Merge bitcoin/bitcoin#24236: Remove utxo db upgrade code

fa9112aac07dc371bfda437d40eb1b841f36f392 Remove utxo db upgrade code (MarcoFalke)

Pull request description:

  It is not possible to upgrade Bitcoin Core pre-segwit (pre-0.13.1) to a recent version without a full IBD from scratch after  commit 19a56d1519fb493c3e1bd5cad55360b6b80fa52b (released in version 22.0).

  Any Bitcoin Core version with the new database format after commit 1088b02f0ccd7358d2b7076bb9e122d59d502d02 (released in version 0.15), can upgrade to any version that is supported as of today.

  This leaves the versions 0.13.1-0.14.x. Even though those versions are unsupported, some users with an existing datadir may want to upgrade to a recent version. However, it seems reasonable to simply ask them to `-reindex` to run a full IBD from scratch. This allows us to remove the utxo db upgrade code.

ACKs for top commit:
  Sjors:
    re-ACK fa9112aac07dc371bfda437d40eb1b841f36f392
  laanwj:
    Code review ACK fa9112aac07dc371bfda437d40eb1b841f36f392

Tree-SHA512: 4243bb35df9ac4892f9fad30fe486d338745952bcff4160bcb0937c772d57b13b800647da14695e21e3655e85ee0d95fa3dc7789ee309d59ad84f422297fecb8

4 files changed, 18 insertions, 131 deletions

diff --git a/src/init.cpp b/src/init.cpp
index f934fd751d..83937c6925 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -1453,8 +1453,9 @@ bool AppInitMain(NodeContext& node, interfaces::BlockAndHeaderTipInfo* tip_info)
                 strLoadError = _("Error initializing block database");
                 break;
             case ChainstateLoadingError::ERROR_CHAINSTATE_UPGRADE_FAILED:
-                strLoadError = _("Error upgrading chainstate database");
-                break;
+                return InitError(_("Unsupported chainstate database format found. "
+                                   "Please restart with -reindex-chainstate. This will "
+                                   "rebuild the chainstate database."));
             case ChainstateLoadingError::ERROR_REPLAYBLOCKS_FAILED:
                 strLoadError = _("Unable to replay blocks. You will need to rebuild the database using -reindex-chainstate.");
                 break;
diff --git a/src/node/chainstate.cpp b/src/node/chainstate.cpp
index d03b9dcac6..d22f71ac8a 100644
--- a/src/node/chainstate.cpp
+++ b/src/node/chainstate.cpp
@@ -90,9 +90,9 @@ std::optional<ChainstateLoadingError> LoadChainstate(bool fReset,
             chainstate->CoinsErrorCatcher().AddReadErrCallback(coins_error_cb);
         }
 
-        // If necessary, upgrade from older database format.
+        // Refuse to load unsupported database format.
         // This is a no-op if we cleared the coinsviewdb with -reindex or -reindex-chainstate
-        if (!chainstate->CoinsDB().Upgrade()) {
+        if (chainstate->CoinsDB().NeedsUpgrade()) {
             return ChainstateLoadingError::ERROR_CHAINSTATE_UPGRADE_FAILED;
         }
 
diff --git a/src/txdb.cpp b/src/txdb.cpp
index 0dafa3b38a..afcd1985f5 100644
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -6,7 +6,6 @@
 #include <txdb.h>
 
 #include <chain.h>
-#include <node/ui_interface.h>
 #include <pow.h>
 #include <random.h>
 #include <shutdown.h>
@@ -18,7 +17,6 @@
 #include <stdint.h>
 
 static constexpr uint8_t DB_COIN{'C'};
-static constexpr uint8_t DB_COINS{'c'};
 static constexpr uint8_t DB_BLOCK_FILES{'f'};
 static constexpr uint8_t DB_BLOCK_INDEX{'b'};
 
@@ -29,6 +27,7 @@ static constexpr uint8_t DB_REINDEX_FLAG{'R'};
 static constexpr uint8_t DB_LAST_BLOCK{'l'};
 
 // Keys used in previous version that might still be found in the DB:
+static constexpr uint8_t DB_COINS{'c'};
 static constexpr uint8_t DB_TXINDEX_BLOCK{'T'};
 //               uint8_t DB_TXINDEX{'t'}
 
@@ -50,6 +49,15 @@ std::optional<bilingual_str> CheckLegacyTxindex(CBlockTreeDB& block_tree_db)
     return std::nullopt;
 }
 
+bool CCoinsViewDB::NeedsUpgrade()
+{
+    std::unique_ptr<CDBIterator> cursor{m_db->NewIterator()};
+    // DB_COINS was deprecated in v0.15.0, commit
+    // 1088b02f0ccd7358d2b7076bb9e122d59d502d02
+    cursor->Seek(std::make_pair(DB_COINS, uint256{}));
+    return cursor->Valid();
+}
+
 namespace {
 
 struct CoinEntry {
@@ -60,7 +68,7 @@ struct CoinEntry {
     SERIALIZE_METHODS(CoinEntry, obj) { READWRITE(obj.key, obj.outpoint->hash, VARINT(obj.outpoint->n)); }
 };
 
-}
+} // namespace
 
 CCoinsViewDB::CCoinsViewDB(fs::path ldb_path, size_t nCacheSize, bool fMemory, bool fWipe) :
     m_db(std::make_unique<CDBWrapper>(ldb_path, nCacheSize, fMemory, fWipe, true)),
@@ -337,125 +345,3 @@ bool CBlockTreeDB::LoadBlockIndexGuts(const Consensus::Params& consensusParams,
 
     return true;
 }
-
-namespace {
-
-//! Legacy class to deserialize pre-pertxout database entries without reindex.
-class CCoins
-{
-public:
-    //! whether transaction is a coinbase
-    bool fCoinBase;
-
-    //! unspent transaction outputs; spent outputs are .IsNull(); spent outputs at the end of the array are dropped
-    std::vector<CTxOut> vout;
-
-    //! at which height this transaction was included in the active block chain
-    int nHeight;
-
-    //! empty constructor
-    CCoins() : fCoinBase(false), vout(0), nHeight(0) { }
-
-    template<typename Stream>
-    void Unserialize(Stream &s) {
-        unsigned int nCode = 0;
-        // version
-        unsigned int nVersionDummy;
-        ::Unserialize(s, VARINT(nVersionDummy));
-        // header code
-        ::Unserialize(s, VARINT(nCode));
-        fCoinBase = nCode & 1;
-        std::vector<bool> vAvail(2, false);
-        vAvail[0] = (nCode & 2) != 0;
-        vAvail[1] = (nCode & 4) != 0;
-        unsigned int nMaskCode = (nCode / 8) + ((nCode & 6) != 0 ? 0 : 1);
-        // spentness bitmask
-        while (nMaskCode > 0) {
-            unsigned char chAvail = 0;
-            ::Unserialize(s, chAvail);
-            for (unsigned int p = 0; p < 8; p++) {
-                bool f = (chAvail & (1 << p)) != 0;
-                vAvail.push_back(f);
-            }
-            if (chAvail != 0)
-                nMaskCode--;
-        }
-        // txouts themself
-        vout.assign(vAvail.size(), CTxOut());
-        for (unsigned int i = 0; i < vAvail.size(); i++) {
-            if (vAvail[i])
-                ::Unserialize(s, Using<TxOutCompression>(vout[i]));
-        }
-        // coinbase height
-        ::Unserialize(s, VARINT_MODE(nHeight, VarIntMode::NONNEGATIVE_SIGNED));
-    }
-};
-
-}
-
-/** Upgrade the database from older formats.
- *
- * Currently implemented: from the per-tx utxo model (0.8..0.14.x) to per-txout.
- */
-bool CCoinsViewDB::Upgrade() {
-    std::unique_ptr<CDBIterator> pcursor(m_db->NewIterator());
-    pcursor->Seek(std::make_pair(DB_COINS, uint256()));
-    if (!pcursor->Valid()) {
-        return true;
-    }
-
-    int64_t count = 0;
-    LogPrintf("Upgrading utxo-set database...\n");
-    LogPrintf("[0%%]..."); /* Continued */
-    uiInterface.ShowProgress(_("Upgrading UTXO database").translated, 0, true);
-    size_t batch_size = 1 << 24;
-    CDBBatch batch(*m_db);
-    int reportDone = 0;
-    std::pair<unsigned char, uint256> key;
-    std::pair<unsigned char, uint256> prev_key = {DB_COINS, uint256()};
-    while (pcursor->Valid()) {
-        if (ShutdownRequested()) {
-            break;
-        }
-        if (pcursor->GetKey(key) && key.first == DB_COINS) {
-            if (count++ % 256 == 0) {
-                uint32_t high = 0x100 * *key.second.begin() + *(key.second.begin() + 1);
-                int percentageDone = (int)(high * 100.0 / 65536.0 + 0.5);
-                uiInterface.ShowProgress(_("Upgrading UTXO database").translated, percentageDone, true);
-                if (reportDone < percentageDone/10) {
-                    // report max. every 10% step
-                    LogPrintf("[%d%%]...", percentageDone); /* Continued */
-                    reportDone = percentageDone/10;
-                }
-            }
-            CCoins old_coins;
-            if (!pcursor->GetValue(old_coins)) {
-                return error("%s: cannot parse CCoins record", __func__);
-            }
-            COutPoint outpoint(key.second, 0);
-            for (size_t i = 0; i < old_coins.vout.size(); ++i) {
-                if (!old_coins.vout[i].IsNull() && !old_coins.vout[i].scriptPubKey.IsUnspendable()) {
-                    Coin newcoin(std::move(old_coins.vout[i]), old_coins.nHeight, old_coins.fCoinBase);
-                    outpoint.n = i;
-                    CoinEntry entry(&outpoint);
-                    batch.Write(entry, newcoin);
-                }
-            }
-            batch.Erase(key);
-            if (batch.SizeEstimate() > batch_size) {
-                m_db->WriteBatch(batch);
-                batch.Clear();
-                m_db->CompactRange(prev_key, key);
-                prev_key = key;
-            }
-            pcursor->Next();
-        } else {
-            break;
-        }
-    }
-    m_db->WriteBatch(batch);
-    m_db->CompactRange({DB_COINS, uint256()}, key);
-    uiInterface.ShowProgress("", 100, false);
-    LogPrintf("[%s].\n", ShutdownRequested() ? "CANCELLED" : "DONE");
-    return !ShutdownRequested();
-}
diff --git a/src/txdb.h b/src/txdb.h
index e70f3cd1f2..faa543b412 100644
--- a/src/txdb.h
+++ b/src/txdb.h
@@ -65,8 +65,8 @@ public:
     bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) override;
     std::unique_ptr<CCoinsViewCursor> Cursor() const override;
 
-    //! Attempt to update from an older database format. Returns whether an error occurred.
-    bool Upgrade();
+    //! Whether an unsupported database format is used.
+    bool NeedsUpgrade();
     size_t EstimateSize() const override;
 
     //! Dynamically alter the underlying leveldb cache size.