        }
+    }
+
+  assert (nameRegs.size () == mapNameRegs.size ());
+  assert (nameUpdates.size () == mapNameUpdates.size ());
+
+  /* Check that nameRegs and nameUpdates are disjoint.  They must be since
+     a name can only be in either category, depending on whether it exists
+     at the moment or not.  */
+  for (const auto& name : nameRegs)
+    assert (nameUpdates.count (name) == 0);
+  for (const auto& name : nameUpdates)
+    assert (nameRegs.count (name) == 0);
+}
+
+bool
+CKevaMemPool::checkTx (const CTransaction& tx) const
+{
+  AssertLockHeld (pool.cs);
+
+  if (!tx.IsNamecoin ())
+    return true;
+
+  /* In principle, multiple name_updates could be performed within the
+     mempool at once (building upon each other).  This is disallowed, though,
+     since the current mempool implementation does not like it.  (We keep
+     track of only a single update tx for each name.)  */
+
+  for (const auto& txout : tx.vout)
+    {
+      const CNameScript nameOp(txout.scriptPubKey);
+      if (!nameOp.isNameOp ())
+        continue;
+
+      switch (nameOp.getNameOp ())
+        {
+        case OP_NAME_NEW:
+          {
+            const valtype& newHash = nameOp.getOpHash ();
+            std::map<valtype, uint256>::const_iterator mi;
+            mi = mapNameNews.find (newHash);
+            if (mi != mapNameNews.end () && mi->second != tx.GetHash ())
+              return false;
+            break;
+          }
+
+        case OP_NAME_FIRSTUPDATE:
+          {
+            const valtype& name = nameOp.getOpName ();
+            if (registersName (name))
+              return false;
+            break;
+          }
+
+        case OP_NAME_UPDATE:
+          {
+            const valtype& name = nameOp.getOpName ();
+            if (updatesName (name))
+              return false;
+            break;
+          }
+
+        default:
+          assert (false);
+        }
+    }
+
+  return true;
+}
+
+/* ************************************************************************** */
+/* CNameConflictTracker.  */
+
+namespace
+{
+
+void
+ConflictTrackerNotifyEntryRemoved (CNameConflictTracker* tracker,
+                                   CTransactionRef txRemoved,
+                                   MemPoolRemovalReason reason)
+{
+  if (reason == MemPoolRemovalReason::NAME_CONFLICT)
+    tracker->AddConflictedEntry (txRemoved);
+}
+
+} // anonymous namespace
+
+CNameConflictTracker::CNameConflictTracker (CTxMemPool &p)
+  : txNameConflicts(std::make_shared<std::vector<CTransactionRef>>()), pool(p)
+{
+  pool.NotifyEntryRemoved.connect (
+    boost::bind (&ConflictTrackerNotifyEntryRemoved, this, _1, _2));
+}
+
+CNameConflictTracker::~CNameConflictTracker ()
+{
+  pool.NotifyEntryRemoved.disconnect (
+    boost::bind (&ConflictTrackerNotifyEntryRemoved, this, _1, _2));
+}
+
+void
+CNameConflictTracker::AddConflictedEntry (CTransactionRef txRemoved)
+{
+  txNameConflicts->emplace_back (std::move (txRemoved));
+}
+
+/* ************************************************************************** */
+
+bool
+CheckNameTransaction (const CTransaction& tx, unsigned nHeight,
+                      const CCoinsView& view,
+                      CValidationState& state, unsigned flags)
+{
+  const std::string strTxid = tx.GetHash ().GetHex ();
+  const char* txid = strTxid.c_str ();
+  const bool fMempool = (flags & SCRIPT_VERIFY_NAMES_MEMPOOL);
+
+  /* Ignore historic bugs.  */
+  CChainParams::BugType type;
+  if (Params ().IsHistoricBug (tx.GetHash (), nHeight, type))
+    return true;
+
+  /* As a first step, try to locate inputs and outputs of the transaction
+     that are name scripts.  At most one input and output should be
+     a name operation.  */
+
+  int nameIn = -1;
+  CNameScript nameOpIn;
+  Coin coinIn;
+  for (unsigned i = 0; i < tx.vin.size (); ++i)
+    {
+      const COutPoint& prevout = tx.vin[i].prevout;
+      Coin coin;
+      if (!view.GetCoin (prevout, coin))
+        return error ("%s: failed to fetch input coin for %s", __func__, txid);
+
+      const CNameScript op(coin.out.scriptPubKey);
+      if (op.isNameOp ())
+        {
+          if (nameIn != -1)
+            return state.Invalid (error ("%s: multiple name inputs into"
+                                         " transaction %s", __func__, txid));
+          nameIn = i;
+          nameOpIn = op;
+          coinIn = coin;
+        }
+    }
+
+  int nameOut = -1;
+  CNameScript nameOpOut;
+  for (unsigned i = 0; i < tx.vout.size (); ++i)
+    {
+      const CNameScript op(tx.vout[i].scriptPubKey);
+      if (op.isNameOp ())
+        {
+          if (nameOut != -1)
+            return state.Invalid (error ("%s: multiple name outputs from"
+                                         " transaction %s", __func__, txid));
+          nameOut = i;
+          nameOpOut = op;
+        }
+    }
+
+  /* Check that no name inputs/outputs are present for a non-Namecoin tx.
+     If that's the case, all is fine.  For a Namecoin tx instead, there
+     should be at least an output (for NAME_NEW, no inputs are expected).  */
+
+  if (!tx.IsNamecoin ())
+    {
+      if (nameIn != -1)
+        return state.Invalid (error ("%s: non-Namecoin tx %s has name inputs",
+                                     __func__, txid));
+      if (nameOut != -1)
+        return state.Invalid (error ("%s: non-Namecoin tx %s at height %u"
+                                     " has name outputs",
+                                     __func__, txid, nHeight));
+
+      return true;
+    }
+
+  assert (tx.IsNamecoin ());
+  if (nameOut == -1)
+    return state.Invalid (error ("%s: Namecoin tx %s has no name outputs",
+                                 __func__, txid));
+
+  /* Reject "greedy names".  */
+  const Consensus::Params& params = Params ().GetConsensus ();
+  if (tx.vout[nameOut].nValue < params.rules->MinNameCoinAmount(nHeight))
+    return state.Invalid (error ("%s: greedy name", __func__));
+
+  /* Handle NAME_NEW now, since this is easy and different from the other
+     operations.  */
+
+  if (nameOpOut.getNameOp () == OP_NAME_NEW)
+    {
+      if (nameIn != -1)
+        return state.Invalid (error ("CheckNameTransaction: NAME_NEW with"
+                                     " previous name input"));
+
+      if (nameOpOut.getOpHash ().size () != 20)
+        return state.Invalid (error ("CheckNameTransaction: NAME_NEW's hash"
+                                     " has wrong size"));
+
+      return true;
+    }
+
+  /* Now that we have ruled out NAME_NEW, check that we have a previous
+     name input that is being updated.  */
+
+  assert (nameOpOut.isAnyUpdate ());
+  if (nameIn == -1)
+    return state.Invalid (error ("CheckNameTransaction: update without"
+                                 " previous name input"));
+  const valtype& name = nameOpOut.getOpName ();
+
+  if (name.size () > MAX_NAME_LENGTH)
+    return state.Invalid (error ("CheckNameTransaction: name too long"));
+  if (nameOpOut.getOpValue ().size () > MAX_VALUE_LENGTH)
+    return state.Invalid (error ("CheckNameTransaction: value too long"));
+
+  /* Process NAME_UPDATE next.  */
+
+  if (nameOpOut.getNameOp () == OP_NAME_UPDATE)
+    {
+      if (!nameOpIn.isAnyUpdate ())
+        return state.Invalid (error ("CheckNameTransaction: NAME_UPDATE with"
+                                     " prev input that is no update"));
+
+      if (name != nameOpIn.getOpName ())
+        return state.Invalid (error ("%s: NAME_UPDATE name mismatch to prev tx"
+                                     " found in %s", __func__, txid));
+
+      /* This is actually redundant, since expired names are removed
+         from the UTXO set and thus not available to be spent anyway.
+         But it does not hurt to enforce this here, too.  It is also
+         exercised by the unit tests.  */
+      CNameData oldName;
+      if (!view.GetName (name, oldName))
+        return state.Invalid (error ("%s: NAME_UPDATE name does not exist",
+                                     __func__));
+      if (oldName.isExpired (nHeight))
+        return state.Invalid (error ("%s: trying to update expired name",
+                                     __func__));
+
+      /* This is an internal consistency check.  If everything is fine,
+         the input coins from the UTXO database should match the
+         name database.  */
+      assert (static_cast<unsigned> (coinIn.nHeight) == oldName.getHeight ());
+      assert (tx.vin[nameIn].prevout == oldName.getUpdateOutpoint ());
+
+      return true;
+    }
+
+  /* Finally, NAME_FIRSTUPDATE.  */
+
+  assert (nameOpOut.getNameOp () == OP_NAME_FIRSTUPDATE);
+  if (nameOpIn.getNameOp () != OP_NAME_NEW)
+    return state.Invalid (error ("CheckNameTransaction: NAME_FIRSTUPDATE"
+                                 " with non-NAME_NEW prev tx"));
+
+  /* Maturity of NAME_NEW is checked only if we're not adding
+     to the mempool.  */
+  if (!fMempool)
+    {
+      assert (static_cast<unsigned> (coinIn.nHeight) != MEMPOOL_HEIGHT);
+      if (coinIn.nHeight + MIN_FIRSTUPDATE_DEPTH > nHeight)
+        return state.Invalid (error ("CheckNameTransaction: NAME_NEW"
+                                     " is not mature for FIRST_UPDATE"));
+    }
+
+  if (nameOpOut.getOpRand ().size () > 20)
+    return state.Invalid (error ("CheckNameTransaction: NAME_FIRSTUPDATE"
+                                 " rand too large, %d bytes",
+                                 nameOpOut.getOpRand ().size ()));
+
+  {
+    valtype toHash(nameOpOut.getOpRand ());
+    toHash.insert (toHash.end (), name.begin (), name.end ());
+    const uint160 hash = Hash160 (toHash);
+    if (hash != uint160 (nameOpIn.getOpHash ()))
+      return state.Invalid (error ("CheckNameTransaction: NAME_FIRSTUPDATE"
+                                   " hash mismatch"));
+  }
+
+  CNameData oldName;
+  if (view.GetName (name, oldName) && !oldName.isExpired (nHeight))
+    return state.Invalid (error ("CheckNameTransaction: NAME_FIRSTUPDATE"
+                                 " on an unexpired name"));
+
+  /* We don't have to specifically check that miners don't create blocks with
+     conflicting NAME_FIRSTUPDATE's, since the mining's CCoinsViewCache
+     takes care of this with the check above already.  */
+
+  return true;
+}
+
+void
+ApplyNameTransaction (const CTransaction& tx, unsigned nHeight,
+                      CCoinsViewCache& view, CBlockUndo& undo)
+{
+  assert (nHeight != MEMPOOL_HEIGHT);
+
+  /* Handle historic bugs that should *not* be applied.  Names that are
+     outputs should be marked as unspendable in this case.  Otherwise,
+     we get an inconsistency between the UTXO set and the name database.  */
+  CChainParams::BugType type;
+  const uint256 txHash = tx.GetHash ();
+  if (Params ().IsHistoricBug (txHash, nHeight, type)
+      && type != CChainParams::BUG_FULLY_APPLY)
+    {
+      if (type == CChainParams::BUG_FULLY_IGNORE)
+        for (unsigned i = 0; i < tx.vout.size (); ++i)
+          {
+            const CNameScript op(tx.vout[i].scriptPubKey);
+            if (op.isNameOp () && op.isAnyUpdate ())
+              view.SpendCoin (COutPoint (txHash, i));
+          }
+      return;
+    }
+
+  /* This check must be done *after* the historic bug fixing above!  Some
+     of the names that must be handled above are actually produced by
+     transactions *not* marked as Namecoin tx.  */
+  if (!tx.IsNamecoin ())
+    return;
+
+  /* Changes are encoded in the outputs.  We don't have to do any checks,
+     so simply apply all these.  */
+
+  for (unsigned i = 0; i < tx.vout.size (); ++i)
+    {
+      const CNameScript op(tx.vout[i].scriptPubKey);
+      if (op.isNameOp () && op.isAnyUpdate ())
+        {
+          const valtype& name = op.getOpName ();
+          LogPrint (BCLog::NAMES, "Updating name at height %d: %s\n",
+                    nHeight, ValtypeToString (name).c_str ());
+
+          CNameTxUndo opUndo;
+          opUndo.fromOldState (name, view);
+          undo.vnameundo.push_back (opUndo);
+
+          CNameData data;
+          data.fromScript (nHeight, COutPoint (tx.GetHash (), i), op);
+          view.SetName (name, data, false);
+        }
+    }
+}
+
+bool
+ExpireNames (unsigned nHeight, CCoinsViewCache& view, CBlockUndo& undo,
+             std::set<valtype>& names)
+{
+  names.clear ();
+
+  /* The genesis block contains no name expirations.  */
+  if (nHeight == 0)
+    return true;
+
+  /* Otherwise, find out at which update heights names have expired
+     since the last block.  If the expiration depth changes, this could
+     be multiple heights at once.  */
+
+  const Consensus::Params& params = Params ().GetConsensus ();
+  const unsigned expDepthOld = params.rules->NameExpirationDepth (nHeight - 1);
+  const unsigned expDepthNow = params.rules->NameExpirationDepth (nHeight);
+
+  if (expDepthNow > nHeight)
+    return true;
+
+  /* Both are inclusive!  The last expireTo was nHeight - 1 - expDepthOld,
+     now we start at this value + 1.  */
+  const unsigned expireFrom = nHeight - expDepthOld;
+  const unsigned expireTo = nHeight - expDepthNow;
+
+  /* It is possible that expireFrom = expireTo + 1, in case that the
+     expiration period is raised together with the block height.  In this
+     case, no names expire in the current step.  This case means that
+     the absolute expiration height "n - expirationDepth(n)" is
+     flat -- which is fine.  */
+  assert (expireFrom <= expireTo + 1);
+
+  /* Find all names that expire at those depths.  Note that GetNamesForHeight
+     clears the output set, to we union all sets here.  */
+  for (unsigned h = expireFrom; h <= expireTo; ++h)
+    {
+      std::set<valtype> newNames;
+      view.GetNamesForHeight (h, newNames);
+      names.insert (newNames.begin (), newNames.end ());
+    }
+
+  /* Expire all those names.  */
+  for (std::set<valtype>::const_iterator i = names.begin ();
+       i != names.end (); ++i)
+    {
+      const std::string nameStr = ValtypeToString (*i);
+
+      CNameData data;
+      if (!view.GetName (*i, data))
+        return error ("%s : name '%s' not found in the database",
+                      __func__, nameStr.c_str ());
+      if (!data.isExpired (nHeight))
+        return error ("%s : name '%s' is not actually expired",
+                      __func__, nameStr.c_str ());
+
+      /* Special rule:  When d/postmortem expires (the name used by
+         libcoin in the name-stealing demonstration), it's coin
+         is already spent.  Ignore.  */
+      if (nHeight == 175868 && nameStr == "d/postmortem")
+        continue;
+
+      const COutPoint& out = data.getUpdateOutpoint ();
+      Coin coin;
+      if (!view.GetCoin(out, coin))
+        return error ("%s : name coin for '%s' is not available",
+                      __func__, nameStr.c_str ());
+      const CNameScript nameOp(coin.out.scriptPubKey);
+      if (!nameOp.isNameOp () || !nameOp.isAnyUpdate ()
+          || nameOp.getOpName () != *i)
+        return error ("%s : name coin to be expired is wrong script", __func__);
+
+      if (!view.SpendCoin (out, &coin))
+        return error ("%s : spending name coin failed", __func__);
+      undo.vexpired.push_back (coin);
+    }
+
+  return true;
+}
+
+bool
+UnexpireNames (unsigned nHeight, CBlockUndo& undo, CCoinsViewCache& view,
+               std::set<valtype>& names)
+{
+  names.clear ();
+
+  /* The genesis block contains no name expirations.  */
+  if (nHeight == 0)
+    return true;
+
+  std::vector<Coin>::reverse_iterator i;
+  for (i = undo.vexpired.rbegin (); i != undo.vexpired.rend (); ++i)
+    {
+      const CNameScript nameOp(i->out.scriptPubKey);
+      if (!nameOp.isNameOp () || !nameOp.isAnyUpdate ())
+        return error ("%s : wrong script to be unexpired", __func__);
+
+      const valtype& name = nameOp.getOpName ();
+      if (names.count (name) > 0)
+        return error ("%s : name '%s' unexpired twice",
+                      __func__, ValtypeToString (name).c_str ());
+      names.insert (name);
+
+      CNameData data;
+      if (!view.GetName (nameOp.getOpName (), data))
+        return error ("%s : no data for name '%s' to be unexpired",
+                      __func__, ValtypeToString (name).c_str ());
+      if (!data.isExpired (nHeight) || data.isExpired (nHeight - 1))
+        return error ("%s : name '%s' to be unexpired is not expired in the DB"
+                      " or it was already expired before the current height",
+                      __func__, ValtypeToString (name).c_str ());
+
+      if (ApplyTxInUndo (std::move(*i), view,
+                         data.getUpdateOutpoint ()) != DISCONNECT_OK)
+        return error ("%s : failed to undo name coin spending", __func__);
+    }
+
+  return true;
+}
+
+void
+CheckNameDB (bool disconnect)
+{
+  const int option
+    = gArgs.GetArg ("-checknamedb", Params ().DefaultCheckNameDB ());
+
+  if (option == -1)
+    return;
+
+  assert (option >= 0);
+  if (option != 0)
+    {
+      if (disconnect || chainActive.Height () % option != 0)
+        return;
+    }
+
+  pcoinsTip->Flush ();
+  const bool ok = pcoinsTip->ValidateNameDB ();
+
+  /* The DB is inconsistent (mismatch between UTXO set and names DB) between
+     (roughly) blocks 139,000 and 180,000.  This is caused by libcoin's
+     "name stealing" bug.  For instance, d/postmortem is removed from
+     the UTXO set shortly after registration (when it is used to steal
+     names), but it remains in the name DB until it expires.  */
+  if (!ok)
+    {
+      const unsigned nHeight = chainActive.Height ();
+      LogPrintf ("ERROR: %s : name database is inconsistent\n", __func__);
+      if (nHeight >= 139000 && nHeight <= 180000)
+        LogPrintf ("This is expected due to 'name stealing'.\n");
+      else
+        assert (false);
+    }
+}
diff --git a/src/keva/main.h b/src/keva/main.h
new file mode 100644
index 000000000..038bfa1f7
--- /dev/null
+++ b/src/keva/main.h
@@ -0,0 +1,324 @@
+// Copyright (c) 2018 Jianping Wu
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef H_BITCOIN_KEVA_MAIN
+#define H_BITCOIN_KEVA_MAIN
+
+#include <amount.h>
+#include <keva/common.h>
+#include <primitives/transaction.h>
+#include <serialize.h>
+#include <uint256.h>
+
+#include <list>
+#include <map>
+#include <memory>
+#include <set>
+#include <string>
+
+class CBlockUndo;
+class CCoinsView;
+class CCoinsViewCache;
+class CTxMemPool;
+class CTxMemPoolEntry;
+class CValidationState;
+
+/* Some constants defining namespace, key and value limits.  */
+static const unsigned MAX_NAMESPACE_LENGTH = 255;
+static const unsigned MAX_KEY_LENGTH       = 255;
+static const unsigned MAX_VALUE_LENGTH     = 1023;
+
+/** The amount of coins to lock in created transactions.  */
+static const CAmount KEVA_LOCKED_AMOUNT = COIN / 100;
+
+/* ************************************************************************** */
+/* CNameTxUndo.  */
+
+/**
+ * Undo information for one name operation.  This contains either the
+ * information that the name was newly created (and should thus be
+ * deleted entirely) or that it was updated including the old value.
+ */
+class CNameTxUndo
+{
+
+private:
+
+  /** The name this concerns.  */
+  valtype name;
+
+  /** Whether this was an entirely new name (no update).  */
+  bool isNew;
+
+  /** The old name value that was overwritten by the operation.  */
+  CNameData oldData;
+
+public:
+
+  ADD_SERIALIZE_METHODS;
+
+  template<typename Stream, typename Operation>
+    inline void SerializationOp (Stream& s, Operation ser_action)
+  {
+    READWRITE (name);
+    READWRITE (isNew);
+    if (!isNew)
+      READWRITE (oldData);
+  }
+
+  /**
+   * Set the data for an update/registration of the given name.  The CCoinsView
+   * is used to find out all the necessary information.
+   * @param nm The name that is being updated.
+   * @param view The (old!) chain state.
+   */
+  void fromOldState (const valtype& nm, const CCoinsView& view);
+
+  /**
+   * Apply the undo to the chain state given.
+   * @param view The chain state to update ("undo").
+   */
+  void apply (CCoinsViewCache& view) const;
+
+};
+
+/* ************************************************************************** */
+/* CKevaMemPool.  */
+
+/**
+ * Handle the keva component of the transaction mempool.  This keeps track
+ * of keva operations that are in the mempool and ensures that all transactions
+ * kept are consistent.  E. g., no two transactions are allowed to register
+ * the same namespace, or the same name with the same namespace.
+ */
+class CKevaMemPool
+{
+
+private:
+
+  /** The parent mempool object.  Used to, e. g., remove conflicting tx.  */
+  CTxMemPool& pool;
+
+  /** Type used for internal indices.  */
+  typedef std::map<valtype, uint256> NamespaceTxMap;
+
+  /** Type used for indexing Tx */
+  typedef std::tuple<valtype, valtype> NamespaceKeyTuple;
+
+  /** Type used for internal indices.  */
+  typedef std::map<NamespaceKeyTuple, uint256> NamespaceKeyTxMap;
+
+
+  /**
+   * Keep track of namespaces that are registered by transactions in the pool.
+   * Map name to registering transaction.
+   */
+  NamespaceTxMap mapNamespaceRegs;
+
+  /** Map pending name updates to transaction IDs.  */
+  NamespaceTxMap mapNamespaceUpdates;
+
+  /**
+   * Keep track of key that are registered by transactions in the pool.
+   * Map key to registering transaction.
+   */
+  NamespaceKeyTxMap mapNamespaceKeyRegs;
+
+public:
+
+  /**
+   * Construct with reference to parent mempool.
+   * @param p The parent pool.
+   */
+  explicit inline CNameMemPool (CTxMemPool& p)
+    : pool(p), mapNamespaceRegs(), mapKeyRegs(), mapNameUpdates()
+  {}
+
+  /**
+   * Check whether a particular namespace is being registered by
+   * some transaction in the mempool.  Does not lock, this is
+   * done by the parent mempool (which calls through afterwards).
+   * @param name The name to check for.
+   * @return True iff there's a matching namespace registration in the pool.
+   */
+  inline bool
+  registersNamespace (const valtype& namespace) const
+  {
+    return mapNamespaceRegs.count (name) > 0;
+  }
+
+  /**
+   * Check whether a particular name has a pending update.  Does not lock.
+   * @param name The name to check for.
+   * @return True iff there's a matching name update in the pool.
+   */
+  inline bool
+  updatesName (const valtype& name) const
+  {
+    return mapNameUpdates.count (name) > 0;
+  }
+
+  /**
+   * Return txid of transaction registering or updating a name.  The returned
+   * txid is null if no such tx exists.
+   * @param name The name to check for.
+   * @return The txid that registers/updates it.  Null if none.
+   */
+  uint256 getTxForName (const valtype& name) const;
+
+  /**
+   * Clear all data.
+   */
+  inline void
+  clear ()
+  {
+    mapNameRegs.clear ();
+    mapNameUpdates.clear ();
+    mapNameNews.clear ();
+  }
+
+  /**
+   * Add an entry without checking it.  It should have been checked
+   * already.  If this conflicts with the mempool, it may throw.
+   * @param hash The tx hash.
+   * @param entry The new mempool entry.
+   */
+  void addUnchecked (const uint256& hash, const CTxMemPoolEntry& entry);
+
+  /**
+   * Remove the given mempool entry.  It is assumed that it is present.
+   * @param entry The entry to remove.
+   */
+  void remove (const CTxMemPoolEntry& entry);
+
+  /**
+   * Remove conflicts for the given tx, based on name operations.  I. e.,
+   * if the tx registers a name that conflicts with another registration
+   * in the mempool, detect this and remove the mempool tx accordingly.
+   * @param tx The transaction for which we look for conflicts.
+   * @param removed Put removed tx here.
+   */
+  void removeConflicts (const CTransaction& tx);
+
+  /**
+   * Remove conflicts in the mempool due to unexpired names.  This removes
+   * conflicting name registrations that are no longer possible.
+   * @param unexpired The set of unexpired names.
+   * @param removed Put removed tx here.
+   */
+  void removeUnexpireConflicts (const std::set<valtype>& unexpired);
+  /**
+   * Remove conflicts in the mempool due to expired names.  This removes
+   * conflicting name updates that are no longer possible.
+   * @param expired The set of expired names.
+   * @param removed Put removed tx here.
+   */
+  void removeExpireConflicts (const std::set<valtype>& expired);
+
+  /**
+   * Perform sanity checks.  Throws if it fails.
+   * @param coins The coins view this represents.
+   */
+  void check (const CCoinsView& coins) const;
+
+  /**
+   * Check if a tx can be added (based on name criteria) without
+   * causing a conflict.
+   * @param tx The transaction to check.
+   * @return True if it doesn't conflict.
+   */
+  bool checkTx (const CTransaction& tx) const;
+
+};
+
+/* ************************************************************************** */
+/* CNameConflictTracker.  */
+
+/**
+ * Utility class that listens to a mempool's removal notifications to track
+ * name conflicts.  This is used for DisconnectTip and unit testing.
+ */
+class CNameConflictTracker
+{
+
+private:
+
+  std::shared_ptr<std::vector<CTransactionRef>> txNameConflicts;
+  CTxMemPool& pool;
+
+public:
+
+  explicit CNameConflictTracker (CTxMemPool &p);
+  ~CNameConflictTracker ();
+
+  inline const std::shared_ptr<const std::vector<CTransactionRef>>
+  GetNameConflicts () const
+  {
+    return txNameConflicts;
+  }
+
+  void AddConflictedEntry (CTransactionRef txRemoved);
+
+};
+
+/* ************************************************************************** */
+
+/**
+ * Check a transaction according to the additional Namecoin rules.  This
+ * ensures that all name operations (if any) are valid and that it has
+ * name operations iff it is marked as Namecoin tx by its version.
+ * @param tx The transaction to check.
+ * @param nHeight Height at which the tx will be.
+ * @param view The current chain state.
+ * @param state Resulting validation state.
+ * @param flags Verification flags.
+ * @return True in case of success.
+ */
+bool CheckNameTransaction (const CTransaction& tx, unsigned nHeight,
+                           const CCoinsView& view,
+                           CValidationState& state, unsigned flags);
+
+/**
+ * Apply the changes of a name transaction to the name database.
+ * @param tx The transaction to apply.
+ * @param nHeight Height at which the tx is.  Used for CNameData.
+ * @param view The chain state to update.
+ * @param undo Record undo information here.
+ */
+void ApplyNameTransaction (const CTransaction& tx, unsigned nHeight,
+                           CCoinsViewCache& view, CBlockUndo& undo);
+
+/**
+ * Expire all names at the given height.  This removes their coins
+ * from the UTXO set.
+ * @param height The new block height.
+ * @param view The coins view to update.
+ * @param undo The block undo object to record undo information.
+ * @param names List all expired names here.
+ * @return True if successful.
+ */
+bool ExpireNames (unsigned nHeight, CCoinsViewCache& view, CBlockUndo& undo,
+                  std::set<valtype>& names);
+
+/**
+ * Undo name coin expirations.  This also does some checks verifying
+ * that all is fine.
+ * @param nHeight The height at which the names were expired.
+ * @param undo The block undo object to use.
+ * @param view The coins view to update.
+ * @param names List all unexpired names here.
+ * @return True if successful.
+ */
+bool UnexpireNames (unsigned nHeight, CBlockUndo& undo,
+                    CCoinsViewCache& view, std::set<valtype>& names);
+
+/**
+ * Check the name database consistency.  This calls CCoinsView::ValidateNameDB,
+ * but only if applicable depending on the -checknamedb setting.  If it fails,
+ * this throws an assertion failure.
+ * @param disconnect Whether we are disconnecting blocks.
+ */
+void CheckNameDB (bool disconnect);
+
+#endif // H_BITCOIN_KEVA_MAIN
diff --git a/src/script/keva.h b/src/script/keva.h
new file mode 100644
index 000000000..e69de29bb
diff --git a/src/wallet/rpckeva.cpp b/src/wallet/rpckeva.cpp
new file mode 100644
index 000000000..d59a088be
--- /dev/null
+++ b/src/wallet/rpckeva.cpp
@@ -0,0 +1,137 @@
+// Copyright (c) 2018 Jianping Wu
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "base58.h"
+#include "coins.h"
+#include "init.h"
+#include "keva/common.h"
+#include "keva/main.h"
+#include "primitives/transaction.h"
+#include "random.h"
+#include "rpc/mining.h"
+#include "rpc/safemode.h"
+#include "rpc/server.h"
+#include "script/kava.h"
+#include "txmempool.h"
+#include "util.h"
+#include "validation.h"
+#include "wallet/coincontrol.h"
+#include "wallet/wallet.h"
+
+#include <univalue.h>
+
+
+/* ************************************************************************** */
+
+UniValue
+keva_put (const JSONRPCRequest& request)
+{
+  CWallet* const pwallet = GetWalletForJSONRPCRequest(request);
+  if (!EnsureWalletIsAvailable (pwallet, request.fHelp))
+    return NullUniValue;
+
+  if (request.fHelp
+      || (request.params.size () != 3 && request.params.size () != 4))
+    throw std::runtime_error (
+        "keva_put \"namespace\" \"key\" \"value\" (\"create_namespace\")\n"
+        "\nUpdate a name and possibly transfer it.\n"
+        + HelpRequiringPassphrase (pwallet) +
+        "\nArguments:\n"
+        "1. \"namespace\"            (string, required) the namespace to insert the key to\n"
+        "2. \"key\"                  (string, required) value for the key\n"
+        "4. \"value\"                (string, required) value for the name\n"
+        "5. \"create_namespace\"     (boolean, optional, default=false) create the namespace if it does not exist yet\n"
+        "\nResult:\n"
+        "\"txid\"             (string) the keva_put's txid\n"
+        "\nExamples:\n"
+        + HelpExampleCli ("keva_put", "\"mynamespace\", \"new-key\", \"new-value\"")
+        + HelpExampleCli ("keva_put", "\"mynamespace\", \"new-key\", \"new-value\", true")
+      );
+
+  RPCTypeCheck (request.params,
+    {UniValue::VSTR, UniValue::VSTR, UniValue::VSTR, UniValue::VSTR, UniValue::VBOOL});
+
+  ObserveSafeMode ();
+
+  const std::string namespaceStr = request.params[0].get_str ();
+  const valtype namespaceVal = ValtypeFromString (namespaceStr);
+  if (namespaceVal.size () > MAX_NAMESPACE_LENGTH)
+    throw JSONRPCError (RPC_INVALID_PARAMETER, "the namespace is too long");
+
+  const std::string keyStr = request.params[1].get_str ();
+  const valtype key = ValtypeFromString (keyStr);
+  if (key.size () > MAX_KEY_LENGTH)
+    throw JSONRPCError (RPC_INVALID_PARAMETER, "the key is too long");
+
+  const std::string valueStr = request.params[2].get_str ();
+  const valtype value = ValtypeFromString (valueStr);
+  if (value.size () > MAX_VALUE_LENGTH)
+    throw JSONRPCError (RPC_INVALID_PARAMETER, "the value is too long");
+
+  bool createNamespace = false;
+  if (!request.params[3].isNull()) {
+    createNamespace = request.params[3].get_bool();
+  }
+
+  /* Reject updates to a name for which the mempool already has
+     a pending update.  This is not a hard rule enforced by network
+     rules, but it is necessary with the current mempool implementation.  */
+  {
+    LOCK (mempool.cs);
+    if (mempool.updatesName (name))
+      throw JSONRPCError (RPC_TRANSACTION_ERROR,
+                          "there is already a pending update for this name");
+  }
+
+  CNameData oldData;
+  {
+    LOCK (cs_main);
+    if (!pcoinsTip->GetName (name, oldData) || oldData.isExpired ())
+      throw JSONRPCError (RPC_TRANSACTION_ERROR,
+                          "this name can not be updated");
+  }
+
+  const COutPoint outp = oldData.getUpdateOutpoint ();
+  const CTxIn txIn(outp);
+
+  /* No more locking required, similarly to name_new.  */
+
+  EnsureWalletIsUnlocked (pwallet);
+
+  CReserveKey keyName(pwallet);
+  CPubKey pubKeyReserve;
+  const bool ok = keyName.GetReservedKey (pubKeyReserve, true);
+  assert (ok);
+  bool usedKey = false;
+
+  CScript addrName;
+  if (request.params.size () == 3)
+    {
+      keyName.ReturnKey ();
+      const CTxDestination dest
+        = DecodeDestination (request.params[2].get_str ());
+      if (!IsValidDestination (dest))
+        throw JSONRPCError (RPC_INVALID_ADDRESS_OR_KEY, "invalid address");
+
+      addrName = GetScriptForDestination (dest);
+    }
+  else
+    {
+      usedKey = true;
+      addrName = GetScriptForDestination (pubKeyReserve.GetID ());
+    }
+
+  const CScript nameScript
+    = CNameScript::buildNameUpdate (addrName, name, value);
+
+  CCoinControl coinControl;
+  CWalletTx wtx;
+  SendMoneyToScript (pwallet, nameScript, &txIn,
+                     NAME_LOCKED_AMOUNT, false, wtx, coinControl);
+
+  if (usedKey)
+    keyName.KeepKey ();
+
+  return wtx.GetHash ().GetHex ();
+}
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index 3c0b4a6dd..6b2dbe6c2 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -3532,6 +3532,8 @@ extern UniValue removeprunedfunds(const JSONRPCRequest& request);
 extern UniValue importmulti(const JSONRPCRequest& request);
 extern UniValue rescanblockchain(const JSONRPCRequest& request);
 
+extern UniValue keva_put(const JSONRPCRequest& request); // in rpckeva.cpp
+
 static const CRPCCommand commands[] =
 { //  category              name                        actor (function)           argNames
     //  --------------------- ------------------------    -----------------------  ----------
@@ -3588,6 +3590,9 @@ static const CRPCCommand commands[] =
     { "wallet",             "rescanblockchain",         &rescanblockchain,         {"start_height", "stop_height"} },
 
     { "generating",         "generate",                 &generate,                 {"nblocks","maxtries"} },
+
+    // Kevacoin-specific wallet calls.
+    { "kevacoin",           "keva_put",                 &keva_put,                 {"namespace", "key", "value", "create_namespace"} }
 };
 
 void RegisterWalletRPCCommands(CRPCTable &t)