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/plugin/description/description.go

@@ -0,0 +1,199 @@
+// 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.
+
+/*
+The description (experimental) plugin generates a Description method for each message.
+The Description method returns a populated google_protobuf.FileDescriptorSet struct.
+This contains the description of the files used to generate this message.
+
+It is enabled by the following extensions:
+
+  - description
+  - description_all
+
+The description plugin also generates a test given it is enabled using one of the following extensions:
+
+  - testgen
+  - testgen_all
+
+Let us look at:
+
+  github.com/gogo/protobuf/test/example/example.proto
+
+Btw all the output can be seen at:
+
+  github.com/gogo/protobuf/test/example/*
+
+The following message:
+
+  message B {
+	option (gogoproto.description) = true;
+	optional A A = 1 [(gogoproto.nullable) = false, (gogoproto.embed) = true];
+	repeated bytes G = 2 [(gogoproto.customtype) = "github.com/gogo/protobuf/test/custom.Uint128", (gogoproto.nullable) = false];
+  }
+
+given to the description plugin, will generate the following code:
+
+  func (this *B) Description() (desc *google_protobuf.FileDescriptorSet) {
+	return ExampleDescription()
+  }
+
+and the following test code:
+
+  func TestDescription(t *testing9.T) {
+	ExampleDescription()
+  }
+
+The hope is to use this struct in some way instead of reflect.
+This package is subject to change, since a use has not been figured out yet.
+
+*/
+package description
+
+import (
+	"bytes"
+	"compress/gzip"
+	"fmt"
+	"github.com/gogo/protobuf/gogoproto"
+	"github.com/gogo/protobuf/proto"
+	descriptor "github.com/gogo/protobuf/protoc-gen-gogo/descriptor"
+	"github.com/gogo/protobuf/protoc-gen-gogo/generator"
+)
+
+type plugin struct {
+	*generator.Generator
+	generator.PluginImports
+}
+
+func NewPlugin() *plugin {
+	return &plugin{}
+}
+
+func (p *plugin) Name() string {
+	return "description"
+}
+
+func (p *plugin) Init(g *generator.Generator) {
+	p.Generator = g
+}
+
+func (p *plugin) Generate(file *generator.FileDescriptor) {
+	used := false
+	localName := generator.FileName(file)
+
+	p.PluginImports = generator.NewPluginImports(p.Generator)
+	descriptorPkg := p.NewImport("github.com/gogo/protobuf/protoc-gen-gogo/descriptor")
+	protoPkg := p.NewImport("github.com/gogo/protobuf/proto")
+	gzipPkg := p.NewImport("compress/gzip")
+	bytesPkg := p.NewImport("bytes")
+	ioutilPkg := p.NewImport("io/ioutil")
+
+	for _, message := range file.Messages() {
+		if !gogoproto.HasDescription(file.FileDescriptorProto, message.DescriptorProto) {
+			continue
+		}
+		if message.DescriptorProto.GetOptions().GetMapEntry() {
+			continue
+		}
+		used = true
+		ccTypeName := generator.CamelCaseSlice(message.TypeName())
+		p.P(`func (this *`, ccTypeName, `) Description() (desc *`, descriptorPkg.Use(), `.FileDescriptorSet) {`)
+		p.In()
+		p.P(`return `, localName, `Description()`)
+		p.Out()
+		p.P(`}`)
+	}
+
+	if used {
+
+		p.P(`func `, localName, `Description() (desc *`, descriptorPkg.Use(), `.FileDescriptorSet) {`)
+		p.In()
+		//Don't generate SourceCodeInfo, since it will create too much code.
+
+		ss := make([]*descriptor.SourceCodeInfo, 0)
+		for _, f := range p.Generator.AllFiles().GetFile() {
+			ss = append(ss, f.SourceCodeInfo)
+			f.SourceCodeInfo = nil
+		}
+		b, err := proto.Marshal(p.Generator.AllFiles())
+		if err != nil {
+			panic(err)
+		}
+		for i, f := range p.Generator.AllFiles().GetFile() {
+			f.SourceCodeInfo = ss[i]
+		}
+		p.P(`d := &`, descriptorPkg.Use(), `.FileDescriptorSet{}`)
+		var buf bytes.Buffer
+		w, _ := gzip.NewWriterLevel(&buf, gzip.BestCompression)
+		w.Write(b)
+		w.Close()
+		b = buf.Bytes()
+		p.P("var gzipped = []byte{")
+		p.In()
+		p.P("// ", len(b), " bytes of a gzipped FileDescriptorSet")
+		for len(b) > 0 {
+			n := 16
+			if n > len(b) {
+				n = len(b)
+			}
+
+			s := ""
+			for _, c := range b[:n] {
+				s += fmt.Sprintf("0x%02x,", c)
+			}
+			p.P(s)
+
+			b = b[n:]
+		}
+		p.Out()
+		p.P("}")
+		p.P(`r := `, bytesPkg.Use(), `.NewReader(gzipped)`)
+		p.P(`gzipr, err := `, gzipPkg.Use(), `.NewReader(r)`)
+		p.P(`if err != nil {`)
+		p.In()
+		p.P(`panic(err)`)
+		p.Out()
+		p.P(`}`)
+		p.P(`ungzipped, err := `, ioutilPkg.Use(), `.ReadAll(gzipr)`)
+		p.P(`if err != nil {`)
+		p.In()
+		p.P(`panic(err)`)
+		p.Out()
+		p.P(`}`)
+		p.P(`if err := `, protoPkg.Use(), `.Unmarshal(ungzipped, d); err != nil {`)
+		p.In()
+		p.P(`panic(err)`)
+		p.Out()
+		p.P(`}`)
+		p.P(`return d`)
+		p.Out()
+		p.P(`}`)
+	}
+}
+
+func init() {
+	generator.RegisterPlugin(NewPlugin())
+}