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readwriteseeker.go
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/
readwriteseeker.go
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package readwriteseeker
import (
"errors"
"io"
"github.com/johncgriffin/overflow"
)
// ReadWriteSeeker is an in-memory io.ReadWriteSeeker implementation
type ReadWriteSeeker struct {
buf []byte
pos int
}
// Write implements the io.Writer interface
func (rws *ReadWriteSeeker) Write(p []byte) (n int, err error) {
minCap := overflow.Addp(rws.pos, len(p))
if minCap > cap(rws.buf) { // Make sure buf has enough capacity:
buf2 := make([]byte, len(rws.buf), overflow.Addp(minCap, len(p))) // add some extra
copy(buf2, rws.buf)
rws.buf = buf2
}
if minCap > len(rws.buf) {
rws.buf = rws.buf[:minCap]
}
copy(rws.buf[rws.pos:], p)
rws.pos += len(p)
return len(p), nil
}
// Seek implements the io.Seeker interface
func (rws *ReadWriteSeeker) Seek(offset int64, whence int) (int64, error) {
newPos, offs := 0, int(offset)
switch whence {
case io.SeekStart:
newPos = offs
case io.SeekCurrent:
newPos = rws.pos + offs
case io.SeekEnd:
newPos = len(rws.buf) + offs
}
if newPos < 0 {
return 0, errors.New("negative result pos")
}
rws.pos = newPos
return int64(newPos), nil
}
// Close is a no-op that implements the io.Closer interface
func (rws *ReadWriteSeeker) Close() error {
return nil
}
// Read implements the io.Reader interface
func (rws *ReadWriteSeeker) Read(b []byte) (n int, err error) {
if rws.pos >= len(rws.buf) {
return 0, io.EOF
}
n = copy(b, rws.buf[rws.pos:])
rws.pos += n
return
}