// 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.
// Package builder implements the code required to build images via Nix. Image
// build data is cached for up to 24 hours to avoid duplicated calls to Nix
// (which are costly even if no building is performed).
package builder
import (
"bytes"
"context"
"encoding/json"
"fmt"
"io"
"io/ioutil"
"log"
"os"
"os/exec"
"strings"
"cloud.google.com/go/storage"
"github.com/google/nixery/config"
)
// Image represents the information necessary for building a container image.
// This can be either a list of package names (corresponding to keys in the
// nixpkgs set) or a Nix expression that results in a *list* of derivations.
type Image struct {
Name string
Tag string
// Names of packages to include in the image. These must correspond
// directly to top-level names of Nix packages in the nixpkgs tree.
Packages []string
}
// ImageFromName parses an image name into the corresponding structure which can
// be used to invoke Nix.
//
// It will expand convenience names under the hood (see the `convenienceNames`
// function below).
func ImageFromName(name string, tag string) Image {
packages := strings.Split(name, "/")
return Image{
Name: name,
Tag: tag,
Packages: convenienceNames(packages),
}
}
// BuildResult represents the output of calling the Nix derivation responsible
// for building registry images.
//
// The `layerLocations` field contains the local filesystem paths to each
// individual image layer that will need to be served, while the `manifest`
// field contains the JSON-representation of the manifest that needs to be
// served to the client.
//
// The later field is simply treated as opaque JSON and passed through.
type BuildResult struct {
Error string `json:"error"`
Pkgs []string `json:"pkgs"`
Manifest json.RawMessage `json:"manifest"`
LayerLocations map[string]struct {
Path string `json:"path"`
Md5 []byte `json:"md5"`
} `json:"layerLocations"`
}
// convenienceNames expands convenience package names defined by Nixery which
// let users include commonly required sets of tools in a container quickly.
//
// Convenience names must be specified as the first package in an image.
//
// Currently defined convenience names are:
//
// * `shell`: Includes bash, coreutils and other common command-line tools
func convenienceNames(packages []string) []string {
shellPackages := []string{"bashInteractive", "coreutils", "moreutils", "nano"}
if packages[0] == "shell" {
return append(packages[1:], shellPackages...)
}
return packages
}
// Call out to Nix and request that an image be built. Nix will, upon success,
// return a manifest for the container image.
func BuildImage(ctx *context.Context, cfg *config.Config, cache *BuildCache, image *Image, bucket *storage.BucketHandle) (*BuildResult, error) {
resultFile, cached := cache.manifestFromCache(image)
if !cached {
packages, err := json.Marshal(image.Packages)
if err != nil {
return nil, err
}
args := []string{
"--argstr", "name", image.Name,
"--argstr", "packages", string(packages),
}
if cfg.Pkgs != nil {
args = append(args, "--argstr", "pkgSource", cfg.Pkgs.Render(image.Tag))
}
cmd := exec.Command("nixery-build-image", args...)
outpipe, err := cmd.StdoutPipe()
if err != nil {
return nil, err
}
errpipe, err := cmd.StderrPipe()
if err != nil {
return nil, err
}
if err = cmd.Start(); err != nil {
log.Println("Error starting nix-build:", err)
return nil, err
}
log.Printf("Started Nix image build for '%s'", image.Name)
stdout, _ := ioutil.ReadAll(outpipe)
stderr, _ := ioutil.ReadAll(errpipe)
if err = cmd.Wait(); err != nil {
// TODO(tazjin): Propagate errors upwards in a usable format.
log.Printf("nix-build execution error: %s\nstdout: %s\nstderr: %s\n", err, stdout, stderr)
return nil, err
}
log.Println("Finished Nix image build")
resultFile = strings.TrimSpace(string(stdout))
cache.cacheManifest(image, resultFile)
}
buildOutput, err := ioutil.ReadFile(resultFile)
if err != nil {
return nil, err
}
// The build output returned by Nix is deserialised to add all
// contained layers to the bucket. Only the manifest itself is
// re-serialised to JSON and returned.
var result BuildResult
err = json.Unmarshal(buildOutput, &result)
if err != nil {
return nil, err
}
for layer, meta := range result.LayerLocations {
if !cache.hasSeenLayer(layer) {
err = uploadLayer(ctx, bucket, layer, meta.Path, meta.Md5)
if err != nil {
return nil, err
}
cache.sawLayer(layer)
}
}
return &result, nil
}
// uploadLayer uploads a single layer to Cloud Storage bucket. Before writing
// any data the bucket is probed to see if the file already exists.
//
// If the file does exist, its MD5 hash is verified to ensure that the stored
// file is not - for example - a fragment of a previous, incomplete upload.
func uploadLayer(ctx *context.Context, bucket *storage.BucketHandle, layer string, path string, md5 []byte) error {
layerKey := fmt.Sprintf("layers/%s", layer)
obj := bucket.Object(layerKey)
// Before uploading a layer to the bucket, probe whether it already
// exists.
//
// If it does and the MD5 checksum matches the expected one, the layer
// upload can be skipped.
attrs, err := obj.Attrs(*ctx)
if err == nil && bytes.Equal(attrs.MD5, md5) {
log.Printf("Layer sha256:%s already exists in bucket, skipping upload", layer)
} else {
writer := obj.NewWriter(*ctx)
file, err := os.Open(path)
if err != nil {
return fmt.Errorf("failed to open layer %s from path %s: %v", layer, path, err)
}
size, err := io.Copy(writer, file)
if err != nil {
return fmt.Errorf("failed to write layer %s to Cloud Storage: %v", layer, err)
}
if err = writer.Close(); err != nil {
return fmt.Errorf("failed to write layer %s to Cloud Storage: %v", layer, err)
}
log.Printf("Uploaded layer sha256:%s (%v bytes written)\n", layer, size)
}
return nil
}
