mirror of
https://source.quilibrium.com/quilibrium/ceremonyclient.git
synced 2024-11-15 04:35:17 +00:00
261 lines
8.1 KiB
Go
261 lines
8.1 KiB
Go
// Copyright 2011 The LevelDB-Go and Pebble 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 base
|
|
|
|
import (
|
|
"bytes"
|
|
"encoding/binary"
|
|
"fmt"
|
|
"strconv"
|
|
"unicode/utf8"
|
|
)
|
|
|
|
// Compare returns -1, 0, or +1 depending on whether a is 'less than', 'equal
|
|
// to' or 'greater than' b. The two arguments can only be 'equal' if their
|
|
// contents are exactly equal. Furthermore, the empty slice must be 'less than'
|
|
// any non-empty slice. Compare is used to compare user keys, such as those
|
|
// passed as arguments to the various DB methods, as well as those returned
|
|
// from Separator, Successor, and Split.
|
|
type Compare func(a, b []byte) int
|
|
|
|
// Equal returns true if a and b are equivalent. For a given Compare,
|
|
// Equal(a,b) must return true iff Compare(a,b) returns zero, that is,
|
|
// Equal is a (potentially faster) specialization of Compare.
|
|
type Equal func(a, b []byte) bool
|
|
|
|
// AbbreviatedKey returns a fixed length prefix of a user key such that AbbreviatedKey(a)
|
|
// < AbbreviatedKey(b) iff a < b and AbbreviatedKey(a) > AbbreviatedKey(b) iff a > b. If
|
|
// AbbreviatedKey(a) == AbbreviatedKey(b) an additional comparison is required to
|
|
// determine if the two keys are actually equal.
|
|
//
|
|
// This helps optimize indexed batch comparisons for cache locality. If a Split
|
|
// function is specified, AbbreviatedKey usually returns the first eight bytes
|
|
// of the user key prefix in the order that gives the correct ordering.
|
|
type AbbreviatedKey func(key []byte) uint64
|
|
|
|
// FormatKey returns a formatter for the user key.
|
|
type FormatKey func(key []byte) fmt.Formatter
|
|
|
|
// FormatValue returns a formatter for the user value. The key is also
|
|
// specified for the value formatter in order to support value formatting that
|
|
// is dependent on the key.
|
|
type FormatValue func(key, value []byte) fmt.Formatter
|
|
|
|
// Separator is used to construct SSTable index blocks. A trivial implementation
|
|
// is `return a`, but appending fewer bytes leads to smaller SSTables.
|
|
//
|
|
// Given keys a, b for which Compare(a, b) < 0, Separator returns a key k such
|
|
// that:
|
|
//
|
|
// 1. Compare(a, k) <= 0, and
|
|
// 2. Compare(k, b) < 0.
|
|
//
|
|
// As a special case, b may be nil in which case the second condition is dropped.
|
|
//
|
|
// For example, if dst, a and b are the []byte equivalents of the strings
|
|
// "aqua", "black" and "blue", then the result may be "aquablb".
|
|
// Similarly, if the arguments were "aqua", "green" and "", then the result
|
|
// may be "aquah".
|
|
type Separator func(dst, a, b []byte) []byte
|
|
|
|
// Successor returns a shortened key given a key a, such that Compare(k, a) >=
|
|
// 0. A simple implementation may return a unchanged. The dst parameter may be
|
|
// used to store the returned key, though it is valid to pass nil. The returned
|
|
// key must be valid to pass to Compare.
|
|
type Successor func(dst, a []byte) []byte
|
|
|
|
// ImmediateSuccessor is invoked with a prefix key ([Split(a) == len(a)]) and
|
|
// returns the smallest key that is larger than the given prefix a.
|
|
// ImmediateSuccessor must return a prefix key k such that:
|
|
//
|
|
// Split(k) == len(k) and Compare(k, a) > 0
|
|
//
|
|
// and there exists no representable k2 such that:
|
|
//
|
|
// Split(k2) == len(k2) and Compare(k2, a) > 0 and Compare(k2, k) < 0
|
|
//
|
|
// As an example, an implementation built on the natural byte ordering using
|
|
// bytes.Compare could append a `\0` to `a`.
|
|
//
|
|
// The dst parameter may be used to store the returned key, though it is valid
|
|
// to pass nil. The returned key must be valid to pass to Compare.
|
|
type ImmediateSuccessor func(dst, a []byte) []byte
|
|
|
|
// Split returns the length of the prefix of the user key that corresponds to
|
|
// the key portion of an MVCC encoding scheme to enable the use of prefix bloom
|
|
// filters.
|
|
//
|
|
// The method will only ever be called with valid MVCC keys, that is, keys that
|
|
// the user could potentially store in the database. Pebble does not know which
|
|
// keys are MVCC keys and which are not, and may call Split on both MVCC keys
|
|
// and non-MVCC keys.
|
|
//
|
|
// A trivial MVCC scheme is one in which Split() returns len(a). This
|
|
// corresponds to assigning a constant version to each key in the database. For
|
|
// performance reasons, it is preferable to use a `nil` split in this case.
|
|
//
|
|
// The returned prefix must have the following properties:
|
|
//
|
|
// 1. The prefix must be a byte prefix:
|
|
//
|
|
// bytes.HasPrefix(a, prefix(a))
|
|
//
|
|
// 2. A key consisting of just a prefix must sort before all other keys with
|
|
// that prefix:
|
|
//
|
|
// Compare(prefix(a), a) < 0 if len(suffix(a)) > 0
|
|
//
|
|
// 3. Prefixes must be used to order keys before suffixes:
|
|
//
|
|
// If Compare(a, b) <= 0, then Compare(prefix(a), prefix(b)) <= 0
|
|
//
|
|
// 4. Suffixes themselves must be valid keys and comparable, respecting the same
|
|
// ordering as within a key.
|
|
//
|
|
// If Compare(prefix(a), prefix(b)) == 0, then Compare(suffix(a), suffix(b)) == Compare(a, b)
|
|
type Split func(a []byte) int
|
|
|
|
// Comparer defines a total ordering over the space of []byte keys: a 'less
|
|
// than' relationship.
|
|
type Comparer struct {
|
|
Compare Compare
|
|
Equal Equal
|
|
AbbreviatedKey AbbreviatedKey
|
|
FormatKey FormatKey
|
|
FormatValue FormatValue
|
|
Separator Separator
|
|
Split Split
|
|
Successor Successor
|
|
ImmediateSuccessor ImmediateSuccessor
|
|
|
|
// Name is the name of the comparer.
|
|
//
|
|
// The Level-DB on-disk format stores the comparer name, and opening a
|
|
// database with a different comparer from the one it was created with
|
|
// will result in an error.
|
|
Name string
|
|
}
|
|
|
|
// DefaultFormatter is the default implementation of user key formatting:
|
|
// non-ASCII data is formatted as escaped hexadecimal values.
|
|
var DefaultFormatter = func(key []byte) fmt.Formatter {
|
|
return FormatBytes(key)
|
|
}
|
|
|
|
// DefaultComparer is the default implementation of the Comparer interface.
|
|
// It uses the natural ordering, consistent with bytes.Compare.
|
|
var DefaultComparer = &Comparer{
|
|
Compare: bytes.Compare,
|
|
Equal: bytes.Equal,
|
|
|
|
AbbreviatedKey: func(key []byte) uint64 {
|
|
if len(key) >= 8 {
|
|
return binary.BigEndian.Uint64(key)
|
|
}
|
|
var v uint64
|
|
for _, b := range key {
|
|
v <<= 8
|
|
v |= uint64(b)
|
|
}
|
|
return v << uint(8*(8-len(key)))
|
|
},
|
|
|
|
FormatKey: DefaultFormatter,
|
|
|
|
Separator: func(dst, a, b []byte) []byte {
|
|
i, n := SharedPrefixLen(a, b), len(dst)
|
|
dst = append(dst, a...)
|
|
|
|
min := len(a)
|
|
if min > len(b) {
|
|
min = len(b)
|
|
}
|
|
if i >= min {
|
|
// Do not shorten if one string is a prefix of the other.
|
|
return dst
|
|
}
|
|
|
|
if a[i] >= b[i] {
|
|
// b is smaller than a or a is already the shortest possible.
|
|
return dst
|
|
}
|
|
|
|
if i < len(b)-1 || a[i]+1 < b[i] {
|
|
i += n
|
|
dst[i]++
|
|
return dst[:i+1]
|
|
}
|
|
|
|
i += n + 1
|
|
for ; i < len(dst); i++ {
|
|
if dst[i] != 0xff {
|
|
dst[i]++
|
|
return dst[:i+1]
|
|
}
|
|
}
|
|
return dst
|
|
},
|
|
|
|
Successor: func(dst, a []byte) (ret []byte) {
|
|
for i := 0; i < len(a); i++ {
|
|
if a[i] != 0xff {
|
|
dst = append(dst, a[:i+1]...)
|
|
dst[len(dst)-1]++
|
|
return dst
|
|
}
|
|
}
|
|
// a is a run of 0xffs, leave it alone.
|
|
return append(dst, a...)
|
|
},
|
|
|
|
ImmediateSuccessor: func(dst, a []byte) (ret []byte) {
|
|
return append(append(dst, a...), 0x00)
|
|
},
|
|
|
|
// This name is part of the C++ Level-DB implementation's default file
|
|
// format, and should not be changed.
|
|
Name: "leveldb.BytewiseComparator",
|
|
}
|
|
|
|
// SharedPrefixLen returns the largest i such that a[:i] equals b[:i].
|
|
// This function can be useful in implementing the Comparer interface.
|
|
func SharedPrefixLen(a, b []byte) int {
|
|
i, n := 0, len(a)
|
|
if n > len(b) {
|
|
n = len(b)
|
|
}
|
|
asUint64 := func(c []byte, i int) uint64 {
|
|
return binary.LittleEndian.Uint64(c[i:])
|
|
}
|
|
for i < n-7 && asUint64(a, i) == asUint64(b, i) {
|
|
i += 8
|
|
}
|
|
for i < n && a[i] == b[i] {
|
|
i++
|
|
}
|
|
return i
|
|
}
|
|
|
|
// FormatBytes formats a byte slice using hexadecimal escapes for non-ASCII
|
|
// data.
|
|
type FormatBytes []byte
|
|
|
|
const lowerhex = "0123456789abcdef"
|
|
|
|
// Format implements the fmt.Formatter interface.
|
|
func (p FormatBytes) Format(s fmt.State, c rune) {
|
|
buf := make([]byte, 0, len(p))
|
|
for _, b := range p {
|
|
if b < utf8.RuneSelf && strconv.IsPrint(rune(b)) {
|
|
buf = append(buf, b)
|
|
continue
|
|
}
|
|
buf = append(buf, `\x`...)
|
|
buf = append(buf, lowerhex[b>>4])
|
|
buf = append(buf, lowerhex[b&0xF])
|
|
}
|
|
s.Write(buf)
|
|
}
|