Add initial containerd *Client

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

client.go

@@ -0,0 +1,61 @@
+package containerd
+
+import (
+	"context"
+	"io/ioutil"
+	"log"
+	"time"
+
+	"github.com/containerd/containerd/api/services/containers"
+	"github.com/pkg/errors"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/grpclog"
+)
+
+// New returns a new containerd client that is connected to the containerd
+// instance provided by address
+func New(address string) (*Client, error) {
+	// reset the grpc logger so that it does not output in the STDIO of the calling process
+	grpclog.SetLogger(log.New(ioutil.Discard, "", log.LstdFlags))
+
+	opts := []grpc.DialOption{
+		grpc.WithInsecure(),
+		grpc.WithTimeout(100 * time.Second),
+		grpc.WithDialer(dialer),
+	}
+	conn, err := grpc.Dial(dialAddress(address), opts...)
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to dial %q", address)
+	}
+	return &Client{
+		conn: conn,
+	}, nil
+}
+
+// Client is the client to interact with containerd and its various services
+// using a uniform interface
+type Client struct {
+	conn *grpc.ClientConn
+}
+
+// Containers returns all containers created in containerd
+func (c *Client) Containers(ctx context.Context) ([]*Container, error) {
+	r, err := c.containers().List(ctx, &containers.ListContainersRequest{})
+	if err != nil {
+		return nil, err
+	}
+	var out []*Container
+	for _, container := range r.Containers {
+		out = append(out, containerFromProto(c, container))
+	}
+	return out, nil
+}
+
+// Close closes the clients connection to containerd
+func (c *Client) Close() error {
+	return c.conn.Close()
+}
+
+func (c *Client) containers() containers.ContainersClient {
+	return containers.NewContainersClient(c.conn)
+}