Move dialer to pkg

Signed-off-by: Michael Crosby <crosbymichael@gmail.com>

pkg/dialer/dialer.go

@@ -0,0 +1,67 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package dialer
+
+import (
+	"net"
+	"time"
+
+	"github.com/pkg/errors"
+)
+
+type dialResult struct {
+	c   net.Conn
+	err error
+}
+
+// Dialer returns a GRPC net.Conn connected to the provided address
+func Dialer(address string, timeout time.Duration) (net.Conn, error) {
+	var (
+		stopC = make(chan struct{})
+		synC  = make(chan *dialResult)
+	)
+	go func() {
+		defer close(synC)
+		for {
+			select {
+			case <-stopC:
+				return
+			default:
+				c, err := dialer(address, timeout)
+				if isNoent(err) {
+					<-time.After(10 * time.Millisecond)
+					continue
+				}
+				synC <- &dialResult{c, err}
+				return
+			}
+		}
+	}()
+	select {
+	case dr := <-synC:
+		return dr.c, dr.err
+	case <-time.After(timeout):
+		close(stopC)
+		go func() {
+			dr := <-synC
+			if dr != nil && dr.c != nil {
+				dr.c.Close()
+			}
+		}()
+		return nil, errors.Errorf("dial %s: timeout", address)
+	}
+}