Add support for proxy plugins in configuration

Signed-off-by: Derek McGowan <derek@mcgstyle.net>

services/server/server.go

@@ -26,19 +26,26 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
+	"sync"
+	"time"
 
 	"github.com/boltdb/bolt"
+	csapi "github.com/containerd/containerd/api/services/content/v1"
+	ssapi "github.com/containerd/containerd/api/services/snapshots/v1"
 	"github.com/containerd/containerd/content"
 	"github.com/containerd/containerd/content/local"
+	csproxy "github.com/containerd/containerd/content/proxy"
+	"github.com/containerd/containerd/defaults"
 	"github.com/containerd/containerd/events/exchange"
 	"github.com/containerd/containerd/log"
 	"github.com/containerd/containerd/metadata"
+	"github.com/containerd/containerd/pkg/dialer"
 	"github.com/containerd/containerd/plugin"
 	"github.com/containerd/containerd/snapshots"
+	ssproxy "github.com/containerd/containerd/snapshots/proxy"
 	metrics "github.com/docker/go-metrics"
 	grpc_prometheus "github.com/grpc-ecosystem/go-grpc-prometheus"
 	"github.com/pkg/errors"
-
 	"google.golang.org/grpc"
 )
 
@@ -62,7 +69,7 @@ func New(ctx context.Context, config *Config) (*Server, error) {
 	if err := apply(ctx, config); err != nil {
 		return nil, err
 	}
-	plugins, err := LoadPlugins(config)
+	plugins, err := LoadPlugins(ctx, config)
 	if err != nil {
 		return nil, err
 	}
@@ -204,7 +211,7 @@ func (s *Server) Stop() {
 
 // LoadPlugins loads all plugins into containerd and generates an ordered graph
 // of all plugins.
-func LoadPlugins(config *Config) ([]*plugin.Registration, error) {
+func LoadPlugins(ctx context.Context, config *Config) ([]*plugin.Registration, error) {
 	// load all plugins into containerd
 	if err := plugin.Load(filepath.Join(config.Root, "plugins")); err != nil {
 		return nil, err
@@ -265,10 +272,85 @@ func LoadPlugins(config *Config) ([]*plugin.Registration, error) {
 		},
 	})
 
+	clients := &proxyClients{}
+	for name, pp := range config.ProxyPlugins {
+		var (
+			t plugin.Type
+			f func(*grpc.ClientConn) interface{}
+
+			address = pp.Address
+		)
+
+		switch pp.Type {
+		case string(plugin.SnapshotPlugin), "snapshot":
+			t = plugin.SnapshotPlugin
+			ssname := name
+			f = func(conn *grpc.ClientConn) interface{} {
+				return ssproxy.NewSnapshotter(ssapi.NewSnapshotsClient(conn), ssname)
+			}
+
+		case string(plugin.ContentPlugin), "content":
+			t = plugin.ContentPlugin
+			f = func(conn *grpc.ClientConn) interface{} {
+				return csproxy.NewContentStore(csapi.NewContentClient(conn))
+			}
+		default:
+			log.G(ctx).WithField("type", pp.Type).Warn("unknown proxy plugin type")
+		}
+
+		plugin.Register(&plugin.Registration{
+			Type: t,
+			ID:   name,
+			InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+				ic.Meta.Exports["address"] = address
+				conn, err := clients.getClient(address)
+				if err != nil {
+					return nil, err
+				}
+				return f(conn), nil
+			},
+		})
+
+	}
+
 	// return the ordered graph for plugins
 	return plugin.Graph(config.DisabledPlugins), nil
 }
 
+type proxyClients struct {
+	m       sync.Mutex
+	clients map[string]*grpc.ClientConn
+}
+
+func (pc *proxyClients) getClient(address string) (*grpc.ClientConn, error) {
+	pc.m.Lock()
+	defer pc.m.Unlock()
+	if pc.clients == nil {
+		pc.clients = map[string]*grpc.ClientConn{}
+	} else if c, ok := pc.clients[address]; ok {
+		return c, nil
+	}
+
+	gopts := []grpc.DialOption{
+		grpc.WithInsecure(),
+		grpc.WithBackoffMaxDelay(3 * time.Second),
+		grpc.WithDialer(dialer.Dialer),
+
+		// TODO(stevvooe): We may need to allow configuration of this on the client.
+		grpc.WithDefaultCallOptions(grpc.MaxCallRecvMsgSize(defaults.DefaultMaxRecvMsgSize)),
+		grpc.WithDefaultCallOptions(grpc.MaxCallSendMsgSize(defaults.DefaultMaxSendMsgSize)),
+	}
+
+	conn, err := grpc.Dial(dialer.DialAddress(address), gopts...)
+	if err != nil {
+		return nil, errors.Wrapf(err, "failed to dial %q", address)
+	}
+
+	pc.clients[address] = conn
+
+	return conn, nil
+}
+
 func trapClosedConnErr(err error) error {
 	if err == nil {
 		return nil