cc35bf0fc3
Extends storage.Persist to accept a Content-Type argument, which in the GCS backend is persisted with the object to ensure that the object is served back with this content-type. This is not yet implemented for the filesystem backend, where the parameter is simply ignored. This should help in the case of clients which expect the returned objects to have content-types set when, for example, fetching layers by digest.
141 lines
3.8 KiB
Go
141 lines
3.8 KiB
Go
// Copyright 2019 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not
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// use this file except in compliance with the License. You may obtain a copy of
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// the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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// License for the specific language governing permissions and limitations under
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// the License.
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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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// 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 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) 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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}
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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) (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)
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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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