63 lines
2.5 KiB
Go
63 lines
2.5 KiB
Go
// Copyright 2019, 2020 OCI Contributors
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// Copyright 2017 Docker, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Package digest provides a generalized type to opaquely represent message
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// digests and their operations within the registry. The Digest type is
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// designed to serve as a flexible identifier in a content-addressable system.
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// More importantly, it provides tools and wrappers to work with
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// hash.Hash-based digests with little effort.
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//
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// Basics
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//
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// The format of a digest is simply a string with two parts, dubbed the
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// "algorithm" and the "digest", separated by a colon:
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//
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// <algorithm>:<digest>
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//
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// An example of a sha256 digest representation follows:
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//
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// sha256:7173b809ca12ec5dee4506cd86be934c4596dd234ee82c0662eac04a8c2c71dc
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//
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// The "algorithm" portion defines both the hashing algorithm used to calculate
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// the digest and the encoding of the resulting digest, which defaults to "hex"
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// if not otherwise specified. Currently, all supported algorithms have their
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// digests encoded in hex strings.
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//
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// In the example above, the string "sha256" is the algorithm and the hex bytes
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// are the "digest".
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//
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// Because the Digest type is simply a string, once a valid Digest is
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// obtained, comparisons are cheap, quick and simple to express with the
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// standard equality operator.
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//
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// Verification
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//
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// The main benefit of using the Digest type is simple verification against a
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// given digest. The Verifier interface, modeled after the stdlib hash.Hash
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// interface, provides a common write sink for digest verification. After
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// writing is complete, calling the Verifier.Verified method will indicate
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// whether or not the stream of bytes matches the target digest.
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//
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// Missing Features
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//
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// In addition to the above, we intend to add the following features to this
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// package:
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//
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// 1. A Digester type that supports write sink digest calculation.
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//
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// 2. Suspend and resume of ongoing digest calculations to support efficient digest verification in the registry.
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//
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package digest
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