Merge pull request opencontainers#339 from wking/should-canonical-json

canonicalization: Add recommendations for canonicalization

Makefile

@@ -30,7 +30,8 @@ DOC_FILES := \
 	layer.md \
 	config.md \
 	manifest.md \
-	manifest-list.md
+	manifest-list.md \
+	canonicalization.md
 
 FIGURE_FILES := \
 	img/media-types.png

README.md

@@ -14,6 +14,7 @@ The OCI Image Format project creates and maintains the software shipping contain
 - [Image Configuration](config.md)
 - [Image Manifest](manifest.md)
 - [Image Manifest List](manifest-list.md)
+- [Canonicalization](canonicalization.md)
 
 ## Overview
 

canonicalization.md

@@ -0,0 +1,21 @@
+# Canonicalization
+
+OCI Images [are](descriptor.md) [content-addressable](image-layout.md).
+One benefit of content-addressable storage is easy deduplication.
+Many images might depend on a particular [layer](layer.md), but there will only be one blob in the [store](image-layout.md).
+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.
+To allow efficient storage, implementations serializing content for blobs SHOULD use a canonical serialization.
+This increases the chance that different implementations can push the same semantic content to the store without creating redundant blobs.
+
+## JSON
+
+[JSON][] content SHOULD be serialized as [canonical JSON][canonical-json].
+Of the [OCI Image Format Specification media types](media-types.md), all the types ending in `+json` contain JSON content.
+Implementations:
+
+* [Go][]: [github.com/docker/go][], which claims to implement [canonical JSON][canonical-json] except for Unicode normalization.
+
+[canonical-json]: http://wiki.laptop.org/go/Canonical_JSON
+[github.com/docker/go]: https://github.com/docker/go/
+[Go]: https://golang.org/
+[JSON]: http://json.org/