immutable.go

Documentation: cuelabs.dev/go/oci/ociregistry/ocifilter

     1  // Copyright 2023 CUE Labs AG
     2  //
     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 ocifilter implements "filter" functions that wrap or combine ociregistry
    16  // implementations in different ways.
    17  package ocifilter
    18  
    19  import (
    20  	"context"
    21  	"fmt"
    22  
    23  	"cuelabs.dev/go/oci/ociregistry"
    24  	"github.com/opencontainers/go-digest"
    25  )
    26  
    27  // Immutable returns a registry wrap r but only allows content to be
    28  // added but not changed once added: nothing can be deleted and tags
    29  // can't be changed.
    30  func Immutable(r ociregistry.Interface) ociregistry.Interface {
    31  	return immutable{r}
    32  }
    33  
    34  type immutable struct {
    35  	ociregistry.Interface
    36  }
    37  
    38  func (r immutable) PushManifest(ctx context.Context, repo string, tag string, contents []byte, mediaType string) (ociregistry.Descriptor, error) {
    39  	if tag == "" {
    40  		return r.Interface.PushManifest(ctx, repo, tag, contents, mediaType)
    41  	}
    42  	dig := digest.FromBytes(contents)
    43  
    44  	if desc, err := r.ResolveTag(ctx, repo, tag); err == nil {
    45  		if desc.Digest == dig {
    46  			// We're trying to push exactly the same content. That's OK.
    47  			return desc, nil
    48  		}
    49  		return ociregistry.Descriptor{}, fmt.Errorf("this store is immutable: %w", ociregistry.ErrDenied)
    50  	}
    51  	desc, err := r.Interface.PushManifest(ctx, repo, tag, contents, mediaType)
    52  	if err != nil {
    53  		return ociregistry.Descriptor{}, err
    54  	}
    55  	// We've pushed the tag but someone else might also have pushed it at the same time.
    56  	// UNFORTUNATELY if there was a race, then there's a small window in time where
    57  	// some client might have seen the tag change underfoot.
    58  	desc, err = r.ResolveTag(ctx, repo, tag)
    59  	if err != nil {
    60  		return ociregistry.Descriptor{}, fmt.Errorf("cannot resolve tag that's just been pushed: %v", err)
    61  	}
    62  	if desc.Digest != dig {
    63  		// We lost the race.
    64  		return ociregistry.Descriptor{}, fmt.Errorf("this store is immutable: %w", ociregistry.ErrDenied)
    65  	}
    66  	return desc, nil
    67  }
    68  
    69  func (r immutable) DeleteBlob(ctx context.Context, repo string, digest ociregistry.Digest) error {
    70  	return ociregistry.ErrDenied
    71  }
    72  
    73  func (r immutable) DeleteManifest(ctx context.Context, repo string, digest ociregistry.Digest) error {
    74  	return ociregistry.ErrDenied
    75  }
    76  
    77  func (r immutable) DeleteTag(ctx context.Context, repo string, name string) error {
    78  	return ociregistry.ErrDenied
    79  }
    80
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