rclone/lib/readers/fakeseeker.go

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package readers
import (
"errors"
"fmt"
"io"
)
// FakeSeeker adapts an io.Seeker into an io.ReadSeeker
type FakeSeeker struct {
in io.Reader
readErr error
length int64
offset int64
read bool
}
// NewFakeSeeker creates a fake io.ReadSeeker from an io.Reader
//
// This can be seeked before reading to discover the length passed in.
func NewFakeSeeker(in io.Reader, length int64) io.ReadSeeker {
if rs, ok := in.(io.ReadSeeker); ok {
return rs
}
return &FakeSeeker{
in: in,
length: length,
}
}
// Seek the stream - possible only before reading
func (r *FakeSeeker) Seek(offset int64, whence int) (abs int64, err error) {
if r.readErr != nil {
return 0, r.readErr
}
if r.read {
return 0, fmt.Errorf("FakeSeeker: can't Seek(%d, %d) after reading", offset, whence)
}
switch whence {
case io.SeekStart:
abs = offset
case io.SeekCurrent:
abs = r.offset + offset
case io.SeekEnd:
abs = r.length + offset
default:
return 0, errors.New("FakeSeeker: invalid whence")
}
if abs < 0 {
return 0, errors.New("FakeSeeker: negative position")
}
r.offset = abs
return abs, nil
}
// Read data from the stream. Will give an error if seeked.
func (r *FakeSeeker) Read(p []byte) (n int, err error) {
if r.readErr != nil {
return 0, r.readErr
}
if !r.read && r.offset != 0 {
return 0, errors.New("FakeSeeker: not at start: can't read")
}
n, err = r.in.Read(p)
if n != 0 {
r.read = true
}
if err != nil {
r.readErr = err
}
return n, err
}