Integer overflow

Canonical guidance

• watch arithmetic that feeds allocation sizes, indexing, and protocol lengths
• check before the operation when overflow would be unsafe
• use fixed-width integers when size guarantees matter

Use when

• counters and accumulators
• byte-size calculations
• offsets and capacity math

Avoid

• assuming int is always large enough
• multiplying lengths without bounds checks
• converting between widths without considering truncation

Preferred pattern

const maxInt = int(^uint(0) >> 1)

func add(a, b int) (int, error) {
	if b > 0 && a > maxInt-b {
		return 0, errors.New("overflow")
	}
	return a + b, nil
}

Anti-pattern

• computing allocation sizes from untrusted input with unchecked arithmetic

Explanation: This anti-pattern is tempting because the math looks small and ordinary, but overflow often shows up exactly in boundary calculations.

Why

• overflow bugs corrupt correctness and can become security problems at boundaries