fix(safe-math): fix #20 by implementing overflow-safe arithmetic across contracts

contracts/creditline-contract/src/safe_math.rs

@@ -0,0 +1,33 @@
+use crate::errors::CreditLineError;
+
+pub fn add_i128(a: i128, b: i128) -> Result<i128, CreditLineError> {
+    a.checked_add(b).ok_or(CreditLineError::Overflow)
+}
+
+pub fn sub_i128(a: i128, b: i128) -> Result<i128, CreditLineError> {
+    a.checked_sub(b).ok_or(CreditLineError::Underflow)
+}
+
+pub fn mul_i128(a: i128, b: i128) -> Result<i128, CreditLineError> {
+    a.checked_mul(b).ok_or(CreditLineError::Overflow)
+}
+
+pub fn div_i128(a: i128, b: i128) -> Result<i128, CreditLineError> {
+    a.checked_div(b).ok_or(CreditLineError::Overflow)
+}
+
+pub fn add_u64(a: u64, b: u64) -> Result<u64, CreditLineError> {
+    a.checked_add(b).ok_or(CreditLineError::Overflow)
+}
+
+pub fn sub_u64(a: u64, b: u64) -> Result<u64, CreditLineError> {
+    a.checked_sub(b).ok_or(CreditLineError::Underflow)
+}
+
+pub fn mul_u64(a: u64, b: u64) -> Result<u64, CreditLineError> {
+    a.checked_mul(b).ok_or(CreditLineError::Overflow)
+}
+
+pub fn div_u64(a: u64, b: u64) -> Result<u64, CreditLineError> {
+    a.checked_div(b).ok_or(CreditLineError::Overflow)
+}

contracts/creditline-contract/src/tests.rs

@@ -3044,3 +3044,21 @@ fn test_repay_installment_zero_amount_rejected() {
     // Zero-amount payment must be rejected
     t.client.repay_installment(&user, &loan_id, &0, &0);
 }
+
+#[test]
+fn test_safe_math_boundaries() {
+    use crate::safe_math;
+    // 0 cases
+    assert_eq!(safe_math::add_i128(0, 0), Ok(0));
+    assert_eq!(safe_math::sub_i128(0, 0), Ok(0));
+    assert_eq!(safe_math::mul_i128(0, 0), Ok(0));
+    assert_eq!(safe_math::div_i128(0, 5), Ok(0));
+
+    // max cases
+    let max = i128::MAX;
+    let min = i128::MIN;
+    assert_eq!(safe_math::add_i128(max, 1), Err(CreditLineError::Overflow));
+    assert_eq!(safe_math::sub_i128(min, 1), Err(CreditLineError::Underflow));
+    assert_eq!(safe_math::mul_i128(max, 2), Err(CreditLineError::Overflow));
+    assert_eq!(safe_math::div_i128(max, 0), Err(CreditLineError::Overflow));
+}