Merge pull request #961 from samjay8/fix/786-topup-resets-last-update-time

fix(contracts): preserve accrued vest time on stream top-up (closes #786)

Author: ogazboiz

contracts/stream_contract/src/lib.rs

@@ -288,9 +288,10 @@ impl StreamContract {
         // Collect protocol fee and get net amount
         let net_amount = Self::collect_fee(&env, &stream.token_address, amount, stream_id);
 
-        // Update stream state
+        // Update stream state. `last_update_time` is intentionally left untouched:
+        // it is the accrual anchor for `calculate_claimable`, and advancing it to
+        // `now` would discard any already-vested, unwithdrawn tokens.
         stream.deposited_amount += net_amount;
-        stream.last_update_time = env.ledger().timestamp();
 
         save_stream(&env, stream_id, &stream);
 

contracts/stream_contract/src/test.rs

@@ -497,6 +497,53 @@ fn test_top_up_emits_event() {
     assert_eq!(payload.new_deposited_amount, 15_000);
 }
 
+#[test]
+fn test_top_up_preserves_already_accrued_claimable() {
+    let env = Env::default();
+    env.mock_all_auths();
+    let (token, _) = create_token(&env);
+    let sender = Address::generate(&env);
+    let recipient = Address::generate(&env);
+    mint(&env, &token, &sender, 2_000);
+
+    let client = create_contract(&env);
+    let id = client.create_stream(&sender, &recipient, &token, &1_000, &1_000);
+
+    // Recipient vests 900 tokens (rate 1/sec) before the top-up.
+    env.ledger().with_mut(|l| l.timestamp += 900);
+    assert_eq!(client.get_claimable_amount(&id), Some(900));
+
+    client.top_up_stream(&sender, &id, &100);
+
+    // Already-accrued, unwithdrawn time must survive the top-up.
+    assert_eq!(client.get_claimable_amount(&id), Some(900));
+}
+
+#[test]
+fn test_top_up_then_cancel_pays_pre_topup_accrued() {
+    let env = Env::default();
+    env.mock_all_auths();
+    let (token, _) = create_token(&env);
+    let sender = Address::generate(&env);
+    let recipient = Address::generate(&env);
+    mint(&env, &token, &sender, 2_000);
+
+    let client = create_contract(&env);
+    let id = client.create_stream(&sender, &recipient, &token, &1_000, &1_000);
+
+    env.ledger().with_mut(|l| l.timestamp += 900);
+    client.top_up_stream(&sender, &id, &100);
+
+    let token_client = token::Client::new(&env, &token);
+    let recipient_balance_before = token_client.balance(&recipient);
+
+    // Cancel immediately after the top-up — no further time should accrue.
+    client.cancel_stream(&sender, &id);
+
+    let recipient_balance_after = token_client.balance(&recipient);
+    assert_eq!(recipient_balance_after - recipient_balance_before, 900);
+}
+
 // ─── withdraw ────────────────────────────────────────────────────────────────
 
 #[test]
@@ -1758,6 +1805,34 @@ fn test_top_up_while_paused_increases_deposited() {
     assert!(new_deposited > old_deposited);
 }
 
+#[test]
+fn test_top_up_while_paused_does_not_advance_last_update_time() {
+    let env = Env::default();
+    env.mock_all_auths();
+    let (token, _) = create_token(&env);
+    let sender = Address::generate(&env);
+    let recipient = Address::generate(&env);
+    mint(&env, &token, &sender, 2_000);
+
+    let client = create_contract(&env);
+    let id = client.create_stream(&sender, &recipient, &token, &1_000, &1_000);
+
+    // Accrue 300s, then pause.
+    env.ledger().with_mut(|l| l.timestamp += 300);
+    client.pause_stream(&sender, &id);
+
+    // More ledger time passes while paused; top up during this window.
+    env.ledger().with_mut(|l| l.timestamp += 200);
+    client.top_up_stream(&sender, &id, &100);
+
+    let stream = client.get_stream(&id).unwrap();
+    assert!(stream.last_update_time <= stream.paused_at.unwrap());
+
+    // Claimable should still reflect the 300s accrued before the pause, not be
+    // wiped out by the top-up pushing last_update_time past paused_at.
+    assert_eq!(client.get_claimable_amount(&id), Some(300));
+}
+
 #[test]
 fn test_withdraw_after_long_stream_runtime_is_bounded() {
     let env = Env::default();