Add dialer for events service

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

runtime/v2/shim/dialer.go

@@ -0,0 +1,87 @@
+/*
+   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 shim
+
+import (
+	"net"
+	"sync"
+
+	v1 "github.com/containerd/containerd/api/services/ttrpc/events/v1"
+	"github.com/containerd/ttrpc"
+	"github.com/pkg/errors"
+)
+
+type dialConnect func() (net.Conn, error)
+
+var errDialerClosed = errors.New("events dialer is closed")
+
+func newDialier(newFn dialConnect) *dialer {
+	return &dialer{
+		newFn: newFn,
+	}
+}
+
+type dialer struct {
+	mu sync.Mutex
+
+	newFn   dialConnect
+	service v1.EventsService
+	conn    net.Conn
+	closed  bool
+}
+
+func (d *dialer) Get() (v1.EventsService, error) {
+	d.mu.Lock()
+	defer d.mu.Unlock()
+
+	if d.closed {
+		return nil, errDialerClosed
+	}
+	if d.service == nil {
+		conn, err := d.newFn()
+		if err != nil {
+			return nil, err
+		}
+		d.conn = conn
+		d.service = v1.NewEventsClient(ttrpc.NewClient(conn))
+	}
+	return d.service, nil
+}
+
+func (d *dialer) Put(err error) {
+	if err != nil {
+		d.mu.Lock()
+		d.conn.Close()
+		d.service = nil
+		d.mu.Unlock()
+	}
+}
+
+func (d *dialer) Close() (err error) {
+	d.mu.Lock()
+	if d.closed {
+		return errDialerClosed
+	}
+	if d.conn != nil {
+		err = d.conn.Close()
+	}
+	d.service = nil
+	d.closed = true
+	d.mu.Unlock()
+
+	return err
+}