backoff: set default values on BackoffConfig

Because most of the fields on `BackoffConfig` are unexported, correctly
using the config requires copying from the default. This sets the
defaults appropriately and falls back to a default if MaxDelay is
negative or zero.

Tests are added to ensure that the backoff is set correctly in common
use cases.

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

backoff.go

@@ -46,6 +46,15 @@ type BackoffConfig struct {
 	jitter float64
 }
 
+func (bc *BackoffConfig) setDefaults() {
+	md := bc.MaxDelay
+	*bc = *DefaultBackoffConfig
+
+	if md > 0 {
+		bc.MaxDelay = md
+	}
+}
+
 func (bc *BackoffConfig) backoff(retries int) (t time.Duration) {
 	if retries == 0 {
 		return bc.baseDelay

backoff_test.go

@@ -0,0 +1,11 @@
+package grpc
+
+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)
+	}
+}

clientconn.go

@@ -115,9 +115,21 @@ 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})
+}
+
 // WithBackoffConfig configures the dialer to use the provided backoff
 // parameters after connection failures.
+//
+// Use WithBackoffMaxDelay until more parameters on BackoffConfig are opened up
+// for use.
 func WithBackoffConfig(b *BackoffConfig) DialOption {
+	// Set defaults to ensure that provided BackoffConfig is valid and
+	// unexported fields get default values.
+	b.setDefaults()
 	return withBackoff(b)
 }
 

clientconn_test.go

@@ -80,3 +80,42 @@ func TestCredentialsMisuse(t *testing.T) {
 		t.Fatalf("Dial(_, _) = _, %v, want _, %v", err, ErrCredentialsMisuse)
 	}
 }
+
+func TestWithBackoffConfigDefault(t *testing.T) {
+	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))
+}
+
+func TestWithBackoffMaxDelay(t *testing.T) {
+	md := DefaultBackoffConfig.MaxDelay / 2
+	expected := BackoffConfig{MaxDelay: md}
+	expected.setDefaults()
+	testBackoffConfigSet(t, &expected, WithBackoffMaxDelay(md))
+}
+
+func testBackoffConfigSet(t *testing.T, expected *BackoffConfig, opts ...DialOption) {
+	opts = append(opts, WithInsecure())
+	conn, err := Dial("foo:80", opts...)
+	if err != nil {
+		t.Fatalf("unexpected error dialing connection: %v", err)
+	}
+
+	if conn.dopts.bs == nil {
+		t.Fatalf("backoff config not set")
+	}
+
+	actual, ok := conn.dopts.bs.(*BackoffConfig)
+	if !ok {
+		t.Fatalf("unexpected type of backoff config: %v", conn.dopts.bs)
+	}
+
+	if *actual != *expected {
+		t.Fatalf("unexpected backoff config on connection: %v, want %v", actual, expected)
+	}
+}