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package objfile
import (
"compress/zlib"
"errors"
"io"
"strconv"
"gopkg.in/src-d/go-git.v4/plumbing"
)
var (
ErrOverflow = errors.New("objfile: declared data length exceeded (overflow)")
)
// Writer writes and encodes data in compressed objfile format to a provided
// io.Writer. Close should be called when finished with the Writer. Close will
// not close the underlying io.Writer.
type Writer struct {
raw io.Writer
zlib io.WriteCloser
hasher plumbing.Hasher
multi io.Writer
closed bool
pending int64 // number of unwritten bytes
}
// NewWriter returns a new Writer writing to w.
//
// The returned Writer implements io.WriteCloser. Close should be called when
// finished with the Writer. Close will not close the underlying io.Writer.
func NewWriter(w io.Writer) *Writer {
return &Writer{
raw: w,
zlib: zlib.NewWriter(w),
}
}
// WriteHeader writes the type and the size and prepares to accept the object's
// contents. If an invalid t is provided, plumbing.ErrInvalidType is returned. If a
// negative size is provided, ErrNegativeSize is returned.
func (w *Writer) WriteHeader(t plumbing.ObjectType, size int64) error {
if !t.Valid() {
return plumbing.ErrInvalidType
}
if size < 0 {
return ErrNegativeSize
}
b := t.Bytes()
b = append(b, ' ')
b = append(b, []byte(strconv.FormatInt(size, 10))...)
b = append(b, 0)
defer w.prepareForWrite(t, size)
_, err := w.zlib.Write(b)
return err
}
func (w *Writer) prepareForWrite(t plumbing.ObjectType, size int64) {
w.pending = size
w.hasher = plumbing.NewHasher(t, size)
w.multi = io.MultiWriter(w.zlib, w.hasher)
}
// Write writes the object's contents. Write returns the error ErrOverflow if
// more than size bytes are written after WriteHeader.
func (w *Writer) Write(p []byte) (n int, err error) {
if w.closed {
return 0, ErrClosed
}
overwrite := false
if int64(len(p)) > w.pending {
p = p[0:w.pending]
overwrite = true
}
n, err = w.multi.Write(p)
w.pending -= int64(n)
if err == nil && overwrite {
err = ErrOverflow
return
}
return
}
// Hash returns the hash of the object data stream that has been written so far.
// It can be called before or after Close.
func (w *Writer) Hash() plumbing.Hash {
return w.hasher.Sum() // Not yet closed, return hash of data written so far
}
// Close releases any resources consumed by the Writer.
//
// Calling Close does not close the wrapped io.Writer originally passed to
// NewWriter.
func (w *Writer) Close() error {
if err := w.zlib.Close(); err != nil {
return err
}
w.closed = true
return nil
}
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