refactor(stdlib): extract FeeProvider interface from GlobalVariableBuilder

Addresses PR #22116 review comment 5: the GlobalVariableBuilder interface
was overloaded with both fee and global-variables concerns. FeeProvider is
now a separate interface with its own implementation.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: spalladino

yarn-project/aztec-node/src/aztec-node/server.test.ts

@@ -25,6 +25,7 @@ import type { L2LogsSource, MerkleTreeReadOperations, WorldStateSynchronizer } f
 import type { L1ToL2MessageSource } from '@aztec/stdlib/messaging';
 import { mockTx } from '@aztec/stdlib/testing';
 import { MerkleTreeId, PublicDataTreeLeaf, PublicDataTreeLeafPreimage } from '@aztec/stdlib/trees';
+import type { FeeProvider } from '@aztec/stdlib/tx';
 import {
   BlockHeader,
   GlobalVariables,
@@ -73,6 +74,7 @@ class TestAztecNodeService extends AztecNodeService {
 describe('aztec node', () => {
   let p2p: MockProxy<P2P>;
   let globalVariablesBuilder: MockProxy<GlobalVariableBuilder>;
+  let feeProvider: MockProxy<FeeProvider>;
   let merkleTreeOps: MockProxy<MerkleTreeReadOperations>;
   let worldState: MockProxy<WorldStateSynchronizer>;
   let l2BlockSource: MockProxy<L2BlockSource>;
@@ -108,7 +110,8 @@ describe('aztec node', () => {
     p2p = mock<P2P>();
 
     globalVariablesBuilder = mock<GlobalVariableBuilder>();
-    globalVariablesBuilder.getCurrentMinFees.mockResolvedValue(new GasFees(0, BlockNumber.ZERO));
+    feeProvider = mock<FeeProvider>();
+    feeProvider.getCurrentMinFees.mockResolvedValue(new GasFees(0, BlockNumber.ZERO));
 
     merkleTreeOps = mock<MerkleTreeReadOperations>();
     merkleTreeOps.findLeafIndices.mockImplementation((treeId: MerkleTreeId, _value: any[]) => {
@@ -196,6 +199,7 @@ describe('aztec node', () => {
       12345,
       rollupVersion.toNumber(),
       globalVariablesBuilder,
+      feeProvider,
       epochCache,
       getPackageVersion() ?? '',
       new TestCircuitVerifier(),
@@ -738,6 +742,7 @@ describe('aztec node', () => {
           12345,
           rollupVersion.toNumber(),
           globalVariablesBuilder,
+          feeProvider,
           epochCache,
           getPackageVersion() ?? '',
           new TestCircuitVerifier(),
@@ -927,6 +932,7 @@ describe('aztec node', () => {
           12345,
           rollupVersion.toNumber(),
           globalVariablesBuilder,
+          feeProvider,
           epochCache,
           getPackageVersion() ?? '',
           new TestCircuitVerifier(),

yarn-project/aztec-node/src/aztec-node/server.ts

@@ -32,7 +32,12 @@ import {
 import { ProtocolContractAddress } from '@aztec/protocol-contracts';
 import { type ProverNode, type ProverNodeDeps, createProverNode } from '@aztec/prover-node';
 import { createKeyStoreForProver } from '@aztec/prover-node/config';
-import { GlobalVariableBuilder, SequencerClient, type SequencerPublisher } from '@aztec/sequencer-client';
+import {
+  FeeProviderImpl,
+  GlobalVariableBuilder,
+  SequencerClient,
+  type SequencerPublisher,
+} from '@aztec/sequencer-client';
 import { PublicProcessorFactory } from '@aztec/simulator/server';
 import {
   AttestationsBlockWatcher,
@@ -86,6 +91,7 @@ import type { NullifierLeafPreimage, PublicDataTreeLeaf, PublicDataTreeLeafPreim
 import { MerkleTreeId, NullifierMembershipWitness, PublicDataWitness } from '@aztec/stdlib/trees';
 import {
   type BlockHeader,
+  type FeeProvider,
   type GlobalVariableBuilder as GlobalVariableBuilderInterface,
   type IndexedTxEffect,
   PublicSimulationOutput,
@@ -151,6 +157,7 @@ export class AztecNodeService implements AztecNode, AztecNodeAdmin, Traceable {
     protected readonly l1ChainId: number,
     protected readonly version: number,
     protected readonly globalVariableBuilder: GlobalVariableBuilderInterface,
+    protected readonly feeProvider: FeeProvider,
     protected readonly epochCache: EpochCacheInterface,
     protected readonly packageVersion: string,
     private peerProofVerifier: ClientProtocolCircuitVerifier,
@@ -478,13 +485,16 @@ export class AztecNodeService implements AztecNode, AztecNodeAdmin, Traceable {
       })
       .catch(err => log.error('Failed to start p2p services after archiver sync', err));
 
-    const globalVariableBuilder = new GlobalVariableBuilder(dateProvider, publicClient, {
+    const globalVariableBuilderConfig = {
       l1Contracts: config.l1Contracts,
       ethereumSlotDuration: config.ethereumSlotDuration,
       rollupVersion: BigInt(config.rollupVersion),
       l1GenesisTime,
       slotDuration: Number(slotDuration),
-    });
+    };
+
+    const globalVariableBuilder = new GlobalVariableBuilder(dateProvider, publicClient, globalVariableBuilderConfig);
+    const feeProvider = new FeeProviderImpl(dateProvider, publicClient, globalVariableBuilderConfig);
 
     // Validator enabled, create/start relevant service
     let sequencer: SequencerClient | undefined;
@@ -612,6 +622,7 @@ export class AztecNodeService implements AztecNode, AztecNodeAdmin, Traceable {
       ethereumChain.chainInfo.id,
       config.rollupVersion,
       globalVariableBuilder,
+      feeProvider,
       epochCache,
       packageVersion,
       peerProofVerifier,
@@ -765,12 +776,12 @@ export class AztecNodeService implements AztecNode, AztecNodeAdmin, Traceable {
   }
 
   public async getCurrentMinFees(): Promise<GasFees> {
-    return await this.globalVariableBuilder.getCurrentMinFees();
+    return await this.feeProvider.getCurrentMinFees();
   }
 
   /** Returns predicted min fees for the current slot and next N slots. */
   public async getPredictedMinFees(manaUsage?: ManaUsageEstimate): Promise<GasFees[]> {
-    return await this.globalVariableBuilder.getPredictedMinFees(manaUsage);
+    return await this.feeProvider.getPredictedMinFees(manaUsage);
   }
 
   public async getMaxPriorityFees(): Promise<GasFees> {

yarn-project/sequencer-client/src/global_variable_builder/global_builder.ts

@@ -12,6 +12,7 @@ import { GasFees, ManaUsageEstimate } from '@aztec/stdlib/gas';
 import type {
   BuildCheckpointGlobalVariablesOpts,
   CheckpointGlobalVariables,
+  FeeProvider,
   GlobalVariableBuilder as GlobalVariableBuilderInterface,
 } from '@aztec/stdlib/tx';
 import { GlobalVariables } from '@aztec/stdlib/tx';
@@ -25,33 +26,22 @@ export type GlobalVariableBuilderConfig = {
   rollupVersion: bigint;
 } & Pick<L1RollupConstants, 'slotDuration' | 'l1GenesisTime'>;
 
-/**
- * Simple global variables builder.
- */
-export class GlobalVariableBuilder implements GlobalVariableBuilderInterface {
-  private log = createLogger('sequencer:global_variable_builder');
+/** Provides current and predicted fee information based on on-chain state. */
+export class FeeProviderImpl implements FeeProvider {
   private currentMinFees: Promise<GasFees> = Promise.resolve(new GasFees(0, 0));
   private currentL1BlockNumber: bigint | undefined = undefined;
 
   private readonly rollupContract: RollupContract;
   private readonly feePredictor: FeePredictor;
   private readonly ethereumSlotDuration: number;
-  private readonly aztecSlotDuration: number;
   private readonly l1GenesisTime: bigint;
 
-  private chainId: Fr;
-  private version: Fr;
-
   constructor(
     private readonly dateProvider: DateProvider,
     private readonly publicClient: ViemPublicClient,
     config: GlobalVariableBuilderConfig,
   ) {
-    this.version = new Fr(config.rollupVersion);
-    this.chainId = new Fr(this.publicClient.chain!.id);
-
     this.ethereumSlotDuration = config.ethereumSlotDuration;
-    this.aztecSlotDuration = config.slotDuration;
     this.l1GenesisTime = config.l1GenesisTime;
 
     this.rollupContract = new RollupContract(this.publicClient, config.l1Contracts.rollupAddress);
@@ -95,6 +85,36 @@ export class GlobalVariableBuilder implements GlobalVariableBuilderInterface {
   public getPredictedMinFees(manaUsage?: ManaUsageEstimate): Promise<GasFees[]> {
     return this.feePredictor.getPredictedMinFees(this.publicClient, manaUsage ?? ManaUsageEstimate.Target);
   }
+}
+
+/**
+ * Simple global variables builder.
+ */
+export class GlobalVariableBuilder implements GlobalVariableBuilderInterface {
+  private log = createLogger('sequencer:global_variable_builder');
+
+  private readonly rollupContract: RollupContract;
+  private readonly ethereumSlotDuration: number;
+  private readonly aztecSlotDuration: number;
+  private readonly l1GenesisTime: bigint;
+
+  private chainId: Fr;
+  private version: Fr;
+
+  constructor(
+    private readonly dateProvider: DateProvider,
+    private readonly publicClient: ViemPublicClient,
+    config: GlobalVariableBuilderConfig,
+  ) {
+    this.version = new Fr(config.rollupVersion);
+    this.chainId = new Fr(this.publicClient.chain!.id);
+
+    this.ethereumSlotDuration = config.ethereumSlotDuration;
+    this.aztecSlotDuration = config.slotDuration;
+    this.l1GenesisTime = config.l1GenesisTime;
+
+    this.rollupContract = new RollupContract(this.publicClient, config.l1Contracts.rollupAddress);
+  }
 
   /**
    * Simple builder of global variables.

yarn-project/sequencer-client/src/global_variable_builder/index.ts

@@ -1,2 +1,2 @@
-export { GlobalVariableBuilder, type GlobalVariableBuilderConfig } from './global_builder.js';
+export { FeeProviderImpl, GlobalVariableBuilder, type GlobalVariableBuilderConfig } from './global_builder.js';
 export { FeePredictor } from './fee_predictor.js';

yarn-project/stdlib/src/tx/fee_provider.ts

@@ -0,0 +1,10 @@
+import type { ManaUsageEstimate } from '../gas/fee_math.js';
+import type { GasFees } from '../gas/gas_fees.js';
+
+/** Provides current and predicted fee information for transaction pricing. */
+export interface FeeProvider {
+  /** Returns the current minimum fees for inclusion in the next block. */
+  getCurrentMinFees(): Promise<GasFees>;
+  /** Returns predicted min fees for each slot in the prediction window. */
+  getPredictedMinFees(manaUsage?: ManaUsageEstimate): Promise<GasFees[]>;
+}

yarn-project/stdlib/src/tx/global_variable_builder.ts

@@ -4,8 +4,6 @@ import type { EthAddress } from '@aztec/foundation/eth-address';
 import type { SlotNumber } from '@aztec/foundation/schemas';
 
 import type { AztecAddress } from '../aztec-address/index.js';
-import type { ManaUsageEstimate } from '../gas/fee_math.js';
-import type { GasFees } from '../gas/gas_fees.js';
 import type { UInt32 } from '../types/index.js';
 import type { CheckpointGlobalVariables, GlobalVariables } from './global_variables.js';
 
@@ -25,11 +23,6 @@ export type BuildCheckpointGlobalVariablesOpts = {
  * Interface for building global variables for Aztec blocks.
  */
 export interface GlobalVariableBuilder {
-  getCurrentMinFees(): Promise<GasFees>;
-
-  /** Returns predicted min fees for the current slot and next N slots. */
-  getPredictedMinFees(manaUsage?: ManaUsageEstimate): Promise<GasFees[]>;
-
   /**
    * Builds global variables for a given block.
    * @param blockNumber - The block number to build global variables for.

yarn-project/stdlib/src/tx/index.ts

@@ -24,6 +24,7 @@ export * from './validator/tx_validator.js';
 export * from './validator/empty_validator.js';
 export * from './validator/error_texts.js';
 export * from './capsule.js';
+export * from './fee_provider.js';
 export * from './global_variable_builder.js';
 export * from './hashed_values.js';
 export * from './indexed_tx_effect.js';

yarn-project/txe/src/state_machine/index.ts

@@ -13,7 +13,7 @@ import { getPackageVersion } from '@aztec/stdlib/update-checker';
 
 import { TXEArchiver } from './archiver.js';
 import { DummyP2P } from './dummy_p2p_client.js';
-import { TXEGlobalVariablesBuilder } from './global_variable_builder.js';
+import { TXEFeeProvider, TXEGlobalVariablesBuilder } from './global_variable_builder.js';
 import { MockEpochCache } from './mock_epoch_cache.js';
 import { TXESynchronizer } from './synchronizer.js';
 
@@ -56,6 +56,7 @@ export class TXEStateMachine {
       VERSION,
       CHAIN_ID,
       new TXEGlobalVariablesBuilder(),
+      new TXEFeeProvider(),
       new MockEpochCache(),
       getPackageVersion() ?? '',
       new TestCircuitVerifier(),