Store/allow tx metadata in all undo records

sipa · sipa · commit 7d991b55dbf0 · 2017-05-26T13:33:39.000-07:00
Previously, transaction metadata (height, coinbase or not, and before
the previous commit also nVersion) was only stored for undo records
that correspond to the last output of a transaction being spent.

This only saves 2 bytes per undo record. Change this to storing this
information for every undo record, and stop complaining for having it
in non-last output spends. This means that undo dat written with
this patch won't be readable by older versions anymore.
diff --git a/src/undo.h b/src/undo.h
@@ -12,8 +12,7 @@
 
 /** Undo information for a CTxIn
  *
- *  Contains the prevout's CTxOut being spent, and if this was the
- *  last output of the affected transaction, its metadata as well
+ *  Contains the prevout's CTxOut being spent, and its metadata as well
  *  (coinbase or not, height). Earlier versions also stored the transaction
  *  version.
  */
diff --git a/src/validation.cpp b/src/validation.cpp
@@ -1082,11 +1082,9 @@ void UpdateCoins(const CTransaction& tx, CCoinsViewCache& inputs, CTxUndo &txund
             // mark an outpoint spent, and construct undo information
             txundo.vprevout.push_back(CTxInUndo(coins->vout[nPos]));
             coins->Spend(nPos);
-            if (coins->vout.size() == 0) {
-                CTxInUndo& undo = txundo.vprevout.back();
-                undo.nHeight = coins->nHeight;
-                undo.fCoinBase = coins->fCoinBase;
-            }
+            CTxInUndo& undo = txundo.vprevout.back();
+            undo.nHeight = coins->nHeight;
+            undo.fCoinBase = coins->fCoinBase;
         }
     }
     // add outputs
@@ -1266,11 +1264,16 @@ int ApplyTxInUndo(const CTxInUndo& undo, CCoinsViewCache& view, const COutPoint&
 
     CCoinsModifier coins = view.ModifyCoins(out.hash);
     if (undo.nHeight != 0) {
-        // undo data contains height: this is the last output of the prevout tx being spent
-        if (!coins->IsPruned()) fClean = false; // overwriting existing transaction
+        if (!coins->IsPruned()) {
+            if (coins->fCoinBase != undo.fCoinBase || (uint32_t)coins->nHeight != undo.nHeight) fClean = false; // metadata mismatch
+        }
+        // restore height/coinbase tx metadata from undo data
         coins->fCoinBase = undo.fCoinBase;
         coins->nHeight = undo.nHeight;
     } else {
+        // Undo data does not contain height/coinbase. This should never happen
+        // for newly created undo entries. Previously, this data was only saved
+        // for the last spend of a transaction's outputs, so check IsPruned().
         if (coins->IsPruned()) fClean = false; // adding output to missing transaction
     }
     if (coins->IsAvailable(out.n)) fClean = false; // overwriting existing output

Original file line number	Diff line number	Diff line change
`@@ -12,8 +12,7 @@`
`12`	`12`
`13`	`13`	`/** Undo information for a CTxIn`
`14`	`14`	`*`
`15`		`- * Contains the prevout's CTxOut being spent, and if this was the`
`16`		`- * last output of the affected transaction, its metadata as well`
	`15`	`+ * Contains the prevout's CTxOut being spent, and its metadata as well`
`17`	`16`	`* (coinbase or not, height). Earlier versions also stored the transaction`
`18`	`17`	`* version.`
`19`	`18`	`*/`