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client.go
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client.go
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// Copyright 2015 CoreOS, Inc.
//
// 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
import (
"errors"
"fmt"
"io/ioutil"
"math/rand"
"net"
"net/http"
"net/url"
"reflect"
"sort"
"sync"
"time"
"golang.org/x/net/context"
)
var (
ErrNoEndpoints = errors.New("client: no endpoints available")
ErrTooManyRedirects = errors.New("client: too many redirects")
ErrClusterUnavailable = errors.New("client: etcd cluster is unavailable or misconfigured")
errTooManyRedirectChecks = errors.New("client: too many redirect checks")
)
var DefaultRequestTimeout = 5 * time.Second
var DefaultTransport CancelableTransport = &http.Transport{
Proxy: http.ProxyFromEnvironment,
Dial: (&net.Dialer{
Timeout: 30 * time.Second,
KeepAlive: 30 * time.Second,
}).Dial,
TLSHandshakeTimeout: 10 * time.Second,
}
type Config struct {
// Endpoints defines a set of URLs (schemes, hosts and ports only)
// that can be used to communicate with a logical etcd cluster. For
// example, a three-node cluster could be provided like so:
//
// Endpoints: []string{
// "http://node1.example.com:2379",
// "http://node2.example.com:2379",
// "http://node3.example.com:2379",
// }
//
// If multiple endpoints are provided, the Client will attempt to
// use them all in the event that one or more of them are unusable.
//
// If Client.Sync is ever called, the Client may cache an alternate
// set of endpoints to continue operation.
Endpoints []string
// Transport is used by the Client to drive HTTP requests. If not
// provided, DefaultTransport will be used.
Transport CancelableTransport
// CheckRedirect specifies the policy for handling HTTP redirects.
// If CheckRedirect is not nil, the Client calls it before
// following an HTTP redirect. The sole argument is the number of
// requests that have alrady been made. If CheckRedirect returns
// an error, Client.Do will not make any further requests and return
// the error back it to the caller.
//
// If CheckRedirect is nil, the Client uses its default policy,
// which is to stop after 10 consecutive requests.
CheckRedirect CheckRedirectFunc
// Username specifies the user credential to add as an authorization header
Username string
// Password is the password for the specified user to add as an authorization header
// to the request.
Password string
// HeaderTimeoutPerRequest specifies the time limit to wait for response
// header in a single request made by the Client. The timeout includes
// connection time, any redirects, and header wait time.
//
// For non-watch GET request, server returns the response body immediately.
// For PUT/POST/DELETE request, server will attempt to commit request
// before responding, which is expected to take `100ms + 2 * RTT`.
// For watch request, server returns the header immediately to notify Client
// watch start. But if server is behind some kind of proxy, the response
// header may be cached at proxy, and Client cannot rely on this behavior.
//
// One API call may send multiple requests to different etcd servers until it
// succeeds. Use context of the API to specify the overall timeout.
//
// A HeaderTimeoutPerRequest of zero means no timeout.
HeaderTimeoutPerRequest time.Duration
}
func (cfg *Config) transport() CancelableTransport {
if cfg.Transport == nil {
return DefaultTransport
}
return cfg.Transport
}
func (cfg *Config) checkRedirect() CheckRedirectFunc {
if cfg.CheckRedirect == nil {
return DefaultCheckRedirect
}
return cfg.CheckRedirect
}
// CancelableTransport mimics net/http.Transport, but requires that
// the object also support request cancellation.
type CancelableTransport interface {
http.RoundTripper
CancelRequest(req *http.Request)
}
type CheckRedirectFunc func(via int) error
// DefaultCheckRedirect follows up to 10 redirects, but no more.
var DefaultCheckRedirect CheckRedirectFunc = func(via int) error {
if via > 10 {
return ErrTooManyRedirects
}
return nil
}
type Client interface {
// Sync updates the internal cache of the etcd cluster's membership.
Sync(context.Context) error
// AutoSync periodically calls Sync() every given interval.
// The recommended sync interval is 10 seconds to 1 minute, which does
// not bring too much overhead to server and makes client catch up the
// cluster change in time.
//
// The example to use it:
//
// for {
// err := client.AutoSync(ctx, 10*time.Second)
// if err == context.DeadlineExceeded || err == context.Canceled {
// break
// }
// log.Print(err)
// }
AutoSync(context.Context, time.Duration) error
// Endpoints returns a copy of the current set of API endpoints used
// by Client to resolve HTTP requests. If Sync has ever been called,
// this may differ from the initial Endpoints provided in the Config.
Endpoints() []string
httpClient
}
func New(cfg Config) (Client, error) {
c := &httpClusterClient{
clientFactory: newHTTPClientFactory(cfg.transport(), cfg.checkRedirect(), cfg.HeaderTimeoutPerRequest),
rand: rand.New(rand.NewSource(int64(time.Now().Nanosecond()))),
}
if cfg.Username != "" {
c.credentials = &credentials{
username: cfg.Username,
password: cfg.Password,
}
}
if err := c.reset(cfg.Endpoints); err != nil {
return nil, err
}
return c, nil
}
type httpClient interface {
Do(context.Context, httpAction) (*http.Response, []byte, error)
}
func newHTTPClientFactory(tr CancelableTransport, cr CheckRedirectFunc, headerTimeout time.Duration) httpClientFactory {
return func(ep url.URL) httpClient {
return &redirectFollowingHTTPClient{
checkRedirect: cr,
client: &simpleHTTPClient{
transport: tr,
endpoint: ep,
headerTimeout: headerTimeout,
},
}
}
}
type credentials struct {
username string
password string
}
type httpClientFactory func(url.URL) httpClient
type httpAction interface {
HTTPRequest(url.URL) *http.Request
}
type httpClusterClient struct {
clientFactory httpClientFactory
endpoints []url.URL
pinned int
credentials *credentials
sync.RWMutex
rand *rand.Rand
}
func (c *httpClusterClient) reset(eps []string) error {
if len(eps) == 0 {
return ErrNoEndpoints
}
neps := make([]url.URL, len(eps))
for i, ep := range eps {
u, err := url.Parse(ep)
if err != nil {
return err
}
neps[i] = *u
}
c.endpoints = shuffleEndpoints(c.rand, neps)
// TODO: pin old endpoint if possible, and rebalance when new endpoint appears
c.pinned = 0
return nil
}
func (c *httpClusterClient) Do(ctx context.Context, act httpAction) (*http.Response, []byte, error) {
action := act
c.RLock()
leps := len(c.endpoints)
eps := make([]url.URL, leps)
n := copy(eps, c.endpoints)
pinned := c.pinned
if c.credentials != nil {
action = &authedAction{
act: act,
credentials: *c.credentials,
}
}
c.RUnlock()
if leps == 0 {
return nil, nil, ErrNoEndpoints
}
if leps != n {
return nil, nil, errors.New("unable to pick endpoint: copy failed")
}
var resp *http.Response
var body []byte
var err error
cerr := &ClusterError{}
for i := pinned; i < leps+pinned; i++ {
k := i % leps
hc := c.clientFactory(eps[k])
resp, body, err = hc.Do(ctx, action)
if err != nil {
cerr.Errors = append(cerr.Errors, err)
// mask previous errors with context error, which is controlled by user
if err == context.Canceled || err == context.DeadlineExceeded {
return nil, nil, err
}
continue
}
if resp.StatusCode/100 == 5 {
switch resp.StatusCode {
case http.StatusInternalServerError, http.StatusServiceUnavailable:
// TODO: make sure this is a no leader response
cerr.Errors = append(cerr.Errors, fmt.Errorf("client: etcd member %s has no leader", eps[k].String()))
default:
cerr.Errors = append(cerr.Errors, fmt.Errorf("client: etcd member %s returns server error [%s]", eps[k].String(), http.StatusText(resp.StatusCode)))
}
continue
}
if k != pinned {
c.Lock()
c.pinned = k
c.Unlock()
}
return resp, body, nil
}
return nil, nil, cerr
}
func (c *httpClusterClient) Endpoints() []string {
c.RLock()
defer c.RUnlock()
eps := make([]string, len(c.endpoints))
for i, ep := range c.endpoints {
eps[i] = ep.String()
}
return eps
}
func (c *httpClusterClient) Sync(ctx context.Context) error {
mAPI := NewMembersAPI(c)
ms, err := mAPI.List(ctx)
if err != nil {
return err
}
c.Lock()
defer c.Unlock()
eps := make([]string, 0)
for _, m := range ms {
eps = append(eps, m.ClientURLs...)
}
sort.Sort(sort.StringSlice(eps))
ceps := make([]string, len(c.endpoints))
for i, cep := range c.endpoints {
ceps[i] = cep.String()
}
sort.Sort(sort.StringSlice(ceps))
// fast path if no change happens
// this helps client to pin the endpoint when no cluster change
if reflect.DeepEqual(eps, ceps) {
return nil
}
return c.reset(eps)
}
func (c *httpClusterClient) AutoSync(ctx context.Context, interval time.Duration) error {
ticker := time.NewTicker(interval)
defer ticker.Stop()
for {
err := c.Sync(ctx)
if err != nil {
return err
}
select {
case <-ctx.Done():
return ctx.Err()
case <-ticker.C:
}
}
}
type roundTripResponse struct {
resp *http.Response
err error
}
type simpleHTTPClient struct {
transport CancelableTransport
endpoint url.URL
headerTimeout time.Duration
}
func (c *simpleHTTPClient) Do(ctx context.Context, act httpAction) (*http.Response, []byte, error) {
req := act.HTTPRequest(c.endpoint)
if err := printcURL(req); err != nil {
return nil, nil, err
}
var hctx context.Context
var hcancel context.CancelFunc
if c.headerTimeout > 0 {
hctx, hcancel = context.WithTimeout(ctx, c.headerTimeout)
} else {
hctx, hcancel = context.WithCancel(ctx)
}
defer hcancel()
reqcancel := requestCanceler(c.transport, req)
rtchan := make(chan roundTripResponse, 1)
go func() {
resp, err := c.transport.RoundTrip(req)
rtchan <- roundTripResponse{resp: resp, err: err}
close(rtchan)
}()
var resp *http.Response
var err error
select {
case rtresp := <-rtchan:
resp, err = rtresp.resp, rtresp.err
case <-hctx.Done():
// cancel and wait for request to actually exit before continuing
reqcancel()
rtresp := <-rtchan
resp = rtresp.resp
switch {
case ctx.Err() != nil:
err = ctx.Err()
case hctx.Err() != nil:
err = fmt.Errorf("client: endpoint %s exceeded header timeout", c.endpoint.String())
default:
panic("failed to get error from context")
}
}
// always check for resp nil-ness to deal with possible
// race conditions between channels above
defer func() {
if resp != nil {
resp.Body.Close()
}
}()
if err != nil {
return nil, nil, err
}
var body []byte
done := make(chan struct{})
go func() {
body, err = ioutil.ReadAll(resp.Body)
done <- struct{}{}
}()
select {
case <-ctx.Done():
resp.Body.Close()
<-done
return nil, nil, ctx.Err()
case <-done:
}
return resp, body, err
}
type authedAction struct {
act httpAction
credentials credentials
}
func (a *authedAction) HTTPRequest(url url.URL) *http.Request {
r := a.act.HTTPRequest(url)
r.SetBasicAuth(a.credentials.username, a.credentials.password)
return r
}
type redirectFollowingHTTPClient struct {
client httpClient
checkRedirect CheckRedirectFunc
}
func (r *redirectFollowingHTTPClient) Do(ctx context.Context, act httpAction) (*http.Response, []byte, error) {
next := act
for i := 0; i < 100; i++ {
if i > 0 {
if err := r.checkRedirect(i); err != nil {
return nil, nil, err
}
}
resp, body, err := r.client.Do(ctx, next)
if err != nil {
return nil, nil, err
}
if resp.StatusCode/100 == 3 {
hdr := resp.Header.Get("Location")
if hdr == "" {
return nil, nil, fmt.Errorf("Location header not set")
}
loc, err := url.Parse(hdr)
if err != nil {
return nil, nil, fmt.Errorf("Location header not valid URL: %s", hdr)
}
next = &redirectedHTTPAction{
action: act,
location: *loc,
}
continue
}
return resp, body, nil
}
return nil, nil, errTooManyRedirectChecks
}
type redirectedHTTPAction struct {
action httpAction
location url.URL
}
func (r *redirectedHTTPAction) HTTPRequest(ep url.URL) *http.Request {
orig := r.action.HTTPRequest(ep)
orig.URL = &r.location
return orig
}
func shuffleEndpoints(r *rand.Rand, eps []url.URL) []url.URL {
p := r.Perm(len(eps))
neps := make([]url.URL, len(eps))
for i, k := range p {
neps[i] = eps[k]
}
return neps
}