135 lines
3.4 KiB
Go
135 lines
3.4 KiB
Go
// Copyright 2022 The TVL Contributors
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// SPDX-License-Identifier: Apache-2.0
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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/sha256"
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"encoding/json"
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"fmt"
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"sort"
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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.gzip"
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configType = "application/vnd.docker.container.image.v1+json"
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// image config constants
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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,omitempty"`
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Size int64 `json:"size"`
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Digest string `json:"digest"`
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// These fields are internal to Nixery and not part of the
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// serialised entry.
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MergeRating uint64 `json:"-"`
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TarHash string `json:",omitempty"`
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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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Config struct {
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Cmd []string `json:"cmd,omitempty"`
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Env []string `json:"env,omitempty"`
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} `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 SHA256
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// hash.
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type ConfigLayer struct {
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Config []byte
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SHA256 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(arch string, hashes []string, cmd 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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if cmd != "" {
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c.Config.Cmd = []string{cmd}
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}
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c.Config.Env = []string{"SSL_CERT_FILE=/etc/ssl/certs/ca-bundle.crt"}
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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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}
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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(arch string, layers []Entry, cmd string) (json.RawMessage, ConfigLayer) {
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// Sort layers by their merge rating, from highest to lowest.
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// This makes it likely for a contiguous chain of shared image
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// layers to appear at the beginning of a layer.
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//
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// Due to moby/moby#38446 Docker considers the order of layers
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// when deciding which layers to download again.
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sort.Slice(layers, func(i, j int) bool {
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return layers[i].MergeRating > layers[j].MergeRating
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})
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hashes := make([]string, len(layers))
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for i, l := range layers {
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hashes[i] = l.TarHash
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l.MediaType = LayerType
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l.TarHash = ""
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layers[i] = l
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}
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c := configLayer(arch, hashes, cmd)
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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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