Update to last common bleve (#3986)

vendor/github.com/couchbase/vellum/encoding.go

@@ -0,0 +1,87 @@
+//  Copyright (c) 2017 Couchbase, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// 		http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package vellum
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+)
+
+const headerSize = 16
+
+type encoderConstructor func(w io.Writer) encoder
+type decoderConstructor func([]byte) decoder
+
+var encoders = map[int]encoderConstructor{}
+var decoders = map[int]decoderConstructor{}
+
+type encoder interface {
+	start() error
+	encodeState(s *builderNode, addr int) (int, error)
+	finish(count, rootAddr int) error
+	reset(w io.Writer)
+}
+
+func loadEncoder(ver int, w io.Writer) (encoder, error) {
+	if cons, ok := encoders[ver]; ok {
+		return cons(w), nil
+	}
+	return nil, fmt.Errorf("no encoder for version %d registered", ver)
+}
+
+func registerEncoder(ver int, cons encoderConstructor) {
+	encoders[ver] = cons
+}
+
+type decoder interface {
+	getRoot() int
+	getLen() int
+	stateAt(addr int, prealloc fstState) (fstState, error)
+}
+
+func loadDecoder(ver int, data []byte) (decoder, error) {
+	if cons, ok := decoders[ver]; ok {
+		return cons(data), nil
+	}
+	return nil, fmt.Errorf("no decoder for version %d registered", ver)
+}
+
+func registerDecoder(ver int, cons decoderConstructor) {
+	decoders[ver] = cons
+}
+
+func decodeHeader(header []byte) (ver int, typ int, err error) {
+	if len(header) < headerSize {
+		err = fmt.Errorf("invalid header < 16 bytes")
+		return
+	}
+	ver = int(binary.LittleEndian.Uint64(header[0:8]))
+	typ = int(binary.LittleEndian.Uint64(header[8:16]))
+	return
+}
+
+// fstState represents a state inside the FTS runtime
+// It is the main contract between the FST impl and the decoder
+// The FST impl should work only with this interface, while only the decoder
+// impl knows the physical representation.
+type fstState interface {
+	Address() int
+	Final() bool
+	FinalOutput() uint64
+	NumTransitions() int
+	TransitionFor(b byte) (int, int, uint64)
+	TransitionAt(i int) byte
+}