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// Copyright 2017 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 tcpproxy
import (
"bufio"
"bytes"
"crypto/tls"
"io"
"net"
)
// AddSNIRoute appends a route to the ipPort listener that says if the
// incoming TLS SNI server name is sni, the connection is given to
// dest. If it doesn't match, rule processing continues for any
// additional routes on ipPort.
//
// The ipPort is any valid net.Listen TCP address.
func (p *Proxy) AddSNIRoute(ipPort, sni string, dest Target) {
p.addRoute(ipPort, sniMatch{sni, dest})
}
type sniMatch struct {
sni string
target Target
}
func (m sniMatch) match(br *bufio.Reader) Target {
if clientHelloServerName(br) == string(m.sni) {
return m.target
}
return nil
}
// clientHelloServerName returns the SNI server name inside the TLS ClientHello,
// without consuming any bytes from br.
// On any error, the empty string is returned.
func clientHelloServerName(br *bufio.Reader) (sni string) {
const recordHeaderLen = 5
hdr, err := br.Peek(recordHeaderLen)
if err != nil {
return ""
}
const recordTypeHandshake = 0x16
if hdr[0] != recordTypeHandshake {
return "" // Not TLS.
}
recLen := int(hdr[3])<<8 | int(hdr[4]) // ignoring version in hdr[1:3]
helloBytes, err := br.Peek(recordHeaderLen + recLen)
if err != nil {
return ""
}
tls.Server(sniSniffConn{r: bytes.NewReader(helloBytes)}, &tls.Config{
GetConfigForClient: func(hello *tls.ClientHelloInfo) (*tls.Config, error) {
sni = hello.ServerName
return nil, nil
},
}).Handshake()
return
}
// sniSniffConn is a net.Conn that reads from r, fails on Writes,
// and crashes otherwise.
type sniSniffConn struct {
r io.Reader
net.Conn // nil; crash on any unexpected use
}
func (c sniSniffConn) Read(p []byte) (int, error) { return c.r.Read(p) }
func (sniSniffConn) Write(p []byte) (int, error) { return 0, io.EOF }
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