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package multihash
import (
"errors"
"io"
"math"
"github.com/multiformats/go-varint"
)
// Reader is an io.Reader wrapper that exposes a function
// to read a whole multihash, parse it, and return it.
type Reader interface {
io.Reader
ReadMultihash() (Multihash, error)
}
// Writer is an io.Writer wrapper that exposes a function
// to write a whole multihash.
type Writer interface {
io.Writer
WriteMultihash(Multihash) error
}
// NewReader wraps an io.Reader with a multihash.Reader
func NewReader(r io.Reader) Reader {
return &mhReader{r}
}
// NewWriter wraps an io.Writer with a multihash.Writer
func NewWriter(w io.Writer) Writer {
return &mhWriter{w}
}
type mhReader struct {
r io.Reader
}
func (r *mhReader) Read(buf []byte) (n int, err error) {
return r.r.Read(buf)
}
func (r *mhReader) ReadByte() (byte, error) {
if br, ok := r.r.(io.ByteReader); ok {
return br.ReadByte()
}
var b [1]byte
n, err := r.r.Read(b[:])
if n == 1 {
return b[0], nil
}
if err == nil {
if n != 0 {
panic("reader returned an invalid length")
}
err = io.ErrNoProgress
}
return 0, err
}
func (r *mhReader) ReadMultihash() (Multihash, error) {
code, err := varint.ReadUvarint(r)
if err != nil {
return nil, err
}
length, err := varint.ReadUvarint(r)
if err != nil {
return nil, err
}
if length > math.MaxInt32 {
return nil, errors.New("digest too long, supporting only <= 2^31-1")
}
buf := make([]byte, varint.UvarintSize(code)+varint.UvarintSize(length)+int(length))
n := varint.PutUvarint(buf, code)
n += varint.PutUvarint(buf[n:], length)
if _, err := io.ReadFull(r.r, buf[n:]); err != nil {
return nil, err
}
return Cast(buf)
}
type mhWriter struct {
w io.Writer
}
func (w *mhWriter) Write(buf []byte) (n int, err error) {
return w.w.Write(buf)
}
func (w *mhWriter) WriteMultihash(m Multihash) error {
_, err := w.w.Write([]byte(m))
return err
}
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