clientv3/balancer: initial commit

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

clientv3/balancer/balancer.go

@@ -0,0 +1,275 @@
+// Copyright 2018 The etcd 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 balancer
+
+import (
+	"fmt"
+	"sync"
+
+	"github.com/coreos/etcd/clientv3/balancer/picker"
+
+	"go.uber.org/zap"
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/resolver"
+	_ "google.golang.org/grpc/resolver/dns"         // register DNS resolver
+	_ "google.golang.org/grpc/resolver/passthrough" // register passthrough resolver
+)
+
+// Balancer defines client balancer interface.
+type Balancer interface {
+	// Builder is called at the beginning to initialize sub-connection states and picker.
+	balancer.Builder
+
+	// Balancer is called on specified client connection. Client initiates gRPC
+	// connection with "grpc.Dial(addr, grpc.WithBalancerName)", and then those resolved
+	// addresses are passed to "grpc/balancer.Balancer.HandleResolvedAddrs".
+	// For each resolved address, balancer calls "balancer.ClientConn.NewSubConn".
+	// "grpc/balancer.Balancer.HandleSubConnStateChange" is called when connectivity state
+	// changes, thus requires failover logic in this method.
+	balancer.Balancer
+
+	// Picker calls "Pick" for every client request.
+	picker.Picker
+
+	// SetEndpoints updates client's endpoints.
+	SetEndpoints(eps ...string)
+}
+
+type baseBalancer struct {
+	policy picker.Policy
+	name   string
+	lg     *zap.Logger
+
+	mu sync.RWMutex
+
+	eps []string
+
+	addrToSc map[resolver.Address]balancer.SubConn
+	scToAddr map[balancer.SubConn]resolver.Address
+	scToSt   map[balancer.SubConn]connectivity.State
+
+	currrentConn balancer.ClientConn
+	currentState connectivity.State
+	csEvltr      *connectivityStateEvaluator
+
+	picker.Picker
+}
+
+// New returns a new balancer from specified picker policy.
+func New(cfg Config) Balancer {
+	bb := &baseBalancer{
+		policy: cfg.Policy,
+		name:   cfg.Policy.String(),
+		lg:     cfg.Logger,
+
+		eps: cfg.Endpoints,
+
+		addrToSc: make(map[resolver.Address]balancer.SubConn),
+		scToAddr: make(map[balancer.SubConn]resolver.Address),
+		scToSt:   make(map[balancer.SubConn]connectivity.State),
+
+		currrentConn: nil,
+		csEvltr:      &connectivityStateEvaluator{},
+
+		// initialize picker always returns "ErrNoSubConnAvailable"
+		Picker: picker.NewErr(balancer.ErrNoSubConnAvailable),
+	}
+	if cfg.Name != "" {
+		bb.name = cfg.Name
+	}
+	if bb.lg == nil {
+		bb.lg = zap.NewNop()
+	}
+
+	balancer.Register(bb)
+	bb.lg.Info(
+		"registered balancer",
+		zap.String("policy", bb.policy.String()),
+		zap.String("name", bb.name),
+	)
+	return bb
+}
+
+// Name implements "grpc/balancer.Builder" interface.
+func (bb *baseBalancer) Name() string { return bb.name }
+
+// Build implements "grpc/balancer.Builder" interface.
+// Build is called initially when creating "ccBalancerWrapper".
+// "grpc.Dial" is called to this client connection.
+// Then, resolved addreses will be handled via "HandleResolvedAddrs".
+func (bb *baseBalancer) Build(cc balancer.ClientConn, opt balancer.BuildOptions) balancer.Balancer {
+	// TODO: support multiple connections
+	bb.mu.Lock()
+	bb.currrentConn = cc
+	bb.mu.Unlock()
+
+	bb.lg.Info(
+		"built balancer",
+		zap.String("policy", bb.policy.String()),
+		zap.String("resolver-target", cc.Target()),
+	)
+	return bb
+}
+
+// HandleResolvedAddrs implements "grpc/balancer.Balancer" interface.
+// gRPC sends initial or updated resolved addresses from "Build".
+func (bb *baseBalancer) HandleResolvedAddrs(addrs []resolver.Address, err error) {
+	if err != nil {
+		bb.lg.Warn("HandleResolvedAddrs called with error", zap.Error(err))
+		return
+	}
+	bb.lg.Info("resolved", zap.Strings("addresses", addrsToStrings(addrs)))
+
+	bb.mu.Lock()
+	defer bb.mu.Unlock()
+
+	resolved := make(map[resolver.Address]struct{})
+	for _, addr := range addrs {
+		resolved[addr] = struct{}{}
+		if _, ok := bb.addrToSc[addr]; !ok {
+			sc, err := bb.currrentConn.NewSubConn([]resolver.Address{addr}, balancer.NewSubConnOptions{})
+			if err != nil {
+				bb.lg.Warn("NewSubConn failed", zap.Error(err), zap.String("address", addr.Addr))
+				continue
+			}
+			bb.addrToSc[addr] = sc
+			bb.scToAddr[sc] = addr
+			bb.scToSt[sc] = connectivity.Idle
+			sc.Connect()
+		}
+	}
+
+	for addr, sc := range bb.addrToSc {
+		if _, ok := resolved[addr]; !ok {
+			// was removed by resolver or failed to create subconn
+			bb.currrentConn.RemoveSubConn(sc)
+			delete(bb.addrToSc, addr)
+
+			bb.lg.Info(
+				"removed subconn",
+				zap.String("address", addr.Addr),
+				zap.String("subconn", scToString(sc)),
+			)
+
+			// Keep the state of this sc in bb.scToSt until sc's state becomes Shutdown.
+			// The entry will be deleted in HandleSubConnStateChange.
+			// (DO NOT) delete(bb.scToAddr, sc)
+			// (DO NOT) delete(bb.scToSt, sc)
+		}
+	}
+}
+
+// HandleSubConnStateChange implements "grpc/balancer.Balancer" interface.
+func (bb *baseBalancer) HandleSubConnStateChange(sc balancer.SubConn, s connectivity.State) {
+	bb.mu.Lock()
+	defer bb.mu.Unlock()
+
+	old, ok := bb.scToSt[sc]
+	if !ok {
+		bb.lg.Warn(
+			"state change for an unknown subconn",
+			zap.String("subconn", scToString(sc)),
+			zap.String("state", s.String()),
+		)
+		return
+	}
+
+	bb.lg.Info(
+		"state changed",
+		zap.Bool("connected", s == connectivity.Ready),
+		zap.String("subconn", scToString(sc)),
+		zap.String("address", bb.scToAddr[sc].Addr),
+		zap.String("old-state", old.String()),
+		zap.String("new-state", s.String()),
+	)
+
+	bb.scToSt[sc] = s
+	switch s {
+	case connectivity.Idle:
+		sc.Connect()
+	case connectivity.Shutdown:
+		// When an address was removed by resolver, b called RemoveSubConn but
+		// kept the sc's state in scToSt. Remove state for this sc here.
+		delete(bb.scToAddr, sc)
+		delete(bb.scToSt, sc)
+	}
+
+	oldAggrState := bb.currentState
+	bb.currentState = bb.csEvltr.recordTransition(old, s)
+
+	// Regenerate picker when one of the following happens:
+	//  - this sc became ready from not-ready
+	//  - this sc became not-ready from ready
+	//  - the aggregated state of balancer became TransientFailure from non-TransientFailure
+	//  - the aggregated state of balancer became non-TransientFailure from TransientFailure
+	if (s == connectivity.Ready) != (old == connectivity.Ready) ||
+		(bb.currentState == connectivity.TransientFailure) != (oldAggrState == connectivity.TransientFailure) {
+		bb.regeneratePicker()
+	}
+
+	bb.currrentConn.UpdateBalancerState(bb.currentState, bb.Picker)
+	return
+}
+
+func (bb *baseBalancer) regeneratePicker() {
+	if bb.currentState == connectivity.TransientFailure {
+		bb.Picker = picker.NewErr(balancer.ErrTransientFailure)
+		return
+	}
+
+	// only pass ready subconns to picker
+	scs := make([]balancer.SubConn, 0)
+	addrToSc := make(map[resolver.Address]balancer.SubConn)
+	scToAddr := make(map[balancer.SubConn]resolver.Address)
+	for addr, sc := range bb.addrToSc {
+		if st, ok := bb.scToSt[sc]; ok && st == connectivity.Ready {
+			scs = append(scs, sc)
+			addrToSc[addr] = sc
+			scToAddr[sc] = addr
+		}
+	}
+
+	switch bb.policy {
+	case picker.RoundrobinBalanced:
+		bb.Picker = picker.NewRoundrobinBalanced(bb.lg, scs, addrToSc, scToAddr)
+
+	default:
+		panic(fmt.Errorf("invalid balancer picker policy (%d)", bb.policy))
+	}
+
+	bb.lg.Info(
+		"generated picker",
+		zap.String("policy", bb.policy.String()),
+		zap.Strings("subconn-ready", scsToStrings(addrToSc)),
+		zap.Int("subconn-size", len(addrToSc)),
+	)
+}
+
+// SetEndpoints updates client's endpoints.
+// TODO: implement this
+func (bb *baseBalancer) SetEndpoints(eps ...string) {
+	addrs := epsToAddrs(eps...)
+	bb.mu.Lock()
+	bb.Picker.UpdateAddrs(addrs)
+	bb.mu.Unlock()
+}
+
+// Close implements "grpc/balancer.Balancer" interface.
+// Close is a nop because base balancer doesn't have internal state to clean up,
+// and it doesn't need to call RemoveSubConn for the SubConns.
+func (bb *baseBalancer) Close() {
+	// TODO
+}

clientv3/balancer/config.go

@@ -0,0 +1,39 @@
+// Copyright 2018 The etcd 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 balancer
+
+import (
+	"github.com/coreos/etcd/clientv3/balancer/picker"
+
+	"go.uber.org/zap"
+)
+
+// Config defines balancer configurations.
+type Config struct {
+	// Policy configures balancer policy.
+	Policy picker.Policy
+
+	// Name defines an additional name for balancer.
+	// Useful for balancer testing to avoid register conflicts.
+	// If empty, defaults to policy name.
+	Name string
+
+	// Logger configures balancer logging.
+	// If nil, logs are discarded.
+	Logger *zap.Logger
+
+	// Endpoints is a list of server endpoints.
+	Endpoints []string
+}

clientv3/balancer/connectivity.go

@@ -0,0 +1,58 @@
+// Copyright 2018 The etcd 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 balancer
+
+import "google.golang.org/grpc/connectivity"
+
+// connectivityStateEvaluator gets updated by addrConns when their
+// states transition, based on which it evaluates the state of
+// ClientConn.
+type connectivityStateEvaluator struct {
+	numReady            uint64 // Number of addrConns in ready state.
+	numConnecting       uint64 // Number of addrConns in connecting state.
+	numTransientFailure uint64 // Number of addrConns in transientFailure.
+}
+
+// recordTransition records state change happening in every subConn and based on
+// that it evaluates what aggregated state should be.
+// It can only transition between Ready, Connecting and TransientFailure. Other states,
+// Idle and Shutdown are transitioned into by ClientConn; in the beginning of the connection
+// before any subConn is created ClientConn is in idle state. In the end when ClientConn
+// closes it is in Shutdown state.
+//
+// recordTransition should only be called synchronously from the same goroutine.
+func (cse *connectivityStateEvaluator) recordTransition(oldState, newState connectivity.State) connectivity.State {
+	// Update counters.
+	for idx, state := range []connectivity.State{oldState, newState} {
+		updateVal := 2*uint64(idx) - 1 // -1 for oldState and +1 for new.
+		switch state {
+		case connectivity.Ready:
+			cse.numReady += updateVal
+		case connectivity.Connecting:
+			cse.numConnecting += updateVal
+		case connectivity.TransientFailure:
+			cse.numTransientFailure += updateVal
+		}
+	}
+
+	// Evaluate.
+	if cse.numReady > 0 {
+		return connectivity.Ready
+	}
+	if cse.numConnecting > 0 {
+		return connectivity.Connecting
+	}
+	return connectivity.TransientFailure
+}

clientv3/balancer/grpc1.7-health_test.go

@@ -30,7 +30,7 @@ import (
 
 var endpoints = []string{"localhost:2379", "localhost:22379", "localhost:32379"}
 
-func TestBalancerGetUnblocking(t *testing.T) {
+func TestOldHealthBalancerGetUnblocking(t *testing.T) {
 	hb := NewGRPC17Health(endpoints, minHealthRetryDuration, func(ep string, dopts ...grpc.DialOption) (*grpc.ClientConn, error) { return nil, nil })
 	defer hb.Close()
 	if addrs := <-hb.Notify(); len(addrs) != len(endpoints) {
@@ -74,7 +74,7 @@ func TestBalancerGetUnblocking(t *testing.T) {
 	}
 }
 
-func TestBalancerGetBlocking(t *testing.T) {
+func TestOldHealthBalancerGetBlocking(t *testing.T) {
 	hb := NewGRPC17Health(endpoints, minHealthRetryDuration, func(ep string, dopts ...grpc.DialOption) (*grpc.ClientConn, error) { return nil, nil })
 	defer hb.Close()
 	if addrs := <-hb.Notify(); len(addrs) != len(endpoints) {
@@ -131,9 +131,9 @@ func TestBalancerGetBlocking(t *testing.T) {
 	}
 }
 
-// TestHealthBalancerGraylist checks one endpoint is tried after the other
+// TestOldHealthBalancerGraylist checks one endpoint is tried after the other
 // due to gray listing.
-func TestHealthBalancerGraylist(t *testing.T) {
+func TestOldHealthBalancerGraylist(t *testing.T) {
 	var wg sync.WaitGroup
 	// Use 3 endpoints so gray list doesn't fallback to all connections
 	// after failing on 2 endpoints.
@@ -192,7 +192,7 @@ func TestHealthBalancerGraylist(t *testing.T) {
 // TestBalancerDoNotBlockOnClose ensures that balancer and grpc don't deadlock each other
 // due to rapid open/close conn. The deadlock causes balancer.Close() to block forever.
 // See issue: https://github.com/coreos/etcd/issues/7283 for more detail.
-func TestBalancerDoNotBlockOnClose(t *testing.T) {
+func TestOldHealthBalancerDoNotBlockOnClose(t *testing.T) {
 	defer testutil.AfterTest(t)
 
 	kcl := newKillConnListener(t, 3)

clientv3/balancer/picker/doc.go

@@ -0,0 +1,16 @@
+// Copyright 2018 The etcd 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 picker defines/implements client balancer picker policy.
+package picker

clientv3/balancer/picker/err.go

@@ -0,0 +1,39 @@
+// Copyright 2018 The etcd 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 picker
+
+import (
+	"context"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/resolver"
+)
+
+// NewErr returns a picker that always returns err on "Pick".
+func NewErr(err error) Picker {
+	return &errPicker{err: err}
+}
+
+type errPicker struct {
+	err error
+}
+
+func (p *errPicker) Pick(context.Context, balancer.PickOptions) (balancer.SubConn, func(balancer.DoneInfo), error) {
+	return nil, nil, p.err
+}
+
+func (p *errPicker) UpdateAddrs(addrs []resolver.Address) {
+	return
+}

clientv3/balancer/picker/picker.go

@@ -0,0 +1,31 @@
+// Copyright 2018 The etcd 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 picker
+
+import (
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/resolver"
+)
+
+// Picker defines balancer Picker methods.
+type Picker interface {
+	balancer.Picker
+
+	// UpdateAddrs updates current endpoints in picker.
+	// Used when endpoints are updated manually.
+	// TODO: handle resolver target change
+	// TODO: handle resolved addresses change
+	UpdateAddrs(addrs []resolver.Address)
+}

clientv3/balancer/picker/picker_policy.go

@@ -0,0 +1,49 @@
+// Copyright 2018 The etcd 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 picker
+
+import "fmt"
+
+// Policy defines balancer picker policy.
+type Policy uint8
+
+const (
+	// TODO: custom picker is not supported yet.
+	// custom defines custom balancer picker.
+	custom Policy = iota
+
+	// RoundrobinBalanced balance loads over multiple endpoints
+	// and implements failover in roundrobin fashion.
+	RoundrobinBalanced Policy = iota
+
+	// TODO: only send loads to pinned address "RoundrobinFailover"
+	// just like how 3.3 client works
+	//
+	// TODO: priotize leader
+	// TODO: health-check
+	// TODO: weighted roundrobin
+	// TODO: power of two random choice
+)
+
+func (p Policy) String() string {
+	switch p {
+	case custom:
+		panic("'custom' picker policy is not supported yet")
+	case RoundrobinBalanced:
+		return "etcd-client-roundrobin-balanced"
+	default:
+		panic(fmt.Errorf("invalid balancer picker policy (%d)", p))
+	}
+}

clientv3/balancer/picker/roundrobin_balanced.go

@@ -0,0 +1,105 @@
+// Copyright 2018 The etcd 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 picker
+
+import (
+	"context"
+	"sync"
+
+	"go.uber.org/zap"
+	"go.uber.org/zap/zapcore"
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/resolver"
+)
+
+// NewRoundrobinBalanced returns a new roundrobin balanced picker.
+func NewRoundrobinBalanced(
+	lg *zap.Logger,
+	scs []balancer.SubConn,
+	addrToSc map[resolver.Address]balancer.SubConn,
+	scToAddr map[balancer.SubConn]resolver.Address,
+) Picker {
+	return &rrBalanced{
+		lg:       lg,
+		scs:      scs,
+		addrToSc: addrToSc,
+		scToAddr: scToAddr,
+	}
+}
+
+type rrBalanced struct {
+	lg *zap.Logger
+
+	mu   sync.RWMutex
+	next int
+	scs  []balancer.SubConn
+
+	addrToSc map[resolver.Address]balancer.SubConn
+	scToAddr map[balancer.SubConn]resolver.Address
+
+	updateAddrs func(addrs []resolver.Address)
+}
+
+// Pick is called for every client request.
+func (rb *rrBalanced) Pick(ctx context.Context, opts balancer.PickOptions) (balancer.SubConn, func(balancer.DoneInfo), error) {
+	rb.mu.RLock()
+	n := len(rb.scs)
+	rb.mu.RUnlock()
+	if n == 0 {
+		return nil, nil, balancer.ErrNoSubConnAvailable
+	}
+
+	rb.mu.Lock()
+	cur := rb.next
+	sc := rb.scs[cur]
+	picked := rb.scToAddr[sc].Addr
+	rb.next = (rb.next + 1) % len(rb.scs)
+	rb.mu.Unlock()
+
+	rb.lg.Debug(
+		"picked",
+		zap.String("address", picked),
+		zap.Int("subconn-index", cur),
+		zap.Int("subconn-size", n),
+	)
+
+	doneFunc := func(info balancer.DoneInfo) {
+		// TODO: error handling?
+		fss := []zapcore.Field{
+			zap.Error(info.Err),
+			zap.String("address", picked),
+			zap.Bool("success", info.Err == nil),
+			zap.Bool("bytes-sent", info.BytesSent),
+			zap.Bool("bytes-received", info.BytesReceived),
+		}
+		if info.Err == nil {
+			rb.lg.Debug("balancer done", fss...)
+		} else {
+			rb.lg.Warn("balancer failed", fss...)
+		}
+	}
+	return sc, doneFunc, nil
+}
+
+// UpdateAddrs
+// TODO: implement this
+func (rb *rrBalanced) UpdateAddrs(addrs []resolver.Address) {
+	rb.mu.Lock()
+	// close all resolved sub-connections first
+	for _, sc := range rb.scs {
+		sc.UpdateAddresses([]resolver.Address{})
+	}
+	rb.mu.Unlock()
+}

clientv3/balancer/utils.go

@@ -0,0 +1,45 @@
+package balancer
+
+import (
+	"fmt"
+	"net/url"
+	"sort"
+
+	"google.golang.org/grpc/balancer"
+	"google.golang.org/grpc/resolver"
+)
+
+func scToString(sc balancer.SubConn) string {
+	return fmt.Sprintf("%p", sc)
+}
+
+func scsToStrings(scs map[resolver.Address]balancer.SubConn) (ss []string) {
+	ss = make([]string, 0, len(scs))
+	for a, sc := range scs {
+		ss = append(ss, fmt.Sprintf("%s (%s)", a.Addr, scToString(sc)))
+	}
+	sort.Strings(ss)
+	return ss
+}
+
+func addrsToStrings(addrs []resolver.Address) (ss []string) {
+	ss = make([]string, len(addrs))
+	for i := range addrs {
+		ss[i] = addrs[i].Addr
+	}
+	sort.Strings(ss)
+	return ss
+}
+
+func epsToAddrs(eps ...string) (addrs []resolver.Address) {
+	addrs = make([]resolver.Address, 0, len(eps))
+	for _, ep := range eps {
+		u, err := url.Parse(ep)
+		if err != nil {
+			addrs = append(addrs, resolver.Address{Addr: ep, Type: resolver.Backend})
+			continue
+		}
+		addrs = append(addrs, resolver.Address{Addr: u.Host, Type: resolver.Backend})
+	}
+	return addrs
+}

clientv3/balancer/utils_test.go

@@ -0,0 +1,20 @@
+package balancer
+
+import (
+	"reflect"
+	"testing"
+
+	"google.golang.org/grpc/resolver"
+)
+
+func Test_epsToAddrs(t *testing.T) {
+	eps := []string{"https://example.com:2379", "127.0.0.1:2379"}
+	exp := []resolver.Address{
+		{Addr: "example.com:2379", Type: resolver.Backend},
+		{Addr: "127.0.0.1:2379", Type: resolver.Backend},
+	}
+	rs := epsToAddrs(eps...)
+	if !reflect.DeepEqual(rs, exp) {
+		t.Fatalf("expected %v, got %v", exp, rs)
+	}
+}