115 lines
2.7 KiB
Go
115 lines
2.7 KiB
Go
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// Package image implements logic for creating the image metadata
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// (such as the image manifest and configuration).
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package manifest
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import (
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"crypto/md5"
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"crypto/sha256"
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"encoding/json"
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"fmt"
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)
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const (
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// manifest constants
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schemaVersion = 2
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// media types
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manifestType = "application/vnd.docker.distribution.manifest.v2+json"
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layerType = "application/vnd.docker.image.rootfs.diff.tar"
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configType = "application/vnd.docker.container.image.v1+json"
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// image config constants
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arch = "amd64"
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os = "linux"
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fsType = "layers"
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)
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type Entry struct {
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MediaType string `json:"mediaType"`
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Size int64 `json:"size"`
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Digest string `json:"digest"`
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}
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type manifest struct {
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SchemaVersion int `json:"schemaVersion"`
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MediaType string `json:"mediaType"`
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Config Entry `json:"config"`
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Layers []Entry `json:"layers"`
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}
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type imageConfig struct {
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Architecture string `json:"architecture"`
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OS string `json:"os"`
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RootFS struct {
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FSType string `json:"type"`
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DiffIDs []string `json:"diff_ids"`
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} `json:"rootfs"`
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// sic! empty struct (rather than `null`) is required by the
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// image metadata deserialiser in Kubernetes
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Config struct{} `json:"config"`
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}
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// ConfigLayer represents the configuration layer to be included in
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// the manifest, containing its JSON-serialised content and the SHA256
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// & MD5 hashes of its input.
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type ConfigLayer struct {
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Config []byte
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SHA256 string
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MD5 string
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}
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// imageConfig creates an image configuration with the values set to
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// the constant defaults.
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//
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// Outside of this module the image configuration is treated as an
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// opaque blob and it is thus returned as an already serialised byte
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// array and its SHA256-hash.
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func configLayer(hashes []string) ConfigLayer {
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c := imageConfig{}
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c.Architecture = arch
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c.OS = os
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c.RootFS.FSType = fsType
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c.RootFS.DiffIDs = hashes
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j, _ := json.Marshal(c)
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return ConfigLayer{
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Config: j,
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SHA256: fmt.Sprintf("%x", sha256.Sum256(j)),
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MD5: fmt.Sprintf("%x", md5.Sum(j)),
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}
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}
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// Manifest creates an image manifest from the specified layer entries
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// and returns its JSON-serialised form as well as the configuration
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// layer.
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//
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// Callers do not need to set the media type for the layer entries.
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func Manifest(layers []Entry) (json.RawMessage, ConfigLayer) {
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hashes := make([]string, len(layers))
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for i, l := range layers {
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l.MediaType = "application/vnd.docker.image.rootfs.diff.tar"
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layers[i] = l
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hashes[i] = l.Digest
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}
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c := configLayer(hashes)
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m := manifest{
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SchemaVersion: schemaVersion,
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MediaType: manifestType,
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Config: Entry{
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MediaType: configType,
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Size: int64(len(c.Config)),
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Digest: "sha256:" + c.SHA256,
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},
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Layers: layers,
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}
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j, _ := json.Marshal(m)
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return json.RawMessage(j), c
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}
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