Update unix dialer to keep retrying if socket is gone

This is needed to support daemon restart as the unix socket is recreated at
every start.

Signed-off-by: Kenfe-Mickael Laventure <mickael.laventure@gmail.com>

client.go

@@ -64,8 +64,9 @@ func New(address string, opts ...ClientOpt) (*Client, error) {
 	gopts := []grpc.DialOption{
 		grpc.WithBlock(),
 		grpc.WithInsecure(),
-		grpc.WithTimeout(100 * time.Second),
+		grpc.WithTimeout(60 * time.Second),
 		grpc.FailOnNonTempDialError(true),
+		grpc.WithBackoffMaxDelay(3 * time.Second),
 		grpc.WithDialer(dialer),
 	}
 	if len(copts.dialOptions) > 0 {

client_unix.go

@@ -5,13 +5,68 @@ package containerd
 import (
 	"fmt"
 	"net"
+	"os"
 	"strings"
+	"syscall"
 	"time"
+
+	"github.com/pkg/errors"
 )
 
+func isNoent(err error) bool {
+	if err != nil {
+		if nerr, ok := err.(*net.OpError); ok {
+			if serr, ok := nerr.Err.(*os.SyscallError); ok {
+				if serr.Err == syscall.ENOENT {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+type dialResult struct {
+	c   net.Conn
+	err error
+}
+
 func dialer(address string, timeout time.Duration) (net.Conn, error) {
+	var (
+		stopC = make(chan struct{})
+		synC  = make(chan *dialResult)
+	)
 	address = strings.TrimPrefix(address, "unix://")
-	return net.DialTimeout("unix", address, timeout)
+	go func() {
+		defer close(synC)
+		for {
+			select {
+			case <-stopC:
+				return
+			default:
+				c, err := net.DialTimeout("unix", 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.Close()
+			}
+		}()
+		return nil, errors.Errorf("dial %s: no such file or directory", address)
+	}
 }
 
 func dialAddress(address string) string {