backoff: make DefaultBackoffConfig a concrete value

To enforce immutability of the `DefaultBackoffConfig`, we've made it a
concrete value. While fields can still be set directly on the value,
taking a copy will not incidentally pull a reference to the variable.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

backoff.go

@@ -8,7 +8,7 @@ import (
 // DefaultBackoffConfig uses values specified for backoff in
 // https://github.com/grpc/grpc/blob/master/doc/connection-backoff.md.
 var (
-	DefaultBackoffConfig = &BackoffConfig{
+	DefaultBackoffConfig = BackoffConfig{
 		MaxDelay:  120 * time.Second,
 		baseDelay: 1.0 * time.Second,
 		factor:    1.6,
@@ -33,7 +33,10 @@ type BackoffConfig struct {
 	// MaxDelay is the upper bound of backoff delay.
 	MaxDelay time.Duration
 
-	// TODO(stevvooe): The following fields are not exported, as allowing changes
+	// TODO(stevvooe): The following fields are not exported, as allowing
+	// changes would violate the current GRPC specification for backoff. If
+	// GRPC decides to allow more interesting backoff strategies, these fields
+	// may be opened up in the future.
 
 	// baseDelay is the amount of time to wait before retrying after the first
 	// failure.
@@ -48,14 +51,14 @@ type BackoffConfig struct {
 
 func (bc *BackoffConfig) setDefaults() {
 	md := bc.MaxDelay
-	*bc = *DefaultBackoffConfig
+	*bc = DefaultBackoffConfig
 
 	if md > 0 {
 		bc.MaxDelay = md
 	}
 }
 
-func (bc *BackoffConfig) backoff(retries int) (t time.Duration) {
+func (bc BackoffConfig) backoff(retries int) (t time.Duration) {
 	if retries == 0 {
 		return bc.baseDelay
 	}

backoff_test.go

@@ -5,7 +5,7 @@ import "testing"
 func TestBackoffConfigDefaults(t *testing.T) {
 	b := BackoffConfig{}
 	b.setDefaults()
-	if b != *DefaultBackoffConfig {
-		t.Fatalf("expected BackoffConfig to pickup default parameters: %v != %v", b, *DefaultBackoffConfig)
+	if b != DefaultBackoffConfig {
+		t.Fatalf("expected BackoffConfig to pickup default parameters: %v != %v", b, DefaultBackoffConfig)
 	}
 }

clientconn.go

@@ -118,7 +118,7 @@ func WithPicker(p Picker) DialOption {
 // WithBackoffMaxDelay configures the dialer to use the provided maximum delay
 // when backing off after failed connection attempts.
 func WithBackoffMaxDelay(md time.Duration) DialOption {
-	return WithBackoffConfig(&BackoffConfig{MaxDelay: md})
+	return WithBackoffConfig(BackoffConfig{MaxDelay: md})
 }
 
 // WithBackoffConfig configures the dialer to use the provided backoff
@@ -126,7 +126,7 @@ func WithBackoffMaxDelay(md time.Duration) DialOption {
 //
 // Use WithBackoffMaxDelay until more parameters on BackoffConfig are opened up
 // for use.
-func WithBackoffConfig(b *BackoffConfig) DialOption {
+func WithBackoffConfig(b BackoffConfig) DialOption {
 	// Set defaults to ensure that provided BackoffConfig is valid and
 	// unexported fields get default values.
 	b.setDefaults()

clientconn_test.go

@@ -82,14 +82,14 @@ func TestCredentialsMisuse(t *testing.T) {
 }
 
 func TestWithBackoffConfigDefault(t *testing.T) {
-	testBackoffConfigSet(t, DefaultBackoffConfig)
+	testBackoffConfigSet(t, &DefaultBackoffConfig)
 }
 
 func TestWithBackoffConfig(t *testing.T) {
 	b := BackoffConfig{MaxDelay: DefaultBackoffConfig.MaxDelay / 2}
 	expected := b
 	expected.setDefaults() // defaults should be set
-	testBackoffConfigSet(t, &expected, WithBackoffConfig(&b))
+	testBackoffConfigSet(t, &expected, WithBackoffConfig(b))
 }
 
 func TestWithBackoffMaxDelay(t *testing.T) {
@@ -110,12 +110,12 @@ func testBackoffConfigSet(t *testing.T, expected *BackoffConfig, opts ...DialOpt
 		t.Fatalf("backoff config not set")
 	}
 
-	actual, ok := conn.dopts.bs.(*BackoffConfig)
+	actual, ok := conn.dopts.bs.(BackoffConfig)
 	if !ok {
-		t.Fatalf("unexpected type of backoff config: %v", conn.dopts.bs)
+		t.Fatalf("unexpected type of backoff config: %#v", conn.dopts.bs)
 	}
 
-	if *actual != *expected {
+	if actual != *expected {
 		t.Fatalf("unexpected backoff config on connection: %v, want %v", actual, expected)
 	}
 }