Replace the concept of virtual block size, introduce the concept of block cost, and express CBS as a function of it

Author: NicolasDorier

src/consensus/consensus.h

@@ -7,7 +7,10 @@
 #define BITCOIN_CONSENSUS_CONSENSUS_H
 
 /** The maximum allowed size for a serialized block, in bytes (network rule) */
-static const unsigned int MAX_BLOCK_SIZE = 1000000;
+static const unsigned int MAX_BLOCK_COST = 4000000;
+
+/** The maximum allowed size for a serialized block, in bytes (network rule) */
+static const unsigned int MAX_BLOCK_SIZE = MAX_BLOCK_COST/4;
 /** The maximum allowed number of signature check operations in a block (network rule) */
 static const unsigned int MAX_BLOCK_SIGOPS = MAX_BLOCK_SIZE/50;
 /** Coinbase transaction outputs can only be spent after this number of new blocks (network rule) */

src/main.cpp

@@ -3004,7 +3004,7 @@ bool CheckBlock(const CBlock& block, CValidationState& state, bool fCheckPOW, bo
     // because we receive the wrong transactions for it.
 
     // Size limits
-    if (block.vtx.empty() || block.vtx.size() > MAX_BLOCK_SIZE || GetVirtualBlockSize(block) > MAX_BLOCK_SIZE)
+    if (block.vtx.empty() || block.vtx.size() > MAX_BLOCK_SIZE || GetBlockCost(block) > MAX_BLOCK_COST)
         return state.DoS(100, error("CheckBlock(): size limits failed"),
                          REJECT_INVALID, "bad-blk-length");
 

src/primitives/block.cpp

@@ -32,11 +32,13 @@ std::string CBlock::ToString() const
     return s.str();
 }
 
-size_t GetVirtualBlockSize(const CBlock& block)
-{
-    // The formula is: vsize = base_size + witness_size / 4.
-    // We can only serialize base or totalbase+witness, however, so the formula
-    // becomes: vsize = base_size + (total_size - base_size) / 4 or
-    // vsize = (total_size + 3 * base_size) / 4.
-    return (::GetSerializeSize(block, SER_NETWORK, 0) * 3 + ::GetSerializeSize(block, SER_NETWORK, SERIALIZE_TRANSACTION_WITNESS) + 3) / 4;
+size_t GetBlockCost(const CBlock& block)
+{    
+    // coreSize is the size of block without witness data
+    size_t coreSize = ::GetSerializeSize(block, SER_NETWORK, 0);
+    size_t totalSize = ::GetSerializeSize(block, SER_NETWORK, SERIALIZE_TRANSACTION_WITNESS);    
+    // size_t witSize = totalSize - coreSize;    
+    // return witSize + 4 * coreSize;
+    // Since totalSize == witSize + coreSize, we can avoid a substraction
+    return totalSize + 3 * coreSize;
 }