further restrict constituent max borrow

Author: moosecat2

programs/drift/src/instructions/lp_pool.rs

@@ -1588,7 +1588,16 @@ fn transfer_from_program_vault<'info>(
 
     let balance_before = constituent.get_full_token_amount(&spot_market)?;
 
-    let max_transfer = constituent.get_max_transfer(&spot_market)?;
+    let max_transfer = constituent
+        .max_borrow_token_amount
+        .cast::<i128>()?
+        .safe_add(
+            constituent
+                .spot_balance
+                .get_signed_token_amount(spot_market)?,
+        )?
+        .max(0)
+        .cast::<u64>()?;
 
     validate!(
         max_transfer >= amount,

programs/drift/src/state/lp_pool.rs

@@ -978,19 +978,6 @@ impl Constituent {
             bytemuck::bytes_of(bump),
         ]
     }
-
-    pub fn get_max_transfer(&self, spot_market: &SpotMarket) -> DriftResult<u64> {
-        let token_amount = self.get_full_token_amount(spot_market)?;
-        let max_transfer = if token_amount < 0 {
-            self.max_borrow_token_amount
-                .saturating_sub(token_amount.abs().cast::<u64>()?)
-        } else {
-            self.max_borrow_token_amount
-                .saturating_add(token_amount.abs().cast::<u64>()?)
-        };
-
-        Ok(max_transfer)
-    }
 }
 
 #[zero_copy]

tests/lpPool.ts

@@ -1571,7 +1571,7 @@ describe('LP Pool', () => {
 			);
 		} catch (e) {
 			console.log(e);
-			assert(e.toString().includes('0x18b9')); // invariant failed
+			assert(e.toString().includes('0x18c1')); // invariant failed
 		}
 	});