1 files changed, 898 insertions, 0 deletions

diff --git a/ext/lmdb-safe/lmdb-safe.hh b/ext/lmdb-safe/lmdb-safe.hh
new file mode 100644
index 0000000..2d5983b
--- /dev/null
+++ b/ext/lmdb-safe/lmdb-safe.hh
@@ -0,0 +1,898 @@
+#pragma once
+#include <string_view>
+#include <lmdb.h>
+#include <iostream>
+#include <fstream>
+#include <set>
+#include <map>
+#include <thread>
+#include <memory>
+#include <string>
+#include <string.h>
+#include <mutex>
+#include <vector>
+#include <algorithm>
+
+#include "config.h"
+
+#ifndef DNSDIST
+#include <boost/range/detail/common.hpp>
+#include <stdint.h>
+#include <netinet/in.h>
+#include <stdexcept>
+#include "../../pdns/misc.hh"
+#endif
+
+using std::string_view;
+
+/* open issues:
+ *
+ * - missing convenience functions (string_view, string)
+ */
+
+/*
+The error strategy. Anything that "should never happen" turns into an exception. But things like 'duplicate entry' or 'no such key' are for you to deal with.
+ */
+
+/*
+  Thread safety: we are as safe as lmdb. You can talk to MDBEnv from as many threads as you want
+*/
+
+/** MDBDbi is our only 'value type' object, as 1) a dbi is actually an integer
+    and 2) per LMDB documentation, we never close it. */
+class MDBDbi
+{
+public:
+  MDBDbi(): d_dbi(-1)
+  {
+  }
+  explicit MDBDbi(MDB_env* env, MDB_txn* txn, string_view dbname, int flags);
+
+  operator const MDB_dbi&() const
+  {
+    return d_dbi;
+  }
+
+  MDB_dbi d_dbi;
+};
+
+class MDBRWTransactionImpl;
+class MDBROTransactionImpl;
+
+using MDBROTransaction = std::unique_ptr<MDBROTransactionImpl>;
+using MDBRWTransaction = std::unique_ptr<MDBRWTransactionImpl>;
+
+class MDBEnv
+{
+public:
+  MDBEnv(const char* fname, int flags, int mode, uint64_t mapsizeMB);
+
+  ~MDBEnv()
+  {
+    //    Only a single thread may call this function. All transactions, databases, and cursors must already be closed before calling this function
+    mdb_env_close(d_env);
+    // but, elsewhere, docs say database handles do not need to be closed?
+  }
+
+  MDBDbi openDB(const string_view dbname, int flags);
+
+  MDBRWTransaction getRWTransaction();
+  MDBROTransaction getROTransaction();
+
+  operator MDB_env*& ()
+  {
+    return d_env;
+  }
+  MDB_env* d_env;
+
+  int getRWTX();
+  void incRWTX();
+  void decRWTX();
+  int getROTX();
+  void incROTX();
+  void decROTX();
+private:
+  std::mutex d_openmut;
+  std::mutex d_countmutex;
+  std::map<std::thread::id, int> d_RWtransactionsOut;
+  std::map<std::thread::id, int> d_ROtransactionsOut;
+};
+
+std::shared_ptr<MDBEnv> getMDBEnv(const char* fname, int flags, int mode, uint64_t mapsizeMB=(sizeof(void *)==4) ? 100 : 16000);
+
+#ifndef DNSDIST
+
+#if !defined(__BYTE_ORDER__) || !defined(__ORDER_LITTLE_ENDIAN__) || !defined(__ORDER_BIG_ENDIAN__)
+#error "your compiler did not define byte order macros"
+#endif
+
+// FIXME do something more portable than __builtin_bswap64
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
+#define _LMDB_SAFE_BSWAP64MAYBE(x) __builtin_bswap64(x)
+#else
+#define _LMDB_SAFE_BSWAP64MAYBE(x) (x)
+#endif
+
+struct MDBOutVal; // forward declaration because of how the functions below tie in with MDBOutVal
+
+namespace LMDBLS {
+  class __attribute__((__packed__)) LSheader {
+  public:
+    uint64_t d_timestamp;
+    uint64_t d_txnid;
+    uint8_t d_version;
+    uint8_t d_flags;
+    uint32_t d_reserved;
+    uint16_t d_numextra;
+
+    LSheader(uint64_t timestamp, uint64_t txnid, uint8_t flags=0, uint8_t version=0, uint8_t numextra=0):
+      d_timestamp(_LMDB_SAFE_BSWAP64MAYBE(timestamp)),
+      d_txnid(_LMDB_SAFE_BSWAP64MAYBE(txnid)),
+      d_version(version),
+      d_flags(flags),
+      d_reserved(0),
+      d_numextra(htons(numextra))
+    {
+
+    }
+
+    std::string toString() {
+      return std::string((char*)this, sizeof(*this)) + std::string(ntohs(d_numextra)*8, '\0');
+    }
+
+
+  };
+
+  static_assert(sizeof(LSheader)==24, "LSheader size is wrong");
+
+  const size_t LS_MIN_HEADER_SIZE = sizeof(LSheader);
+  const size_t LS_BLOCK_SIZE = 8;
+  const size_t LS_NUMEXTRA_OFFSET = 22;
+  const uint8_t LS_FLAG_DELETED = 0x01;
+
+  const LSheader* LSassertFixedHeaderSize(std::string_view val);
+  size_t LScheckHeaderAndGetSize(std::string_view val, size_t datasize=0);
+  size_t LScheckHeaderAndGetSize(const MDBOutVal *val, size_t datasize=0);
+  bool LSisDeleted(std::string_view val);
+
+  extern bool s_flag_deleted;
+}
+
+#undef _LMDB_SAFE_BSWAP64MAYBE
+
+#endif /* ifndef DNSDIST */
+
+
+struct MDBOutVal
+{
+  operator MDB_val&()
+  {
+    return d_mdbval;
+  }
+
+#ifndef DNSDIST
+  template <class T,
+          typename std::enable_if<std::is_integral<T>::value,
+                                  T>::type* = nullptr> const
+  T get()
+  {
+    T ret;
+
+    size_t offset = LMDBLS::LScheckHeaderAndGetSize(this, sizeof(T));
+
+    memcpy(&ret, reinterpret_cast<const char *>(d_mdbval.mv_data)+offset, sizeof(T));
+
+    static_assert(sizeof(T) == 4, "this code currently only supports 32 bit integers");
+    ret = ntohl(ret);
+    return ret;
+  }
+
+  template <class T,
+          typename std::enable_if<std::is_integral<T>::value,
+                                  T>::type* = nullptr> const
+  T getNoStripHeader()
+  {
+    T ret;
+    if(d_mdbval.mv_size != sizeof(T))
+      throw std::runtime_error("MDB data has wrong length for type");
+
+    memcpy(&ret, d_mdbval.mv_data, sizeof(T));
+
+    static_assert(sizeof(T) == 4, "this code currently only supports 32 bit integers");
+    ret = ntohl(ret);
+    return ret;
+  }
+
+#endif /* ifndef DNSDIST */
+
+  template <class T,
+            typename std::enable_if<std::is_class<T>::value,T>::type* = nullptr>
+  T get() const;
+
+
+#ifndef DNSDIST
+  template <class T,
+            typename std::enable_if<std::is_class<T>::value,T>::type* = nullptr>
+  T getNoStripHeader() const;
+#endif
+
+  MDB_val d_mdbval;
+};
+
+template<> inline std::string MDBOutVal::get<std::string>() const
+{
+#ifndef DNSDIST
+  size_t offset = LMDBLS::LScheckHeaderAndGetSize(this);
+
+  return std::string((char*)d_mdbval.mv_data+offset, d_mdbval.mv_size-offset);
+}
+
+template<> inline std::string MDBOutVal::getNoStripHeader<std::string>() const
+{
+#endif
+  return std::string((char*)d_mdbval.mv_data, d_mdbval.mv_size);
+}
+
+template<> inline string_view MDBOutVal::get<string_view>() const
+{
+#ifndef DNSDIST
+  size_t offset = LMDBLS::LScheckHeaderAndGetSize(this);
+
+  return string_view((char*)d_mdbval.mv_data+offset, d_mdbval.mv_size-offset);
+}
+
+template<> inline string_view MDBOutVal::getNoStripHeader<string_view>() const
+{
+#endif
+  return string_view((char*)d_mdbval.mv_data, d_mdbval.mv_size);
+}
+
+class MDBInVal
+{
+public:
+  MDBInVal(const MDBOutVal& rhs): d_mdbval(rhs.d_mdbval)
+  {
+  }
+
+#ifndef DNSDIST
+  template <class T,
+            typename std::enable_if<std::is_integral<T>::value,
+                                    T>::type* = nullptr>
+  MDBInVal(T i)
+  {
+    static_assert(sizeof(T) == 4, "this code currently only supports 32 bit integers");
+    auto j = htonl(i);    // all actual usage in our codebase is 32 bits. If that ever changes, this will break the build and avoid runtime surprises
+    memcpy(&d_memory[0], &j, sizeof(j));
+
+    d_mdbval.mv_size = sizeof(T);
+    d_mdbval.mv_data = d_memory;;
+  }
+#endif
+
+  MDBInVal(const char* s)
+  {
+    d_mdbval.mv_size = strlen(s);
+    d_mdbval.mv_data = (void*)s;
+  }
+
+  MDBInVal(const string_view& v)
+  {
+    d_mdbval.mv_size = v.size();
+    d_mdbval.mv_data = (void*)&v[0];
+  }
+
+  MDBInVal(const std::string& v)
+  {
+    d_mdbval.mv_size = v.size();
+    d_mdbval.mv_data = (void*)&v[0];
+  }
+
+
+  template<typename T>
+  static MDBInVal fromStruct(const T& t)
+  {
+    MDBInVal ret;
+    ret.d_mdbval.mv_size = sizeof(T);
+    ret.d_mdbval.mv_data = (void*)&t;
+    return ret;
+  }
+
+  operator MDB_val&()
+  {
+    return d_mdbval;
+  }
+  MDB_val d_mdbval;
+private:
+  MDBInVal(){}
+#ifndef DNSDIST
+  char d_memory[sizeof(double)];
+#endif
+};
+
+class MDBROCursor;
+
+class MDBROTransactionImpl
+{
+protected:
+  MDBROTransactionImpl(MDBEnv *parent, MDB_txn *txn);
+
+private:
+  static MDB_txn *openROTransaction(MDBEnv *env, MDB_txn *parent, int flags=0);
+
+  MDBEnv* d_parent;
+  std::vector<MDBROCursor*> d_cursors;
+
+protected:
+  MDB_txn* d_txn;
+
+  void closeROCursors();
+
+public:
+  explicit MDBROTransactionImpl(MDBEnv* parent, int flags=0);
+
+  MDBROTransactionImpl(const MDBROTransactionImpl& src) = delete;
+  MDBROTransactionImpl &operator=(const MDBROTransactionImpl& src) = delete;
+
+  // The move constructor/operator cannot be made safe due to Object Slicing with MDBRWTransaction.
+  MDBROTransactionImpl(MDBROTransactionImpl&& rhs) = delete;
+  MDBROTransactionImpl &operator=(MDBROTransactionImpl &&rhs) = delete;
+
+  virtual ~MDBROTransactionImpl();
+
+  virtual void abort();
+  virtual void commit();
+
+  int get(MDB_dbi dbi, const MDBInVal& key, MDBOutVal& val)
+  {
+    if(!d_txn)
+      throw std::runtime_error("Attempt to use a closed RO transaction for get");
+
+    int rc = mdb_get(d_txn, dbi, const_cast<MDB_val*>(&key.d_mdbval),
+                     const_cast<MDB_val*>(&val.d_mdbval));
+
+    if(rc && rc != MDB_NOTFOUND) {
+      throw std::runtime_error("getting data: " + std::string(mdb_strerror(rc)));
+    }
+
+#ifndef DNSDIST
+    if(rc != MDB_NOTFOUND) {  // key was found, value was retrieved
+      std::string sval = val.getNoStripHeader<std::string>();
+      if (LMDBLS::LSisDeleted(sval)) {  // but it was deleted
+        rc = MDB_NOTFOUND;
+      }
+    }
+#endif
+
+    return rc;
+  }
+
+  int get(MDB_dbi dbi, const MDBInVal& key, string_view& val)
+  {
+    MDBOutVal out;
+    int rc = get(dbi, key, out);
+    if(!rc)
+      val = out.get<string_view>();
+    return rc;
+  }
+
+
+  // this is something you can do, readonly
+  MDBDbi openDB(string_view dbname, int flags)
+  {
+    return MDBDbi( d_parent->d_env, d_txn, dbname, flags);
+  }
+
+  MDBROCursor getCursor(const MDBDbi&);
+  MDBROCursor getROCursor(const MDBDbi&);
+
+  operator MDB_txn*()
+  {
+    return d_txn;
+  }
+
+  inline operator bool() const {
+    return d_txn;
+  }
+
+  inline MDBEnv &environment()
+  {
+    return *d_parent;
+  }
+};
+
+/*
+   A cursor in a read-only transaction must be closed explicitly, before or after its transaction ends. It can be reused with mdb_cursor_renew() before finally closing it.
+
+   "If the parent transaction commits, the cursor must not be used again."
+*/
+
+template<class Transaction, class T>
+class MDBGenCursor
+{
+private:
+  std::vector<T*> *d_registry;
+  MDB_cursor* d_cursor{nullptr};
+public:
+  MDB_txn* d_txn{nullptr}; // ew, public
+  uint64_t d_txtime{0};
+
+  MDBGenCursor():
+    d_registry(nullptr),
+    d_cursor(nullptr),
+    d_txn(nullptr)
+  {
+
+  }
+
+  MDBGenCursor(std::vector<T*> &registry, MDB_cursor *cursor, MDB_txn *txn=nullptr, uint64_t txtime=0):
+    d_registry(&registry),
+    d_cursor(cursor),
+    d_txn(txn),
+    d_txtime(txtime)
+  {
+    registry.emplace_back(static_cast<T*>(this));
+  }
+
+private:
+  void move_from(MDBGenCursor *src)
+  {
+    if (!d_registry) {
+      return;
+    }
+
+    auto iter = std::find(d_registry->begin(),
+                          d_registry->end(),
+                          src);
+    if (iter != d_registry->end()) {
+      *iter = static_cast<T*>(this);
+    } else {
+      d_registry->emplace_back(static_cast<T*>(this));
+    }
+  }
+
+public:
+  MDBGenCursor(const MDBGenCursor &src) = delete;
+
+  MDBGenCursor(MDBGenCursor &&src) noexcept:
+    d_registry(src.d_registry),
+    d_cursor(src.d_cursor)
+  {
+    move_from(&src);
+    src.d_registry = nullptr;
+    src.d_cursor = nullptr;
+  }
+
+  MDBGenCursor &operator=(const MDBGenCursor &src) = delete;
+
+  MDBGenCursor &operator=(MDBGenCursor &&src) noexcept
+  {
+    d_registry = src.d_registry;
+    d_cursor = src.d_cursor;
+    move_from(&src);
+    src.d_registry = nullptr;
+    src.d_cursor = nullptr;
+    return *this;
+  }
+
+  ~MDBGenCursor()
+  {
+    close();
+  }
+
+  /*
+   to support (skip) entries marked deleted=1 in the LS header, we need to do some magic here
+   this table notes, for each cursor op:
+   * the maximum number of entries we may need to look at (1 or inf)
+   * the subsequent op that needs to be done to skip over a deleted entry (or MDB_NOTFOUND to give up and say no)
+   (table partially copied from http://www.lmdb.tech/doc/group__mdb.html#ga1206b2af8b95e7f6b0ef6b28708c9127 which I hope is a stable URL)
+   (ops only relevant for DUPSORT/DUPFIXED have been omitted)
+   (table is grouped by "skip op")
+
+  | base op            | maxentries | skip op      | doc description of base op
+  | MDB_FIRST          | inf        | MDB_NEXT     | Position at first key/data item
+  | MDB_NEXT           | inf        | MDB_NEXT     | Position at next data item
+  | MDB_SET_RANGE      | inf        | MDB_NEXT     | Position at first key greater than or equal to specified key.
+  | MDB_LAST           | inf        | MDB_PREV     | Position at last key/data item
+  | MDB_PREV           | inf        | MDB_PREV     | Position at previous data item
+  | MDB_GET_CURRENT    | 1          | MDB_NOTFOUND | Return key/data at current cursor position
+  | MDB_SET            | 1          | MDB_NOTFOUND | Position at specified key
+  | MDB_SET_KEY        | 1          | MDB_NOTFOUND | Position at specified key, return key + data
+  */
+
+private:
+  int skipDeleted(MDBOutVal& key, MDBOutVal& data, MDB_cursor_op op, int rc)
+  {
+#ifndef DNSDIST
+    // when we get here
+    // * mdb_cursor_get has been called once
+    // * it did not return an error, but it might have returned MDB_NOTFOUND
+    // * if it returned MDB_NOTFOUND, there is nothing for us to do and we pass that on
+
+    if (rc == MDB_NOTFOUND) {
+      return rc;
+    }
+
+    // when we get here
+    // * mdb_cursor_get has been called at least once
+    // * it found an entry, as far as LMDB is concerned, so key+data contain something
+    // * but that might be a LS deleted=1 entry
+    // * we know the cursor op that got us here
+
+    while (true) {
+      auto sval = data.getNoStripHeader<std::string_view>();
+
+      if (!LMDBLS::LSisDeleted(sval)) {
+        // done!
+
+        return rc;
+      }
+
+      // the found entry is set deleted, so we need to do something
+
+      // if this was a 1-entry op, this is the end
+      if (op == MDB_GET_CURRENT || op == MDB_SET || op == MDB_SET_KEY) {
+        return MDB_NOTFOUND;
+      }
+
+      // otherwise, we need to try to carry on
+      // all ops that do not map to NOTFOUND map to NEXT or PREV, including NEXT and PREV themselves
+      // so we just override the op to NEXT or PREV
+      if (op == MDB_FIRST || op == MDB_NEXT || op == MDB_SET_RANGE) {
+        op = MDB_NEXT;
+      }
+      else if (op == MDB_LAST || op == MDB_PREV) {
+        op = MDB_PREV;
+      }
+      else {
+        throw std::runtime_error("got unsupported mdb cursor op");
+      }
+
+      rc = mdb_cursor_get(d_cursor, &key.d_mdbval, &data.d_mdbval, op);
+      if(rc && rc != MDB_NOTFOUND) {
+         throw std::runtime_error("Unable to get from cursor: " + std::string(mdb_strerror(rc)));
+      }
+
+      if (rc == MDB_NOTFOUND) {
+        // we ended up finding nothing, so tell the caller
+        return rc;
+      }
+
+      // when we get here
+      // * the situation is just like the last time I wrote "when we get here"
+      // * except mdb_cursor_get has been called at least twice
+      // * so let's go back
+    }
+#else /* ifndef DNSDIST */
+    return rc;
+#endif
+  }
+
+public:
+  int get(MDBOutVal& key, MDBOutVal& data, MDB_cursor_op op)
+  {
+    int rc = mdb_cursor_get(d_cursor, &key.d_mdbval, &data.d_mdbval, op);
+    if(rc && rc != MDB_NOTFOUND)
+       throw std::runtime_error("Unable to get from cursor: " + std::string(mdb_strerror(rc)));
+    return skipDeleted(key, data, op, rc);
+  }
+
+  int find(const MDBInVal& in, MDBOutVal& key, MDBOutVal& data)
+  {
+    key.d_mdbval = in.d_mdbval;
+    int rc=mdb_cursor_get(d_cursor, const_cast<MDB_val*>(&key.d_mdbval), &data.d_mdbval, MDB_SET);
+    if(rc && rc != MDB_NOTFOUND)
+       throw std::runtime_error("Unable to find from cursor: " + std::string(mdb_strerror(rc)));
+    return skipDeleted(key, data, MDB_SET, rc);
+  }
+
+  int lower_bound(const MDBInVal& in, MDBOutVal& key, MDBOutVal& data)
+  {
+    key.d_mdbval = in.d_mdbval;
+
+    int rc = mdb_cursor_get(d_cursor, const_cast<MDB_val*>(&key.d_mdbval), &data.d_mdbval, MDB_SET_RANGE);
+    if(rc && rc != MDB_NOTFOUND)
+       throw std::runtime_error("Unable to lower_bound from cursor: " + std::string(mdb_strerror(rc)));
+    return skipDeleted(key, data, MDB_SET_RANGE, rc);
+  }
+
+
+  int nextprev(MDBOutVal& key, MDBOutVal& data, MDB_cursor_op op)
+  {
+    int rc = mdb_cursor_get(d_cursor, const_cast<MDB_val*>(&key.d_mdbval), &data.d_mdbval, op);
+    if(rc && rc != MDB_NOTFOUND)
+       throw std::runtime_error("Unable to prevnext from cursor: " + std::string(mdb_strerror(rc)));
+    return skipDeleted(key, data, op, rc);
+  }
+
+  int next(MDBOutVal& key, MDBOutVal& data)
+  {
+    return nextprev(key, data, MDB_NEXT);
+  }
+
+  int prev(MDBOutVal& key, MDBOutVal& data)
+  {
+    return nextprev(key, data, MDB_PREV);
+  }
+
+  int currentlast(MDBOutVal& key, MDBOutVal& data, MDB_cursor_op op)
+  {
+    int rc = mdb_cursor_get(d_cursor, const_cast<MDB_val*>(&key.d_mdbval), &data.d_mdbval, op);
+    if(rc && rc != MDB_NOTFOUND)
+       throw std::runtime_error("Unable to next from cursor: " + std::string(mdb_strerror(rc)));
+    return skipDeleted(key, data, op, rc);
+  }
+
+  int current(MDBOutVal& key, MDBOutVal& data)
+  {
+    return currentlast(key, data, MDB_GET_CURRENT);
+  }
+  int last(MDBOutVal& key, MDBOutVal& data)
+  {
+    return currentlast(key, data, MDB_LAST);
+  }
+  int first(MDBOutVal& key, MDBOutVal& data)
+  {
+    return currentlast(key, data, MDB_FIRST);
+  }
+
+  operator MDB_cursor*()
+  {
+    return d_cursor;
+  }
+
+  operator bool() const
+  {
+    return d_cursor;
+  }
+
+  void close()
+  {
+    if (d_registry) {
+      auto iter = std::find(d_registry->begin(),
+                            d_registry->end(),
+                            static_cast<T*>(this));
+      if (iter != d_registry->end()) {
+        d_registry->erase(iter);
+      }
+      d_registry = nullptr;
+    }
+    if (d_cursor) {
+      mdb_cursor_close(d_cursor);
+      d_cursor = nullptr;
+    }
+  }
+};
+
+class MDBROCursor : public MDBGenCursor<MDBROTransactionImpl, MDBROCursor>
+{
+public:
+  MDBROCursor() = default;
+  using MDBGenCursor<MDBROTransactionImpl, MDBROCursor>::MDBGenCursor;
+  MDBROCursor(const MDBROCursor &src) = delete;
+  MDBROCursor(MDBROCursor &&src) = default;
+  MDBROCursor &operator=(const MDBROCursor &src) = delete;
+  MDBROCursor &operator=(MDBROCursor &&src) = default;
+  ~MDBROCursor() = default;
+
+};
+
+class MDBRWCursor;
+
+class MDBRWTransactionImpl: public MDBROTransactionImpl
+{
+protected:
+  MDBRWTransactionImpl(MDBEnv* parent, MDB_txn* txn);
+
+private:
+  static MDB_txn *openRWTransaction(MDBEnv* env, MDB_txn *parent, int flags);
+
+private:
+  std::vector<MDBRWCursor*> d_rw_cursors;
+
+  uint64_t d_txtime{0};
+
+  void closeRWCursors();
+  inline void closeRORWCursors() {
+    closeROCursors();
+    closeRWCursors();
+  }
+
+public:
+  explicit MDBRWTransactionImpl(MDBEnv* parent, int flags=0);
+
+  MDBRWTransactionImpl(const MDBRWTransactionImpl& rhs) = delete;
+  MDBRWTransactionImpl(MDBRWTransactionImpl&& rhs) = delete;
+  MDBRWTransactionImpl &operator=(const MDBRWTransactionImpl& rhs) = delete;
+  MDBRWTransactionImpl &operator=(MDBRWTransactionImpl&& rhs) = delete;
+
+  ~MDBRWTransactionImpl() override;
+
+  void commit() override;
+  void abort() override;
+
+  void clear(MDB_dbi dbi);
+
+#ifndef DNSDIST
+  void put(MDB_dbi dbi, const MDBInVal& key, const MDBInVal& val, int flags=0)
+  {
+    if(!d_txn)
+      throw std::runtime_error("Attempt to use a closed RW transaction for put");
+    int rc;
+
+    size_t txid = mdb_txn_id(d_txn);
+
+    if (d_txtime == 0) { throw std::runtime_error("got zero txtime"); }
+
+    std::string ins =
+      LMDBLS::LSheader(d_txtime, txid).toString()+
+      std::string((const char*)val.d_mdbval.mv_data, val.d_mdbval.mv_size);
+
+    MDBInVal pval = ins;
+
+    if((rc=mdb_put(d_txn, dbi,
+                   const_cast<MDB_val*>(&key.d_mdbval),
+                   const_cast<MDB_val*>(&pval.d_mdbval), flags))) {
+      throw std::runtime_error("putting data: " + std::string(mdb_strerror(rc)));
+    }
+  }
+#else
+  void put(MDB_dbi dbi, const MDBInVal& key, const MDBInVal& val, int flags=0)
+  {
+    if(!d_txn)
+      throw std::runtime_error("Attempt to use a closed RW transaction for put");
+    int rc;
+    if((rc=mdb_put(d_txn, dbi,
+                   const_cast<MDB_val*>(&key.d_mdbval),
+                   const_cast<MDB_val*>(&val.d_mdbval), flags)))
+      throw std::runtime_error("putting data: " + std::string(mdb_strerror(rc)));
+  }
+#endif
+
+  int del(MDBDbi& dbi, const MDBInVal& key)
+  {
+    int rc;
+    rc=mdb_del(d_txn, dbi, (MDB_val*)&key.d_mdbval, 0);
+    if(rc && rc != MDB_NOTFOUND)
+      throw std::runtime_error("deleting data: " + std::string(mdb_strerror(rc)));
+#ifndef DNSDIST
+    if(rc != MDB_NOTFOUND && LMDBLS::s_flag_deleted) {
+      // if it did exist, we need to mark it as deleted now
+
+      size_t txid = mdb_txn_id(d_txn);
+      if (d_txtime == 0) { throw std::runtime_error("got zero txtime"); }
+
+      std::string ins =
+        // std::string((const char*)&txid, sizeof(txid)) +
+        LMDBLS::LSheader(d_txtime, txid, LMDBLS::LS_FLAG_DELETED).toString();
+
+      MDBInVal pval = ins;
+
+      if((rc=mdb_put(d_txn, dbi,
+                     const_cast<MDB_val*>(&key.d_mdbval),
+                     const_cast<MDB_val*>(&pval.d_mdbval), 0))) {
+              throw std::runtime_error("marking data deleted: " + std::string(mdb_strerror(rc)));
+      }
+    }
+#endif
+    return rc;
+  }
+
+
+  int get(MDBDbi& dbi, const MDBInVal& key, MDBOutVal& val)
+  {
+    if(!d_txn)
+      throw std::runtime_error("Attempt to use a closed RW transaction for get");
+
+    int rc = mdb_get(d_txn, dbi, const_cast<MDB_val*>(&key.d_mdbval),
+                     const_cast<MDB_val*>(&val.d_mdbval));
+    if(rc && rc != MDB_NOTFOUND) {
+          throw std::runtime_error("getting data: " + std::string(mdb_strerror(rc)));
+    }
+
+#ifndef DNSDIST
+    if(rc != MDB_NOTFOUND) {  // key was found, value was retrieved
+      auto sval = val.getNoStripHeader<std::string_view>();
+      if (LMDBLS::LSisDeleted(sval)) {  // but it was deleted
+        rc = MDB_NOTFOUND;
+      }
+    }
+#endif
+
+    return rc;
+  }
+
+  MDBDbi openDB(string_view dbname, int flags)
+  {
+    return MDBDbi(environment().d_env, d_txn, dbname, flags);
+  }
+
+  MDBRWCursor getRWCursor(const MDBDbi&);
+  MDBRWCursor getCursor(const MDBDbi&);
+
+  MDBRWTransaction getRWTransaction();
+  MDBROTransaction getROTransaction();
+
+};
+
+/* "A cursor in a write-transaction can be closed before its transaction ends, and will otherwise be closed when its transaction ends"
+   This is a problem for us since it may means we are closing the cursor twice, which is bad
+*/
+class MDBRWCursor : public MDBGenCursor<MDBRWTransactionImpl, MDBRWCursor>
+{
+public:
+  MDBRWCursor() = default;
+  using MDBGenCursor<MDBRWTransactionImpl, MDBRWCursor>::MDBGenCursor;
+  MDBRWCursor(const MDBRWCursor &src) = delete;
+  MDBRWCursor(MDBRWCursor &&src) = default;
+  MDBRWCursor &operator=(const MDBRWCursor &src) = delete;
+  MDBRWCursor &operator=(MDBRWCursor &&src) = default;
+  ~MDBRWCursor() = default;
+
+#ifndef DNSDIST
+  void put(const MDBOutVal& key, const MDBInVal& data)
+  {
+    size_t txid = mdb_txn_id(this->d_txn);
+
+    if (d_txtime == 0) { throw std::runtime_error("got zero txtime"); }
+
+    std::string ins =
+      LMDBLS::LSheader(d_txtime, txid).toString()+
+      std::string((const char*)data.d_mdbval.mv_data, data.d_mdbval.mv_size);
+
+    MDBInVal pval = ins;
+
+    int rc = mdb_cursor_put(*this,
+                            const_cast<MDB_val*>(&key.d_mdbval),
+                            const_cast<MDB_val*>(&pval.d_mdbval), MDB_CURRENT);
+    if(rc)
+      throw std::runtime_error("mdb_cursor_put: " + std::string(mdb_strerror(rc)));
+  }
+#else
+  void put(const MDBOutVal& key, const MDBInVal& data)
+  {
+    int rc = mdb_cursor_put(*this,
+                            const_cast<MDB_val*>(&key.d_mdbval),
+                            const_cast<MDB_val*>(&data.d_mdbval), MDB_CURRENT);
+    if(rc)
+      throw std::runtime_error("mdb_cursor_put: " + std::string(mdb_strerror(rc)));
+  }
+#endif
+
+#ifndef DNSDIST
+  int del(int flags=0)
+  {
+    MDBOutVal key, val;
+
+    if (LMDBLS::s_flag_deleted) {
+      int rc_get = mdb_cursor_get (*this, &key.d_mdbval, &val.d_mdbval, MDB_GET_CURRENT);
+
+      if(rc_get) {
+              throw std::runtime_error("getting key to mark data as deleted: " + std::string(mdb_strerror(rc_get)));
+      }
+
+      size_t txid = mdb_txn_id(d_txn);
+      if (d_txtime == 0) { throw std::runtime_error("got zero txtime"); }
+
+      std::string ins =
+        LMDBLS::LSheader(d_txtime, txid, LMDBLS::LS_FLAG_DELETED).toString();
+
+      std::string skey((const char*)key.d_mdbval.mv_data, key.d_mdbval.mv_size);
+
+      MDBInVal pkey = MDBInVal(skey);
+      MDBInVal pval = ins;
+
+      int rc_put = mdb_cursor_put(*this,
+                     const_cast<MDB_val*>(&pkey.d_mdbval),
+                     const_cast<MDB_val*>(&pval.d_mdbval), 0 /* MDB_CURRENT */);
+      if(rc_put) {
+              throw std::runtime_error("marking data deleted: " + std::string(mdb_strerror(rc_put)));
+      }
+      return rc_put;
+    }
+    else {
+      // do a normal delete
+      return mdb_cursor_del(*this, flags);
+    }
+  }
+#endif
+};