// Copyright 2022 The TVL Contributors
// SPDX-License-Identifier: Apache-2.0
// The nixery server implements a container registry that transparently builds
// container images based on Nix derivations.
//
// The Nix derivation used for image creation is responsible for creating
// objects that are compatible with the registry API. The targeted registry
// protocol is currently Docker's.
//
// When an image is requested, the required contents are parsed out of the
// request and a Nix-build is initiated that eventually responds with the
// manifest as well as information linking each layer digest to a local
// filesystem path.
package main
import (
"context"
"crypto/sha256"
"encoding/json"
"fmt"
"io"
"io/ioutil"
"net/http"
"regexp"
"github.com/google/nixery/builder"
"github.com/google/nixery/config"
"github.com/google/nixery/layers"
"github.com/google/nixery/logs"
mf "github.com/google/nixery/manifest"
"github.com/google/nixery/storage"
log "github.com/sirupsen/logrus"
)
// ManifestMediaType is the Content-Type used for the manifest itself. This
// corresponds to the "Image Manifest V2, Schema 2" described on this page:
//
// https://docs.docker.com/registry/spec/manifest-v2-2/
const manifestMediaType string = "application/vnd.docker.distribution.manifest.v2+json"
// This variable will be initialised during the build process and set
// to the hash of the entire Nixery source tree.
var version string = "devel"
// Regexes matching the V2 Registry API routes. This only includes the
// routes required for serving images, since pushing and other such
// functionality is not available.
var (
manifestRegex = regexp.MustCompile(`^/v2/([\w|\-|\.|\_|\/]+)/manifests/([\w|\-|\.|\_]+)$`)
blobRegex = regexp.MustCompile(`^/v2/([\w|\-|\.|\_|\/]+)/(blobs|manifests)/sha256:(\w+)$`)
)
// Downloads the popularity information for the package set from the
// URL specified in Nixery's configuration.
func downloadPopularity(url string) (layers.Popularity, error) {
resp, err := http.Get(url)
if err != nil {
return nil, err
}
if resp.StatusCode != 200 {
return nil, fmt.Errorf("popularity download from '%s' returned status: %s\n", url, resp.Status)
}
j, err := ioutil.ReadAll(resp.Body)
if err != nil {
return nil, err
}
var pop layers.Popularity
err = json.Unmarshal(j, &pop)
if err != nil {
return nil, err
}
return pop, nil
}
// Error format corresponding to the registry protocol V2 specification. This
// allows feeding back errors to clients in a way that can be presented to
// users.
type registryError struct {
Code string `json:"code"`
Message string `json:"message"`
}
type registryErrors struct {
Errors []registryError `json:"errors"`
}
func writeError(w http.ResponseWriter, status int, code, message string) {
err := registryErrors{
Errors: []registryError{
{code, message},
},
}
json, _ := json.Marshal(err)
w.WriteHeader(status)
w.Header().Add("Content-Type", "application/json")
w.Write(json)
}
type registryHandler struct {
state *builder.State
}
// Serve a manifest by tag, building it via Nix and populating caches
// if necessary.
func (h *registryHandler) serveManifestTag(w http.ResponseWriter, r *http.Request, name string, tag string) {
log.WithFields(log.Fields{
"image": name,
"tag": tag,
}).Info("requesting image manifest")
image := builder.ImageFromName(name, tag)
buildResult, err := builder.BuildImage(r.Context(), h.state, &image)
if err != nil {
writeError(w, 500, "UNKNOWN", "image build failure")
log.WithError(err).WithFields(log.Fields{
"image": name,
"tag": tag,
}).Error("failed to build image manifest")
return
}
// Some error types have special handling, which is applied
// here.
if buildResult.Error == "not_found" {
s := fmt.Sprintf("Could not find Nix packages: %v", buildResult.Pkgs)
writeError(w, 404, "MANIFEST_UNKNOWN", s)
log.WithFields(log.Fields{
"image": name,
"tag": tag,
"packages": buildResult.Pkgs,
}).Warn("could not find Nix packages")
return
}
// This marshaling error is ignored because we know that this
// field represents valid JSON data.
manifest, _ := json.Marshal(buildResult.Manifest)
w.Header().Add("Content-Type", manifestMediaType)
// The manifest needs to be persisted to the blob storage (to become
// available for clients that fetch manifests by their hash, e.g.
// containerd) and served to the client.
//
// Since we have no stable key to address this manifest (it may be
// uncacheable, yet still addressable by blob) we need to separate
// out the hashing, uploading and serving phases. The latter is
// especially important as clients may start to fetch it by digest
// as soon as they see a response.
sha256sum := fmt.Sprintf("%x", sha256.Sum256(manifest))
path := "layers/" + sha256sum
ctx := context.TODO()
_, _, err = h.state.Storage.Persist(ctx, path, mf.ManifestType, func(sw io.Writer) (string, int64, error) {
// We already know the hash, so no additional hash needs to be
// constructed here.
written, err := sw.Write(manifest)
return sha256sum, int64(written), err
})
if err != nil {
writeError(w, 500, "MANIFEST_UPLOAD", "could not upload manifest to blob store")
log.WithError(err).WithFields(log.Fields{
"image": name,
"tag": tag,
}).Error("could not upload manifest")
return
}
w.Write(manifest)
}
// serveBlob serves a blob from storage by digest
func (h *registryHandler) serveBlob(w http.ResponseWriter, r *http.Request, blobType, digest string) {
storage := h.state.Storage
err := storage.Serve(digest, r, w)
if err != nil {
log.WithError(err).WithFields(log.Fields{
"type": blobType,
"digest": digest,
"backend": storage.Name(),
}).Error("failed to serve blob from storage backend")
}
}
// ServeHTTP dispatches HTTP requests to the matching handlers.
func (h *registryHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// Acknowledge that we speak V2 with an empty response
if r.RequestURI == "/v2/" {
return
}
// Build & serve a manifest by tag
manifestMatches := manifestRegex.FindStringSubmatch(r.RequestURI)
if len(manifestMatches) == 3 {
h.serveManifestTag(w, r, manifestMatches[1], manifestMatches[2])
return
}
// Serve a blob by digest
layerMatches := blobRegex.FindStringSubmatch(r.RequestURI)
if len(layerMatches) == 4 {
h.serveBlob(w, r, layerMatches[2], layerMatches[3])
return
}
log.WithField("uri", r.RequestURI).Info("unsupported registry route")
w.WriteHeader(404)
}
func main() {
logs.Init(version)
cfg, err := config.FromEnv()
if err != nil {
log.WithError(err).Fatal("failed to load configuration")
}
var s storage.Backend
switch cfg.Backend {
case config.GCS:
s, err = storage.NewGCSBackend()
case config.FileSystem:
s, err = storage.NewFSBackend()
}
if err != nil {
log.WithError(err).Fatal("failed to initialise storage backend")
}
log.WithField("backend", s.Name()).Info("initialised storage backend")
cache, err := builder.NewCache()
if err != nil {
log.WithError(err).Fatal("failed to instantiate build cache")
}
var pop layers.Popularity
if cfg.PopUrl != "" {
pop, err = downloadPopularity(cfg.PopUrl)
if err != nil {
log.WithError(err).WithField("popURL", cfg.PopUrl).
Fatal("failed to fetch popularity information")
}
}
state := builder.State{
Cache: &cache,
Cfg: cfg,
Pop: pop,
Storage: s,
}
log.WithFields(log.Fields{
"version": version,
"port": cfg.Port,
}).Info("starting Nixery")
// All /v2/ requests belong to the registry handler.
http.Handle("/v2/", ®istryHandler{
state: &state,
})
// All other roots are served by the static file server.
webDir := http.Dir(cfg.WebDir)
http.Handle("/", http.FileServer(webDir))
log.Fatal(http.ListenAndServe(":"+cfg.Port, nil))
}
