miner: bugfix: fix duplicate weight reservation in block assembler

- This commit renamed coinbase_max_additional_weight to block_reserved_weight.

- Also clarify that the reservation is for block header, transaction count
  and coinbase transaction.

Author: ismaelsadeeq

src/init.cpp

@@ -19,6 +19,7 @@
 #include <common/args.h>
 #include <common/system.h>
 #include <consensus/amount.h>
+#include <consensus/consensus.h>
 #include <deploymentstatus.h>
 #include <hash.h>
 #include <httprpc.h>

src/ipc/capnp/mining.capnp

@@ -35,7 +35,7 @@ interface BlockTemplate $Proxy.wrap("interfaces::BlockTemplate") {
 
 struct BlockCreateOptions $Proxy.wrap("node::BlockCreateOptions") {
     useMempool @0 :Bool $Proxy.name("use_mempool");
-    coinbaseMaxAdditionalWeight @1 :UInt64 $Proxy.name("coinbase_max_additional_weight");
+    blockReservedWeight @1 :UInt64 $Proxy.name("block_reserved_weight");
     coinbaseOutputMaxAdditionalSigops @2 :UInt64 $Proxy.name("coinbase_output_max_additional_sigops");
 }
 

src/node/miner.cpp

@@ -67,11 +67,11 @@ void RegenerateCommitments(CBlock& block, ChainstateManager& chainman)
 
 static BlockAssembler::Options ClampOptions(BlockAssembler::Options options)
 {
-    Assert(options.coinbase_max_additional_weight <= DEFAULT_BLOCK_MAX_WEIGHT);
+    Assert(options.block_reserved_weight <= MAX_BLOCK_WEIGHT);
     Assert(options.coinbase_output_max_additional_sigops <= MAX_BLOCK_SIGOPS_COST);
-    // Limit weight to between coinbase_max_additional_weight and DEFAULT_BLOCK_MAX_WEIGHT for sanity:
-    // Coinbase (reserved) outputs can safely exceed -blockmaxweight, but the rest of the block template will be empty.
-    options.nBlockMaxWeight = std::clamp<size_t>(options.nBlockMaxWeight, options.coinbase_max_additional_weight, DEFAULT_BLOCK_MAX_WEIGHT);
+    // Limit weight to between block_reserved_weight and MAX_BLOCK_WEIGHT for sanity:
+    // block_reserved_weight can safely exceed -blockmaxweight, but the rest of the block template will be empty.
+    options.nBlockMaxWeight = std::clamp<size_t>(options.nBlockMaxWeight, options.block_reserved_weight, MAX_BLOCK_WEIGHT);
     return options;
 }
 
@@ -97,8 +97,8 @@ void BlockAssembler::resetBlock()
 {
     inBlock.clear();
 
-    // Reserve space for coinbase tx
-    nBlockWeight = m_options.coinbase_max_additional_weight;
+    // Reserve space for fixed-size block header, txs count, and coinbase tx.
+    nBlockWeight = m_options.block_reserved_weight;
     nBlockSigOpsCost = m_options.coinbase_output_max_additional_sigops;
 
     // These counters do not include coinbase tx
@@ -386,7 +386,7 @@ void BlockAssembler::addPackageTxs(int& nPackagesSelected, int& nDescendantsUpda
             ++nConsecutiveFailed;
 
             if (nConsecutiveFailed > MAX_CONSECUTIVE_FAILURES && nBlockWeight >
-                    m_options.nBlockMaxWeight - m_options.coinbase_max_additional_weight) {
+                    m_options.nBlockMaxWeight - m_options.block_reserved_weight) {
                 // Give up if we're close to full and haven't succeeded in a while
                 break;
             }

src/node/types.h

@@ -14,6 +14,7 @@
 #define BITCOIN_NODE_TYPES_H
 
 #include <cstddef>
+#include <policy/policy.h>
 #include <script/script.h>
 
 namespace node {
@@ -34,11 +35,10 @@ struct BlockCreateOptions {
      */
     bool use_mempool{true};
     /**
-     * The maximum additional weight which the pool will add to the coinbase
-     * scriptSig, witness and outputs. This must include any additional
-     * weight needed for larger CompactSize encoded lengths.
+     * The default reserved weight for the fixed-size block header,
+     * transaction count and coinbase transaction.
      */
-    size_t coinbase_max_additional_weight{4000};
+    size_t block_reserved_weight{DEFAULT_BLOCK_RESERVED_WEIGHT};
     /**
      * The maximum additional sigops which the pool will add in coinbase
      * transaction outputs.

src/policy/policy.h

@@ -20,7 +20,8 @@ class CFeeRate;
 class CScript;
 
 /** Default for -blockmaxweight, which controls the range of block weights the mining code will create **/
-static constexpr unsigned int DEFAULT_BLOCK_MAX_WEIGHT{MAX_BLOCK_WEIGHT - 4000};
+static constexpr unsigned int DEFAULT_BLOCK_MAX_WEIGHT{MAX_BLOCK_WEIGHT};
+static constexpr unsigned int DEFAULT_BLOCK_RESERVED_WEIGHT{8000};
 /** Default for -blockmintxfee, which sets the minimum feerate for a transaction in blocks created by mining code **/
 static constexpr unsigned int DEFAULT_BLOCK_MIN_TX_FEE{1000};
 /** The maximum weight for transactions we're willing to relay/mine */

src/test/fuzz/mini_miner.cpp

@@ -13,6 +13,7 @@
 
 #include <node/miner.h>
 #include <node/mini_miner.h>
+#include <node/types.h>
 #include <primitives/transaction.h>
 #include <random.h>
 #include <txmempool.h>
@@ -157,9 +158,10 @@ FUZZ_TARGET(mini_miner_selection, .init = initialize_miner)
             }
         }
 
-        // Stop if pool reaches DEFAULT_BLOCK_MAX_WEIGHT because BlockAssembler will stop when the
+        const auto block_adjusted_max_weight = MAX_BLOCK_WEIGHT - DEFAULT_BLOCK_RESERVED_WEIGHT;
+        // Stop if pool reaches block_adjusted_max_weight because BlockAssembler will stop when the
         // block template reaches that, but the MiniMiner will keep going.
-        if (pool.GetTotalTxSize() + GetVirtualTransactionSize(*tx) >= DEFAULT_BLOCK_MAX_WEIGHT) break;
+        if (pool.GetTotalTxSize() + GetVirtualTransactionSize(*tx) >= block_adjusted_max_weight) break;
         TestMemPoolEntryHelper entry;
         const CAmount fee{ConsumeMoney(fuzzed_data_provider, /*max=*/MAX_MONEY/100000)};
         assert(MoneyRange(fee));
@@ -181,7 +183,7 @@ FUZZ_TARGET(mini_miner_selection, .init = initialize_miner)
 
     node::BlockAssembler::Options miner_options;
     miner_options.blockMinFeeRate = target_feerate;
-    miner_options.nBlockMaxWeight = DEFAULT_BLOCK_MAX_WEIGHT;
+    miner_options.nBlockMaxWeight = MAX_BLOCK_WEIGHT;
     miner_options.test_block_validity = false;
     miner_options.coinbase_output_script = CScript() << OP_0;
 

test/functional/mining_basic.py

@@ -26,6 +26,7 @@
     CBlock,
     CBlockHeader,
     COIN,
+    DEFAULT_BLOCK_RESERVED_WEIGHT,
     ser_uint256,
 )
 from test_framework.p2p import P2PDataStore
@@ -77,7 +78,7 @@ def mine_chain(self):
         mining_info = self.nodes[0].getmininginfo()
         assert_equal(mining_info['blocks'], 200)
         assert_equal(mining_info['currentblocktx'], 0)
-        assert_equal(mining_info['currentblockweight'], 4000)
+        assert_equal(mining_info['currentblockweight'], DEFAULT_BLOCK_RESERVED_WEIGHT)
 
         self.log.info('test blockversion')
         self.restart_node(0, extra_args=[f'-mocktime={t}', '-blockversion=1337'])

test/functional/test_framework/messages.py

@@ -33,6 +33,7 @@
 
 MAX_LOCATOR_SZ = 101
 MAX_BLOCK_WEIGHT = 4000000
+DEFAULT_BLOCK_RESERVED_WEIGHT = 8000
 MAX_BLOOM_FILTER_SIZE = 36000
 MAX_BLOOM_HASH_FUNCS = 50