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// Copyright 2015 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
// 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 httpproxy
import (
const (
// DefaultMaxIdleConnsPerHost indicates the default maximum idle connection
// count maintained between proxy and each member. We set it to 128 to
// let proxy handle 128 concurrent requests in long term smoothly.
// If the number of concurrent requests is bigger than this value,
// proxy needs to create one new connection when handling each request in
// the delta, which is bad because the creation consumes resource and
// may eat up ephemeral ports.
DefaultMaxIdleConnsPerHost = 128
// GetProxyURLs is a function which should return the current set of URLs to
// which client requests should be proxied. This function will be queried
// periodically by the proxy Handler to refresh the set of available
// backends.
type GetProxyURLs func() []string
// NewHandler creates a new HTTP handler, listening on the given transport,
// which will proxy requests to an etcd cluster.
// The handler will periodically update its view of the cluster.
func NewHandler(t *http.Transport, urlsFunc GetProxyURLs, failureWait time.Duration, refreshInterval time.Duration) http.Handler {
if t.TLSClientConfig != nil {
// Enable http2, see Issue 5033.
err := http2.ConfigureTransport(t)
if err != nil {
plog.Infof("Error enabling Transport HTTP/2 support: %v", err)
p := &reverseProxy{
director: newDirector(urlsFunc, failureWait, refreshInterval),
transport: t,
mux := http.NewServeMux()
mux.Handle("/", p)
mux.HandleFunc("/v2/config/local/proxy", p.configHandler)
return mux
// NewReadonlyHandler wraps the given HTTP handler to allow only GET requests
func NewReadonlyHandler(hdlr http.Handler) http.Handler {
readonly := readonlyHandlerFunc(hdlr)
return http.HandlerFunc(readonly)
func readonlyHandlerFunc(next http.Handler) func(http.ResponseWriter, *http.Request) {
return func(w http.ResponseWriter, req *http.Request) {
if req.Method != "GET" {
next.ServeHTTP(w, req)
func (p *reverseProxy) configHandler(w http.ResponseWriter, r *http.Request) {
if !allowMethod(w, r.Method, "GET") {
eps := p.director.endpoints()
epstr := make([]string, len(eps))
for i, e := range eps {
epstr[i] = e.URL.String()
proxyConfig := struct {
Endpoints []string `json:"endpoints"`
Endpoints: epstr,
// allowMethod verifies that the given method is one of the allowed methods,
// and if not, it writes an error to w. A boolean is returned indicating
// whether or not the method is allowed.
func allowMethod(w http.ResponseWriter, m string, ms ...string) bool {
for _, meth := range ms {
if m == meth {
return true
w.Header().Set("Allow", strings.Join(ms, ","))
http.Error(w, "Method Not Allowed", http.StatusMethodNotAllowed)
return false
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