provider.go

Documentation: oras.land/oras-go/pkg/oras

     1  /*
     2  Copyright The ORAS Authors.
     3  Licensed under the Apache License, Version 2.0 (the "License");
     4  you may not use this file except in compliance with the License.
     5  You may obtain a copy of the License at
     6  
     7  http://www.apache.org/licenses/LICENSE-2.0
     8  
     9  Unless required by applicable law or agreed to in writing, software
    10  distributed under the License is distributed on an "AS IS" BASIS,
    11  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  See the License for the specific language governing permissions and
    13  limitations under the License.
    14  */
    15  package oras
    16  
    17  import (
    18  	"context"
    19  	"errors"
    20  	"io"
    21  
    22  	"github.com/containerd/containerd/content"
    23  	"github.com/containerd/containerd/remotes"
    24  	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
    25  )
    26  
    27  // ProviderWrapper wraps a remote.Fetcher to make a content.Provider, which is useful for things
    28  type ProviderWrapper struct {
    29  	Fetcher remotes.Fetcher
    30  }
    31  
    32  func (p *ProviderWrapper) ReaderAt(ctx context.Context, desc ocispec.Descriptor) (content.ReaderAt, error) {
    33  	if p.Fetcher == nil {
    34  		return nil, errors.New("no Fetcher provided")
    35  	}
    36  	return &fetcherReaderAt{
    37  		ctx:     ctx,
    38  		fetcher: p.Fetcher,
    39  		desc:    desc,
    40  		offset:  0,
    41  	}, nil
    42  }
    43  
    44  type fetcherReaderAt struct {
    45  	ctx     context.Context
    46  	fetcher remotes.Fetcher
    47  	desc    ocispec.Descriptor
    48  	rc      io.ReadCloser
    49  	offset  int64
    50  }
    51  
    52  func (f *fetcherReaderAt) Close() error {
    53  	if f.rc == nil {
    54  		return nil
    55  	}
    56  	return f.rc.Close()
    57  }
    58  
    59  func (f *fetcherReaderAt) Size() int64 {
    60  	return f.desc.Size
    61  }
    62  
    63  func (f *fetcherReaderAt) ReadAt(p []byte, off int64) (n int, err error) {
    64  	// if we do not have a readcloser, get it
    65  	if f.rc == nil || f.offset != off {
    66  		rc, err := f.fetcher.Fetch(f.ctx, f.desc)
    67  		if err != nil {
    68  			return 0, err
    69  		}
    70  		f.rc = rc
    71  	}
    72  
    73  	n, err = io.ReadFull(f.rc, p)
    74  	if err != nil {
    75  		return n, err
    76  	}
    77  	f.offset += int64(n)
    78  	return n, err
    79  }
    80
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