feat: example of private token transfer event (#7242)

A small extension on some of the work @sklppy88 have been doing lately
to satisfy @rahul-kothari and have an example where you end up with your
"transfer history".

The events currently only have neat macros autogenerated for when we are
using a struct of fields only, but works just fine for us here.

---------

Co-authored-by: esau <[email protected]>

noir-projects/aztec-nr/aztec/src/encrypted_logs/encrypted_event_emission.nr

@@ -1,6 +1,7 @@
 use crate::{
     context::PrivateContext, event::event_interface::EventInterface,
-    encrypted_logs::payload::compute_encrypted_event_log, oracle::logs_traits::LensForEncryptedEvent
+    encrypted_logs::payload::compute_encrypted_event_log, oracle::logs_traits::LensForEncryptedEvent,
+    oracle::unsafe_rand::unsafe_rand
 };
 use dep::protocol_types::{address::AztecAddress, grumpkin_point::GrumpkinPoint};
 
@@ -20,6 +21,20 @@ fn emit_with_keys<Event, NB, MB, OB>(
 }
 
 pub fn encode_and_encrypt_event<Event, NB, MB, OB>(
+    context: &mut PrivateContext,
+    ov: AztecAddress,
+    iv: AztecAddress
+) -> fn[(&mut PrivateContext, AztecAddress, AztecAddress)](Event) -> () where Event: EventInterface<NB, MB>, [u8; NB]: LensForEncryptedEvent<NB, OB> {
+    | e: Event | {
+        let header = context.get_header();
+        let ovpk = header.get_ovpk_m(context, ov);
+        let ivpk = header.get_ivpk_m(context, iv);
+        let randomness = unsafe_rand();
+        emit_with_keys(context, randomness, e, ovpk, ivpk);
+    }
+}
+
+pub fn encode_and_encrypt_event_with_randomness<Event, NB, MB, OB>(
     context: &mut PrivateContext,
     randomness: Field,
     ov: AztecAddress,
@@ -34,6 +49,17 @@ pub fn encode_and_encrypt_event<Event, NB, MB, OB>(
 }
 
 pub fn encode_and_encrypt_event_with_keys<Event, NB, MB, OB>(
+    context: &mut PrivateContext,
+    ovpk: GrumpkinPoint,
+    ivpk: GrumpkinPoint
+) -> fn[(&mut PrivateContext, GrumpkinPoint, GrumpkinPoint)](Event) -> () where Event: EventInterface<NB, MB>, [u8; NB]: LensForEncryptedEvent<NB, OB> {
+    | e: Event | {
+        let randomness = unsafe_rand();
+        emit_with_keys(context, randomness, e, ovpk, ivpk);
+    }
+}
+
+pub fn encode_and_encrypt_event_with_keys_with_randomness<Event, NB, MB, OB>(
     context: &mut PrivateContext,
     randomness: Field,
     ovpk: GrumpkinPoint,

noir-projects/noir-contracts/contracts/test_contract/src/main.nr

@@ -8,7 +8,7 @@ contract Test {
         PrivateContext, PrivateImmutable, PrivateSet, SharedImmutable
     };
     use dep::aztec::encrypted_logs::encrypted_note_emission::encode_and_encrypt_note;
-    use dep::aztec::encrypted_logs::encrypted_event_emission::encode_and_encrypt_event_with_keys;
+    use dep::aztec::encrypted_logs::encrypted_event_emission::encode_and_encrypt_event_with_keys_with_randomness;
 
     use dep::aztec::protocol_types::{
         abis::private_circuit_public_inputs::PrivateCircuitPublicInputs,
@@ -271,7 +271,7 @@ contract Test {
         let event = ExampleEvent { value0: fields[0], value1: fields[1], value2: fields[2], value3: fields[3], value4: fields[4] };
 
         event.emit(
-            encode_and_encrypt_event_with_keys(
+            encode_and_encrypt_event_with_keys_with_randomness(
                 &mut context,
                 // testing only - a secret random value is passed in here to salt / mask the address
                 5,
@@ -288,7 +288,7 @@ contract Test {
             let otherEvent = ExampleEvent { value0: 1, value1: 2, value2: 3, value3: 4, value4: 5 };
 
             otherEvent.emit(
-                encode_and_encrypt_event_with_keys(
+                encode_and_encrypt_event_with_keys_with_randomness(
                     &mut context,
                     // testing only - a randomness of 0 signals the kerels to not mask the address
                     0,

noir-projects/noir-contracts/contracts/test_log_contract/src/main.nr

@@ -7,7 +7,7 @@ contract TestLog {
     use dep::value_note::value_note::ValueNote;
     use dep::aztec::encrypted_logs::incoming_body::EncryptedLogIncomingBody;
     use dep::aztec::event::event_interface::EventInterface;
-    use dep::aztec::encrypted_logs::encrypted_event_emission::{encode_and_encrypt_event, encode_and_encrypt_event_with_keys};
+    use dep::aztec::encrypted_logs::encrypted_event_emission::encode_and_encrypt_event_with_randomness;
     use dep::aztec::unencrypted_logs::unencrypted_event_emission::encode_event;
 
     #[aztec(event)]
@@ -49,7 +49,7 @@ contract TestLog {
         let event0 = ExampleEvent0 { value0: preimages[0], value1: preimages[1] };
 
         event0.emit(
-            encode_and_encrypt_event(
+            encode_and_encrypt_event_with_randomness(
                 &mut context,
                 randomness[0],
                 // outgoing is set to other, incoming is set to msg sender
@@ -72,7 +72,7 @@ contract TestLog {
         let event1 = ExampleEvent1 { value2: preimages[2], value3: preimages[3] };
 
         event1.emit(
-            encode_and_encrypt_event(
+            encode_and_encrypt_event_with_randomness(
                 &mut context,
                 randomness[1],
                 // outgoing is set to other, incoming is set to msg sender

noir-projects/noir-contracts/contracts/token_contract/src/main.nr

@@ -18,7 +18,10 @@ contract Token {
     use dep::aztec::{
         hash::compute_secret_hash,
         prelude::{NoteGetterOptions, Map, PublicMutable, SharedImmutable, PrivateSet, AztecAddress},
-        encrypted_logs::encrypted_note_emission::{encode_and_encrypt_note, encode_and_encrypt_note_with_keys}
+        encrypted_logs::{
+        encrypted_note_emission::{encode_and_encrypt_note, encode_and_encrypt_note_with_keys},
+        encrypted_event_emission::{encode_and_encrypt_event, encode_and_encrypt_event_with_keys}
+    }
     };
 
     // docs:start:import_authwit
@@ -28,6 +31,13 @@ contract Token {
     use crate::types::{transparent_note::TransparentNote, token_note::{TokenNote, TOKEN_NOTE_LEN}, balances_map::BalancesMap};
     // docs:end::imports
 
+    #[aztec(event)]
+    struct Transfer {
+        from: Field,
+        to: Field,
+        amount: Field,
+    }
+
     // docs:start:storage_struct
     #[aztec(storage)]
     struct Storage {
@@ -324,6 +334,8 @@ contract Token {
         let amount = U128::from_integer(amount);
         storage.balances.sub(from, amount).emit(encode_and_encrypt_note_with_keys(&mut context, from_ovpk, from_ivpk));
         storage.balances.add(to, amount).emit(encode_and_encrypt_note_with_keys(&mut context, from_ovpk, to_ivpk));
+
+        Transfer { from: from.to_field(), to: to.to_field(), amount: amount.to_field() }.emit(encode_and_encrypt_event_with_keys(&mut context, from_ovpk, to_ivpk));
     }
     // docs:end:transfer
 

yarn-project/end-to-end/src/e2e_token_contract/transfer_private.test.ts

@@ -1,10 +1,12 @@
 import {
   AztecAddress,
   CompleteAddress,
+  EventType,
   Fr,
   computeAuthWitMessageHash,
   computeInnerAuthWitHashFromAction,
 } from '@aztec/aztec.js';
+import { TokenContract } from '@aztec/noir-contracts.js';
 
 import { DUPLICATE_NULLIFIER_ERROR } from '../fixtures/fixtures.js';
 import { TokenContractTest } from './token_contract_test.js';
@@ -32,8 +34,16 @@ describe('e2e_token_contract transfer private', () => {
     const balance0 = await asset.methods.balance_of_private(accounts[0].address).simulate();
     const amount = balance0 / 2n;
     expect(amount).toBeGreaterThan(0n);
-    await asset.methods.transfer(accounts[1].address, amount).send().wait();
+    const tx = await asset.methods.transfer(accounts[1].address, amount).send().wait();
     tokenSim.transferPrivate(accounts[0].address, accounts[1].address, amount);
+
+    const events = await wallets[1].getEvents(EventType.Encrypted, TokenContract.events.Transfer, tx.blockNumber!, 1);
+
+    expect(events[0]).toEqual({
+      from: accounts[0].address,
+      to: accounts[1].address,
+      amount: new Fr(amount),
+    });
   });
 
   it('transfer less than balance to non-deployed account', async () => {