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104 lines
4 KiB
Markdown
104 lines
4 KiB
Markdown
# go-digest
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[](https://godoc.org/github.com/opencontainers/go-digest) [](https://goreportcard.com/report/github.com/opencontainers/go-digest) [](https://travis-ci.org/opencontainers/go-digest)
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Common digest package used across the container ecosystem.
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Please see the [godoc](https://godoc.org/github.com/opencontainers/go-digest) for more information.
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# What is a digest?
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A digest is just a hash.
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The most common use case for a digest is to create a content
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identifier for use in [Content Addressable Storage](https://en.wikipedia.org/wiki/Content-addressable_storage)
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systems:
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```go
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id := digest.FromBytes([]byte("my content"))
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```
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In the example above, the id can be used to uniquely identify
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the byte slice "my content". This allows two disparate applications
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to agree on a verifiable identifier without having to trust one
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another.
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An identifying digest can be verified, as follows:
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```go
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if id != digest.FromBytes([]byte("my content")) {
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return errors.New("the content has changed!")
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}
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```
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A `Verifier` type can be used to handle cases where an `io.Reader`
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makes more sense:
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```go
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rd := getContent()
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verifier := id.Verifier()
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io.Copy(verifier, rd)
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if !verifier.Verified() {
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return errors.New("the content has changed!")
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}
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```
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Using [Merkle DAGs](https://en.wikipedia.org/wiki/Merkle_tree), this
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can power a rich, safe, content distribution system.
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# Usage
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While the [godoc](https://godoc.org/github.com/opencontainers/go-digest) is
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considered the best resource, a few important items need to be called
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out when using this package.
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1. Make sure to import the hash implementations into your application
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or the package will panic. You should have something like the
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following in the main (or other entrypoint) of your application:
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```go
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import (
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_ "crypto/sha256"
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_ "crypto/sha512"
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)
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```
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This may seem inconvenient but it allows you replace the hash
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implementations with others, such as https://github.com/stevvooe/resumable.
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2. Even though `digest.Digest` may be assemable as a string, _always_
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verify your input with `digest.Parse` or use `Digest.Validate`
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when accepting untrusted input. While there are measures to
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avoid common problems, this will ensure you have valid digests
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in the rest of your application.
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# Stability
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The Go API, at this stage, is considered stable, unless otherwise noted.
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As always, before using a package export, read the [godoc](https://godoc.org/github.com/opencontainers/go-digest).
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# Contributing
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This package is considered fairly complete. It has been in production
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in thousands (millions?) of deployments and is fairly battle-hardened.
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New additions will be met with skepticism. If you think there is a
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missing feature, please file a bug clearly describing the problem and
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the alternatives you tried before submitting a PR.
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# Reporting security issues
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Please DO NOT file a public issue, instead send your report privately to
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security@opencontainers.org.
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The maintainers take security seriously. If you discover a security issue,
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please bring it to their attention right away!
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If you are reporting a security issue, do not create an issue or file a pull
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request on GitHub. Instead, disclose the issue responsibly by sending an email
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to security@opencontainers.org (which is inhabited only by the maintainers of
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the various OCI projects).
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# Copyright and license
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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/.
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