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reader.go
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/
reader.go
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package delta
import (
"errors"
"io"
)
const (
stateSize = 256
)
type readCloser struct {
rc io.ReadCloser
state [stateSize]byte
delta int
}
func (rc *readCloser) Close() (err error) {
if rc.rc != nil {
err = rc.rc.Close()
rc.rc = nil
}
return
}
func (rc *readCloser) Read(p []byte) (int, error) {
if rc.rc == nil {
return 0, errors.New("delta: Read after Close")
}
n, err := rc.rc.Read(p)
if err != nil {
return n, err
}
var (
buffer [stateSize]byte
j int
)
copy(buffer[:], rc.state[:rc.delta])
for i := 0; i < n; {
for j = 0; j < rc.delta && i < n; i++ {
p[i] = buffer[j] + p[i]
buffer[j] = p[i]
j++
}
}
if j == rc.delta {
j = 0
}
copy(rc.state[:], buffer[j:rc.delta])
copy(rc.state[rc.delta-j:], buffer[:j])
return n, nil
}
// NewReader returns a new Delta io.ReadCloser.
func NewReader(p []byte, _ uint64, readers []io.ReadCloser) (io.ReadCloser, error) {
if len(readers) != 1 {
return nil, errors.New("delta: need exactly one reader")
}
if len(p) != 1 {
return nil, errors.New("delta: not enough properties")
}
return &readCloser{
rc: readers[0],
delta: int(p[0] + 1),
}, nil
}