docker api

vendor/github.com/opencontainers/go-digest/README.md

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+# go-digest
+
+[![GoDoc](https://godoc.org/github.com/opencontainers/go-digest?status.svg)](https://godoc.org/github.com/opencontainers/go-digest) [![Go Report Card](https://goreportcard.com/badge/github.com/opencontainers/go-digest)](https://goreportcard.com/report/github.com/opencontainers/go-digest) [![Build Status](https://travis-ci.org/opencontainers/go-digest.svg?branch=master)](https://travis-ci.org/opencontainers/go-digest)
+
+Common digest package used across the container ecosystem.
+
+Please see the [godoc](https://godoc.org/github.com/opencontainers/go-digest) for more information.
+
+# What is a digest?
+
+A digest is just a [hash](https://en.wikipedia.org/wiki/Hash_function).
+
+The most common use case for a digest is to create a content identifier for use in [Content Addressable Storage](https://en.wikipedia.org/wiki/Content-addressable_storage) systems:
+
+```go
+id := digest.FromBytes([]byte("my content"))
+```
+
+In the example above, the id can be used to uniquely identify the byte slice "my content".
+This allows two disparate applications to agree on a verifiable identifier without having to trust one another.
+
+An identifying digest can be verified, as follows:
+
+```go
+if id != digest.FromBytes([]byte("my content")) {
+  return errors.New("the content has changed!")
+}
+```
+
+A `Verifier` type can be used to handle cases where an `io.Reader` makes more sense:
+
+```go
+rd := getContent()
+verifier := id.Verifier()
+io.Copy(verifier, rd)
+
+if !verifier.Verified() {
+  return errors.New("the content has changed!")
+}
+```
+
+Using [Merkle DAGs](https://en.wikipedia.org/wiki/Merkle_tree), this can power a rich, safe, content distribution system.
+
+# Usage
+
+While the [godoc](https://godoc.org/github.com/opencontainers/go-digest) is considered the best resource, a few important items need to be called out when using this package.
+
+1. Make sure to import the hash implementations into your application or the package will panic.
+    You should have something like the following in the main (or other entrypoint) of your application:
+   
+    ```go
+    import (
+        _ "crypto/sha256"
+        _ "crypto/sha512"
+    )
+    ```
+    This may seem inconvenient but it allows you replace the hash 
+    implementations with others, such as https://github.com/stevvooe/resumable.
+ 
+2. Even though `digest.Digest` may be assemblable as a string, _always_ verify your input with `digest.Parse` or use `Digest.Validate` when accepting untrusted input.
+    While there are measures to avoid common problems, this will ensure you have valid digests in the rest of your application.
+
+3. While alternative encodings of hash values (digests) are possible (for example, base64), this package deals exclusively with hex-encoded digests.
+
+# Stability
+
+The Go API, at this stage, is considered stable, unless otherwise noted.
+
+As always, before using a package export, read the [godoc](https://godoc.org/github.com/opencontainers/go-digest).
+
+# Contributing
+
+This package is considered fairly complete.
+It has been in production in thousands (millions?) of deployments and is fairly battle-hardened.
+New additions will be met with skepticism.
+If you think there is a missing feature, please file a bug clearly describing the problem and the alternatives you tried before submitting a PR.
+
+## Code of Conduct
+
+Participation in the OpenContainers community is governed by [OpenContainer's Code of Conduct][code-of-conduct].
+
+## Security
+
+If you find an issue, please follow the [security][security] protocol to report it.
+
+# Copyright and license
+
+Copyright © 2019, 2020 OCI Contributors
+Copyright © 2016 Docker, Inc.
+All rights reserved, except as follows.
+Code is released under the [Apache 2.0 license](LICENSE).
+This `README.md` file and the [`CONTRIBUTING.md`](CONTRIBUTING.md) file are licensed under the Creative Commons Attribution 4.0 International License under the terms and conditions set forth in the file [`LICENSE.docs`](LICENSE.docs).
+You may obtain a duplicate copy of the same license, titled CC BY-SA 4.0, at http://creativecommons.org/licenses/by-sa/4.0/.
+
+[security]: https://github.com/opencontainers/org/blob/master/security
+[code-of-conduct]: https://github.com/opencontainers/org/blob/master/CODE_OF_CONDUCT.md