Copy grpc xDS client from grpc-go

Signed-off-by: Miek Gieben <miek@miek.nl>

plugin/traffic/xds/client.go

@@ -0,0 +1,105 @@
+/*
+ *
+ * Copyright 2019 gRPC 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 client implementation a full fledged gRPC client for the xDS API
+// used by the xds resolver and balancer implementations.
+package xds
+
+import (
+	"errors"
+	"fmt"
+	"sync"
+
+	"github.com/coredns/coredns/plugin/traffic/xds/bootstrap"
+
+	"google.golang.org/grpc"
+)
+
+// Options provides all parameters required for the creation of an xDS client.
+type Options struct {
+	// Config contains a fully populated bootstrap config. It is the
+	// responsibility of the caller to use some sane defaults here if the
+	// bootstrap process returned with certain fields left unspecified.
+	Config bootstrap.Config
+	// DialOpts contains dial options to be used when dialing the xDS server.
+	DialOpts []grpc.DialOption
+}
+
+// Client is a full fledged gRPC client which queries a set of discovery APIs
+// (collectively termed as xDS) on a remote management server, to discover
+// various dynamic resources. A single client object will be shared by the xds
+// resolver and balancer implementations.
+type Client struct {
+	opts Options
+	cc   *grpc.ClientConn // Connection to the xDS server
+	v2c  *v2Client        // Actual xDS client implementation using the v2 API
+
+	mu              sync.Mutex
+	serviceCallback func(ServiceUpdate, error)
+	ldsCancel       func()
+	rdsCancel       func()
+}
+
+// New returns a new xdsClient configured with opts.
+func New(opts Options) (*Client, error) {
+	switch {
+	case opts.Config.BalancerName == "":
+		return nil, errors.New("xds: no xds_server name provided in options")
+	case opts.Config.Creds == nil:
+		return nil, errors.New("xds: no credentials provided in options")
+	case opts.Config.NodeProto == nil:
+		return nil, errors.New("xds: no node_proto provided in options")
+	}
+
+	dopts := append([]grpc.DialOption{opts.Config.Creds}, opts.DialOpts...)
+	cc, err := grpc.Dial(opts.Config.BalancerName, dopts...)
+	if err != nil {
+		// An error from a non-blocking dial indicates something serious.
+		return nil, fmt.Errorf("xds: failed to dial balancer {%s}: %v", opts.Config.BalancerName, err)
+	}
+
+	c := &Client{
+		opts: opts,
+		cc:   cc,
+		v2c:  newV2Client(cc, opts.Config.NodeProto, nil), // todo re-add backoff (exponential)
+	}
+	return c, nil
+}
+
+// Close closes the gRPC connection to the xDS server.
+func (c *Client) Close() {
+	// TODO: Should we invoke the registered callbacks here with an error that
+	// the client is closed?
+	c.v2c.close()
+	c.cc.Close()
+}
+
+// ServiceUpdate contains update about the service.
+type ServiceUpdate struct {
+	Cluster string
+}
+
+// WatchCluster uses CDS to discover information about the provided clusterName.
+func (c *Client) WatchCluster(clusterName string, cdsCb func(CDSUpdate, error)) (cancel func()) {
+	return c.v2c.watchCDS(clusterName, cdsCb)
+}
+
+// WatchEDS watches the ghost.
+func (c *Client) WatchEDS(clusterName string, edsCb func(*EDSUpdate, error)) (cancel func()) {
+	return c.v2c.watchEDS(clusterName, edsCb)
+}