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// Copyright 2019 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
// 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"
"encoding/json"
"fmt"
"log"
"net/http"
"regexp"
"time"
"cloud.google.com/go/storage"
"github.com/google/nixery/builder"
"github.com/google/nixery/config"
)
// 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"
// 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|\-|\.|\_]+)$`)
layerRegex = regexp.MustCompile(`^/v2/([\w|\-|\.|\_|\/]+)/blobs/sha256:(\w+)$`)
)
// layerRedirect constructs the public URL of the layer object in the Cloud
// Storage bucket, signs it and redirects the user there.
//
// Signing the URL allows unauthenticated clients to retrieve objects from the
// bucket.
//
// The Docker client is known to follow redirects, but this might not be true
// for all other registry clients.
func constructLayerUrl(cfg *config.Config, digest string) (string, error) {
log.Printf("Redirecting layer '%s' request to bucket '%s'\n", digest, cfg.Bucket)
object := "layers/" + digest
if cfg.Signing != nil {
opts := *cfg.Signing
opts.Expires = time.Now().Add(5 * time.Minute)
return storage.SignedURL(cfg.Bucket, object, &opts)
} else {
return ("https://storage.googleapis.com/" + cfg.Bucket + "/" + object), nil
}
}
// prepareBucket configures the handle to a Cloud Storage bucket in which
// individual layers will be stored after Nix builds. Nixery does not directly
// serve layers to registry clients, instead it redirects them to the public
// URLs of the Cloud Storage bucket.
//
// The bucket is required for Nixery to function correctly, hence fatal errors
// are generated in case it fails to be set up correctly.
func prepareBucket(ctx *context.Context, cfg *config.Config) *storage.BucketHandle {
client, err := storage.NewClient(*ctx)
if err != nil {
log.Fatalln("Failed to set up Cloud Storage client:", err)
}
bkt := client.Bucket(cfg.Bucket)
if _, err := bkt.Attrs(*ctx); err != nil {
log.Fatalln("Could not access configured bucket", err)
}
return bkt
}
// 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 {
cfg *config.Config
ctx *context.Context
bucket *storage.BucketHandle
}
func (h *registryHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
// Acknowledge that we speak V2 with an empty response
if r.RequestURI == "/v2/" {
return
}
// Serve the manifest (straight from Nix)
manifestMatches := manifestRegex.FindStringSubmatch(r.RequestURI)
if len(manifestMatches) == 3 {
imageName := manifestMatches[1]
imageTag := manifestMatches[2]
log.Printf("Requesting manifest for image %q at tag %q", imageName, imageTag)
image := builder.ImageFromName(imageName, imageTag)
buildResult, err := builder.BuildImage(h.ctx, h.cfg, &image, h.bucket)
if err != nil {
writeError(w, 500, "UNKNOWN", "image build failure")
log.Println("Failed to build image manifest", err)
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.Println(s)
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)
w.Write(manifest)
return
}
// Serve an image layer. For this we need to first ask Nix for
// the manifest, then proceed to extract the correct layer from
// it.
layerMatches := layerRegex.FindStringSubmatch(r.RequestURI)
if len(layerMatches) == 3 {
digest := layerMatches[2]
url, err := constructLayerUrl(h.cfg, digest)
if err != nil {
log.Printf("Failed to sign GCS URL: %s\n", err)
writeError(w, 500, "UNKNOWN", "could not serve layer")
return
}
w.Header().Set("Location", url)
w.WriteHeader(303)
return
}
log.Printf("Unsupported registry route: %s\n", r.RequestURI)
w.WriteHeader(404)
}
func main() {
cfg := config.FromEnv()
ctx := context.Background()
bucket := prepareBucket(&ctx, cfg)
log.Printf("Starting Kubernetes Nix controller on port %s\n", cfg.Port)
// All /v2/ requests belong to the registry handler.
http.Handle("/v2/", ®istryHandler{
cfg: cfg,
ctx: &ctx,
bucket: bucket,
})
// 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))
}
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