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/vanity/foreach.go

@@ -0,0 +1,125 @@
+// Extensions for Protocol Buffers to create more go like structures.
+//
+// Copyright (c) 2015, Vastech SA (PTY) LTD. All rights reserved.
+// http://github.com/gogo/protobuf/gogoproto
+//
+// 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 vanity
+
+import descriptor "github.com/gogo/protobuf/protoc-gen-gogo/descriptor"
+
+func ForEachFile(files []*descriptor.FileDescriptorProto, f func(file *descriptor.FileDescriptorProto)) {
+	for _, file := range files {
+		f(file)
+	}
+}
+
+func OnlyProto2(files []*descriptor.FileDescriptorProto) []*descriptor.FileDescriptorProto {
+	outs := make([]*descriptor.FileDescriptorProto, 0, len(files))
+	for i, file := range files {
+		if file.GetSyntax() == "proto3" {
+			continue
+		}
+		outs = append(outs, files[i])
+	}
+	return outs
+}
+
+func OnlyProto3(files []*descriptor.FileDescriptorProto) []*descriptor.FileDescriptorProto {
+	outs := make([]*descriptor.FileDescriptorProto, 0, len(files))
+	for i, file := range files {
+		if file.GetSyntax() != "proto3" {
+			continue
+		}
+		outs = append(outs, files[i])
+	}
+	return outs
+}
+
+func ForEachMessageInFiles(files []*descriptor.FileDescriptorProto, f func(msg *descriptor.DescriptorProto)) {
+	for _, file := range files {
+		ForEachMessage(file.MessageType, f)
+	}
+}
+
+func ForEachMessage(msgs []*descriptor.DescriptorProto, f func(msg *descriptor.DescriptorProto)) {
+	for _, msg := range msgs {
+		f(msg)
+		ForEachMessage(msg.NestedType, f)
+	}
+}
+
+func ForEachFieldInFilesExcludingExtensions(files []*descriptor.FileDescriptorProto, f func(field *descriptor.FieldDescriptorProto)) {
+	for _, file := range files {
+		ForEachFieldExcludingExtensions(file.MessageType, f)
+	}
+}
+
+func ForEachFieldInFiles(files []*descriptor.FileDescriptorProto, f func(field *descriptor.FieldDescriptorProto)) {
+	for _, file := range files {
+		for _, ext := range file.Extension {
+			f(ext)
+		}
+		ForEachField(file.MessageType, f)
+	}
+}
+
+func ForEachFieldExcludingExtensions(msgs []*descriptor.DescriptorProto, f func(field *descriptor.FieldDescriptorProto)) {
+	for _, msg := range msgs {
+		for _, field := range msg.Field {
+			f(field)
+		}
+		ForEachField(msg.NestedType, f)
+	}
+}
+
+func ForEachField(msgs []*descriptor.DescriptorProto, f func(field *descriptor.FieldDescriptorProto)) {
+	for _, msg := range msgs {
+		for _, field := range msg.Field {
+			f(field)
+		}
+		for _, ext := range msg.Extension {
+			f(ext)
+		}
+		ForEachField(msg.NestedType, f)
+	}
+}
+
+func ForEachEnumInFiles(files []*descriptor.FileDescriptorProto, f func(enum *descriptor.EnumDescriptorProto)) {
+	for _, file := range files {
+		for _, enum := range file.EnumType {
+			f(enum)
+		}
+	}
+}
+
+func ForEachEnum(msgs []*descriptor.DescriptorProto, f func(field *descriptor.EnumDescriptorProto)) {
+	for _, msg := range msgs {
+		for _, field := range msg.EnumType {
+			f(field)
+		}
+		ForEachEnum(msg.NestedType, f)
+	}
+}