fix server-rendered results by generating result pages into a buffer and reading...

[debiancodesearch.git] / index / read.go

// Copyright 2011 The Go 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 index

// Index format.
//
// An index stored on disk has the format:
//
//      "csearch index 1\n"
//      list of paths
//      list of names
//      list of posting lists
//      name index
//      posting list index
//      trailer
//
// The list of paths is a sorted sequence of NUL-terminated file or directory names.
// The index covers the file trees rooted at those paths.
// The list ends with an empty name ("\x00").
//
// The list of names is a sorted sequence of NUL-terminated file names.
// The initial entry in the list corresponds to file #0,
// the next to file #1, and so on.  The list ends with an
// empty name ("\x00").
//
// The list of posting lists are a sequence of posting lists.
// Each posting list has the form:
//
//      trigram [3]
//      deltas [v]...
//
// The trigram gives the 3 byte trigram that this list describes.  The
// delta list is a sequence of varint-encoded deltas between file
// IDs, ending with a zero delta.  For example, the delta list [2,5,1,1,0]
// encodes the file ID list 1, 6, 7, 8.  The delta list [0] would
// encode the empty file ID list, but empty posting lists are usually
// not recorded at all.  The list of posting lists ends with an entry
// with trigram "\xff\xff\xff" and a delta list consisting a single zero.
//
// The indexes enable efficient random access to the lists.  The name
// index is a sequence of 4-byte big-endian values listing the byte
// offset in the name list where each name begins.  The posting list
// index is a sequence of index entries describing each successive
// posting list.  Each index entry has the form:
//
//      trigram [3]
//      file count [4]
//      offset [4]
//
// Index entries are only written for the non-empty posting lists,
// so finding the posting list for a specific trigram requires a
// binary search over the posting list index.  In practice, the majority
// of the possible trigrams are never seen, so omitting the missing
// ones represents a significant storage savings.
//
// The trailer has the form:
//
//      offset of path list [4]
//      offset of name list [4]
//      offset of posting lists [4]
//      offset of name index [4]
//      offset of posting list index [4]
//      "\ncsearch trailr\n"

import (
        "bytes"
        "encoding/binary"
        "log"
        "os"
        "runtime"
        "sort"
        "syscall"
)

const (
        magic        = "csearch index 1\n"
        trailerMagic = "\ncsearch trailr\n"
)

// An Index implements read-only access to a trigram index.
type Index struct {
        File      string
        Verbose   bool
        data      mmapData
        pathData  uint32
        nameData  uint32
        postData  uint32
        nameIndex uint32
        postIndex uint32
        numName   int
        numPost   int
}

const postEntrySize = 3 + 4 + 4

func Open(file string) *Index {
        mm := mmap(file)
        if len(mm.d) < 4*4+len(trailerMagic) || string(mm.d[len(mm.d)-len(trailerMagic):]) != trailerMagic {
                corrupt(file)
        }
        n := uint32(len(mm.d) - len(trailerMagic) - 5*4)
        ix := &Index{data: mm}
        ix.File = file
        ix.pathData = ix.uint32(n)
        ix.nameData = ix.uint32(n + 4)
        ix.postData = ix.uint32(n + 8)
        ix.nameIndex = ix.uint32(n + 12)
        ix.postIndex = ix.uint32(n + 16)
        ix.numName = int((ix.postIndex-ix.nameIndex)/4) - 1
        ix.numPost = int((n - ix.postIndex) / postEntrySize)
        return ix
}

func (ix *Index) Close() {
        if err := syscall.Munmap(ix.data.orig); err != nil {
                log.Fatalf("munmap: %v", err)
        }
        ix.data.f.Close()
}

// slice returns the slice of index data starting at the given byte offset.
// If n >= 0, the slice must have length at least n and is truncated to length n.
func (ix *Index) slice(off uint32, n int) []byte {
        o := int(off)
        if uint32(o) != off || n >= 0 && o+n > len(ix.data.d) {
                corrupt(ix.File)
        }
        if n < 0 {
                return ix.data.d[o:]
        }
        return ix.data.d[o : o+n]
}

// uint32 returns the uint32 value at the given offset in the index data.
func (ix *Index) uint32(off uint32) uint32 {
        return binary.BigEndian.Uint32(ix.slice(off, 4))
}

// uvarint returns the varint value at the given offset in the index data.
func (ix *Index) uvarint(off uint32) uint32 {
        v, n := binary.Uvarint(ix.slice(off, -1))
        if n <= 0 {
                corrupt(ix.File)
        }
        return uint32(v)
}

// Paths returns the list of indexed paths.
func (ix *Index) Paths() []string {
        off := ix.pathData
        var x []string
        for {
                s := ix.str(off)
                if len(s) == 0 {
                        break
                }
                x = append(x, string(s))
                off += uint32(len(s) + 1)
        }
        return x
}

// NameBytes returns the name corresponding to the given fileid.
func (ix *Index) NameBytes(fileid uint32) []byte {
        off := ix.uint32(ix.nameIndex + 4*fileid)
        return ix.str(ix.nameData + off)
}

func (ix *Index) str(off uint32) []byte {
        str := ix.slice(off, -1)
        i := bytes.IndexByte(str, '\x00')
        if i < 0 {
                corrupt(ix.File)
        }
        return str[:i]
}

// Name returns the name corresponding to the given fileid.
func (ix *Index) Name(fileid uint32) string {
        return string(ix.NameBytes(fileid))
}

// listAt returns the index list entry at the given offset.
func (ix *Index) listAt(off uint32) (trigram, count, offset uint32) {
        d := ix.slice(ix.postIndex+off, postEntrySize)
        trigram = uint32(d[0])<<16 | uint32(d[1])<<8 | uint32(d[2])
        count = binary.BigEndian.Uint32(d[3:])
        offset = binary.BigEndian.Uint32(d[3+4:])
        return
}

func (ix *Index) dumpPosting() {
        d := ix.slice(ix.postIndex, postEntrySize*ix.numPost)
        for i := 0; i < ix.numPost; i++ {
                j := i * postEntrySize
                t := uint32(d[j])<<16 | uint32(d[j+1])<<8 | uint32(d[j+2])
                count := int(binary.BigEndian.Uint32(d[j+3:]))
                offset := binary.BigEndian.Uint32(d[j+3+4:])
                log.Printf("%#x: %d at %d", t, count, offset)
        }
}

func (ix *Index) findList(trigram uint32) (count int, offset uint32) {
        // binary search
        d := ix.slice(ix.postIndex, postEntrySize*ix.numPost)
        i := sort.Search(ix.numPost, func(i int) bool {
                i *= postEntrySize
                t := uint32(d[i])<<16 | uint32(d[i+1])<<8 | uint32(d[i+2])
                return t >= trigram
        })
        if i >= ix.numPost {
                return 0, 0
        }
        i *= postEntrySize
        t := uint32(d[i])<<16 | uint32(d[i+1])<<8 | uint32(d[i+2])
        if t != trigram {
                return 0, 0
        }
        count = int(binary.BigEndian.Uint32(d[i+3:]))
        offset = binary.BigEndian.Uint32(d[i+3+4:])
        return
}

type postReader struct {
        ix       *Index
        count    int
        offset   uint32
        fileid   uint32
        d        []byte
        restrict []uint32
}

func (r *postReader) init(ix *Index, trigram uint32, restrict []uint32) {
        count, offset := ix.findList(trigram)
        if count == 0 {
                return
        }
        r.ix = ix
        r.count = count
        r.offset = offset
        r.fileid = ^uint32(0)
        r.d = ix.slice(ix.postData+offset+3, -1)
        r.restrict = restrict
}

func (r *postReader) max() int {
        return int(r.count)
}

func (r *postReader) next() bool {
        for r.count > 0 {
                r.count--
                delta64, n := binary.Uvarint(r.d)
                delta := uint32(delta64)
                if n <= 0 || delta == 0 {
                        corrupt(r.ix.File)
                }
                r.d = r.d[n:]
                r.fileid += delta
                if r.restrict != nil {
                        i := 0
                        for i < len(r.restrict) && r.restrict[i] < r.fileid {
                                i++
                        }
                        r.restrict = r.restrict[i:]
                        if len(r.restrict) == 0 || r.restrict[0] != r.fileid {
                                continue
                        }
                }
                return true
        }
        // list should end with terminating 0 delta
        if r.d != nil && (len(r.d) == 0 || r.d[0] != 0) {
                corrupt(r.ix.File)
        }
        r.fileid = ^uint32(0)
        return false
}

func (ix *Index) PostingList(trigram uint32) []uint32 {
        return ix.postingList(trigram, nil)
}

func (ix *Index) postingList(trigram uint32, restrict []uint32) []uint32 {
        var r postReader
        r.init(ix, trigram, restrict)
        return myPostingList(r.d, r.max(), restrict)
}

func (ix *Index) PostingAnd(list []uint32, trigram uint32) []uint32 {
        return ix.postingAnd(list, trigram, nil)
}

func (ix *Index) postingAnd(list []uint32, trigram uint32, restrict []uint32) []uint32 {
        var r postReader
        r.init(ix, trigram, restrict)
        return myPostingAnd(r.d, r.max(), list, restrict)
}

func (ix *Index) PostingOr(list []uint32, trigram uint32) []uint32 {
        return ix.postingOr(list, trigram, nil)
}

func (ix *Index) postingOr(list []uint32, trigram uint32, restrict []uint32) []uint32 {
        var r postReader
        r.init(ix, trigram, restrict)
        return myPostingOr(r.d, r.max(), list, restrict)
}

func (ix *Index) PostingQuery(q *Query) []uint32 {
        return ix.postingQuery(q, nil)
}

// Implements sort.Interface
type trigramCnt struct {
        trigram uint32
        count   int
        listcnt int
}

type trigramCnts []trigramCnt

func (t trigramCnts) Len() int {
        return len(t)
}

func (t trigramCnts) Less(i, j int) bool {
        return t[i].count < t[j].count
}

func (t trigramCnts) Swap(i, j int) {
        t[i], t[j] = t[j], t[i]
}

func (ix *Index) postingQuery(q *Query, restrict []uint32) (ret []uint32) {
        var list []uint32
        switch q.Op {
        case QNone:
                // nothing
        case QAll:
                if restrict != nil {
                        return restrict
                }
                list = make([]uint32, ix.numName)
                for i := range list {
                        list[i] = uint32(i)
                }
                return list
        case QAnd:
                // "Query planner": we first sort the posting lists by their
                // length (ascending)
                withCount := make(trigramCnts, len(q.Trigram))
                for idx, t := range q.Trigram {
                        tri := uint32(t[0])<<16 | uint32(t[1])<<8 | uint32(t[2])
                        count, _ := ix.findList(tri)
                        withCount[idx] = trigramCnt{tri, count, 0}
                }
                sort.Sort(withCount)

                stoppedAt := 0
                for idx, t := range withCount {
                        previous := len(list)
                        if list == nil {
                                list = ix.postingList(t.trigram, restrict)
                        } else {
                                list = ix.postingAnd(list, t.trigram, restrict)
                        }
                        if len(list) == 0 {
                                return nil
                        }
                        withCount[idx].listcnt = len(list)
                        if previous > 0 {
                                minIdx := 0.70 * float32(len(withCount))
                                if (previous-len(list)) < 10 && stoppedAt == 0 && float32(idx) > minIdx {
                                        stoppedAt = len(list)
                                }
                        }
                        if previous > 0 && (previous-len(list)) < 10 {
                                //fmt.Printf("difference is %d, break!\n", previous - len(list))
                                break
                        }
                }

                for _, sub := range q.Sub {
                        if list == nil {
                                list = restrict
                        }
                        list = ix.postingQuery(sub, list)
                        if len(list) == 0 {
                                return nil
                        }
                }
        case QOr:
                for _, t := range q.Trigram {
                        tri := uint32(t[0])<<16 | uint32(t[1])<<8 | uint32(t[2])
                        if list == nil {
                                list = ix.postingList(tri, restrict)
                        } else {
                                list = ix.postingOr(list, tri, restrict)
                        }
                }
                for _, sub := range q.Sub {
                        list1 := ix.postingQuery(sub, restrict)
                        list = mergeOr(list, list1)
                }
        }
        return list
}

func mergeOr(l1, l2 []uint32) []uint32 {
        var l []uint32
        i := 0
        j := 0
        for i < len(l1) || j < len(l2) {
                switch {
                case j == len(l2) || (i < len(l1) && l1[i] < l2[j]):
                        l = append(l, l1[i])
                        i++
                case i == len(l1) || (j < len(l2) && l1[i] > l2[j]):
                        l = append(l, l2[j])
                        j++
                case l1[i] == l2[j]:
                        l = append(l, l1[i])
                        i++
                        j++
                }
        }
        return l
}

func corrupt(file string) {
        log.Fatal("corrupt index: remove " + file)
}

// An mmapData is mmap'ed read-only data from a file.
type mmapData struct {
        f    *os.File
        d    []byte
        orig []byte
}

// mmap maps the given file into memory.
func mmap(file string) mmapData {
        f, err := os.Open(file)
        if err != nil {
                log.Fatal(err)
        }
        return mmapFile(f)
}

// File returns the name of the index file to use.
// It is either $CSEARCHINDEX or $HOME/.csearchindex.
func File() string {
        f := os.Getenv("CSEARCHINDEX")
        if f != "" {
                return f
        }
        var home string
        if runtime.GOOS == "windows" {
                home = os.Getenv("HOMEPATH")
        } else {
                home = os.Getenv("HOME")
        }
        return home + "/.csearchindex"
}