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ondemandreader.go
62 lines (51 loc) · 1.08 KB
/
ondemandreader.go
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// SPDX-FileCopyrightText: 2022 SAP SE or an SAP affiliate company and Open Component Model contributors.
//
// SPDX-License-Identifier: Apache-2.0
package accessio
import (
"io"
"sync"
"github.com/open-component-model/ocm/pkg/errors"
)
type ReaderProvider interface {
Reader() (io.ReadCloser, error)
}
type OnDemandReader struct {
lock sync.Mutex
provider ReaderProvider
reader io.ReadCloser
err error
}
var _ io.Reader = (*OnDemandReader)(nil)
func NewOndemandReader(p ReaderProvider) io.ReadCloser {
return &OnDemandReader{provider: p}
}
func (o *OnDemandReader) Read(p []byte) (n int, err error) {
o.lock.Lock()
defer o.lock.Unlock()
if o.reader == nil {
r, err := o.provider.Reader()
if err != nil {
o.err = err
return 0, err
}
o.reader = r
}
data, err := o.reader.Read(p)
if err != nil && !errors.Is(err, io.EOF) {
o.err = err
}
return data, err
}
func (o *OnDemandReader) Close() error {
o.lock.Lock()
defer o.lock.Unlock()
if o.reader == nil {
return o.err
}
if o.err != nil {
o.reader.Close()
return o.err
}
return o.reader.Close()
}