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 16 package content 17 18 import ( 19 "context" 20 "fmt" 21 "io" 22 23 "github.com/containerd/containerd/remotes" 24 ocispec "github.com/opencontainers/image-spec/specs-go/v1" 25 ) 26 27 // MultiReader store to read content from multiple stores. It finds the content by asking each underlying 28 // store to find the content, which it does based on the hash. 29 // 30 // Example: 31 // fileStore := NewFileStore(rootPath) 32 // memoryStore := NewMemoryStore() 33 // // load up content in fileStore and memoryStore 34 // multiStore := MultiReader([]content.Provider{fileStore, memoryStore}) 35 // 36 // You now can use multiStore anywhere that content.Provider is accepted 37 type MultiReader struct { 38 stores []remotes.Fetcher 39 } 40 41 // AddStore add a store to read from 42 func (m *MultiReader) AddStore(store ...remotes.Fetcher) { 43 m.stores = append(m.stores, store...) 44 } 45 46 // ReaderAt get a reader 47 func (m MultiReader) Fetch(ctx context.Context, desc ocispec.Descriptor) (io.ReadCloser, error) { 48 for _, store := range m.stores { 49 r, err := store.Fetch(ctx, desc) 50 if r != nil && err == nil { 51 return r, nil 52 } 53 } 54 // we did not find any 55 return nil, fmt.Errorf("not found") 56 } 57