1// Copyright (c) 2017 Couchbase, Inc. 2// 3// Licensed under the Apache License, Version 2.0 (the "License"); 4// you may not use this file except in compliance with the License. 5// You may obtain a copy of the License at 6// 7// http://www.apache.org/licenses/LICENSE-2.0 8// 9// Unless required by applicable law or agreed to in writing, software 10// distributed under the License is distributed on an "AS IS" BASIS, 11// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 12// See the License for the specific language governing permissions and 13// limitations under the License. 14 15package vellum 16 17import ( 18 "encoding/binary" 19 "fmt" 20 "io" 21) 22 23const headerSize = 16 24 25type encoderConstructor func(w io.Writer) encoder 26type decoderConstructor func([]byte) decoder 27 28var encoders = map[int]encoderConstructor{} 29var decoders = map[int]decoderConstructor{} 30 31type encoder interface { 32 start() error 33 encodeState(s *builderNode, addr int) (int, error) 34 finish(count, rootAddr int) error 35 reset(w io.Writer) 36} 37 38func loadEncoder(ver int, w io.Writer) (encoder, error) { 39 if cons, ok := encoders[ver]; ok { 40 return cons(w), nil 41 } 42 return nil, fmt.Errorf("no encoder for version %d registered", ver) 43} 44 45func registerEncoder(ver int, cons encoderConstructor) { 46 encoders[ver] = cons 47} 48 49type decoder interface { 50 clear() 51 getRoot() int 52 getLen() int 53 reload(data []byte) 54 stateAt(addr int, prealloc fstState) (fstState, error) 55} 56 57func loadDecoder(ver int, data []byte) (decoder, error) { 58 if cons, ok := decoders[ver]; ok { 59 return cons(data), nil 60 } 61 return nil, fmt.Errorf("no decoder for version %d registered", ver) 62} 63 64func registerDecoder(ver int, cons decoderConstructor) { 65 decoders[ver] = cons 66} 67 68func decodeHeader(header []byte) (ver int, typ int, err error) { 69 if len(header) < headerSize { 70 err = fmt.Errorf("invalid header < 16 bytes") 71 return 72 } 73 ver = int(binary.LittleEndian.Uint64(header[0:8])) 74 typ = int(binary.LittleEndian.Uint64(header[8:16])) 75 return 76} 77 78// fstState represents a state inside the FTS runtime 79// It is the main contract between the FST impl and the decoder 80// The FST impl should work only with this interface, while only the decoder 81// impl knows the physical representation. 82type fstState interface { 83 Address() int 84 Final() bool 85 FinalOutput() uint64 86 NumTransitions() int 87 TransitionFor(b byte) (int, int, uint64) 88 TransitionAt(i int) byte 89} 90