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package limit
import (
"errors"
"io"
"sync/atomic"
)
var ErrLimitExceeded = errors.New("reader limit exceeded")
// LimitedReaderAt supports running a callback in case of reaching a read limit
// (bytes), and allows using a smaller limit than a defined offset for a read.
type LimitedReaderAt struct {
read int64
limit int64
parent io.ReaderAt
limitFunc func(int64)
}
func (r *LimitedReaderAt) ReadAt(p []byte, off int64) (int, error) {
if max := r.limit - r.read; int64(len(p)) > max {
p = p[0:max]
}
n, err := r.parent.ReadAt(p, off)
atomic.AddInt64(&r.read, int64(n))
if r.read >= r.limit {
r.limitFunc(r.read)
return n, ErrLimitExceeded
}
return n, err
}
func NewLimitedReaderAt(reader io.ReaderAt, limit int64, limitFunc func(int64)) io.ReaderAt {
return &LimitedReaderAt{parent: reader, limit: limit, limitFunc: limitFunc}
}
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