lib/protocol, lib/discover, lib/db: Use protocol buffer serialization (fixes #3080)

This changes the BEP protocol to use protocol buffer serialization
instead of XDR, and therefore also the database format. The local
discovery protocol is also updated to be protocol buffer format.

GitHub-Pull-Request: https://github.com/syncthing/syncthing/pull/3276
LGTM: AudriusButkevicius

vendor/github.com/gogo/protobuf/test/custom/custom.go

@@ -0,0 +1,145 @@
+// Copyright (c) 2013, Vastech SA (PTY) LTD. All rights reserved.
+// http://github.com/gogo/protobuf
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions are
+// met:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * Redistributions in binary form must reproduce the above
+// copyright notice, this list of conditions and the following disclaimer
+// in the documentation and/or other materials provided with the
+// distribution.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+/*
+	Package custom contains custom types for test and example purposes.
+	These types are used by the test structures generated by gogoprotobuf.
+*/
+package custom
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"unsafe"
+)
+
+type Uint128 [2]uint64
+
+func (u Uint128) Marshal() ([]byte, error) {
+	buffer := make([]byte, 16)
+	_, err := u.MarshalTo(buffer)
+	return buffer, err
+}
+
+func (u Uint128) MarshalTo(data []byte) (n int, err error) {
+	PutLittleEndianUint128(data, 0, u)
+	return 16, nil
+}
+
+func GetLittleEndianUint64(b []byte, offset int) uint64 {
+	return *(*uint64)(unsafe.Pointer(&b[offset]))
+}
+
+func PutLittleEndianUint64(b []byte, offset int, v uint64) {
+	b[offset] = byte(v)
+	b[offset+1] = byte(v >> 8)
+	b[offset+2] = byte(v >> 16)
+	b[offset+3] = byte(v >> 24)
+	b[offset+4] = byte(v >> 32)
+	b[offset+5] = byte(v >> 40)
+	b[offset+6] = byte(v >> 48)
+	b[offset+7] = byte(v >> 56)
+}
+
+func PutLittleEndianUint128(buffer []byte, offset int, v [2]uint64) {
+	PutLittleEndianUint64(buffer, offset, v[0])
+	PutLittleEndianUint64(buffer, offset+8, v[1])
+}
+
+func GetLittleEndianUint128(buffer []byte, offset int) (value [2]uint64) {
+	value[0] = GetLittleEndianUint64(buffer, offset)
+	value[1] = GetLittleEndianUint64(buffer, offset+8)
+	return
+}
+
+func (u *Uint128) Unmarshal(data []byte) error {
+	if data == nil {
+		u = nil
+		return nil
+	}
+	if len(data) == 0 {
+		pu := Uint128{}
+		*u = pu
+		return nil
+	}
+	if len(data) != 16 {
+		return errors.New("Uint128: invalid length")
+	}
+	pu := Uint128(GetLittleEndianUint128(data, 0))
+	*u = pu
+	return nil
+}
+
+func (u Uint128) MarshalJSON() ([]byte, error) {
+	data, err := u.Marshal()
+	if err != nil {
+		return nil, err
+	}
+	return json.Marshal(data)
+}
+
+func (u Uint128) Size() int {
+	return 16
+}
+
+func (u *Uint128) UnmarshalJSON(data []byte) error {
+	v := new([]byte)
+	err := json.Unmarshal(data, v)
+	if err != nil {
+		return err
+	}
+	return u.Unmarshal(*v)
+}
+
+func (this Uint128) Equal(that Uint128) bool {
+	return this == that
+}
+
+func (this Uint128) Compare(that Uint128) int {
+	thisdata, err := this.Marshal()
+	if err != nil {
+		panic(err)
+	}
+	thatdata, err := that.Marshal()
+	if err != nil {
+		panic(err)
+	}
+	return bytes.Compare(thisdata, thatdata)
+}
+
+type randy interface {
+	Intn(n int) int
+}
+
+func NewPopulatedUint128(r randy) *Uint128 {
+	data := make([]byte, 16)
+	for i := 0; i < 16; i++ {
+		data[i] = byte(r.Intn(255))
+	}
+	u := Uint128(GetLittleEndianUint128(data, 0))
+	return &u
+}