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forgejo/vendor/github.com/djherbis/buffer/wrapio/limitwrap.go

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package wrapio
import (
"encoding/gob"
"io"
"github.com/djherbis/buffer/limio"
)
// ReadWriterAt implements io.ReaderAt and io.WriterAt
type ReadWriterAt interface {
io.ReaderAt
io.WriterAt
}
// Wrapper implements a io.ReadWriter and ReadWriterAt such that
// when reading/writing goes past N bytes, it "wraps" back to the beginning.
type Wrapper struct {
// N is the offset at which to "wrap" back to the start
N int64
// L is the length of the data written
L int64
// O is our offset in the data
O int64
rwa ReadWriterAt
}
// NewWrapper creates a Wrapper based on ReadWriterAt rwa.
// L is the current length, O is the current offset, and N is offset at which we "wrap".
func NewWrapper(rwa ReadWriterAt, L, O, N int64) *Wrapper {
return &Wrapper{
L: L,
O: O,
N: N,
rwa: rwa,
}
}
// Len returns the # of bytes in the Wrapper
func (wpr *Wrapper) Len() int64 {
return wpr.L
}
// Cap returns the "wrap" offset (max # of bytes)
func (wpr *Wrapper) Cap() int64 {
return wpr.N
}
// Reset seeks to the start (0 offset), and sets the length to 0.
func (wpr *Wrapper) Reset() {
wpr.O = 0
wpr.L = 0
}
// SetReadWriterAt lets you switch the underlying Read/WriterAt
func (wpr *Wrapper) SetReadWriterAt(rwa ReadWriterAt) {
wpr.rwa = rwa
}
// Read reads from the current offset into p, wrapping at Cap()
func (wpr *Wrapper) Read(p []byte) (n int, err error) {
n, err = wpr.ReadAt(p, 0)
wpr.L -= int64(n)
wpr.O += int64(n)
wpr.O %= wpr.N
return n, err
}
// ReadAt reads from the current offset+off into p, wrapping at Cap()
func (wpr *Wrapper) ReadAt(p []byte, off int64) (n int, err error) {
wrap := NewWrapReader(wpr.rwa, wpr.O+off, wpr.N)
r := io.LimitReader(wrap, wpr.L-off)
return r.Read(p)
}
// Write writes p to the end of the Wrapper (at Len()), wrapping at Cap()
func (wpr *Wrapper) Write(p []byte) (n int, err error) {
return wpr.WriteAt(p, wpr.L)
}
// WriteAt writes p at the current offset+off, wrapping at Cap()
func (wpr *Wrapper) WriteAt(p []byte, off int64) (n int, err error) {
wrap := NewWrapWriter(wpr.rwa, wpr.O+off, wpr.N)
w := limio.LimitWriter(wrap, wpr.N-off)
n, err = w.Write(p)
if wpr.L < off+int64(n) {
wpr.L = int64(n) + off
}
return n, err
}
func init() {
gob.Register(&Wrapper{})
}