/
make.go
205 lines (173 loc) · 3.86 KB
/
make.go
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package cdb
import (
"os"
"io"
"bufio"
"strconv"
"container/vector"
"encoding/binary"
)
var BadFormatError = os.NewError("bad format")
// Make reads cdb-formatted records from r and writes a cdb-format database
// to w. See the documentation for Dump for details on the input record format.
func Make(w io.WriteSeeker, r io.Reader) (err os.Error) {
defer func() { // Centralize error handling.
if e := recover(); e != nil {
err = e.(os.Error)
}
}()
if _, err = w.Seek(int64(headerSize), 0); err != nil {
return
}
buf := make([]byte, 8)
rb := bufio.NewReader(r)
wb := bufio.NewWriter(w)
hash := cdbHash()
hw := io.MultiWriter(hash, wb) // Computes hash when writing record key.
rr := &recReader{rb}
htables := make(map[uint32]*vector.Vector)
pos := headerSize
// Read all records and write to output.
for {
// Record format is "+klen,dlen:key->data\n"
c := rr.readByte()
if c == '\n' { // end of records
break
}
if c != '+' {
return BadFormatError
}
klen, dlen := rr.readNum(','), rr.readNum(':')
writeNums(wb, klen, dlen, buf)
hash.Reset()
rr.copyn(hw, klen)
rr.eatByte('-')
rr.eatByte('>')
rr.copyn(wb, dlen)
rr.eatByte('\n')
h := hash.Sum32()
tableNum := h % 256
if htables[tableNum] == nil {
htables[tableNum] = new(vector.Vector)
}
htables[tableNum].Push(slot{h, pos})
pos += 8 + klen + dlen
}
// Write hash tables and header.
// Create and reuse a single hash table.
maxSlots := 0
for _, slots := range htables {
if slots.Len() > maxSlots {
maxSlots = slots.Len()
}
}
slotTable := make([]slot, maxSlots*2)
header := make([]byte, headerSize)
// Write hash tables.
for i := uint32(0); i < 256; i++ {
slots := htables[i]
if slots == nil {
putNum(header[i*8:], pos)
continue
}
nslots := uint32(slots.Len() * 2)
hashSlotTable := slotTable[:nslots]
// Reset table slots.
for j := 0; j < len(hashSlotTable); j++ {
hashSlotTable[j].h = 0
hashSlotTable[j].pos = 0
}
for j := 0; j < slots.Len(); j++ {
slot := slots.At(j).(slot)
slotPos := (slot.h / 256) % nslots
for hashSlotTable[slotPos].pos != 0 {
slotPos++
if slotPos == uint32(len(hashSlotTable)) {
slotPos = 0
}
}
hashSlotTable[slotPos] = slot
}
if err = writeSlots(wb, hashSlotTable, buf); err != nil {
return
}
putNum(header[i*8:], pos)
putNum(header[i*8+4:], nslots)
pos += 8 * nslots
}
if err = wb.Flush(); err != nil {
return
}
if _, err = w.Seek(0, 0); err != nil {
return
}
_, err = w.Write(header)
return
}
type recReader struct {
*bufio.Reader
}
func (rr *recReader) readByte() byte {
c, err := rr.ReadByte()
if err != nil {
panic(err)
}
return c
}
func (rr *recReader) eatByte(c byte) {
if rr.readByte() != c {
panic(os.NewError("unexpected character"))
}
}
// There is no strconv.Atoui32, so make one here.
func atoui32(s string) (n uint32, err os.Error) {
iu64, err := strconv.Atoui64(s)
if err != nil {
return 0, err
}
n = uint32(iu64)
if uint64(n) != iu64 {
return 0, &strconv.NumError{s, os.ERANGE}
}
return n, nil
}
func (rr *recReader) readNum(delim byte) uint32 {
s, err := rr.ReadString(delim)
if err != nil {
panic(err)
}
s = s[:len(s)-1] // Strip delim
n, err := atoui32(s)
if err != nil {
panic(err)
}
return n
}
func (rr *recReader) copyn(w io.Writer, n uint32) {
if _, err := io.Copyn(w, rr, int64(n)); err != nil {
panic(err)
}
}
func putNum(buf []byte, x uint32) {
binary.LittleEndian.PutUint32(buf, x)
}
func writeNums(w io.Writer, x, y uint32, buf []byte) {
putNum(buf, x)
putNum(buf[4:], y)
if _, err := w.Write(buf[:8]); err != nil {
panic(err)
}
}
type slot struct {
h, pos uint32
}
func writeSlots(w io.Writer, slots []slot, buf []byte) (err os.Error) {
for _, np := range slots {
putNum(buf, np.h)
putNum(buf[4:], np.pos)
if _, err = w.Write(buf[:8]); err != nil {
return
}
}
return nil
}