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