26 lines
1.5 KiB
Markdown
26 lines
1.5 KiB
Markdown
# Extensibility
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Implementations that are reading/processing [manifests](manifest.md) or [image indexes](image-index.md) MUST NOT generate an error if they encounter an unknown property.
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Instead they MUST ignore unknown properties.
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# Canonicalization
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* OCI Images are [content-addressable](https://en.wikipedia.org/wiki/Content-addressable_storage). See [descriptors](descriptor.md) for more.
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* One benefit of content-addressable storage is easy deduplication.
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* Many images might depend on a particular [layer](layer.md), but there will only be one blob in the [store](image-layout.md).
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* With a different serialization, that same semantic layer would have a different hash, and if both versions of the layer are referenced there will be two blobs with the same semantic content.
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* To allow efficient storage, implementations serializing content for blobs SHOULD use a canonical serialization.
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* This increases the chance that different implementations can push the same semantic content to the store without creating redundant blobs.
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## JSON
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[JSON][] content SHOULD be serialized as [canonical JSON][canonical-json].
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Of the [OCI Image Format Specification media types](media-types.md), all the types ending in `+json` contain JSON content.
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Implementations:
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* [Go][]: [github.com/docker/go][], which claims to implement [canonical JSON][canonical-json] except for Unicode normalization.
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[canonical-json]: http://wiki.laptop.org/go/Canonical_JSON
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[github.com/docker/go]: https://github.com/docker/go/
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[Go]: https://golang.org/
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[JSON]: http://json.org/
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