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converter.go
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converter.go
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package io
import (
"io"
"io/ioutil"
"sync"
)
var (
_ io.ByteReader = (*readerPlusByte)(nil)
_ io.ByteReader = (*readSeekerPlusByte)(nil)
_ io.ByteReader = (*discardingReadSeekerPlusByte)(nil)
_ io.ReadSeeker = (*discardingReadSeekerPlusByte)(nil)
_ io.ReaderAt = (*readSeekerAt)(nil)
)
type (
readerPlusByte struct {
io.Reader
byteBuf [1]byte // escapes via io.Reader.Read; preallocate
}
readSeekerPlusByte struct {
io.ReadSeeker
byteBuf [1]byte // escapes via io.Reader.Read; preallocate
}
discardingReadSeekerPlusByte struct {
io.Reader
offset int64
byteBuf [1]byte // escapes via io.Reader.Read; preallocate
}
ByteReadSeeker interface {
io.ReadSeeker
io.ByteReader
}
readSeekerAt struct {
rs io.ReadSeeker
mu sync.Mutex
}
)
func ToByteReader(r io.Reader) io.ByteReader {
if br, ok := r.(io.ByteReader); ok {
return br
}
return &readerPlusByte{Reader: r}
}
func ToByteReadSeeker(r io.Reader) ByteReadSeeker {
if brs, ok := r.(ByteReadSeeker); ok {
return brs
}
if rs, ok := r.(io.ReadSeeker); ok {
return &readSeekerPlusByte{ReadSeeker: rs}
}
return &discardingReadSeekerPlusByte{Reader: r}
}
func ToReaderAt(rs io.ReadSeeker) io.ReaderAt {
if ra, ok := rs.(io.ReaderAt); ok {
return ra
}
return &readSeekerAt{rs: rs}
}
func (rb *readerPlusByte) ReadByte() (byte, error) {
_, err := io.ReadFull(rb, rb.byteBuf[:])
return rb.byteBuf[0], err
}
func (rsb *readSeekerPlusByte) ReadByte() (byte, error) {
_, err := io.ReadFull(rsb, rsb.byteBuf[:])
return rsb.byteBuf[0], err
}
func (drsb *discardingReadSeekerPlusByte) ReadByte() (byte, error) {
_, err := io.ReadFull(drsb, drsb.byteBuf[:])
return drsb.byteBuf[0], err
}
func (drsb *discardingReadSeekerPlusByte) Read(p []byte) (read int, err error) {
read, err = drsb.Reader.Read(p)
drsb.offset += int64(read)
return
}
func (drsb *discardingReadSeekerPlusByte) Seek(offset int64, whence int) (int64, error) {
switch whence {
case io.SeekStart:
n := offset - drsb.offset
if n < 0 {
panic("unsupported rewind via whence: io.SeekStart")
}
_, err := io.CopyN(ioutil.Discard, drsb, n)
return drsb.offset, err
case io.SeekCurrent:
_, err := io.CopyN(ioutil.Discard, drsb, offset)
return drsb.offset, err
default:
panic("unsupported whence: io.SeekEnd")
}
}
func (rsa *readSeekerAt) ReadAt(p []byte, off int64) (n int, err error) {
rsa.mu.Lock()
defer rsa.mu.Unlock()
if _, err := rsa.rs.Seek(off, io.SeekStart); err != nil {
return 0, err
}
return rsa.rs.Read(p)
}