255 lines
6.2 KiB
Go
255 lines
6.2 KiB
Go
// Copyright (c) 2017 Couchbase, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package vellum
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import (
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"io"
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"github.com/willf/bitset"
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)
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// FST is an in-memory representation of a finite state transducer,
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// capable of returning the uint64 value associated with
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// each []byte key stored, as well as enumerating all of the keys
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// in order.
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type FST struct {
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f io.Closer
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ver int
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len int
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typ int
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data []byte
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decoder decoder
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}
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func new(data []byte, f io.Closer) (rv *FST, err error) {
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rv = &FST{
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data: data,
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f: f,
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}
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rv.ver, rv.typ, err = decodeHeader(data)
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if err != nil {
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return nil, err
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}
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rv.decoder, err = loadDecoder(rv.ver, rv.data)
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if err != nil {
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return nil, err
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}
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rv.len = rv.decoder.getLen()
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return rv, nil
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}
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// Contains returns true if this FST contains the specified key.
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func (f *FST) Contains(val []byte) (bool, error) {
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_, exists, err := f.Get(val)
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return exists, err
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}
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// Get returns the value associated with the key. NOTE: a value of zero
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// does not imply the key does not exist, you must consult the second
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// return value as well.
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func (f *FST) Get(input []byte) (uint64, bool, error) {
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return f.get(input, nil)
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}
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func (f *FST) get(input []byte, prealloc fstState) (uint64, bool, error) {
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var total uint64
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curr := f.decoder.getRoot()
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state, err := f.decoder.stateAt(curr, prealloc)
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if err != nil {
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return 0, false, err
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}
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for i := range input {
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_, curr, output := state.TransitionFor(input[i])
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if curr == noneAddr {
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return 0, false, nil
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}
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state, err = f.decoder.stateAt(curr, state)
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if err != nil {
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return 0, false, err
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}
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total += output
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}
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if state.Final() {
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total += state.FinalOutput()
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return total, true, nil
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}
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return 0, false, nil
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}
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// Version returns the encoding version used by this FST instance.
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func (f *FST) Version() int {
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return f.ver
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}
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// Len returns the number of entries in this FST instance.
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func (f *FST) Len() int {
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return f.len
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}
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// Type returns the type of this FST instance.
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func (f *FST) Type() int {
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return f.typ
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}
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// Close will unmap any mmap'd data (if managed by vellum) and it will close
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// the backing file (if managed by vellum). You MUST call Close() for any
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// FST instance that is created.
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func (f *FST) Close() error {
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if f.f != nil {
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err := f.f.Close()
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if err != nil {
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return err
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}
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}
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f.data = nil
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f.decoder = nil
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return nil
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}
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// Start returns the start state of this Automaton
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func (f *FST) Start() int {
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return f.decoder.getRoot()
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}
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// IsMatch returns if this state is a matching state in this Automaton
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func (f *FST) IsMatch(addr int) bool {
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match, _ := f.IsMatchWithVal(addr)
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return match
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}
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// CanMatch returns if this state can ever transition to a matching state
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// in this Automaton
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func (f *FST) CanMatch(addr int) bool {
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if addr == noneAddr {
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return false
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}
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return true
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}
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// WillAlwaysMatch returns if from this state the Automaton will always
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// be in a matching state
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func (f *FST) WillAlwaysMatch(int) bool {
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return false
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}
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// Accept returns the next state for this Automaton on input of byte b
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func (f *FST) Accept(addr int, b byte) int {
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next, _ := f.AcceptWithVal(addr, b)
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return next
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}
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// IsMatchWithVal returns if this state is a matching state in this Automaton
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// and also returns the final output value for this state
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func (f *FST) IsMatchWithVal(addr int) (bool, uint64) {
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s, err := f.decoder.stateAt(addr, nil)
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if err != nil {
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return false, 0
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}
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return s.Final(), s.FinalOutput()
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}
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// AcceptWithVal returns the next state for this Automaton on input of byte b
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// and also returns the output value for the transition
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func (f *FST) AcceptWithVal(addr int, b byte) (int, uint64) {
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s, err := f.decoder.stateAt(addr, nil)
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if err != nil {
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return noneAddr, 0
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}
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_, next, output := s.TransitionFor(b)
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return next, output
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}
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// Iterator returns a new Iterator capable of enumerating the key/value pairs
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// between the provided startKeyInclusive and endKeyExclusive.
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func (f *FST) Iterator(startKeyInclusive, endKeyExclusive []byte) (*FSTIterator, error) {
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return newIterator(f, startKeyInclusive, endKeyExclusive, nil)
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}
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// Search returns a new Iterator capable of enumerating the key/value pairs
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// between the provided startKeyInclusive and endKeyExclusive that also
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// satisfy the provided automaton.
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func (f *FST) Search(aut Automaton, startKeyInclusive, endKeyExclusive []byte) (*FSTIterator, error) {
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return newIterator(f, startKeyInclusive, endKeyExclusive, aut)
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}
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// Debug is only intended for debug purposes, it simply asks the underlying
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// decoder visit each state, and pass it to the provided callback.
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func (f *FST) Debug(callback func(int, interface{}) error) error {
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addr := f.decoder.getRoot()
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set := bitset.New(uint(addr))
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stack := addrStack{addr}
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stateNumber := 0
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stack, addr = stack[:len(stack)-1], stack[len(stack)-1]
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for addr != noneAddr {
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if set.Test(uint(addr)) {
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stack, addr = stack.Pop()
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continue
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}
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set.Set(uint(addr))
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state, err := f.decoder.stateAt(addr, nil)
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if err != nil {
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return err
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}
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err = callback(stateNumber, state)
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if err != nil {
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return err
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}
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for i := 0; i < state.NumTransitions(); i++ {
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tchar := state.TransitionAt(i)
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_, dest, _ := state.TransitionFor(tchar)
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stack = append(stack, dest)
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}
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stateNumber++
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stack, addr = stack.Pop()
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}
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return nil
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}
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type addrStack []int
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func (a addrStack) Pop() (addrStack, int) {
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l := len(a)
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if l < 1 {
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return a, noneAddr
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}
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return a[:l-1], a[l-1]
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}
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// Reader() returns a Reader instance that a single thread may use to
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// retrieve data from the FST
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func (f *FST) Reader() (*Reader, error) {
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return &Reader{f: f}, nil
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}
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// A Reader is meant for a single threaded use
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type Reader struct {
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f *FST
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prealloc fstStateV1
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}
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func (r *Reader) Get(input []byte) (uint64, bool, error) {
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return r.f.get(input, &r.prealloc)
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}
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