add ratelimit.None helper for disabling retry quotas

.changelog/df6f67adcf634eb48c3c35f3cc763f09.json

@@ -0,0 +1,8 @@
+{
+    "id": "df6f67ad-cf63-4eb4-8c3c-35f3cc763f09",
+    "type": "feature",
+    "description": "Add no-op rate limiting implementation `ratelimit.None`, which allows disabling of client-side retry quota behavior.",
+    "modules": [
+        "."
+    ]
+}

aws/ratelimit/none.go

@@ -0,0 +1,20 @@
+package ratelimit
+
+import "context"
+
+// None implements a no-op rate limiter which effectively disables client-side
+// rate limiting (also known as "retry quotas").
+//
+// GetToken does nothing and always returns a nil error. The returned
+// token-release function does nothing, and always returns a nil error.
+//
+// AddTokens does nothing and always returns a nil error.
+var None = &none{}
+
+type none struct{}
+
+func (*none) GetToken(ctx context.Context, cost uint) (func() error, error) {
+	return func() error { return nil }, nil
+}
+
+func (*none) AddTokens(v uint) error { return nil }

aws/retry/standard.go

@@ -123,6 +123,17 @@ type StandardOptions struct {
 
 	// Provides the rate limiting strategy for rate limiting attempt retries
 	// across all attempts the retryer is being used with.
+	//
+	// A RateLimiter operates as a token bucket with a set capacity, where
+	// attempt failures events consume tokens. A retry attempt that attempts to
+	// consume more tokens than what's available results in operation failure.
+	// The default implementation is parameterized as follows:
+	//   - a capacity of 500 (DefaultRetryRateTokens)
+	//   - a retry caused by a timeout costs 10 tokens (DefaultRetryCost)
+	//   - a retry caused by other errors costs 5 tokens (DefaultRetryTimeoutCost)
+	//   - an operation that succeeds on the 1st attempt adds 1 token (DefaultNoRetryIncrement)
+	//
+	// You can disable rate limiting by setting this field to ratelimit.None.
 	RateLimiter RateLimiter
 
 	// The cost to deduct from the RateLimiter's token bucket per retry.