MOVEONLY: Move key handling code out of wallet to keyman file

Start moving wallet and ismine code to scriptpubkeyman.h, scriptpubkeyman.cpp

The easiest way to review this commit is to run:

   git log -p -n1 --color-moved=dimmed_zebra

And check that everything is a move (other than includes and copyrights comments).

This commit is move-only and doesn't change code or affect behavior.

src/wallet/scriptpubkeyman.h

@@ -0,0 +1,115 @@
+// Copyright (c) 2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_WALLET_SCRIPTPUBKEYMAN_H
+#define BITCOIN_WALLET_SCRIPTPUBKEYMAN_H
+
+#include <script/signingprovider.h>
+#include <script/standard.h>
+#include <wallet/crypter.h>
+#include <wallet/ismine.h>
+#include <wallet/walletdb.h>
+#include <wallet/walletutil.h>
+
+#include <boost/signals2/signal.hpp>
+
+enum class OutputType;
+
+//! Default for -keypool
+static const unsigned int DEFAULT_KEYPOOL_SIZE = 1000;
+
+/** A key from a CWallet's keypool
+ *
+ * The wallet holds one (for pre HD-split wallets) or several keypools. These
+ * are sets of keys that have not yet been used to provide addresses or receive
+ * change.
+ *
+ * The Bitcoin Core wallet was originally a collection of unrelated private
+ * keys with their associated addresses. If a non-HD wallet generated a
+ * key/address, gave that address out and then restored a backup from before
+ * that key's generation, then any funds sent to that address would be
+ * lost definitively.
+ *
+ * The keypool was implemented to avoid this scenario (commit: 10384941). The
+ * wallet would generate a set of keys (100 by default). When a new public key
+ * was required, either to give out as an address or to use in a change output,
+ * it would be drawn from the keypool. The keypool would then be topped up to
+ * maintain 100 keys. This ensured that as long as the wallet hadn't used more
+ * than 100 keys since the previous backup, all funds would be safe, since a
+ * restored wallet would be able to scan for all owned addresses.
+ *
+ * A keypool also allowed encrypted wallets to give out addresses without
+ * having to be decrypted to generate a new private key.
+ *
+ * With the introduction of HD wallets (commit: f1902510), the keypool
+ * essentially became an address look-ahead pool. Restoring old backups can no
+ * longer definitively lose funds as long as the addresses used were from the
+ * wallet's HD seed (since all private keys can be rederived from the seed).
+ * However, if many addresses were used since the backup, then the wallet may
+ * not know how far ahead in the HD chain to look for its addresses. The
+ * keypool is used to implement a 'gap limit'. The keypool maintains a set of
+ * keys (by default 1000) ahead of the last used key and scans for the
+ * addresses of those keys.  This avoids the risk of not seeing transactions
+ * involving the wallet's addresses, or of re-using the same address.
+ *
+ * The HD-split wallet feature added a second keypool (commit: 02592f4c). There
+ * is an external keypool (for addresses to hand out) and an internal keypool
+ * (for change addresses).
+ *
+ * Keypool keys are stored in the wallet/keystore's keymap. The keypool data is
+ * stored as sets of indexes in the wallet (setInternalKeyPool,
+ * setExternalKeyPool and set_pre_split_keypool), and a map from the key to the
+ * index (m_pool_key_to_index). The CKeyPool object is used to
+ * serialize/deserialize the pool data to/from the database.
+ */
+class CKeyPool
+{
+public:
+    //! The time at which the key was generated. Set in AddKeypoolPubKeyWithDB
+    int64_t nTime;
+    //! The public key
+    CPubKey vchPubKey;
+    //! Whether this keypool entry is in the internal keypool (for change outputs)
+    bool fInternal;
+    //! Whether this key was generated for a keypool before the wallet was upgraded to HD-split
+    bool m_pre_split;
+
+    CKeyPool();
+    CKeyPool(const CPubKey& vchPubKeyIn, bool internalIn);
+
+    ADD_SERIALIZE_METHODS;
+
+    template <typename Stream, typename Operation>
+    inline void SerializationOp(Stream& s, Operation ser_action) {
+        int nVersion = s.GetVersion();
+        if (!(s.GetType() & SER_GETHASH))
+            READWRITE(nVersion);
+        READWRITE(nTime);
+        READWRITE(vchPubKey);
+        if (ser_action.ForRead()) {
+            try {
+                READWRITE(fInternal);
+            }
+            catch (std::ios_base::failure&) {
+                /* flag as external address if we can't read the internal boolean
+                   (this will be the case for any wallet before the HD chain split version) */
+                fInternal = false;
+            }
+            try {
+                READWRITE(m_pre_split);
+            }
+            catch (std::ios_base::failure&) {
+                /* flag as postsplit address if we can't read the m_pre_split boolean
+                   (this will be the case for any wallet that upgrades to HD chain split)*/
+                m_pre_split = false;
+            }
+        }
+        else {
+            READWRITE(fInternal);
+            READWRITE(m_pre_split);
+        }
+    }
+};
+
+#endif // BITCOIN_WALLET_SCRIPTPUBKEYMAN_H