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* Copyright 2017 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
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
package grpc
import (
// ccResolverWrapper is a wrapper on top of cc for resolvers.
// It implements resolver.ClientConnection interface.
type ccResolverWrapper struct {
cc *ClientConn
resolver resolver.Resolver
addrCh chan []resolver.Address
scCh chan string
done chan struct{}
// split2 returns the values from strings.SplitN(s, sep, 2).
// If sep is not found, it returns "", s instead.
func split2(s, sep string) (string, string) {
spl := strings.SplitN(s, sep, 2)
if len(spl) < 2 {
return "", s
return spl[0], spl[1]
// parseTarget splits target into a struct containing scheme, authority and
// endpoint.
func parseTarget(target string) (ret resolver.Target) {
ret.Scheme, ret.Endpoint = split2(target, "://")
ret.Authority, ret.Endpoint = split2(ret.Endpoint, "/")
return ret
// newCCResolverWrapper parses for scheme and gets the resolver
// builder for this scheme. It then builds the resolver and starts the
// monitoring goroutine for it.
// This function could return nil, nil, in tests for old behaviors.
// TODO(bar) never return nil, nil when DNS becomes the default resolver.
func newCCResolverWrapper(cc *ClientConn) (*ccResolverWrapper, error) {
target := parseTarget(
grpclog.Infof("dialing to target with scheme: %q", target.Scheme)
rb := resolver.Get(target.Scheme)
if rb == nil {
// TODO(bar) return error when DNS becomes the default (implemented and
// registered by DNS package).
grpclog.Infof("could not get resolver for scheme: %q", target.Scheme)
return nil, nil
ccr := &ccResolverWrapper{
cc: cc,
addrCh: make(chan []resolver.Address, 1),
scCh: make(chan string, 1),
done: make(chan struct{}),
var err error
ccr.resolver, err = rb.Build(target, ccr, resolver.BuildOption{})
if err != nil {
return nil, err
go ccr.watcher()
return ccr, nil
// watcher processes address updates and service config updates sequencially.
// Otherwise, we need to resolve possible races between address and service
// config (e.g. they specify different balancer types).
func (ccr *ccResolverWrapper) watcher() {
for {
select {
case <-ccr.done:
select {
case addrs := <-ccr.addrCh:
grpclog.Infof("ccResolverWrapper: sending new addresses to balancer wrapper: %v", addrs)
// TODO(bar switching) this should never be nil. Pickfirst should be default.
if != nil {
// TODO(bar switching) create balancer if it's nil?, nil)
case sc := <-ccr.scCh:
grpclog.Infof("ccResolverWrapper: got new service config: %v", sc)
case <-ccr.done:
func (ccr *ccResolverWrapper) close() {
// NewAddress is called by the resolver implemenetion to send addresses to gRPC.
func (ccr *ccResolverWrapper) NewAddress(addrs []resolver.Address) {
select {
case <-ccr.addrCh:
ccr.addrCh <- addrs
// NewServiceConfig is called by the resolver implemenetion to send service
// configs to gPRC.
func (ccr *ccResolverWrapper) NewServiceConfig(sc string) {
select {
case <-ccr.scCh:
ccr.scCh <- sc