From 9a025be1517ee35a45379d7ae1285051ca1d59f8 Mon Sep 17 00:00:00 2001
From: Jianping Wu <jianping.wu@gmail.com>
Date: Wed, 12 Dec 2018 15:19:21 -0800
Subject: [PATCH] Implemented keva_filter.

---
 src/coins.cpp            |   8 +-
 src/coins.h              |   8 +-
 src/keva/common.cpp      | 126 +++++++++-----------
 src/keva/common.h        |  42 ++++---
 src/keva/main.cpp        |  23 +---
 src/keva/main.h          |   2 +-
 src/script/keva.h        |   2 +-
 src/test/keva_tests.cpp  |  17 ++-
 src/txdb.cpp             |  31 ++---
 src/txdb.h               |   2 +-
 src/wallet/rpckeva.cpp   | 247 +++++++++++++++++++++++++++++++++++++--
 src/wallet/rpcwallet.cpp |   4 +-
 12 files changed, 355 insertions(+), 157 deletions(-)

diff --git a/src/coins.cpp b/src/coins.cpp
index b9a74e712..fcc591513 100644
--- a/src/coins.cpp
+++ b/src/coins.cpp
@@ -13,7 +13,7 @@ std::vector<uint256> CCoinsView::GetHeadBlocks() const { return std::vector<uint
 bool CCoinsView::GetNamespace(const valtype &nameSpace, CKevaData &data) const { return false; }
 bool CCoinsView::GetName(const valtype &nameSpace, const valtype &key, CKevaData &data) const { return false; }
 bool CCoinsView::GetNamesForHeight(unsigned nHeight, std::set<valtype>& names) const { return false; }
-CNameIterator* CCoinsView::IterateNames() const { assert (false); }
+CKevaIterator* CCoinsView::IterateKeys(const valtype& nameSpace) const { assert (false); }
 bool CCoinsView::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock, const CKevaCache &names) { return false; }
 CCoinsViewCursor *CCoinsView::Cursor() const { return nullptr; }
 bool CCoinsView::ValidateNameDB() const { return false; }
@@ -38,7 +38,7 @@ bool CCoinsViewBacked::GetName(const valtype &nameSpace, const valtype &key, CKe
 bool CCoinsViewBacked::GetNamesForHeight(unsigned nHeight, std::set<valtype>& names) const {
     return base->GetNamesForHeight(nHeight, names);
 }
-CNameIterator* CCoinsViewBacked::IterateNames() const { return base->IterateNames(); }
+CKevaIterator* CCoinsViewBacked::IterateKeys(const valtype& nameSpace) const { return base->IterateKeys(nameSpace); }
 void CCoinsViewBacked::SetBackend(CCoinsView &viewIn) { base = &viewIn; }
 bool CCoinsViewBacked::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock, const CKevaCache &names) {
     return base->BatchWrite(mapCoins, hashBlock, names);
@@ -190,8 +190,8 @@ bool CCoinsViewCache::GetNamesForHeight(unsigned nHeight, std::set<valtype>& nam
     return true;
 }
 
-CNameIterator* CCoinsViewCache::IterateNames() const {
-    return cacheNames.iterateNames(base->IterateNames());
+CKevaIterator* CCoinsViewCache::IterateKeys(const valtype& nameSpace) const {
+    return cacheNames.iterateKeys(base->IterateKeys(nameSpace));
 }
 
 /* undo is set if the change is due to disconnecting blocks / going back in
diff --git a/src/coins.h b/src/coins.h
index 5e0f178e2..9a529c74c 100644
--- a/src/coins.h
+++ b/src/coins.h
@@ -173,8 +173,8 @@ public:
     // Query for names that were updated at the given height
     virtual bool GetNamesForHeight(unsigned nHeight, std::set<valtype>& names) const;
 
-    // Get a name iterator.
-    virtual CNameIterator* IterateNames() const;
+    // Get a key iterator.
+    virtual CKevaIterator* IterateKeys(const valtype& nameSpace) const;
 
     //! Do a bulk modification (multiple Coin changes + BestBlock change).
     //! The passed mapCoins can be modified.
@@ -209,7 +209,7 @@ public:
     bool GetNamespace(const valtype& nameSpace, CKevaData& data) const override;
     bool GetName(const valtype& nameSpace, const valtype& key, CKevaData& data) const override;
     bool GetNamesForHeight(unsigned nHeight, std::set<valtype>& names) const override;
-    CNameIterator* IterateNames() const override;
+    CKevaIterator* IterateKeys(const valtype& nameSpace) const override;
     void SetBackend(CCoinsView &viewIn);
     bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock, const CKevaCache &names) override;
     CCoinsViewCursor *Cursor() const override;
@@ -251,7 +251,7 @@ public:
     bool GetNamespace(const valtype &nameSpace, CKevaData& data) const override;
     bool GetName(const valtype &nameSpace, const valtype &key, CKevaData& data) const override;
     bool GetNamesForHeight(unsigned nHeight, std::set<valtype>& names) const override;
-    CNameIterator* IterateNames() const override;
+    CKevaIterator* IterateKeys(const valtype& nameSpace) const override;
     bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock, const CKevaCache &names) override;
     CCoinsViewCursor* Cursor() const override {
         throw std::logic_error("CCoinsViewCache cursor iteration not supported.");
diff --git a/src/keva/common.cpp b/src/keva/common.cpp
index ad2ab24e2..dceb0b602 100644
--- a/src/keva/common.cpp
+++ b/src/keva/common.cpp
@@ -2,7 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-// Copyright (c) 2018 Jianping Wu
+// Copyright (c) 2018 the Kevacoin Core Developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -10,9 +10,6 @@
 
 #include <script/keva.h>
 
-typedef std::vector<unsigned char> valtype;
-
-bool fNameHistory = false;
 
 /* ************************************************************************** */
 /* CKevaData.  */
@@ -36,9 +33,9 @@ CKevaData::fromScript (unsigned h, const COutPoint& out,
 }
 
 /* ************************************************************************** */
-/* CNameIterator.  */
+/* CKevaIterator.  */
 
-CNameIterator::~CNameIterator ()
+CKevaIterator::~CKevaIterator ()
 {
   /* Nothing to be done here.  This may be overwritten by
      subclasses if they need a destructor.  */
@@ -47,8 +44,7 @@ CNameIterator::~CNameIterator ()
 /* ************************************************************************** */
 /* CKevaCacheNameIterator.  */
 
-// JWU TODO: this doesn't work at all!!!!
-class CCacheNameIterator : public CNameIterator
+class CCacheKeyIterator : public CKevaIterator
 {
 
 private:
@@ -57,12 +53,14 @@ private:
   const CKevaCache& cache;
 
   /** Base iterator to combine with the cache.  */
-  CNameIterator* base;
+  CKevaIterator* base;
 
   /** Whether or not the base iterator has more entries.  */
   bool baseHasMore;
-  /** "Next" name of the base iterator.  */
-  valtype baseName;
+
+  /** "Next" key of the base iterator.  */
+  valtype baseKey;
+
   /** "Next" data of the base iterator.  */
   CKevaData baseData;
 
@@ -72,7 +70,7 @@ private:
   /* Call the base iterator's next() routine to fill in the internal
      "cache" for the next entry.  This already skips entries that are
      marked as deleted in the cache.  */
-  void advanceBaseIterator ();
+  void advanceBaseIterator();
 
 public:
 
@@ -81,104 +79,92 @@ public:
    * @param c The cache object to use.
    * @param b The base iterator.
    */
-  CCacheNameIterator (const CKevaCache& c, CNameIterator* b);
+  CCacheKeyIterator(const CKevaCache& c, CKevaIterator* b);
 
   /* Destruct, this deletes also the base iterator.  */
-  ~CCacheNameIterator ();
+  ~CCacheKeyIterator();
 
   /* Implement iterator methods.  */
-  void seek (const valtype& name);
-  bool next (valtype& name, CKevaData& data);
+  void seek(const valtype& key);
+  bool next(valtype& key, CKevaData& data);
 
 };
 
-CCacheNameIterator::CCacheNameIterator (const CKevaCache& c, CNameIterator* b)
-  : cache(c), base(b)
+CCacheKeyIterator::CCacheKeyIterator(const CKevaCache& c, CKevaIterator* b)
+  : cache(c), base(b), CKevaIterator(b->getNamespace())
 {
   /* Add a seek-to-start to ensure that everything is consistent.  This call
      may be superfluous if we seek to another position afterwards anyway,
      but it should also not hurt too much.  */
-  seek (valtype ());
+  seek(valtype());
 }
 
-CCacheNameIterator::~CCacheNameIterator ()
+CCacheKeyIterator::~CCacheKeyIterator()
 {
   delete base;
 }
 
 void
-CCacheNameIterator::advanceBaseIterator ()
+CCacheKeyIterator::advanceBaseIterator()
 {
   assert (baseHasMore);
-  do
-    baseHasMore = base->next (baseName, baseData);
-  while (baseHasMore && cache.isDeleted(baseName, baseName));
+  do {
+    baseHasMore = base->next(baseKey, baseData);
+  } while (baseHasMore && cache.isDeleted(nameSpace, baseKey));
 }
 
 void
-CCacheNameIterator::seek(const valtype& start)
+CCacheKeyIterator::seek(const valtype& start)
 {
-  // JWU TODO: fix this!
-#if 0
-  cacheIter = cache.entries.lower_bound(start);
-#endif
+  cacheIter = cache.entries.lower_bound(std::make_tuple(nameSpace, start));
   base->seek(start);
 
   baseHasMore = true;
   advanceBaseIterator();
 }
 
-bool CCacheNameIterator::next (valtype& name, CKevaData& data)
+bool CCacheKeyIterator::next(valtype& key, CKevaData& data)
 {
-#if 0
-  // JWU TODO: fix this!
-
   /* Exit early if no more data is available in either the cache
      nor the base iterator.  */
-  if (!baseHasMore && cacheIter == cache.entries.end ())
+  if (!baseHasMore && cacheIter == cache.entries.end())
     return false;
 
   /* Determine which source to use for the next.  */
   bool useBase;
   if (!baseHasMore)
     useBase = false;
-  else if (cacheIter == cache.entries.end ())
+  else if (cacheIter == cache.entries.end())
     useBase = true;
-  else
-    {
-      /* A special case is when both iterators are equal.  In this case,
-         we want to use the cached version.  We also have to advance
-         the base iterator.  */
-      if (baseName == cacheIter->first)
-        advanceBaseIterator ();
-
-      /* Due to advancing the base iterator above, it may happen that
-         no more base entries are present.  Handle this gracefully.  */
-      if (!baseHasMore)
-        useBase = false;
-      else
-        {
-          assert (baseName != cacheIter->first);
-
-          CKevaCache::NameComparator cmp;
-          useBase = cmp (baseName, cacheIter->first);
-        }
+  else {
+    /* A special case is when both iterators are equal.  In this case,
+        we want to use the cached version.  We also have to advance
+        the base iterator.  */
+    if (baseKey == std::get<1>(cacheIter->first))
+      advanceBaseIterator ();
+
+    /* Due to advancing the base iterator above, it may happen that
+        no more base entries are present.  Handle this gracefully.  */
+    if (!baseHasMore)
+      useBase = false;
+    else {
+      assert(baseKey != std::get<1>(cacheIter->first));
+
+      CKevaCache::KeyComparator cmp;
+      useBase = cmp(std::make_tuple(nameSpace, baseKey), cacheIter->first);
     }
+  }
 
   /* Use the correct source now and advance it.  */
-  if (useBase)
-    {
-      name = baseName;
-      data = baseData;
-      advanceBaseIterator ();
-    }
-  else
-    {
-      name = cacheIter->first;
-      data = cacheIter->second;
-      ++cacheIter;
-    }
-#endif
+  if (useBase) {
+    key = baseKey;
+    data = baseData;
+    advanceBaseIterator();
+  } else {
+    key = std::get<1>(cacheIter->first);
+    data = cacheIter->second;
+    ++cacheIter;
+  }
   return true;
 }
 
@@ -235,10 +221,10 @@ CKevaCache::remove(const valtype& nameSpace, const valtype& key)
   deleted.insert(name);
 }
 
-CNameIterator*
-CKevaCache::iterateNames(CNameIterator* base) const
+CKevaIterator*
+CKevaCache::iterateKeys(CKevaIterator* base) const
 {
-  return new CCacheNameIterator (*this, base);
+  return new CCacheKeyIterator(*this, base);
 }
 
 void
diff --git a/src/keva/common.h b/src/keva/common.h
index d2e22153b..e3d669c09 100644
--- a/src/keva/common.h
+++ b/src/keva/common.h
@@ -2,7 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-// Copyright (c) 2018 Jianping Wu
+// Copyright (c) 2018
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -246,37 +246,47 @@ public:
 };
 
 /* ************************************************************************** */
-/* CNameIterator.  */
+/* CKevaIterator.  */
 
 /**
  * Interface for iterators over the name database.
  */
-class CNameIterator
+class CKevaIterator
 {
+protected:
+  const valtype& nameSpace;
 
 public:
 
+  CKevaIterator(const valtype& ns) :nameSpace(ns)
+  {}
+
   // Virtual destructor in case subclasses need them.
-  virtual ~CNameIterator ();
+  virtual ~CKevaIterator();
+
+  const valtype& getNamespace() {
+    return nameSpace;
+  }
 
   /**
    * Seek to a given lower bound.
-   * @param start The name to seek to.
+   * @param start The key to seek to.
    */
-  virtual void seek (const valtype& name) = 0;
+  virtual void seek(const valtype& start) = 0;
 
   /**
-   * Get the next name.  Returns false if no more names are available.
-   * @param name Put the name here.
-   * @param data Put the name's data here.
-   * @return True if successful, false if no more names.
+   * Get the next key.  Returns false if no more keys are available.
+   * @param nameSpace Put the namespace here.
+   * @param key Put the key here.
+   * @param data Put the key's data here.
+   * @return True if successful, false if no more keys.
    */
-  virtual bool next (valtype& name, CKevaData& data) = 0;
+  virtual bool next(valtype& key, CKevaData& data) = 0;
 
 };
 
 /* ************************************************************************** */
-/* CNameCache.  */
+/* CKevaCache.  */
 
 /**
  * Cache / record of updates to the name database.  In addition to
@@ -293,7 +303,7 @@ private:
    * This is used to sort the cache entry map in the same way as the
    * database is sorted.
    */
-  class NameComparator
+  class KeyComparator
   {
   public:
     inline bool operator() (const std::tuple<valtype, valtype> a,
@@ -314,7 +324,7 @@ public:
    * Type of name entry map.  This is public because it is also used
    * by the unit tests.
    */
-  typedef std::map<std::tuple<valtype, valtype>, CKevaData, NameComparator> EntryMap;
+  typedef std::map<std::tuple<valtype, valtype>, CKevaData, KeyComparator> EntryMap;
 
   typedef std::tuple<valtype, valtype> NamespaceKeyType;
 
@@ -326,7 +336,7 @@ private:
   /** Deleted names.  */
   std::set<NamespaceKeyType> deleted;
 
-  friend class CCacheNameIterator;
+  friend class CCacheKeyIterator;
 
 public:
 
@@ -379,7 +389,7 @@ public:
   /* Return a name iterator that combines a "base" iterator with the changes
      made to it according to the cache.  The base iterator is taken
      ownership of.  */
-  CNameIterator* iterateNames (CNameIterator* base) const;
+  CKevaIterator* iterateKeys(CKevaIterator* base) const;
 
   /* Query the cached changes to the expire index.  In particular,
      for a given height and a given set of names that were indexed to
diff --git a/src/keva/main.cpp b/src/keva/main.cpp
index 3e6821d7d..4379d3a97 100644
--- a/src/keva/main.cpp
+++ b/src/keva/main.cpp
@@ -2,7 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-// Copyright (c) 2018 Jianping Wu
+// Copyright (c) 2018 the Kevacoin Core Developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -133,27 +133,6 @@ void CKevaMemPool::remove(const CTxMemPoolEntry& entry)
 void
 CKevaMemPool::removeConflicts(const CTransaction& tx)
 {
-  // JWU TODO: is this required at all?
-#if 0
-  AssertLockHeld (pool.cs);
-
-  if (!tx.IsKevacoin ())
-    return;
-
-  for (const auto& txout : tx.vout) {
-    const CKevaScript nameOp(txout.scriptPubKey);
-    if (nameOp.isKevaOp() && nameOp.getKevaOp() == OP_KEVA_PUT) {
-      const valtype& nameSpace = nameOp.getOpNamespace();
-      const NamespaceTxMap::const_iterator mit = mapNamespaceRegs.find(nameSpace);
-      if (mit != mapNamespaceRegs.end()) {
-        const CTxMemPool::txiter mit2 = pool.mapTx.find(mit->second);
-        assert(mit2 != pool.mapTx.end());
-        pool.removeRecursive (mit2->GetTx(),
-                              MemPoolRemovalReason::KEVA_CONFLICT);
-      }
-    }
-  }
-#endif
 }
 
 bool CKevaMemPool::validateNamespace(const CTransaction& tx, const valtype& nameSpace) const
diff --git a/src/keva/main.h b/src/keva/main.h
index 9cd2acc58..bb42c013f 100644
--- a/src/keva/main.h
+++ b/src/keva/main.h
@@ -2,7 +2,7 @@
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-// Copyright (c) 2018 Jianping Wu
+// Copyright (c) 2018 the Kevacoin Core Developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
diff --git a/src/script/keva.h b/src/script/keva.h
index 901d7b103..74c5641c9 100644
--- a/src/script/keva.h
+++ b/src/script/keva.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2018 Jianping Wu
+// Copyright (c) 2018 the Kevacoin Core Developers
 // Distributed under the MIT software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
diff --git a/src/test/keva_tests.cpp b/src/test/keva_tests.cpp
index 340d81283..de593d2ee 100644
--- a/src/test/keva_tests.cpp
+++ b/src/test/keva_tests.cpp
@@ -180,7 +180,7 @@ private:
   /**
    * "Fake" name iterator returned.
    */
-  class Iterator : public CNameIterator
+  class Iterator : public CKevaIterator
   {
   public:
 
@@ -198,8 +198,8 @@ private:
 
 public:
 
-  CNameIterator*
-  IterateNames() const
+  CKevaIterator*
+  IterateKeys() const
   {
     return new Iterator();
   }
@@ -271,7 +271,7 @@ private:
    * @param iter The iterator to use.
    * @return The resulting entry list.
    */
-  static EntryList getNamesFromIterator (CNameIterator& iter);
+  static EntryList getNamesFromIterator (CKevaIterator& iter);
 
 public:
 
@@ -340,7 +340,7 @@ NameIterationTester::verify (const CCoinsView& view) const
 
   /* Seek the iterator to the end first for "maximum confusion".  This ensures
      that seeking to valtype() works.  */
-  std::unique_ptr<CNameIterator> iter(view.IterateNames());
+  std::unique_ptr<CKevaIterator> iter(view.IterateKeys());
   const valtype end = ValtypeFromString ("zzzzzzzzzzzzzzzz");
   {
     valtype name;
@@ -392,14 +392,14 @@ NameIterationTester::EntryList
 NameIterationTester::getNamesFromView (const CCoinsView& view,
                                        const valtype& start)
 {
-  std::unique_ptr<CNameIterator> iter(view.IterateNames());
+  std::unique_ptr<CKevaIterator> iter(view.IterateKeys());
   iter->seek (start);
 
   return getNamesFromIterator (*iter);
 }
 
 NameIterationTester::EntryList
-NameIterationTester::getNamesFromIterator (CNameIterator& iter)
+NameIterationTester::getNamesFromIterator (CKevaIterator& iter)
 {
   EntryList res;
 
@@ -702,9 +702,6 @@ BOOST_AUTO_TEST_CASE (name_tx_verification)
 
 BOOST_AUTO_TEST_CASE(keva_updates_undo)
 {
-  /* Enable name history to test this on the go.  */
-  fNameHistory = true;
-
   const valtype nameSpace = ValtypeFromString ("database-test-namespace");
   const valtype displayName = ValtypeFromString ("display name");
   const valtype key1 = ValtypeFromString ("key1");
diff --git a/src/txdb.cpp b/src/txdb.cpp
index 972915552..c364d2a55 100644
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -84,7 +84,7 @@ std::vector<uint256> CCoinsViewDB::GetHeadBlocks() const {
     return vhashHeadBlocks;
 }
 
-class CDbNameIterator : public CNameIterator
+class CDbKeyIterator : public CKevaIterator
 {
 
 private:
@@ -94,42 +94,43 @@ private:
 
 public:
 
-    ~CDbNameIterator();
+    ~CDbKeyIterator();
 
     /**
      * Construct a new name iterator for the database.
      * @param db The database to create the iterator for.
      */
-    CDbNameIterator(const CDBWrapper& db);
+    CDbKeyIterator(const CDBWrapper& db, const valtype& nameSpace);
 
     /* Implement iterator methods.  */
     void seek(const valtype& start);
-    bool next(valtype& name, CKevaData& data);
+    bool next(valtype& key, CKevaData& data);
 
 };
 
-CDbNameIterator::~CDbNameIterator() {
+CDbKeyIterator::~CDbKeyIterator() {
     delete iter;
 }
 
-CDbNameIterator::CDbNameIterator(const CDBWrapper& db)
-    : iter(const_cast<CDBWrapper*>(&db)->NewIterator())
+CDbKeyIterator::CDbKeyIterator(const CDBWrapper& db, const valtype& ns)
+    : iter(const_cast<CDBWrapper*>(&db)->NewIterator()), CKevaIterator(ns)
 {
     seek(valtype());
 }
 
-void CDbNameIterator::seek(const valtype& start) {
-    iter->Seek(std::make_pair(DB_NAME, start));
+void CDbKeyIterator::seek(const valtype& start) {
+    iter->Seek(std::make_pair(DB_NAME, std::make_pair(nameSpace, start)));
 }
 
-bool CDbNameIterator::next(valtype& name, CKevaData& data) {
+bool CDbKeyIterator::next(valtype& key, CKevaData& data) {
     if (!iter->Valid())
         return false;
 
-    std::pair<char, valtype> key;
-    if (!iter->GetKey(key) || key.first != DB_NAME)
+    std::pair<char, std::pair<valtype, valtype>> curKey;
+    if (!iter->GetKey(curKey) || curKey.first != DB_NAME)
         return false;
-    name = key.second;
+
+    key = std::get<1>(curKey.second);
 
     if (!iter->GetValue(data)) {
         return error("%s : failed to read data from iterator", __func__);
@@ -139,8 +140,8 @@ bool CDbNameIterator::next(valtype& name, CKevaData& data) {
     return true;
 }
 
-CNameIterator* CCoinsViewDB::IterateNames() const {
-    return new CDbNameIterator(db);
+CKevaIterator* CCoinsViewDB::IterateKeys(const valtype& nameSpace) const {
+    return new CDbKeyIterator(db, nameSpace);
 }
 
 bool CCoinsViewDB::GetNamespace(const valtype &nameSpace, CKevaData &data) const {
diff --git a/src/txdb.h b/src/txdb.h
index 8ddbf1855..a05778054 100644
--- a/src/txdb.h
+++ b/src/txdb.h
@@ -79,7 +79,7 @@ public:
     bool GetNamespace(const valtype &nameSpace, CKevaData &data) const override;
     bool GetName(const valtype &nameSpace, const valtype &key, CKevaData &data) const override;
     bool GetNamesForHeight(unsigned nHeight, std::set<valtype>& names) const override;
-    CNameIterator* IterateNames() const override;
+    CKevaIterator* IterateKeys(const valtype& nameSpace) const override;
     bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock, const CKevaCache &names) override;
     CCoinsViewCursor *Cursor() const override;
 
diff --git a/src/wallet/rpckeva.cpp b/src/wallet/rpckeva.cpp
index 535ea1d7b..3c4c4244c 100644
--- a/src/wallet/rpckeva.cpp
+++ b/src/wallet/rpckeva.cpp
@@ -1,4 +1,8 @@
-// Copyright (c) 2018 Jianping Wu
+// Copyright (c) 2014-2017 Daniel Kraft
+// Distributed under the MIT/X11 software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+// Copyright (c) 2018 the Kevacoin Core Developers
 // Distributed under the MIT/X11 software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
@@ -20,6 +24,7 @@
 #include "wallet/wallet.h"
 
 #include <univalue.h>
+#include <boost/xpressive/xpressive_dynamic.hpp>
 
 const int NAMESPACE_LENGTH           =  21;
 const std::string DUMMY_NAMESPACE    =  "___DUMMY_NAMESPACE___";
@@ -33,7 +38,7 @@ UniValue keva_namespace(const JSONRPCRequest& request)
   if (!EnsureWalletIsAvailable (pwallet, request.fHelp))
     return NullUniValue;
 
-  if (request.fHelp || request.params.size () != 1)
+  if (request.fHelp || request.params.size() != 1)
     throw std::runtime_error (
         "keva_namespace \"display_name\"\n"
         "\nRegister a namespace with the given display name.\n"
@@ -55,7 +60,7 @@ UniValue keva_namespace(const JSONRPCRequest& request)
 
   const std::string displayNameStr = request.params[0].get_str();
   const valtype displayName = ValtypeFromString (displayNameStr);
-  if (displayName.size () > MAX_NAMESPACE_LENGTH) {
+  if (displayName.size() > MAX_NAMESPACE_LENGTH) {
     throw JSONRPCError (RPC_INVALID_PARAMETER, "the name is too long");
   }
 
@@ -140,7 +145,7 @@ UniValue keva_list_namespaces(const JSONRPCRequest& request)
 
       CKevaScript kevaOp;
       int nOut = -1;
-      for (unsigned i = 0; i < tx.tx->vout.size (); ++i)
+      for (unsigned i = 0; i < tx.tx->vout.size(); ++i)
         {
           const CKevaScript cur(tx.tx->vout[i].scriptPubKey);
           if (cur.isKevaOp ())
@@ -236,17 +241,17 @@ UniValue keva_put(const JSONRPCRequest& request)
   if (!DecodeKevaNamespace(namespaceStr, Params(), nameSpace)) {
     throw JSONRPCError (RPC_INVALID_PARAMETER, "invalid namespace id");
   }
-  if (nameSpace.size () > MAX_NAMESPACE_LENGTH)
+  if (nameSpace.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)
+  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)
+  if (value.size() > MAX_VALUE_LENGTH)
     throw JSONRPCError (RPC_INVALID_PARAMETER, "the value is too long");
 
   EnsureWalletIsUnlocked(pwallet);
@@ -317,13 +322,13 @@ UniValue keva_delete(const JSONRPCRequest& request)
   if (!DecodeKevaNamespace(namespaceStr, Params(), nameSpace)) {
     throw JSONRPCError (RPC_INVALID_PARAMETER, "invalid namespace id");
   }
-  if (nameSpace.size () > MAX_NAMESPACE_LENGTH) {
+  if (nameSpace.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) {
+  if (key.size() > MAX_KEY_LENGTH) {
     throw JSONRPCError (RPC_INVALID_PARAMETER, "the key is too long");
   }
 
@@ -414,12 +419,12 @@ UniValue keva_get(const JSONRPCRequest& request)
   if (!DecodeKevaNamespace(namespaceStr, Params(), nameSpace)) {
     throw JSONRPCError (RPC_INVALID_PARAMETER, "invalid namespace id");
   }
-  if (nameSpace.size () > MAX_NAMESPACE_LENGTH)
+  if (nameSpace.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)
+  if (key.size() > MAX_KEY_LENGTH)
     throw JSONRPCError (RPC_INVALID_PARAMETER, "the key is too long");
 
   CKevaData data;
@@ -445,7 +450,7 @@ UniValue keva_get(const JSONRPCRequest& request)
 
 UniValue keva_pending(const JSONRPCRequest& request)
 {
-  if (request.fHelp || request.params.size () > 1)
+  if (request.fHelp || request.params.size() > 1)
     throw std::runtime_error (
         "keva_pending (\"namespace\")\n"
         "\nList unconfirmed keva operations in the mempool.\n"
@@ -523,3 +528,221 @@ UniValue keva_pending(const JSONRPCRequest& request)
 
   return arr;
 }
+
+/**
+ * Return the help string description to use for keva info objects.
+ * @param indent Indentation at the line starts.
+ * @param trailing Trailing string (e. g., comma for an array of these objects).
+ * @return The description string.
+ */
+std::string getKevaInfoHelp (const std::string& indent, const std::string& trailing)
+{
+  std::ostringstream res;
+
+  res << indent << "{" << std::endl;
+  res << indent << "  \"name\": xxxxx,           "
+      << "(string) the requested name" << std::endl;
+  res << indent << "  \"value\": xxxxx,          "
+      << "(string) the name's current value" << std::endl;
+  res << indent << "  \"txid\": xxxxx,           "
+      << "(string) the name's last update tx" << std::endl;
+  res << indent << "  \"address\": xxxxx,        "
+      << "(string) the address holding the name" << std::endl;
+  res << indent << "  \"height\": xxxxx,         "
+      << "(numeric) the name's last update height" << std::endl;
+  res << indent << "}" << trailing << std::endl;
+
+  return res.str ();
+}
+
+/**
+ * Utility routine to construct a "name info" object to return.  This is used
+ * for name_show and also name_list.
+ * @param name The name.
+ * @param value The name's value.
+ * @param outp The last update's outpoint.
+ * @param addr The name's address script.
+ * @param height The name's last update height.
+ * @return A JSON object to return.
+ */
+UniValue
+getKevaInfo (const valtype& name, const valtype& value, const COutPoint& outp,
+             const CScript& addr, int height)
+{
+  UniValue obj(UniValue::VOBJ);
+  obj.pushKV("name", ValtypeToString(name));
+  obj.pushKV("value", ValtypeToString(value));
+  obj.pushKV("txid", outp.hash.GetHex());
+  obj.pushKV("vout", static_cast<int>(outp.n));
+
+  /* Try to extract the address.  May fail if we can't parse the script
+     as a "standard" script.  */
+  CTxDestination dest;
+  std::string addrStr;
+  if (ExtractDestination(addr, dest))
+    addrStr = EncodeDestination(dest);
+  else
+    addrStr = "<nonstandard>";
+  obj.pushKV("address", addrStr);
+
+  /* Calculate expiration data.  */
+  const int curHeight = chainActive.Height ();
+  const Consensus::Params& params = Params ().GetConsensus ();
+  obj.pushKV("height", height);
+
+  return obj;
+}
+
+/**
+ * Return name info object for a CNameData object.
+ * @param name The name.
+ * @param data The name's data.
+ * @return A JSON object to return.
+ */
+UniValue
+getKevaInfo (const valtype& name, const CKevaData& data)
+{
+  return getKevaInfo(name, data.getValue (), data.getUpdateOutpoint (),
+                      data.getAddress (), data.getHeight ());
+}
+
+
+UniValue keva_filter(const JSONRPCRequest& request)
+{
+  if (request.fHelp || request.params.size() > 6 || request.params.size() == 0)
+    throw std::runtime_error(
+        "keva_filter (\"namespaceId\" (\"regexp\" (\"from\" (\"nb\" (\"stat\")))))\n"
+        "\nScan and list keys matching a regular expression.\n"
+        "\nArguments:\n"
+        "1. \"namespace\"   (string) namespace Id\n"
+        "2. \"regexp\"      (string, optional) filter keys with this regexp\n"
+        "3. \"maxage\"      (numeric, optional, default=36000) only consider names updated in the last \"maxage\" blocks; 0 means all names\n"
+        "4. \"from\"        (numeric, optional, default=0) return from this position onward; index starts at 0\n"
+        "5. \"nb\"          (numeric, optional, default=0) return only \"nb\" entries; 0 means all\n"
+        "6. \"stat\"        (string, optional) if set to the string \"stat\", print statistics instead of returning the names\n"
+        "\nResult:\n"
+        "[\n"
+        + getKevaInfoHelp ("  ", ",") +
+        "  ...\n"
+        "]\n"
+        "\nExamples:\n"
+        + HelpExampleCli ("keva_filter", "\"\" 5")
+        + HelpExampleCli ("keva_filter", "\"^id/\"")
+        + HelpExampleCli ("keva_filter", "\"^id/\" 36000 0 0 \"stat\"")
+        + HelpExampleRpc ("keva_scan", "\"^d/\"")
+      );
+
+  RPCTypeCheck(request.params, {
+                  UniValue::VSTR, UniValue::VSTR, UniValue::VNUM,
+                  UniValue::VNUM, UniValue::VNUM, UniValue::VSTR
+               });
+
+  if (IsInitialBlockDownload()) {
+    throw JSONRPCError(RPC_CLIENT_IN_INITIAL_DOWNLOAD,
+                       "Kevacoin is downloading blocks...");
+  }
+
+  ObserveSafeMode();
+
+  /* ********************** */
+  /* Interpret parameters.  */
+
+  bool haveRegexp(false);
+  boost::xpressive::sregex regexp;
+
+  valtype nameSpace;
+  int maxage(36000), from(0), nb(0);
+  bool stats(false);
+
+  if (request.params.size() >= 1) {
+    const std::string namespaceStr = request.params[0].get_str();
+    valtype nameSpace;
+    if (!DecodeKevaNamespace(namespaceStr, Params(), nameSpace)) {
+      throw JSONRPCError (RPC_INVALID_PARAMETER, "invalid namespace id");
+    }
+  }
+
+  if (request.params.size() >= 2) {
+    haveRegexp = true;
+    regexp = boost::xpressive::sregex::compile (request.params[1].get_str());
+  }
+
+  if (request.params.size() >= 3)
+    maxage = request.params[2].get_int();
+  if (maxage < 0)
+    throw JSONRPCError(RPC_INVALID_PARAMETER,
+                        "'maxage' should be non-negative");
+
+  if (request.params.size() >= 4)
+    from = request.params[3].get_int ();
+
+  if (from < 0)
+    throw JSONRPCError (RPC_INVALID_PARAMETER, "'from' should be non-negative");
+
+  if (request.params.size() >= 5)
+    nb = request.params[4].get_int ();
+
+  if (nb < 0)
+    throw JSONRPCError (RPC_INVALID_PARAMETER, "'nb' should be non-negative");
+
+  if (request.params.size() >= 6) {
+    if (request.params[5].get_str() != "stat")
+      throw JSONRPCError (RPC_INVALID_PARAMETER,
+                          "fifth argument must be the literal string 'stat'");
+    stats = true;
+  }
+
+  /* ******************************************* */
+  /* Iterate over names to build up the result.  */
+
+  UniValue keys(UniValue::VARR);
+  unsigned count(0);
+
+  LOCK (cs_main);
+
+  valtype key;
+  CKevaData data;
+  std::unique_ptr<CKevaIterator> iter(pcoinsTip->IterateKeys(nameSpace));
+  while (iter->next(key, data)) {
+    const int age = chainActive.Height() - data.getHeight();
+    assert(age >= 0);
+    if (maxage != 0 && age >= maxage)
+      continue;
+
+    if (haveRegexp) {
+      const std::string keyStr = ValtypeToString(key);
+      boost::xpressive::smatch matches;
+      if (!boost::xpressive::regex_search(keyStr, matches, regexp))
+        continue;
+    }
+
+    if (from > 0) {
+      --from;
+      continue;
+    }
+    assert(from == 0);
+
+    if (stats)
+      ++count;
+    else
+      keys.push_back(getKevaInfo(key, data));
+
+    if (nb > 0) {
+      --nb;
+      if (nb == 0)
+        break;
+    }
+  }
+
+  /* ********************************************************** */
+  /* Return the correct result (take stats mode into account).  */
+
+  if (stats) {
+    UniValue res(UniValue::VOBJ);
+    res.pushKV("blocks", chainActive.Height());
+    res.pushKV("count", static_cast<int>(count));
+    return res;
+  }
+
+  return keys;
+}
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index bf0f5b239..56ee0c1a3 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -3597,6 +3597,7 @@ extern UniValue keva_delete(const JSONRPCRequest& request);
 extern UniValue keva_get(const JSONRPCRequest& request);
 extern UniValue keva_list_namespaces(const JSONRPCRequest& request);
 extern UniValue keva_pending(const JSONRPCRequest& request);
+extern UniValue keva_filter(const JSONRPCRequest& request);
 
 static const CRPCCommand commands[] =
 { //  category              name                        actor (function)           argNames
@@ -3661,7 +3662,8 @@ static const CRPCCommand commands[] =
     { "kevacoin",           "keva_put",                 &keva_put,                 {"namespace", "key", "value"} },
     { "kevacoin",           "keva_delete",              &keva_delete,              {"namespace", "key"} },
     { "kevacoin",           "keva_get",                 &keva_get,                 {"namespace", "key"} },
-    { "kevacoin",           "keva_pending",             &keva_pending,             {"namespace"} }
+    { "kevacoin",           "keva_pending",             &keva_pending,             {"namespace"} },
+    { "kevacoin",           "keva_filter",              &keva_filter,              {"namespace", "regexp", "from", "nb", "stat"} }
 };
 
 void RegisterWalletRPCCommands(CRPCTable &t)