core, core/rawdb: fix transaction indexing (ethereum#24024)

This PR fixes a special corner case in transaction indexing.

When the chain is rewound by SetHead to a historical point which is even lower than the transaction indexes tail, then system will report Failed to decode block body error all the time, because the relevant blocks are already deleted.

In order to avoid this "non-critical-but-annoying" issue, we can recap the indexing target to head+1(to is excluded, so it means indexing transactions from 0 to head).

core/blockchain.go

@@ -2204,7 +2204,14 @@ func (bc *BlockChain) maintainTxIndex(ancients uint64) {
 		// If a previous indexing existed, make sure that we fill in any missing entries
 		if bc.txLookupLimit == 0 || head < bc.txLookupLimit {
 			if *tail > 0 {
-				rawdb.IndexTransactions(bc.db, 0, *tail, bc.quit)
+				// It can happen when chain is rewound to a historical point which
+				// is even lower than the indexes tail, recap the indexing target
+				// to new head to avoid reading non-existent block bodies.
+				end := *tail
+				if end > head+1 {
+					end = head + 1
+				}
+				rawdb.IndexTransactions(bc.db, 0, end, bc.quit)
 			}
 			return
 		}

core/rawdb/chain_iterator.go

@@ -247,7 +247,8 @@ func indexTransactions(db ethdb.Database, from uint64, to uint64, interrupt chan
 	}
 }
 
-// IndexTransactions creates txlookup indices of the specified block range.
+// IndexTransactions creates txlookup indices of the specified block range. The from
+// is included while to is excluded.
 //
 // This function iterates canonical chain in reverse order, it has one main advantage:
 // We can write tx index tail flag periodically even without the whole indexing
@@ -339,6 +340,7 @@ func unindexTransactions(db ethdb.Database, from uint64, to uint64, interrupt ch
 }
 
 // UnindexTransactions removes txlookup indices of the specified block range.
+// The from is included while to is excluded.
 //
 // There is a passed channel, the whole procedure will be interrupted if any
 // signal received.