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package iohelpers
import (
"io"
"sync"
)
// LazyReadCloser provides an interface to a ReadCloser that will open on the
// first access. The wrapped io.ReadCloser must be provided by 'open'.
func LazyReadCloser(open func() (io.ReadCloser, error)) io.ReadCloser {
return &lazyReadCloser{
opened: sync.Once{},
open: open,
}
}
type lazyReadCloser struct {
r io.ReadCloser
// caches the error that came from open(), if any
openErr error
open func() (io.ReadCloser, error)
opened sync.Once
}
var _ io.ReadCloser = (*lazyReadCloser)(nil)
func (l *lazyReadCloser) openReader() (r io.ReadCloser, err error) {
l.opened.Do(func() {
l.r, l.openErr = l.open()
})
return l.r, l.openErr
}
func (l *lazyReadCloser) Close() error {
r, err := l.openReader()
if err != nil {
return err
}
return r.Close()
}
func (l *lazyReadCloser) Read(p []byte) (n int, err error) {
r, err := l.openReader()
if err != nil {
return 0, err
}
return r.Read(p)
}
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