WIP

yarn-project/acir-simulator/src/client/function_selectors.ts

@@ -1,9 +1,5 @@
-import { FUNCTION_SELECTOR_NUM_BYTES } from '@aztec/circuits.js';
-import { computeFunctionSelector } from '@aztec/foundation/abi';
+import { FunctionSelector } from '@aztec/circuits.js';
 
 export const computeNoteHashAndNullifierSignature = 'compute_note_hash_and_nullifier(field,field,field,array)';
 
-export const computeNoteHashAndNullifierSelector = computeFunctionSelector(
-  computeNoteHashAndNullifierSignature,
-  FUNCTION_SELECTOR_NUM_BYTES,
-);
+export const computeNoteHashAndNullifierSelector = FunctionSelector.fromSignature(computeNoteHashAndNullifierSignature);

yarn-project/circuits.js/src/abis/abis.test.ts

@@ -1,6 +1,6 @@
 import times from 'lodash.times';
 
-import { AztecAddress, Fr, FunctionData, FunctionLeafPreimage, NewContractData } from '../index.js';
+import { AztecAddress, Fr, FunctionData, FunctionLeafPreimage, FunctionSelector, NewContractData } from '../index.js';
 import { makeAztecAddress, makeEthAddress, makePoint, makeTxRequest, makeVerificationKey } from '../tests/factories.js';
 import { CircuitsWasm } from '../wasm/circuits_wasm.js';
 import {
@@ -46,34 +46,18 @@ describe('abis wasm bindings', () => {
   });
 
   it('computes a function leaf', () => {
-    const leaf = new FunctionLeafPreimage(Buffer.from([0, 0, 0, 123]), false, true, Fr.ZERO, Fr.ZERO);
+    const leaf = new FunctionLeafPreimage(new FunctionSelector(Buffer.from([0, 0, 0, 123])), false, true, Fr.ZERO, Fr.ZERO);
     const res = computeFunctionLeaf(wasm, leaf);
     expect(res).toMatchSnapshot();
   });
 
-  it('compute function leaf should revert if buffer is over 4 bytes', () => {
-    expect(() => {
-      new FunctionLeafPreimage(Buffer.from([0, 0, 0, 0, 123]), false, true, Fr.ZERO, Fr.ZERO);
-    }).toThrow('Function selector must be 4 bytes long, got 5 bytes.');
-  });
-
-  it('function leaf toBuffer should revert if buffer is over 4 bytes ', () => {
-    const initBuffer = Buffer.from([0, 0, 0, 123]);
-    const largerBuffer = Buffer.from([0, 0, 0, 0, 123]);
-    expect(() => {
-      const leaf = new FunctionLeafPreimage(initBuffer, false, true, Fr.ZERO, Fr.ZERO);
-      leaf.functionSelector = largerBuffer;
-      leaf.toBuffer();
-    }).toThrow('Function selector must be 4 bytes long, got 5 bytes.');
-  });
-
   it('computes function tree root', () => {
     const res = computeFunctionTreeRoot(wasm, [new Fr(0n), new Fr(0n), new Fr(0n), new Fr(0n)]);
     expect(res).toMatchSnapshot();
   });
 
   it('hashes constructor info', () => {
-    const functionData = new FunctionData(Buffer.alloc(4), false, true, true);
+    const functionData = new FunctionData(FunctionSelector.empty(), false, true, true);
     const argsHash = new Fr(42);
     const vkHash = Buffer.alloc(32);
     const res = hashConstructor(wasm, functionData, argsHash, vkHash);

yarn-project/circuits.js/src/contract/contract_deployment_info.ts

@@ -5,9 +5,9 @@ import {
   computeVarArgsHash,
   hashConstructor,
 } from '@aztec/circuits.js/abis';
-import { ContractAbi, encodeArguments, generateFunctionSelector } from '@aztec/foundation/abi';
+import { ContractAbi, encodeArguments } from '@aztec/foundation/abi';
 
-import { CircuitsWasm, DeploymentInfo, Fr, FunctionData, PublicKey } from '../index.js';
+import { CircuitsWasm, DeploymentInfo, Fr, FunctionData, FunctionSelector, PublicKey } from '../index.js';
 import { generateFunctionLeaves, hashVKStr, isConstructor } from './contract_tree/contract_tree.js';
 
 /**
@@ -37,7 +37,7 @@ export async function getContractDeploymentInfo(
   const constructorVkHash = Fr.fromBuffer(vkHash);
   const functions = abi.functions.map(f => ({
     ...f,
-    selector: generateFunctionSelector(f.name, f.parameters),
+    selector: FunctionSelector.fromNameAndParameters(f.name, f.parameters),
   }));
   const leaves = generateFunctionLeaves(functions, wasm);
   const functionTreeRoot = computeFunctionTreeRoot(wasm, leaves);

yarn-project/circuits.js/src/contract/contract_tree/contract_tree.ts

@@ -1,6 +1,6 @@
-import { CircuitsWasm, ContractFunctionDao, Fr, FunctionData, FunctionLeafPreimage } from '@aztec/circuits.js';
+import { CircuitsWasm, ContractFunctionDao, Fr, FunctionData, FunctionLeafPreimage, FunctionSelector } from '@aztec/circuits.js';
 import { computeFunctionLeaf, hashVK } from '@aztec/circuits.js/abis';
-import { FunctionType, generateFunctionSelector } from '@aztec/foundation/abi';
+import { FunctionType } from '@aztec/foundation/abi';
 
 /**
  * Computes the hash of a hex-encoded string representation of a verification key (vk).
@@ -69,7 +69,7 @@ export function generateFunctionLeaves(functions: ContractFunctionDao[], wasm: C
   const result: Fr[] = [];
   for (let i = 0; i < targetFunctions.length; i++) {
     const f = targetFunctions[i];
-    const selector = generateFunctionSelector(f.name, f.parameters);
+    const selector = FunctionSelector.fromNameAndParameters(f.name, f.parameters);
     const isInternal = f.isInternal;
     const isPrivate = f.functionType === FunctionType.SECRET;
     // All non-unconstrained functions have vks

yarn-project/circuits.js/src/structs/function_data.test.ts

@@ -1,11 +1,12 @@
 import { expectSerializeToMatchSnapshot } from '../tests/expectSerialize.js';
 import { FunctionData } from './function_data.js';
+import { FunctionSelector } from './function_selector.js';
 
 describe('basic FunctionData serialization', () => {
   it(`serializes a trivial FunctionData and prints it`, async () => {
     // Test the data case: writing (mostly) sequential numbers
     await expectSerializeToMatchSnapshot(
-      new FunctionData(Buffer.from([0, 0, 0, 123]), false, true, true).toBuffer(),
+      new FunctionData(new FunctionSelector(Buffer.from([0, 0, 0, 123])), false, true, true).toBuffer(),
       'abis__test_roundtrip_serialize_function_data',
     );
   });

yarn-project/circuits.js/src/structs/function_data.ts

@@ -1,22 +1,21 @@
-import { FunctionAbi, FunctionType, generateFunctionSelector } from '@aztec/foundation/abi';
-import { BufferReader, deserializeUInt32, numToUInt32BE } from '@aztec/foundation/serialize';
+import { FunctionAbi, FunctionType } from '@aztec/foundation/abi';
+import { BufferReader, deserializeUInt32 } from '@aztec/foundation/serialize';
 
 import { ContractFunctionDao } from '../index.js';
 import { serializeToBuffer } from '../utils/serialize.js';
-
-const FUNCTION_SELECTOR_LENGTH = 4;
+import { FunctionSelector } from './function_selector.js';
 
 /**
  * Function description for circuit.
  * @see abis/function_data.hpp
  */
 export class FunctionData {
-  /**
-   * Function selector of the function being called.
-   */
-  public functionSelectorBuffer: Buffer;
   constructor(
-    functionSelector: Buffer | number,
+    /**
+     * Function selector of the function being called.
+     * TODO: rename to functionSelector once the functionSelector getter is removed
+     */
+    private _functionSelector: FunctionSelector,
     /**
      * Indicates whether the function is only callable by self or not.
      */
@@ -29,23 +28,11 @@ export class FunctionData {
      * Indicates whether the function is a constructor.
      */
     public isConstructor: boolean,
-  ) {
-    if (functionSelector instanceof Buffer) {
-      if (functionSelector.byteLength !== FUNCTION_SELECTOR_LENGTH) {
-        throw new Error(
-          `Function selector must be ${FUNCTION_SELECTOR_LENGTH} bytes long, got ${functionSelector.byteLength} bytes.`,
-        );
-      }
-      this.functionSelectorBuffer = functionSelector;
-    } else {
-      // create a new numeric buffer with 4 bytes
-      this.functionSelectorBuffer = numToUInt32BE(functionSelector);
-    }
-  }
+  ) {}
 
   static fromAbi(abi: FunctionAbi | ContractFunctionDao): FunctionData {
     return new FunctionData(
-      generateFunctionSelector(abi.name, abi.parameters),
+      FunctionSelector.fromNameAndParameters(abi.name, abi.parameters),
       abi.isInternal,
       abi.functionType === FunctionType.SECRET,
       abi.name === 'constructor',
@@ -55,23 +42,23 @@ export class FunctionData {
   // For serialization, must match function_selector name in C++ and return as number
   // TODO(AD) somehow remove this cruft, probably by using a buffer selector in C++
   get functionSelector(): number {
-    return deserializeUInt32(this.functionSelectorBuffer).elem;
+    return deserializeUInt32(this._functionSelector.value).elem;
   }
 
   /**
    * Serialize this as a buffer.
    * @returns The buffer.
    */
   toBuffer(): Buffer {
-    return serializeToBuffer(this.functionSelectorBuffer, this.isInternal, this.isPrivate, this.isConstructor);
+    return serializeToBuffer(this._functionSelector.value, this.isInternal, this.isPrivate, this.isConstructor);
   }
 
   /**
    * Returns whether this instance is empty.
    * @returns True if the function selector is zero.
    */
   isEmpty() {
-    return this.functionSelectorBuffer.equals(Buffer.alloc(FUNCTION_SELECTOR_LENGTH, 0));
+    return this._functionSelector.isEmpty();
   }
 
   /**
@@ -94,7 +81,7 @@ export class FunctionData {
     isConstructor?: boolean;
   }): FunctionData {
     return new FunctionData(
-      Buffer.alloc(FUNCTION_SELECTOR_LENGTH, 0),
+      FunctionSelector.empty(),
       args?.isInternal ?? false,
       args?.isPrivate ?? false,
       args?.isConstructor ?? false,
@@ -109,7 +96,7 @@ export class FunctionData {
   static fromBuffer(buffer: Buffer | BufferReader): FunctionData {
     const reader = BufferReader.asReader(buffer);
     return new FunctionData(
-      reader.readBytes(FUNCTION_SELECTOR_LENGTH),
+      reader.readObject(FunctionSelector),
       reader.readBoolean(),
       reader.readBoolean(),
       reader.readBoolean(),

yarn-project/circuits.js/src/structs/function_leaf_preimage.test.ts

@@ -2,12 +2,13 @@ import { Fr } from '@aztec/foundation/fields';
 
 import { expectSerializeToMatchSnapshot } from '../tests/expectSerialize.js';
 import { FunctionLeafPreimage } from './function_leaf_preimage.js';
+import { FunctionSelector } from './function_selector.js';
 
 describe('basic FunctionLeafPreimage serialization', () => {
   it(`serializes a trivial Function Leaf Preimage and prints it`, async () => {
     // Test the data case: writing (mostly) sequential numbers
     await expectSerializeToMatchSnapshot(
-      new FunctionLeafPreimage(Buffer.from([0, 0, 0, 123]), false, true, Fr.ZERO, Fr.ZERO).toBuffer(),
+      new FunctionLeafPreimage(new FunctionSelector(Buffer.from([0, 0, 0, 123])), false, true, Fr.ZERO, Fr.ZERO).toBuffer(),
       'abis__test_roundtrip_serialize_function_leaf_preimage',
     );
   });

yarn-project/circuits.js/src/structs/function_leaf_preimage.ts

@@ -2,19 +2,18 @@ import { Fr } from '@aztec/foundation/fields';
 import { BufferReader } from '@aztec/foundation/serialize';
 
 import { serializeToBuffer } from '../utils/serialize.js';
+import { FunctionSelector } from './function_selector.js';
 
 /**
  * A class representing the "preimage" of a function tree leaf.
  * @see abis/function_leaf_preimage.hpp
  */
 export class FunctionLeafPreimage {
-  readonly FUNCTION_SELECTOR_LENGTH = 4;
-
   constructor(
     /**
-     * Function selector `FUNCTION_SELECTOR_LENGTH` bytes long.
+     * Function selector.
      */
-    public functionSelector: Buffer,
+    public functionSelector: FunctionSelector,
     /**
      * Indicates whether the function is only callable by self or not.
      */
@@ -32,28 +31,13 @@ export class FunctionLeafPreimage {
      */
     public acirHash: Fr,
   ) {
-    this.assertFunctionSelectorLength(functionSelector);
-  }
-
-  /**
-   * Assert the function selector buffer length matches `FUNCTION_SELECTOR_LENGTH`.
-   * @param functionSelector - The buffer containing the function selector.
-   * @throws If the function selector buffer length does not match `FUNCTION_SELECTOR_LENGTH`.
-   */
-  private assertFunctionSelectorLength(functionSelector: Buffer) {
-    if (functionSelector.byteLength !== this.FUNCTION_SELECTOR_LENGTH) {
-      throw new Error(
-        `Function selector must be ${this.FUNCTION_SELECTOR_LENGTH} bytes long, got ${functionSelector.byteLength} bytes.`,
-      );
-    }
   }
 
   /**
    * Serialize this as a buffer.
    * @returns The buffer.
    */
   toBuffer(): Buffer {
-    this.assertFunctionSelectorLength(this.functionSelector);
     return serializeToBuffer(this.functionSelector, this.isInternal, this.isPrivate, this.vkHash, this.acirHash);
   }
 
@@ -65,7 +49,7 @@ export class FunctionLeafPreimage {
   static fromBuffer(buffer: Buffer | BufferReader): FunctionLeafPreimage {
     const reader = BufferReader.asReader(buffer);
     return new FunctionLeafPreimage(
-      reader.readBytes(4),
+      reader.readObject(FunctionSelector),
       reader.readBoolean(),
       reader.readBoolean(),
       reader.readFr(),

yarn-project/circuits.js/src/structs/function_selector.ts

@@ -0,0 +1,75 @@
+import { ABIParameter } from '@aztec/foundation/abi';
+import { keccak } from '@aztec/foundation/crypto';
+import { BufferReader } from '@aztec/foundation/serialize';
+
+import { FUNCTION_SELECTOR_NUM_BYTES } from '../cbind/constants.gen.js';
+
+/**
+ * A function selector is the first 4 bytes of the hash of a function signature.
+ */
+export class FunctionSelector {
+  /**
+   * The size of the hash in bytes.
+   */
+  public static SIZE = FUNCTION_SELECTOR_NUM_BYTES;
+
+  constructor(/** buffer containing the function selector */ public value: Buffer) {
+    if (value.length !== FunctionSelector.SIZE) {
+      throw new Error(`Function selector must be ${FunctionSelector.SIZE} bytes long, got ${value.length} bytes.`);
+    }
+  }
+
+  /**
+   * Checks if the function selector is empty (all bytes are 0).
+   * @returns True if the function selector is empty (all bytes are 0).
+   */
+  public isEmpty(): boolean {
+    return this.value.equals(Buffer.alloc(FunctionSelector.SIZE));
+  }
+
+  /**
+   * Serialize as a buffer.
+   * @returns The buffer.
+   */
+  toBuffer(): Buffer {
+    return this.value;
+  }
+
+  /**
+   * Deserializes from a buffer or reader, corresponding to a write in cpp.
+   * @param buffer - Buffer  or BufferReader to read from.
+   * @returns The FunctionSelector.
+   */
+  static fromBuffer(buffer: Buffer | BufferReader): FunctionSelector {
+    const reader = BufferReader.asReader(buffer);
+    return new FunctionSelector(reader.readBytes(FunctionSelector.SIZE));
+  }
+
+  /**
+   * Creates a function selector from a signature.
+   * @param signature - Signature of the function to generate the selector for (e.g. "transfer(field,field)").
+   * @returns Function selector.
+   */
+  static fromSignature(signature: string): FunctionSelector {
+    return new FunctionSelector(keccak(Buffer.from(signature)).subarray(0, FunctionSelector.SIZE));
+  }
+
+  /**
+   * Creates a function selector for a given function name and parameters.
+   * @param name - The name of the function.
+   * @param parameters - An array of ABIParameter objects, each containing the type information of a function parameter.
+   * @returns A Buffer containing the 4-byte function selector.
+   */
+  static fromNameAndParameters(name: string, parameters: ABIParameter[]) {
+    const signature = name === 'constructor' ? name : `${name}(${parameters.map(p => p.type.kind).join(',')})`;
+    return FunctionSelector.fromSignature(signature);
+  }
+
+  /**
+   * Creates an empty function selector.
+   * @returns An empty function selector.
+   */
+  static empty(): FunctionSelector {
+    return new FunctionSelector(Buffer.alloc(FunctionSelector.SIZE));
+  }
+}

yarn-project/circuits.js/src/structs/index.ts

@@ -24,6 +24,7 @@ export * from './tx_request.js';
 export * from './tx_context.js';
 export * from './verification_key.js';
 export * from './function_leaf_preimage.js';
+export * from './function_selector.js';
 export * from './aggregation_object.js';
 export * from './membership_witness.js';
 export * from './read_request_membership_witness.js';

yarn-project/circuits.js/src/tests/factories.ts

@@ -25,6 +25,7 @@ import {
   Fq,
   Fr,
   FunctionData,
+  FunctionSelector,
   G1AffineElement,
   HISTORIC_BLOCKS_TREE_HEIGHT,
   KernelCircuitPublicInputs,
@@ -135,10 +136,10 @@ export function makeConstantData(seed = 1): CombinedConstantData {
  * @param seed - The seed to use for generating the selector.
  * @returns A selector.
  */
-export function makeSelector(seed: number): Buffer {
-  const buffer = Buffer.alloc(4);
+export function makeSelector(seed: number): FunctionSelector {
+  const buffer = Buffer.alloc(FunctionSelector.SIZE);
   buffer.writeUInt32BE(seed, 0);
-  return buffer;
+  return new FunctionSelector(buffer);
 }
 
 /**