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client.go
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client.go
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// Copyright 2016 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 clientv3
import (
"errors"
"io/ioutil"
"log"
"net"
"net/url"
"strings"
"sync"
"time"
"github.com/coreos/etcd/etcdserver/api/v3rpc/rpctypes"
"golang.org/x/net/context"
"google.golang.org/grpc"
"google.golang.org/grpc/credentials"
"google.golang.org/grpc/metadata"
)
var (
ErrNoAvailableEndpoints = errors.New("etcdclient: no available endpoints")
)
// Client provides and manages an etcd v3 client session.
type Client struct {
Cluster
KV
Lease
Watcher
Auth
Maintenance
conn *grpc.ClientConn
cfg Config
creds *credentials.TransportAuthenticator
mu sync.RWMutex // protects connection selection and error list
errors []error // errors passed to retryConnection
ctx context.Context
cancel context.CancelFunc
// fields below are managed by connMonitor
// reconnc accepts writes which signal the client should reconnect
reconnc chan error
// newconnc is closed on successful connect and set to a fresh channel
newconnc chan struct{}
lastConnErr error
}
// New creates a new etcdv3 client from a given configuration.
func New(cfg Config) (*Client, error) {
if cfg.RetryDialer == nil {
cfg.RetryDialer = dialEndpointList
}
if len(cfg.Endpoints) == 0 {
return nil, ErrNoAvailableEndpoints
}
return newClient(&cfg)
}
// NewFromURL creates a new etcdv3 client from a URL.
func NewFromURL(url string) (*Client, error) {
return New(Config{Endpoints: []string{url}})
}
// NewFromConfigFile creates a new etcdv3 client from a configuration file.
func NewFromConfigFile(path string) (*Client, error) {
cfg, err := configFromFile(path)
if err != nil {
return nil, err
}
return New(*cfg)
}
// Close shuts down the client's etcd connections.
func (c *Client) Close() error {
c.mu.Lock()
defer c.mu.Unlock()
if c.cancel == nil {
return nil
}
c.cancel()
c.cancel = nil
connc := c.newconnc
c.mu.Unlock()
c.connStartRetry(nil)
c.Watcher.Close()
c.Lease.Close()
<-connc
c.mu.Lock()
if c.lastConnErr != c.ctx.Err() {
return c.lastConnErr
}
return nil
}
// Ctx is a context for "out of band" messages (e.g., for sending
// "clean up" message when another context is canceled). It is
// canceled on client Close().
func (c *Client) Ctx() context.Context { return c.ctx }
// Endpoints lists the registered endpoints for the client.
func (c *Client) Endpoints() []string { return c.cfg.Endpoints }
// Errors returns all errors that have been observed since called last.
func (c *Client) Errors() (errs []error) {
c.mu.Lock()
defer c.mu.Unlock()
errs = c.errors
c.errors = nil
return errs
}
// Dial establishes a connection for a given endpoint using the client's config
func (c *Client) Dial(endpoint string) (*grpc.ClientConn, error) {
opts := []grpc.DialOption{
grpc.WithBlock(),
grpc.WithTimeout(c.cfg.DialTimeout),
}
if c.creds != nil {
opts = append(opts, grpc.WithTransportCredentials(*c.creds))
} else {
opts = append(opts, grpc.WithInsecure())
}
proto := "tcp"
if url, uerr := url.Parse(endpoint); uerr == nil && url.Scheme == "unix" {
proto = "unix"
// strip unix:// prefix so certs work
endpoint = url.Host
}
f := func(a string, t time.Duration) (net.Conn, error) {
select {
case <-c.ctx.Done():
return nil, c.ctx.Err()
default:
}
return net.DialTimeout(proto, a, t)
}
opts = append(opts, grpc.WithDialer(f))
conn, err := grpc.Dial(endpoint, opts...)
if err != nil {
return nil, err
}
return conn, nil
}
// WithRequireLeader requires client requests to only succeed
// when the cluster has a leader.
func WithRequireLeader(ctx context.Context) context.Context {
md := metadata.Pairs(rpctypes.MetadataRequireLeaderKey, rpctypes.MetadataHasLeader)
return metadata.NewContext(ctx, md)
}
func newClient(cfg *Config) (*Client, error) {
if cfg == nil {
cfg = &Config{RetryDialer: dialEndpointList}
}
var creds *credentials.TransportAuthenticator
if cfg.TLS != nil {
c := credentials.NewTLS(cfg.TLS)
creds = &c
}
// use a temporary skeleton client to bootstrap first connection
ctx, cancel := context.WithCancel(context.TODO())
conn, err := cfg.RetryDialer(&Client{cfg: *cfg, creds: creds, ctx: ctx})
if err != nil {
return nil, err
}
client := &Client{
conn: conn,
cfg: *cfg,
creds: creds,
ctx: ctx,
cancel: cancel,
reconnc: make(chan error),
newconnc: make(chan struct{}),
}
go client.connMonitor()
client.Cluster = NewCluster(client)
client.KV = NewKV(client)
client.Lease = NewLease(client)
client.Watcher = NewWatcher(client)
client.Auth = NewAuth(client)
client.Maintenance = NewMaintenance(client)
if cfg.Logger != nil {
logger.Set(cfg.Logger)
} else {
// disable client side grpc by default
logger.Set(log.New(ioutil.Discard, "", 0))
}
return client, nil
}
// ActiveConnection returns the current in-use connection
func (c *Client) ActiveConnection() *grpc.ClientConn {
c.mu.RLock()
defer c.mu.RUnlock()
return c.conn
}
// retryConnection establishes a new connection
func (c *Client) retryConnection(err error) (newConn *grpc.ClientConn, dialErr error) {
c.mu.Lock()
defer c.mu.Unlock()
if err != nil {
c.errors = append(c.errors, err)
}
if c.conn != nil {
c.conn.Close()
if st, _ := c.conn.State(); st != grpc.Shutdown {
// wait so grpc doesn't leak sleeping goroutines
c.conn.WaitForStateChange(context.Background(), st)
}
}
if c.cancel == nil {
// client has called Close() so don't try to dial out
return nil, c.ctx.Err()
}
c.conn, dialErr = c.cfg.RetryDialer(c)
if dialErr != nil {
c.errors = append(c.errors, dialErr)
}
return c.conn, dialErr
}
// connStartRetry schedules a reconnect if one is not already running
func (c *Client) connStartRetry(err error) {
select {
case c.reconnc <- err:
default:
}
}
// connWait waits for a reconnect to be processed
func (c *Client) connWait(ctx context.Context, err error) (*grpc.ClientConn, error) {
c.mu.Lock()
ch := c.newconnc
c.mu.Unlock()
c.connStartRetry(err)
select {
case <-ctx.Done():
return nil, ctx.Err()
case <-ch:
}
c.mu.Lock()
defer c.mu.Unlock()
return c.conn, c.lastConnErr
}
// connMonitor monitors the connection and handles retries
func (c *Client) connMonitor() {
var err error
for {
select {
case err = <-c.reconnc:
case <-c.ctx.Done():
_, err = c.retryConnection(c.ctx.Err())
c.mu.Lock()
c.lastConnErr = err
close(c.newconnc)
c.mu.Unlock()
return
}
conn, connErr := c.retryConnection(err)
c.mu.Lock()
c.lastConnErr = connErr
c.conn = conn
close(c.newconnc)
c.newconnc = make(chan struct{})
c.mu.Unlock()
}
}
// dialEndpointList attempts to connect to each endpoint in order until a
// connection is established.
func dialEndpointList(c *Client) (*grpc.ClientConn, error) {
var err error
for _, ep := range c.Endpoints() {
conn, curErr := c.Dial(ep)
if curErr != nil {
err = curErr
} else {
return conn, nil
}
}
return nil, err
}
// isHaltErr returns true if the given error and context indicate no forward
// progress can be made, even after reconnecting.
func isHaltErr(ctx context.Context, err error) bool {
isRPCError := strings.HasPrefix(grpc.ErrorDesc(err), "etcdserver: ")
return isRPCError || ctx.Err() != nil
}