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/union/union.go

@@ -0,0 +1,207 @@
+// 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 onlyone plugin generates code for the onlyone extension.
+All fields must be nullable and only one of the fields may be set, like a union.
+Two methods are generated
+
+  GetValue() interface{}
+
+and
+
+  SetValue(v interface{}) (set bool)
+
+These provide easier interaction with a onlyone.
+
+The onlyone extension is not called union as this causes compile errors in the C++ generated code.
+There can only be one ;)
+
+It is enabled by the following extensions:
+
+  - onlyone
+  - onlyone_all
+
+The onlyone plugin also generates a test given it is enabled using one of the following extensions:
+
+  - testgen
+  - testgen_all
+
+Lets 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 U {
+	  option (gogoproto.onlyone) = true;
+	  optional A A = 1;
+	  optional B B = 2;
+  }
+
+given to the onlyone plugin, will generate code which looks a lot like this:
+
+	func (this *U) GetValue() interface{} {
+		if this.A != nil {
+			return this.A
+		}
+		if this.B != nil {
+			return this.B
+		}
+		return nil
+	}
+
+	func (this *U) SetValue(value interface{}) bool {
+		switch vt := value.(type) {
+		case *A:
+			this.A = vt
+		case *B:
+			this.B = vt
+		default:
+			return false
+		}
+		return true
+	}
+
+and the following test code:
+
+  func TestUUnion(t *testing.T) {
+	popr := math_rand.New(math_rand.NewSource(time.Now().UnixNano()))
+	p := NewPopulatedU(popr)
+	v := p.GetValue()
+	msg := &U{}
+	if !msg.SetValue(v) {
+		t.Fatalf("Union: Could not set Value")
+	}
+	if !p.Equal(msg) {
+		t.Fatalf("%#v !Union Equal %#v", msg, p)
+	}
+  }
+
+*/
+package union
+
+import (
+	"github.com/gogo/protobuf/gogoproto"
+	"github.com/gogo/protobuf/protoc-gen-gogo/generator"
+)
+
+type union struct {
+	*generator.Generator
+	generator.PluginImports
+}
+
+func NewUnion() *union {
+	return &union{}
+}
+
+func (p *union) Name() string {
+	return "union"
+}
+
+func (p *union) Init(g *generator.Generator) {
+	p.Generator = g
+}
+
+func (p *union) Generate(file *generator.FileDescriptor) {
+	p.PluginImports = generator.NewPluginImports(p.Generator)
+
+	for _, message := range file.Messages() {
+		if !gogoproto.IsUnion(file.FileDescriptorProto, message.DescriptorProto) {
+			continue
+		}
+		if message.DescriptorProto.HasExtension() {
+			panic("onlyone does not currently support extensions")
+		}
+		if message.DescriptorProto.GetOptions().GetMapEntry() {
+			continue
+		}
+
+		ccTypeName := generator.CamelCaseSlice(message.TypeName())
+		p.P(`func (this *`, ccTypeName, `) GetValue() interface{} {`)
+		p.In()
+		for _, field := range message.Field {
+			fieldname := p.GetFieldName(message, field)
+			if fieldname == "Value" {
+				panic("cannot have a onlyone message " + ccTypeName + " with a field named Value")
+			}
+			p.P(`if this.`, fieldname, ` != nil {`)
+			p.In()
+			p.P(`return this.`, fieldname)
+			p.Out()
+			p.P(`}`)
+		}
+		p.P(`return nil`)
+		p.Out()
+		p.P(`}`)
+		p.P(``)
+		p.P(`func (this *`, ccTypeName, `) SetValue(value interface{}) bool {`)
+		p.In()
+		p.P(`switch vt := value.(type) {`)
+		p.In()
+		for _, field := range message.Field {
+			fieldname := p.GetFieldName(message, field)
+			goTyp, _ := p.GoType(message, field)
+			p.P(`case `, goTyp, `:`)
+			p.In()
+			p.P(`this.`, fieldname, ` = vt`)
+			p.Out()
+		}
+		p.P(`default:`)
+		p.In()
+		for _, field := range message.Field {
+			fieldname := p.GetFieldName(message, field)
+			if field.IsMessage() {
+				goTyp, _ := p.GoType(message, field)
+				obj := p.ObjectNamed(field.GetTypeName()).(*generator.Descriptor)
+
+				if gogoproto.IsUnion(obj.File(), obj.DescriptorProto) {
+					p.P(`this.`, fieldname, ` = new(`, generator.GoTypeToName(goTyp), `)`)
+					p.P(`if set := this.`, fieldname, `.SetValue(value); set {`)
+					p.In()
+					p.P(`return true`)
+					p.Out()
+					p.P(`}`)
+					p.P(`this.`, fieldname, ` = nil`)
+				}
+			}
+		}
+		p.P(`return false`)
+		p.Out()
+		p.P(`}`)
+		p.P(`return true`)
+		p.Out()
+		p.P(`}`)
+	}
+}
+
+func init() {
+	generator.RegisterPlugin(NewUnion())
+}