gasLimit (#12)

beacon/engine/gen_blockparams.go

@@ -24,6 +24,7 @@ func (p PayloadAttributes) MarshalJSON() ([]byte, error) {
 		// <specular modification>
 		Transactions          []hexutil.Bytes     `json:"transactions,omitempty"  gencodec:"optional"`
 		NoTxPool              bool                `json:"noTxPool,omitempty" gencodec:"optional"`
+		GasLimit              *hexutil.Uint64     `json:"gasLimit,omitempty" gencodec:"optional"`
 		// <specular modification/>
 	}
 	var enc PayloadAttributes
@@ -40,6 +41,7 @@ func (p PayloadAttributes) MarshalJSON() ([]byte, error) {
 		}
 	}
 	enc.NoTxPool = p.NoTxPool
+	enc.GasLimit = (*hexutil.Uint64)(p.GasLimit)
 	// <specular modification/>
 	return json.Marshal(&enc)
 }
@@ -55,6 +57,7 @@ func (p *PayloadAttributes) UnmarshalJSON(input []byte) error {
 		// <specular modification>
 		Transactions          []hexutil.Bytes     `json:"transactions,omitempty"  gencodec:"optional"`
 		NoTxPool              *bool               `json:"noTxPool,omitempty" gencodec:"optional"`
+		GasLimit              *hexutil.Uint64     `json:"gasLimit,omitempty" gencodec:"optional"`
 		// <specular modification/>
 	}
 	var dec PayloadAttributes
@@ -89,6 +92,9 @@ func (p *PayloadAttributes) UnmarshalJSON(input []byte) error {
 	if dec.NoTxPool != nil {
 		p.NoTxPool = *dec.NoTxPool
 	}
+	if dec.GasLimit != nil {
+		p.GasLimit = (*uint64)(dec.GasLimit)
+	}
 	// <specular modification/>
 	return nil
 }

beacon/engine/types.go

@@ -42,6 +42,8 @@ type PayloadAttributes struct {
 	// NoTxPool is a field for L2s: if true, the no transactions are taken out of the tx-pool,
 	// only transactions from the above Transactions list will be included.
 	NoTxPool bool `json:"noTxPool,omitempty" gencodec:"optional"`
+	// GasLimit is a field for L2s: if set, this sets the exact gas limit the block produced with.
+	GasLimit *uint64 `json:"gasLimit,omitempty" gencodec:"optional"`
 	// <specular modification//>
 }
 
@@ -50,6 +52,7 @@ type payloadAttributesMarshaling struct {
 	Timestamp hexutil.Uint64
 	// <specular modification>
 	Transactions []hexutil.Bytes
+	GasLimit     *hexutil.Uint64
 	// <specular modification/>
 }
 

consensus/misc/eip1559/eip1559.go

@@ -37,9 +37,15 @@ func VerifyEIP1559Header(config *params.ChainConfig, parent, header *types.Heade
 	if !config.IsLondon(parent.Number) {
 		parentGasLimit = parent.GasLimit * config.ElasticityMultiplier()
 	}
-	if err := misc.VerifyGaslimit(parentGasLimit, header.GasLimit); err != nil {
-		return err
+
+	// <specular modification>
+	if !config.EnableL2GasLimitApi { // gasLimit can adjust instantly on L2s
+		if err := misc.VerifyGaslimit(parentGasLimit, header.GasLimit); err != nil {
+			return err
+		}
 	}
+	// <specular modification>
+
 	// Verify the header is not malformed
 	if header.BaseFee == nil {
 		return errors.New("header is missing baseFee")

eth/catalyst/api.go

@@ -367,6 +367,9 @@ func (api *ConsensusAPI) forkchoiceUpdated(update engine.ForkchoiceStateV1, payl
 	// will replace it arbitrarily many times in between.
 	if payloadAttributes != nil {
 		// <specular modification>
+		if api.eth.BlockChain().Config().EnableL2GasLimitApi && payloadAttributes.GasLimit == nil {
+			return engine.STATUS_INVALID, engine.InvalidPayloadAttributes.With(errors.New("gasLimit parameter is required"))
+		}
 		transactions := make(types.Transactions, 0, len(payloadAttributes.Transactions))
 		for i, otx := range payloadAttributes.Transactions {
 			var tx types.Transaction
@@ -387,6 +390,7 @@ func (api *ConsensusAPI) forkchoiceUpdated(update engine.ForkchoiceStateV1, payl
 			// <specular modification>
 			NoTxPool:     payloadAttributes.NoTxPool,
 			Transactions: transactions,
+			GasLimit:     payloadAttributes.GasLimit,
 			// <specular modification/>
 		}
 		id := args.Id()

miner/payload_building.go

@@ -42,8 +42,9 @@ type BuildPayloadArgs struct {
 	Withdrawals  types.Withdrawals // The provided withdrawals
 	BeaconRoot   *common.Hash      // The provided beaconRoot (Cancun)
 	// <specular modification>
-	NoTxPool     bool                 // Specular addition: option to disable tx pool contents from being included
-	Transactions []*types.Transaction // Specular addition: txs forced into the block via engine API
+	NoTxPool     bool                 // L2 engine api addition: option to disable tx pool contents from being included
+	Transactions []*types.Transaction // L2 engine api addition: txs forced into the block via engine API
+	GasLimit     *uint64              // L2 engine api addition: override gas limit of the block to build
 	// <specular modification/>
 }
 
@@ -68,6 +69,9 @@ func (args *BuildPayloadArgs) Id() engine.PayloadID {
 			hasher.Write(h[:])
 		}
 	}
+	if args.GasLimit != nil {
+		binary.Write(hasher, binary.BigEndian, *args.GasLimit)
+	}
 	// <specular modification/>
 	var out engine.PayloadID
 	copy(out[:], hasher.Sum(nil)[:8])
@@ -193,6 +197,10 @@ func (w *worker) buildPayload(args *BuildPayloadArgs) (*Payload, error) {
 	// Build the initial version with no transaction included. It should be fast
 	// enough to run. The empty payload can at least make sure there is something
 	// to deliver for not missing slot.
+
+	// <specular modification>
+	// With L2s, the "empty" block is constructed from provided txs only, i.e. no tx-pool usage.
+	// <specular modification/>
 	emptyParams := &generateParams{
 		timestamp:   args.Timestamp,
 		forceTime:   true,
@@ -203,7 +211,8 @@ func (w *worker) buildPayload(args *BuildPayloadArgs) (*Payload, error) {
 		beaconRoot:  args.BeaconRoot,
 		noTxs:       true,
 		// <specular modification>
-		txs: args.Transactions,
+		txs:      args.Transactions,
+		gasLimit: args.GasLimit,
 		// <specular modification/>
 	}
 	empty := w.getSealingBlock(emptyParams)
@@ -245,7 +254,8 @@ func (w *worker) buildPayload(args *BuildPayloadArgs) (*Payload, error) {
 			beaconRoot:  args.BeaconRoot,
 			noTxs:       false,
 			// <specular modification>
-			txs: args.Transactions,
+			txs:      args.Transactions,
+			gasLimit: args.GasLimit,
 			// <specular modification/>
 		}
 

miner/worker.go

@@ -902,7 +902,8 @@ type generateParams struct {
 	beaconRoot  *common.Hash      // The beacon root (cancun field).
 	noTxs       bool              // Flag whether an empty block without any transaction is expected
 	// <specular modification>
-	txs types.Transactions // Transactions to include at the start of the block
+	txs      types.Transactions // Transactions to include at the start of the block
+	gasLimit *uint64            // Optional gas limit override
 	// <specular modification/>
 }
 
@@ -958,6 +959,15 @@ func (w *worker) prepareWork(genParams *generateParams) (*environment, error) {
 			header.GasLimit = core.CalcGasLimit(parentGasLimit, w.config.GasCeil)
 		}
 	}
+	// <specular modification>
+	if genParams.gasLimit != nil { // override gas limit if specified
+		header.GasLimit = *genParams.gasLimit
+	} else if w.chain.Config().EnableL2GasLimitApi && w.config.GasCeil != 0 {
+		// configure the gas limit of pending blocks with the miner gas limit config when L2 gas limit config is enabled
+		header.GasLimit = w.config.GasCeil
+	}
+	// <specular modification/>
+
 	// Apply EIP-4844, EIP-4788.
 	if w.chainConfig.IsCancun(header.Number, header.Time) {
 		var excessBlobGas uint64
@@ -1031,6 +1041,9 @@ func (w *worker) generateWork(params *generateParams) *newPayloadResult {
 	}
 	defer work.discard()
 	// <specular modification>
+	if work.gasPool == nil {
+		work.gasPool = new(core.GasPool).AddGas(work.header.GasLimit)
+	}
 	for _, tx := range params.txs {
 		from, _ := types.Sender(work.signer, tx)
 		work.state.SetTxContext(tx.Hash(), work.tcount)

params/config.go

@@ -333,6 +333,10 @@ type ChainConfig struct {
 	Ethash    *EthashConfig `json:"ethash,omitempty"`
 	Clique    *CliqueConfig `json:"clique,omitempty"`
 	IsDevMode bool          `json:"isDev,omitempty"`
+
+	// <specular modification>
+	EnableL2GasLimitApi bool `json:"enableL2GasLimitApi,omitempty"`
+	// <specular modification/>
 }
 
 // EthashConfig is the consensus engine configs for proof-of-work based sealing.
@@ -365,6 +369,10 @@ func (c *ChainConfig) Description() string {
 	}
 	banner += fmt.Sprintf("Chain ID:  %v (%s)\n", c.ChainID, network)
 	switch {
+	// <specular modification>
+	case c.EnableL2GasLimitApi:
+		banner += "Consensus: L2 gas limit API enabled\n"
+	// <specular modification/>
 	case c.Ethash != nil:
 		if c.TerminalTotalDifficulty == nil {
 			banner += "Consensus: Ethash (proof-of-work)\n"