feat(server): Implement package for creating image manifests
The new manifest package creates image manifests and their configuration. This previously happened in Nix, but is now part of the server's workload. This relates to #50.
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114
tools/nixery/server/manifest/manifest.go
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114
tools/nixery/server/manifest/manifest.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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