From 4feaea59267437a0841aa14f445cee7556a0c0b4 Mon Sep 17 00:00:00 2001
From: Santiago Palladino <santiago@aztecprotocol.com>
Date: Wed, 28 Feb 2024 12:26:11 -0300
Subject: [PATCH] feat: Add aztec-nr private functions for initialization
 nullifier (#4807)

Adds helper functions for emitting and checking an initialization
nullifier in private-land.
---
 .../aztec-nr/aztec/src/initializer.nr         | 29 ++++++++++++++++
 noir-projects/aztec-nr/aztec/src/lib.nr       |  1 +
 .../stateful_test_contract/src/main.nr        | 18 ++++++++--
 .../circuits.js/src/structs/side_effects.ts   |  4 +++
 .../src/e2e_deploy_contract.test.ts           | 33 +++++++++++++++++++
 .../pxe/src/kernel_prover/kernel_prover.ts    |  2 +-
 .../src/client/private_execution.test.ts      |  3 +-
 7 files changed, 85 insertions(+), 5 deletions(-)
 create mode 100644 noir-projects/aztec-nr/aztec/src/initializer.nr

diff --git a/noir-projects/aztec-nr/aztec/src/initializer.nr b/noir-projects/aztec-nr/aztec/src/initializer.nr
new file mode 100644
index 00000000000..ac7fff02522
--- /dev/null
+++ b/noir-projects/aztec-nr/aztec/src/initializer.nr
@@ -0,0 +1,29 @@
+use dep::protocol_types::hash::silo_nullifier;
+use crate::context::PrivateContext;
+
+pub fn mark_as_initialized(context: &mut PrivateContext) {
+  let init_nullifier = compute_unsiloed_contract_initialization_nullifier(context);
+  context.push_new_nullifier(init_nullifier, 0);
+
+  // We push a commitment as well and use this value to check initialization,
+  // since we cannot yet read a nullifier from the same tx in which it was emitted.
+  // Eventually, when that's supported, we should delete this note_hash and
+  // have all checks rely on reading the nullifier directly.
+  // TODO(@spalladino) Remove when possible.
+  context.push_new_note_hash(init_nullifier);
+}
+
+// TODO(@spalladino): Add a variant using PublicContext once we can read nullifiers or note hashes from public-land.
+pub fn assert_is_initialized(context: &mut PrivateContext) {
+  let init_nullifier = compute_contract_initialization_nullifier(context);
+  context.push_read_request(init_nullifier);
+}
+
+pub fn compute_contract_initialization_nullifier(context: &mut PrivateContext) -> Field {
+  let address = context.this_address();
+  silo_nullifier(address, compute_unsiloed_contract_initialization_nullifier(context))
+}
+
+pub fn compute_unsiloed_contract_initialization_nullifier(context: &mut PrivateContext) -> Field {
+  context.this_address().to_field()
+}
diff --git a/noir-projects/aztec-nr/aztec/src/lib.nr b/noir-projects/aztec-nr/aztec/src/lib.nr
index 49ecf959cb1..2d6eeb862c9 100644
--- a/noir-projects/aztec-nr/aztec/src/lib.nr
+++ b/noir-projects/aztec-nr/aztec/src/lib.nr
@@ -4,6 +4,7 @@ mod deploy;
 mod hash;
 mod hasher;
 mod history;
+mod initializer;
 mod key;
 mod log;
 mod messaging;
diff --git a/noir-projects/noir-contracts/contracts/stateful_test_contract/src/main.nr b/noir-projects/noir-contracts/contracts/stateful_test_contract/src/main.nr
index 42637e67d35..094556ac7a0 100644
--- a/noir-projects/noir-contracts/contracts/stateful_test_contract/src/main.nr
+++ b/noir-projects/noir-contracts/contracts/stateful_test_contract/src/main.nr
@@ -1,6 +1,5 @@
 // A contract used for testing a random hodgepodge of small features from simulator and end-to-end tests.
 contract StatefulTest {
-    use dep::aztec::protocol_types::{address::AztecAddress, abis::function_selector::FunctionSelector};
     use dep::std::option::Option;
     use dep::value_note::{balance_utils, utils::{increment, decrement}, value_note::{VALUE_NOTE_LEN, ValueNote}};
     use dep::aztec::{
@@ -8,7 +7,9 @@ contract StatefulTest {
         context::{PrivateContext, PublicContext, Context},
         note::{note_header::NoteHeader, utils as note_utils},
         state_vars::{Map, PublicMutable, PrivateSet},
-        oracle::get_contract_instance::get_contract_instance
+        oracle::get_contract_instance::get_contract_instance,
+        initializer::{mark_as_initialized, assert_is_initialized},
+        protocol_types::{address::AztecAddress, abis::function_selector::FunctionSelector},
     };
 
     struct Storage {
@@ -18,12 +19,22 @@ contract StatefulTest {
 
     #[aztec(private)]
     fn constructor(owner: AztecAddress, value: Field) {
-        let selector = FunctionSelector::from_signature("create_note((Field),Field)");
+        let selector = FunctionSelector::from_signature("internal_create_note((Field),Field)");
         let _res = context.call_private_function(context.this_address(), selector, [owner.to_field(), value]);
+        mark_as_initialized(&mut context);
     }
 
     #[aztec(private)]
     fn create_note(owner: AztecAddress, value: Field) {
+        assert_is_initialized(&mut context);
+        if (value != 0) {
+            let loc = storage.notes.at(owner);
+            increment(loc, value, owner);
+        }
+    }
+
+    #[aztec(private)]
+    internal fn internal_create_note(owner: AztecAddress, value: Field) {
         if (value != 0) {
             let loc = storage.notes.at(owner);
             increment(loc, value, owner);
@@ -32,6 +43,7 @@ contract StatefulTest {
 
     #[aztec(private)]
     fn destroy_and_create(recipient: AztecAddress, amount: Field) {
+        assert_is_initialized(&mut context);
         let sender = context.msg_sender();
 
         let sender_notes = storage.notes.at(sender);
diff --git a/yarn-project/circuits.js/src/structs/side_effects.ts b/yarn-project/circuits.js/src/structs/side_effects.ts
index a39eb52420c..98fdaa715e9 100644
--- a/yarn-project/circuits.js/src/structs/side_effects.ts
+++ b/yarn-project/circuits.js/src/structs/side_effects.ts
@@ -33,6 +33,10 @@ export class SideEffect implements SideEffectType {
     public counter: Fr,
   ) {}
 
+  toString(): string {
+    return `value=${this.value.toString()} counter=${this.counter.toString()}`;
+  }
+
   /**
    * Serialize this as a buffer.
    * @returns The buffer.
diff --git a/yarn-project/end-to-end/src/e2e_deploy_contract.test.ts b/yarn-project/end-to-end/src/e2e_deploy_contract.test.ts
index 7c7247e9016..828b534a5ff 100644
--- a/yarn-project/end-to-end/src/e2e_deploy_contract.test.ts
+++ b/yarn-project/end-to-end/src/e2e_deploy_contract.test.ts
@@ -213,6 +213,39 @@ describe('e2e_deploy_contract', () => {
       expect(await contracts[0].methods.summed_values(owner).view()).toEqual(42n);
       expect(await contracts[1].methods.summed_values(owner).view()).toEqual(52n);
     }, 30_000);
+
+    it('refuses to initialize a contract twice', async () => {
+      const owner = await registerRandomAccount(pxe);
+      const initArgs: StatefulContractCtorArgs = [owner, 42];
+      const contract = await registerContract(wallet, StatefulTestContract, initArgs);
+      await contract.methods
+        .constructor(...initArgs)
+        .send()
+        .wait();
+      await expect(
+        contract.methods
+          .constructor(...initArgs)
+          .send()
+          .wait(),
+      ).rejects.toThrow(/dropped/);
+    });
+
+    it('refuses to call a private function that requires initialization', async () => {
+      const owner = await registerRandomAccount(pxe);
+      const initArgs: StatefulContractCtorArgs = [owner, 42];
+      const contract = await registerContract(wallet, StatefulTestContract, initArgs);
+      // TODO(@spalladino): It'd be nicer to be able to fail the assert with a more descriptive message,
+      // but the best we can do for now is pushing a read request to the kernel and wait for it to fail.
+      // Maybe we need an unconstrained check for the read request that runs within the app circuit simulation
+      // so we can bail earlier with a more descriptive error? I should create an issue for this.
+      await expect(contract.methods.create_note(owner, 10).send().wait()).rejects.toThrow(
+        /The read request.*does not match/,
+      );
+    });
+
+    it('refuses to call a public function that requires initialization', async () => {
+      // TODO(@spalladino)
+    });
   });
 
   describe('registering a contract class', () => {
diff --git a/yarn-project/pxe/src/kernel_prover/kernel_prover.ts b/yarn-project/pxe/src/kernel_prover/kernel_prover.ts
index aa8aa944e63..5fc8f3412e3 100644
--- a/yarn-project/pxe/src/kernel_prover/kernel_prover.ts
+++ b/yarn-project/pxe/src/kernel_prover/kernel_prover.ts
@@ -337,7 +337,7 @@ export class KernelProver {
       const result = noteHashes.findIndex(equalToRR);
       if (result == -1) {
         throw new Error(
-          `The read request at index ${i} with value ${readRequests[i].toString()} does not match to any commitment.`,
+          `The read request at index ${i} ${readRequests[i].toString()} does not match to any commitment.`,
         );
       } else {
         hints[i] = new Fr(result);
diff --git a/yarn-project/simulator/src/client/private_execution.test.ts b/yarn-project/simulator/src/client/private_execution.test.ts
index 2bd6f735c57..09d568bfd18 100644
--- a/yarn-project/simulator/src/client/private_execution.test.ts
+++ b/yarn-project/simulator/src/client/private_execution.test.ts
@@ -411,7 +411,8 @@ describe('Private Execution test suite', () => {
       expect(changeNote.note.items[0]).toEqual(new Fr(40n));
 
       const readRequests = sideEffectArrayToValueArray(
-        nonEmptySideEffects(result.callStackItem.publicInputs.readRequests),
+        // We remove the first element which is the read request for the initialization commitment
+        nonEmptySideEffects(result.callStackItem.publicInputs.readRequests.slice(1)),
       );
 
       expect(readRequests).toHaveLength(consumedNotes.length);