Add 'user friendly' datastore API.

service/rawdatastore/invertible.go

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-package rawdatastore
-
-import (
-        "bytes"
-)
-
-// Buffer is the interface which corresponds to the subset of *bytes.Buffer
-// that this package requires.
-type Buffer interface {
-        String() string
-        Grow(int)
-
-        Read([]byte) (int, error)
-        ReadByte() (byte, error)
-
-        Write([]byte) (int, error)
-        WriteByte(c byte) error
-        WriteString(s string) (int, error)
-}
-
-var _ Buffer = (*bytes.Buffer)(nil)
-
-// InvertibleBuffer is just like Buffer, except that it also has a stateful
-// Invert() method, which will cause all reads and writes to/from it to be
-// inverted (e.g. every byte XOR 0xFF).
-//
-// Implementing queries requires manipulating the index entries (e.g.
-// synthesizing them, parsing them, etc.). In particular, when you have
-// a reverse-sorted field (e.g. high to low instead of low to high), it's
-// achieved by having all the bits inverted.
-//
-// All the serialization formats include delimiter information, which the
-// parsers only know to parse non-inverted. If we don't have this buffer, we'd
-// basically have to invert every byte in the []byte array when we're trying to
-// decode a reverse-ordered field (including the bytes of all fields after the
-// one we intend to parse) so that the parser can consume as many bytes as it
-// needs (and it only knows the number of bytes it needs as it decodes them).
-// This InvertibleBuffer lets that happen on the fly without having to flip the
-// whole []byte.
-//
-// If you know you need it, you'll know it's the right thing. If you're not sure
-// then you definitely don't need it!
-type InvertibleBuffer interface {
-        Buffer
-        Invert()
-}
-
-type invertibleBuffer struct {
-        Buffer
-        invert bool
-}
-
-// Invertible returns an InvertibleBuffer based on the Buffer.
-func Invertible(b Buffer) InvertibleBuffer {
-        return &invertibleBuffer{b, false}
-}
-
-func (ib *invertibleBuffer) Read(bs []byte) (int, error) {
-        n, err := ib.Buffer.Read(bs)
-        if ib.invert {
-                for i, b := range bs {
-                        bs[i] = b ^ 0xFF
-                }
-        }
-        return n, err
-}
-
-func (ib *invertibleBuffer) WriteString(s string) (int, error) {
-        if ib.invert {
-                ib.Grow(len(s))
-                for i := 0; i < len(s); i++ {
-                        if err := ib.Buffer.WriteByte(s[i] ^ 0xFF); err != nil {
-                                return i, err
-                        }
-                }
-                return len(s), nil
-        }
-        return ib.Buffer.WriteString(s)
-}
-
-func (ib *invertibleBuffer) Write(bs []byte) (int, error) {
-        if ib.invert {
-                ib.Grow(len(bs))
-                for i, b := range bs {
-                        if err := ib.Buffer.WriteByte(b ^ 0xFF); err != nil {
-                                return i, err
-                        }
-                }
-                return len(bs), nil
-        }
-        return ib.Buffer.Write(bs)
-}
-
-func (ib *invertibleBuffer) WriteByte(b byte) error {
-        if ib.invert {
-                b = b ^ 0xFF
-        }
-        return ib.Buffer.WriteByte(b)
-}
-
-func (ib *invertibleBuffer) ReadByte() (byte, error) {
-        ret, err := ib.Buffer.ReadByte()
-        if ib.invert {
-                ret = ret ^ 0xFF
-        }
-        return ret, err
-}
-
-func (ib *invertibleBuffer) Invert() {
-        ib.invert = !ib.invert
-}