Move TLS utilities into a separate package

lib/tlsutil/tlsutil.go

@@ -0,0 +1,120 @@
+// Copyright (C) 2014 The Syncthing Authors.
+//
+// This Source Code Form is subject to the terms of the Mozilla Public
+// License, v. 2.0. If a copy of the MPL was not distributed with this file,
+// You can obtain one at http://mozilla.org/MPL/2.0/.
+
+package tlsutil
+
+import (
+	"bufio"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/tls"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"fmt"
+	"io"
+	"math/big"
+	mr "math/rand"
+	"net"
+	"os"
+	"time"
+)
+
+func NewCertificate(certFile, keyFile, tlsDefaultCommonName string, tlsRSABits int) (tls.Certificate, error) {
+	priv, err := rsa.GenerateKey(rand.Reader, tlsRSABits)
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("generate key: %s", err)
+	}
+
+	notBefore := time.Now()
+	notAfter := time.Date(2049, 12, 31, 23, 59, 59, 0, time.UTC)
+
+	template := x509.Certificate{
+		SerialNumber: new(big.Int).SetInt64(mr.Int63()),
+		Subject: pkix.Name{
+			CommonName: tlsDefaultCommonName,
+		},
+		NotBefore: notBefore,
+		NotAfter:  notAfter,
+
+		KeyUsage:              x509.KeyUsageKeyEncipherment | x509.KeyUsageDigitalSignature,
+		ExtKeyUsage:           []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth, x509.ExtKeyUsageClientAuth},
+		BasicConstraintsValid: true,
+	}
+
+	derBytes, err := x509.CreateCertificate(rand.Reader, &template, &template, &priv.PublicKey, priv)
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("create cert: %s", err)
+	}
+
+	certOut, err := os.Create(certFile)
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("save cert: %s", err)
+	}
+	err = pem.Encode(certOut, &pem.Block{Type: "CERTIFICATE", Bytes: derBytes})
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("save cert: %s", err)
+	}
+	err = certOut.Close()
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("save cert: %s", err)
+	}
+
+	keyOut, err := os.OpenFile(keyFile, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0600)
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("save key: %s", err)
+	}
+	err = pem.Encode(keyOut, &pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(priv)})
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("save key: %s", err)
+	}
+	err = keyOut.Close()
+	if err != nil {
+		return tls.Certificate{}, fmt.Errorf("save key: %s", err)
+	}
+
+	return tls.LoadX509KeyPair(certFile, keyFile)
+}
+
+type DowngradingListener struct {
+	net.Listener
+	TLSConfig *tls.Config
+}
+
+func (l *DowngradingListener) Accept() (net.Conn, error) {
+	conn, err := l.Listener.Accept()
+	if err != nil {
+		return nil, err
+	}
+
+	br := bufio.NewReader(conn)
+	conn.SetReadDeadline(time.Now().Add(1 * time.Second))
+	bs, err := br.Peek(1)
+	conn.SetReadDeadline(time.Time{})
+	if err != nil {
+		// We hit a read error here, but the Accept() call succeeded so we must not return an error.
+		// We return the connection as is and let whoever tries to use it deal with the error.
+		return conn, nil
+	}
+
+	wrapper := &WrappedConnection{br, conn}
+
+	// 0x16 is the first byte of a TLS handshake
+	if bs[0] == 0x16 {
+		return tls.Server(wrapper, l.TLSConfig), nil
+	}
+
+	return wrapper, nil
+}
+
+type WrappedConnection struct {
+	io.Reader
+	net.Conn
+}
+
+func (c *WrappedConnection) Read(b []byte) (n int, err error) {
+	return c.Reader.Read(b)
+}