package idxfile
import (
"crypto/sha1"
"encoding/binary"
"hash"
"io"
)
// An Encoder writes idx files to an output stream.
type Encoder struct {
io.Writer
hash hash.Hash
}
// NewEncoder returns a new encoder that writes to w.
func NewEncoder(w io.Writer) *Encoder {
h := sha1.New()
mw := io.MultiWriter(w, h)
return &Encoder{mw, h}
}
// Encode writes the idx in an idx file format to the stream of the encoder.
func (e *Encoder) Encode(idx *Idxfile) (int, error) {
flow := []func(*Idxfile) (int, error){
e.encodeHeader,
e.encodeFanout,
e.encodeHashes,
e.encodeCRC32,
e.encodeOffsets,
e.encodeChecksums,
}
sz := 0
for _, f := range flow {
i, err := f(idx)
sz += i
if err != nil {
return sz, err
}
}
return sz, nil
}
func (e *Encoder) encodeHeader(idx *Idxfile) (int, error) {
c, err := e.Write(idxHeader)
if err != nil {
return c, err
}
return c + 4, e.writeInt32(idx.Version)
}
func (e *Encoder) encodeFanout(idx *Idxfile) (int, error) {
fanout := idx.calculateFanout()
for _, c := range fanout {
if err := e.writeInt32(c); err != nil {
return 0, err
}
}
return 1024, nil
}
func (e *Encoder) encodeHashes(idx *Idxfile) (int, error) {
return e.encodeEntryField(idx, true)
}
func (e *Encoder) encodeCRC32(idx *Idxfile) (int, error) {
return e.encodeEntryField(idx, false)
}
func (e *Encoder) encodeEntryField(idx *Idxfile, isHash bool) (int, error) {
sz := 0
for _, ent := range idx.Entries {
var data []byte
if isHash {
data = ent.Hash[:]
} else {
data = ent.CRC32[:]
}
i, err := e.Write(data)
sz += i
if err != nil {
return sz, err
}
}
return sz, nil
}
func (e *Encoder) encodeOffsets(idx *Idxfile) (int, error) {
sz := 0
for _, ent := range idx.Entries {
if err := e.writeInt32(uint32(ent.Offset)); err != nil {
return sz, err
}
sz += 4
}
return sz, nil
}
func (e *Encoder) encodeChecksums(idx *Idxfile) (int, error) {
if _, err := e.Write(idx.PackfileChecksum[:]); err != nil {
return 0, err
}
copy(idx.IdxChecksum[:], e.hash.Sum(nil)[:20])
if _, err := e.Write(idx.IdxChecksum[:]); err != nil {
return 0, err
}
return 40, nil
}
func (e *Encoder) writeInt32(value uint32) error {
return binary.Write(e, binary.BigEndian, value)
}
