Update operationTimeout to handle unset/zero DefaultTimeout

Updates operationTimeout so that if DefaultTimeout is unset (aka zero)
operationTimeout will not set a default timeout on the context.

feature/ec2/imds/request_middleware.go

@@ -227,6 +227,9 @@ const (
 // stack was called with does not have a deadline. The next middleware must
 // complete before the timeout, or the context will be canceled.
 //
+// If DefaultTimeout is zero, no default timeout will be used if the Context
+// does not have a timeout.
+//
 // The next middleware must also ensure that any resources that are also
 // canceled by the stack's context are completely consumed before returning.
 // Otherwise the timeout cleanup will race the resource being consumed
@@ -242,7 +245,7 @@ func (m *operationTimeout) HandleInitialize(
 ) (
 	output middleware.InitializeOutput, metadata middleware.Metadata, err error,
 ) {
-	if _, ok := ctx.Deadline(); !ok {
+	if _, ok := ctx.Deadline(); !ok && m.DefaultTimeout != 0 {
 		var cancelFn func()
 		ctx, cancelFn = context.WithTimeout(ctx, m.DefaultTimeout)
 		defer cancelFn()

feature/ec2/imds/request_middleware_test.go

@@ -136,7 +136,11 @@ func TestOperationTimeoutMiddleware(t *testing.T) {
 		) (
 			out middleware.InitializeOutput, metadata middleware.Metadata, err error,
 		) {
-			if err := sdk.SleepWithContext(ctx, time.Second); err != nil {
+			if _, ok := ctx.Deadline(); !ok {
+				return out, metadata, fmt.Errorf("expect context deadline to be set")
+			}
+
+			if err := sdk.SleepWithContext(ctx, time.Millisecond); err != nil {
 				return out, metadata, err
 			}
 
@@ -151,6 +155,26 @@ func TestOperationTimeoutMiddleware(t *testing.T) {
 	}
 }
 
+func TestOperationTimeoutMiddleware_noDefaultTimeout(t *testing.T) {
+	m := &operationTimeout{}
+
+	_, _, err := m.HandleInitialize(context.Background(), middleware.InitializeInput{},
+		middleware.InitializeHandlerFunc(func(
+			ctx context.Context, input middleware.InitializeInput,
+		) (
+			out middleware.InitializeOutput, metadata middleware.Metadata, err error,
+		) {
+			if t, ok := ctx.Deadline(); ok {
+				return out, metadata, fmt.Errorf("expect no context deadline, got %v", t)
+			}
+
+			return out, metadata, nil
+		}))
+	if err != nil {
+		t.Fatalf("expect no error, got %v", err)
+	}
+}
+
 func TestOperationTimeoutMiddleware_withCustomDeadline(t *testing.T) {
 	m := &operationTimeout{
 		DefaultTimeout: time.Nanosecond,