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// Copyright 2016 Google 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 main
import (
"context"
"crypto/tls"
"net"
"time"
)
type acmeCacheEntry struct {
backend string
expires time.Time
}
// ACME locates backends that are attempting ACME SNI-based validation.
type ACME struct {
backends []string
// *.acme.invalid domain to cache entry
cache map[string]acmeCacheEntry
}
// Match returns the backend for hostname, if one is found.
func (s *ACME) Match(hostname string) string {
c := s.cache[hostname]
if time.Now().Before(c.expires) {
return c.backend
}
// Cache entry is either expired or invalid, need to figure out
// which backend is the right one.
ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()
ch := make(chan string, len(s.backends))
for _, backend := range s.backends {
go tryAcme(ctx, ch, backend, hostname)
}
for range s.backends {
backend := <-ch
if backend != "" {
s.cache[hostname] = acmeCacheEntry{backend, time.Now().Add(5 * time.Second)}
return backend
}
}
// No usable backends found :(
s.cache[hostname] = acmeCacheEntry{"", time.Now().Add(5 * time.Second)}
return ""
}
func tryAcme(ctx context.Context, ch chan string, backend, hostname string) {
var res string
var err error
defer func() { ch <- res }()
dialer := net.Dialer{Timeout: 10 * time.Second}
conn, err := dialer.DialContext(ctx, "tcp", backend)
if err != nil {
return
}
defer conn.Close()
deadline, ok := ctx.Deadline()
if ok {
conn.SetDeadline(deadline)
}
client := tls.Client(conn, &tls.Config{
ServerName: hostname,
InsecureSkipVerify: true,
})
if err != nil {
return
}
if err = client.Handshake(); err != nil {
return
}
certs := client.ConnectionState().PeerCertificates
if len(certs) == 0 {
return
}
if err = certs[0].VerifyHostname(hostname); err != nil {
return
}
res = backend
}
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