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reader.go
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/
reader.go
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package kebab
import (
"bytes"
"crypto/sha256"
"encoding/json"
"fmt"
"io"
)
type Reader struct {
bucket Bucket
buf []byte
n int
boxes []boxhash
bn int
total int64
}
func NewReader(bucket Bucket) (*Reader, error) {
r := &Reader{
bucket: bucket,
}
metajson, err := r.bucket.Get("meta")
if err != nil {
return nil, fmt.Errorf("Get(%q): %s", "meta", err)
}
var meta Metadata
if err := json.Unmarshal(metajson, &meta); err != nil {
return nil, fmt.Errorf("failed to parse metadata: %s", err)
}
r.boxes = meta.Boxes
return r, nil
}
func (r *Reader) Read(p []byte) (n int, err error) {
defer func() { r.total += int64(n) }()
if r.n == len(r.buf) {
if err = r.fill(); err != nil {
return 0, err
}
}
n = copy(p, r.buf[r.n:])
r.n += n
return n, nil
}
func (r *Reader) fill() (err error) {
if r.bn == len(r.boxes) {
return io.EOF
}
key := fmt.Sprintf("%05d", r.bn)
if r.buf, err = r.bucket.Get(key); err != nil {
return err
}
h := sha256.Sum256(r.buf)
if !bytes.Equal(h[:], r.boxes[r.bn][:]) {
return fmt.Errorf("Get(%q): hash mismatch", key)
}
r.n = 0
r.bn += 1
return nil
}
func (r *Reader) Size() int64 {
return r.total
}