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diff --git a/pkg/v1/tarball/README.md b/pkg/v1/tarball/README.md new file mode 100644 index 0000000..03f339b --- /dev/null +++ b/pkg/v1/tarball/README.md @@ -0,0 +1,280 @@ +# `tarball` + +[](https://godoc.org/github.com/google/go-containerregistry/pkg/v1/tarball) + +This package produces tarballs that can consumed via `docker load`. Note +that this is a _different_ format from the [`legacy`](/pkg/legacy/tarball) +tarballs that are produced by `docker save`, but this package is still able to +read the legacy tarballs produced by `docker save`. + +## Usage + +```go +package main + +import ( + "os" + + "github.com/google/go-containerregistry/pkg/name" + "github.com/google/go-containerregistry/pkg/v1/tarball" +) + +func main() { + // Read a tarball from os.Args[1] that contains ubuntu. + tag, err := name.NewTag("ubuntu") + if err != nil { + panic(err) + } + img, err := tarball.ImageFromPath(os.Args[1], &tag) + if err != nil { + panic(err) + } + + // Write that tarball to os.Args[2] with a different tag. + newTag, err := name.NewTag("ubuntu:newest") + if err != nil { + panic(err) + } + f, err := os.Create(os.Args[2]) + if err != nil { + panic(err) + } + defer f.Close() + + if err := tarball.Write(newTag, img, f); err != nil { + panic(err) + } +} +``` + +## Structure + +<p align="center"> + <img src="/images/tarball.dot.svg" /> +</p> + +Let's look at what happens when we write out a tarball: + + +### `ubuntu:latest` + +``` +$ crane pull ubuntu ubuntu.tar && mkdir ubuntu && tar xf ubuntu.tar -C ubuntu && rm ubuntu.tar +$ tree ubuntu/ +ubuntu/ +├── 423ae2b273f4c17ceee9e8482fa8d071d90c7d052ae208e1fe4963fceb3d6954.tar.gz +├── b6b53be908de2c0c78070fff0a9f04835211b3156c4e73785747af365e71a0d7.tar.gz +├── de83a2304fa1f7c4a13708a0d15b9704f5945c2be5cbb2b3ed9b2ccb718d0b3d.tar.gz +├── f9a83bce3af0648efaa60b9bb28225b09136d2d35d0bed25ac764297076dec1b.tar.gz +├── manifest.json +└── sha256:72300a873c2ca11c70d0c8642177ce76ff69ae04d61a5813ef58d40ff66e3e7c + +0 directories, 6 files +``` + +There are a couple interesting files here. + +`manifest.json` is the entrypoint: a list of [`tarball.Descriptor`s](https://godoc.org/github.com/google/go-containerregistry/pkg/v1/tarball#Descriptor) +that describe the images contained in this tarball. + +For each image, this has the `RepoTags` (how it was pulled), a `Config` file +that points to the image's config file, a list of `Layers`, and (optionally) +`LayerSources`. + +``` +$ jq < ubuntu/manifest.json +[ + { + "Config": "sha256:72300a873c2ca11c70d0c8642177ce76ff69ae04d61a5813ef58d40ff66e3e7c", + "RepoTags": [ + "ubuntu" + ], + "Layers": [ + "423ae2b273f4c17ceee9e8482fa8d071d90c7d052ae208e1fe4963fceb3d6954.tar.gz", + "de83a2304fa1f7c4a13708a0d15b9704f5945c2be5cbb2b3ed9b2ccb718d0b3d.tar.gz", + "f9a83bce3af0648efaa60b9bb28225b09136d2d35d0bed25ac764297076dec1b.tar.gz", + "b6b53be908de2c0c78070fff0a9f04835211b3156c4e73785747af365e71a0d7.tar.gz" + ] + } +] +``` + +The config file and layers are exactly what you would expect, and match the +registry representations of the same artifacts. You'll notice that the +`manifest.json` contains similar information as the registry manifest, but isn't +quite the same: + +``` +$ crane manifest ubuntu@sha256:0925d086715714114c1988f7c947db94064fd385e171a63c07730f1fa014e6f9 +{ + "schemaVersion": 2, + "mediaType": "application/vnd.docker.distribution.manifest.v2+json", + "config": { + "mediaType": "application/vnd.docker.container.image.v1+json", + "size": 3408, + "digest": "sha256:72300a873c2ca11c70d0c8642177ce76ff69ae04d61a5813ef58d40ff66e3e7c" + }, + "layers": [ + { + "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip", + "size": 26692096, + "digest": "sha256:423ae2b273f4c17ceee9e8482fa8d071d90c7d052ae208e1fe4963fceb3d6954" + }, + { + "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip", + "size": 35365, + "digest": "sha256:de83a2304fa1f7c4a13708a0d15b9704f5945c2be5cbb2b3ed9b2ccb718d0b3d" + }, + { + "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip", + "size": 852, + "digest": "sha256:f9a83bce3af0648efaa60b9bb28225b09136d2d35d0bed25ac764297076dec1b" + }, + { + "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip", + "size": 163, + "digest": "sha256:b6b53be908de2c0c78070fff0a9f04835211b3156c4e73785747af365e71a0d7" + } + ] +} +``` + +This makes it difficult to maintain image digests when roundtripping images +through the tarball format, so it's not a great format if you care about +provenance. + +The ubuntu example didn't have any `LayerSources` -- let's look at another image +that does. + +### `hello-world:nanoserver` + +``` +$ crane pull hello-world:nanoserver@sha256:63c287625c2b0b72900e562de73c0e381472a83b1b39217aef3856cd398eca0b nanoserver.tar +$ mkdir nanoserver && tar xf nanoserver.tar -C nanoserver && rm nanoserver.tar +$ tree nanoserver/ +nanoserver/ +├── 10d1439be4eb8819987ec2e9c140d44d74d6b42a823d57fe1953bd99948e1bc0.tar.gz +├── a35da61c356213336e646756218539950461ff2bf096badf307a23add6e70053.tar.gz +├── be21f08f670160cbae227e3053205b91d6bfa3de750b90c7e00bd2c511ccb63a.tar.gz +├── manifest.json +└── sha256:bc5d255ea81f83c8c38a982a6d29a6f2198427d258aea5f166e49856896b2da6 + +0 directories, 5 files + +$ jq < nanoserver/manifest.json +[ + { + "Config": "sha256:bc5d255ea81f83c8c38a982a6d29a6f2198427d258aea5f166e49856896b2da6", + "RepoTags": [ + "index.docker.io/library/hello-world:i-was-a-digest" + ], + "Layers": [ + "a35da61c356213336e646756218539950461ff2bf096badf307a23add6e70053.tar.gz", + "be21f08f670160cbae227e3053205b91d6bfa3de750b90c7e00bd2c511ccb63a.tar.gz", + "10d1439be4eb8819987ec2e9c140d44d74d6b42a823d57fe1953bd99948e1bc0.tar.gz" + ], + "LayerSources": { + "sha256:26fd2d9d4c64a4f965bbc77939a454a31b607470f430b5d69fc21ded301fa55e": { + "mediaType": "application/vnd.docker.image.rootfs.foreign.diff.tar.gzip", + "size": 101145811, + "digest": "sha256:a35da61c356213336e646756218539950461ff2bf096badf307a23add6e70053", + "urls": [ + "https://mcr.microsoft.com/v2/windows/nanoserver/blobs/sha256:a35da61c356213336e646756218539950461ff2bf096badf307a23add6e70053" + ] + } + } + } +] +``` + +A couple things to note about this `manifest.json` versus the other: +* The `RepoTags` field is a bit weird here. `hello-world` is a multi-platform + image, so We had to pull this image by digest, since we're (I'm) on + amd64/linux and wanted to grab a windows image. Since the tarball format + expects a tag under `RepoTags`, and we didn't pull by tag, we replace the + digest with a sentinel `i-was-a-digest` "tag" to appease docker. +* The `LayerSources` has enough information to reconstruct the foreign layers + pointer when pushing/pulling from the registry. For legal reasons, microsoft + doesn't want anyone but them to serve windows base images, so the mediaType + here indicates a "foreign" or "non-distributable" layer with an URL for where + you can download it from microsoft (see the [OCI + image-spec](https://github.com/opencontainers/image-spec/blob/master/layer.md#non-distributable-layers)). + +We can look at what's in the registry to explain both of these things: +``` +$ crane manifest hello-world:nanoserver | jq . +{ + "manifests": [ + { + "digest": "sha256:63c287625c2b0b72900e562de73c0e381472a83b1b39217aef3856cd398eca0b", + "mediaType": "application/vnd.docker.distribution.manifest.v2+json", + "platform": { + "architecture": "amd64", + "os": "windows", + "os.version": "10.0.17763.1040" + }, + "size": 1124 + } + ], + "mediaType": "application/vnd.docker.distribution.manifest.list.v2+json", + "schemaVersion": 2 +} + + +# Note the media type and "urls" field. +$ crane manifest hello-world:nanoserver@sha256:63c287625c2b0b72900e562de73c0e381472a83b1b39217aef3856cd398eca0b | jq . +{ + "schemaVersion": 2, + "mediaType": "application/vnd.docker.distribution.manifest.v2+json", + "config": { + "mediaType": "application/vnd.docker.container.image.v1+json", + "size": 1721, + "digest": "sha256:bc5d255ea81f83c8c38a982a6d29a6f2198427d258aea5f166e49856896b2da6" + }, + "layers": [ + { + "mediaType": "application/vnd.docker.image.rootfs.foreign.diff.tar.gzip", + "size": 101145811, + "digest": "sha256:a35da61c356213336e646756218539950461ff2bf096badf307a23add6e70053", + "urls": [ + "https://mcr.microsoft.com/v2/windows/nanoserver/blobs/sha256:a35da61c356213336e646756218539950461ff2bf096badf307a23add6e70053" + ] + }, + { + "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip", + "size": 1669, + "digest": "sha256:be21f08f670160cbae227e3053205b91d6bfa3de750b90c7e00bd2c511ccb63a" + }, + { + "mediaType": "application/vnd.docker.image.rootfs.diff.tar.gzip", + "size": 949, + "digest": "sha256:10d1439be4eb8819987ec2e9c140d44d74d6b42a823d57fe1953bd99948e1bc0" + } + ] +} +``` + +The `LayerSources` map is keyed by the diffid. Note that `sha256:26fd2d9d4c64a4f965bbc77939a454a31b607470f430b5d69fc21ded301fa55e` matches the first layer in the config file: +``` +$ jq '.[0].LayerSources' < nanoserver/manifest.json +{ + "sha256:26fd2d9d4c64a4f965bbc77939a454a31b607470f430b5d69fc21ded301fa55e": { + "mediaType": "application/vnd.docker.image.rootfs.foreign.diff.tar.gzip", + "size": 101145811, + "digest": "sha256:a35da61c356213336e646756218539950461ff2bf096badf307a23add6e70053", + "urls": [ + "https://mcr.microsoft.com/v2/windows/nanoserver/blobs/sha256:a35da61c356213336e646756218539950461ff2bf096badf307a23add6e70053" + ] + } +} + +$ jq < nanoserver/sha256\:bc5d255ea81f83c8c38a982a6d29a6f2198427d258aea5f166e49856896b2da6 | jq .rootfs +{ + "type": "layers", + "diff_ids": [ + "sha256:26fd2d9d4c64a4f965bbc77939a454a31b607470f430b5d69fc21ded301fa55e", + "sha256:601cf7d78c62e4b4d32a7bbf96a17606a9cea5bd9d22ffa6f34aa431d056b0e8", + "sha256:a1e1a3bf6529adcce4d91dce2cad86c2604a66b507ccbc4d2239f3da0ec5aab9" + ] +} +``` |