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|
package contentutil
import (
"context"
"io"
"github.com/containerd/containerd/content"
"github.com/containerd/containerd/remotes"
ocispecs "github.com/opencontainers/image-spec/specs-go/v1"
"github.com/pkg/errors"
)
func FromFetcher(f remotes.Fetcher) content.Provider {
return &fetchedProvider{
f: f,
}
}
type fetchedProvider struct {
f remotes.Fetcher
}
func (p *fetchedProvider) ReaderAt(ctx context.Context, desc ocispecs.Descriptor) (content.ReaderAt, error) {
rc, err := p.f.Fetch(ctx, desc)
if err != nil {
return nil, err
}
return &readerAt{Reader: rc, Closer: rc, size: desc.Size}, nil
}
type readerAt struct {
io.Reader
io.Closer
size int64
offset int64
}
func (r *readerAt) ReadAt(b []byte, off int64) (int, error) {
if ra, ok := r.Reader.(io.ReaderAt); ok {
return ra.ReadAt(b, off)
}
if r.offset != off {
if seeker, ok := r.Reader.(io.Seeker); ok {
if _, err := seeker.Seek(off, io.SeekStart); err != nil {
return 0, err
}
r.offset = off
} else {
return 0, errors.Errorf("unsupported offset")
}
}
var totalN int
for len(b) > 0 {
n, err := r.Reader.Read(b)
if err == io.EOF && n == len(b) {
err = nil
}
r.offset += int64(n)
totalN += n
b = b[n:]
if err != nil {
return totalN, err
}
}
return totalN, nil
}
func (r *readerAt) Size() int64 {
return r.size
}
|
