1 files changed, 529 insertions, 0 deletions
diff --git a/tools/nixery/builder/builder.go b/tools/nixery/builder/builder.go
new file mode 100644
index 0000000000..4279cb0a11
--- /dev/null
+++ b/tools/nixery/builder/builder.go
@@ -0,0 +1,529 @@
+// 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 logic for assembling container
+// images. It shells out to Nix to retrieve all required Nix-packages
+// and assemble the symlink layer and then creates the required
+// tarballs in-process.
+package builder
+
+import (
+	"bufio"
+	"bytes"
+	"compress/gzip"
+	"context"
+	"crypto/sha256"
+	"encoding/json"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"sort"
+	"strings"
+
+	"github.com/google/nixery/config"
+	"github.com/google/nixery/manifest"
+	"github.com/google/nixery/storage"
+	log "github.com/sirupsen/logrus"
+)
+
+// The maximum number of layers in an image is 125. To allow for
+// extensibility, the actual number of layers Nixery is "allowed" to
+// use up is set at a lower point.
+const LayerBudget int = 94
+
+// State holds the runtime state that is carried around in Nixery and
+// passed to builder functions.
+type State struct {
+	Storage storage.Backend
+	Cache   *LocalCache
+	Cfg     config.Config
+	Pop     Popularity
+}
+
+// Architecture represents the possible CPU architectures for which
+// container images can be built.
+//
+// The default architecture is amd64, but support for ARM platforms is
+// available within nixpkgs and can be toggled via meta-packages.
+type Architecture struct {
+	// Name of the system tuple to pass to Nix
+	nixSystem string
+
+	// Name of the architecture as used in the OCI manifests
+	imageArch string
+}
+
+var amd64 = Architecture{"x86_64-linux", "amd64"}
+var arm64 = Architecture{"aarch64-linux", "arm64"}
+
+// 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
+
+	// Architecture for which to build the image. Nixery defaults
+	// this to amd64 if not specified via meta-packages.
+	Arch *Architecture
+}
+
+// BuildResult represents the data returned from the server to the
+// HTTP handlers. Error information is propagated straight from Nix
+// for errors inside of the build that should be fed back to the
+// client (such as missing packages).
+type BuildResult struct {
+	Error    string          `json:"error"`
+	Pkgs     []string        `json:"pkgs"`
+	Manifest json.RawMessage `json:"manifest"`
+}
+
+// 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) and append packages that are always included (cacert, iana-etc).
+//
+// Once assembled the image structure uses a sorted representation of
+// the name. This is to avoid unnecessarily cache-busting images if
+// only the order of requested packages has changed.
+func ImageFromName(name string, tag string) Image {
+	pkgs := strings.Split(name, "/")
+	arch, expanded := metaPackages(pkgs)
+	expanded = append(expanded, "cacert", "iana-etc")
+
+	sort.Strings(pkgs)
+	sort.Strings(expanded)
+
+	return Image{
+		Name:     strings.Join(pkgs, "/"),
+		Tag:      tag,
+		Packages: expanded,
+		Arch:     arch,
+	}
+}
+
+// ImageResult represents the output of calling the Nix derivation
+// responsible for preparing an image.
+type ImageResult struct {
+	// These fields are populated in case of an error
+	Error string   `json:"error"`
+	Pkgs  []string `json:"pkgs"`
+
+	// These fields are populated in case of success
+	Graph        runtimeGraph `json:"runtimeGraph"`
+	SymlinkLayer struct {
+		Size    int    `json:"size"`
+		TarHash string `json:"tarHash"`
+		Path    string `json:"path"`
+	} `json:"symlinkLayer"`
+}
+
+// metaPackages expands package names defined by Nixery which either
+// include sets of packages or trigger certain image-building
+// behaviour.
+//
+// Meta-packages must be specified as the first packages in an image
+// name.
+//
+// Currently defined meta-packages are:
+//
+// * `shell`: Includes bash, coreutils and other common command-line tools
+// * `arm64`: Causes Nixery to build images for the ARM64 architecture
+func metaPackages(packages []string) (*Architecture, []string) {
+	arch := &amd64
+
+	var metapkgs []string
+	lastMeta := 0
+	for idx, p := range packages {
+		if p == "shell" || p == "arm64" {
+			metapkgs = append(metapkgs, p)
+			lastMeta = idx + 1
+		} else {
+			break
+		}
+	}
+
+	// Chop off the meta-packages from the front of the package
+	// list
+	packages = packages[lastMeta:]
+
+	for _, p := range metapkgs {
+		switch p {
+		case "shell":
+			packages = append(packages, "bashInteractive", "coreutils", "moreutils", "nano")
+		case "arm64":
+			arch = &arm64
+		}
+	}
+
+	return arch, packages
+}
+
+// logNix logs each output line from Nix. It runs in a goroutine per
+// output channel that should be live-logged.
+func logNix(image, cmd string, r io.ReadCloser) {
+	scanner := bufio.NewScanner(r)
+	for scanner.Scan() {
+		log.WithFields(log.Fields{
+			"image": image,
+			"cmd":   cmd,
+		}).Info("[nix] " + scanner.Text())
+	}
+}
+
+func callNix(program, image string, args []string) ([]byte, error) {
+	cmd := exec.Command(program, args...)
+
+	outpipe, err := cmd.StdoutPipe()
+	if err != nil {
+		return nil, err
+	}
+
+	errpipe, err := cmd.StderrPipe()
+	if err != nil {
+		return nil, err
+	}
+	go logNix(image, program, errpipe)
+
+	if err = cmd.Start(); err != nil {
+		log.WithError(err).WithFields(log.Fields{
+			"image": image,
+			"cmd":   program,
+		}).Error("error invoking Nix")
+
+		return nil, err
+	}
+
+	log.WithFields(log.Fields{
+		"cmd":   program,
+		"image": image,
+	}).Info("invoked Nix build")
+
+	stdout, _ := ioutil.ReadAll(outpipe)
+
+	if err = cmd.Wait(); err != nil {
+		log.WithError(err).WithFields(log.Fields{
+			"image":  image,
+			"cmd":    program,
+			"stdout": stdout,
+		}).Info("failed to invoke Nix")
+
+		return nil, err
+	}
+
+	resultFile := strings.TrimSpace(string(stdout))
+	buildOutput, err := ioutil.ReadFile(resultFile)
+	if err != nil {
+		log.WithError(err).WithFields(log.Fields{
+			"image": image,
+			"file":  resultFile,
+		}).Info("failed to read Nix result file")
+
+		return nil, err
+	}
+
+	return buildOutput, nil
+}
+
+// Call out to Nix and request metadata for the image to be built. All
+// required store paths for the image will be realised, but layers
+// will not yet be created from them.
+//
+// This function is only invoked if the manifest is not found in any
+// cache.
+func prepareImage(s *State, image *Image) (*ImageResult, error) {
+	packages, err := json.Marshal(image.Packages)
+	if err != nil {
+		return nil, err
+	}
+
+	srcType, srcArgs := s.Cfg.Pkgs.Render(image.Tag)
+
+	args := []string{
+		"--timeout", s.Cfg.Timeout,
+		"--argstr", "packages", string(packages),
+		"--argstr", "srcType", srcType,
+		"--argstr", "srcArgs", srcArgs,
+		"--argstr", "system", image.Arch.nixSystem,
+	}
+
+	output, err := callNix("nixery-prepare-image", image.Name, args)
+	if err != nil {
+		// granular error logging is performed in callNix already
+		return nil, err
+	}
+
+	log.WithFields(log.Fields{
+		"image": image.Name,
+		"tag":   image.Tag,
+	}).Info("finished image preparation via Nix")
+
+	var result ImageResult
+	err = json.Unmarshal(output, &result)
+	if err != nil {
+		return nil, err
+	}
+
+	return &result, nil
+}
+
+// Groups layers and checks whether they are present in the cache
+// already, otherwise calls out to Nix to assemble layers.
+//
+// Newly built layers are uploaded to the bucket. Cache entries are
+// added only after successful uploads, which guarantees that entries
+// retrieved from the cache are present in the bucket.
+func prepareLayers(ctx context.Context, s *State, image *Image, result *ImageResult) ([]manifest.Entry, error) {
+	grouped := groupLayers(&result.Graph, &s.Pop, LayerBudget)
+
+	var entries []manifest.Entry
+
+	// Splits the layers into those which are already present in
+	// the cache, and those that are missing.
+	//
+	// Missing layers are built and uploaded to the storage
+	// bucket.
+	for _, l := range grouped {
+		if entry, cached := layerFromCache(ctx, s, l.Hash()); cached {
+			entries = append(entries, *entry)
+		} else {
+			lh := l.Hash()
+
+			// While packing store paths, the SHA sum of
+			// the uncompressed layer is computed and
+			// written to `tarhash`.
+			//
+			// TODO(tazjin): Refactor this to make the
+			// flow of data cleaner.
+			var tarhash string
+			lw := func(w io.Writer) error {
+				var err error
+				tarhash, err = packStorePaths(&l, w)
+				return err
+			}
+
+			entry, err := uploadHashLayer(ctx, s, lh, lw)
+			if err != nil {
+				return nil, err
+			}
+			entry.MergeRating = l.MergeRating
+			entry.TarHash = tarhash
+
+			var pkgs []string
+			for _, p := range l.Contents {
+				pkgs = append(pkgs, packageFromPath(p))
+			}
+
+			log.WithFields(log.Fields{
+				"layer":    lh,
+				"packages": pkgs,
+				"tarhash":  tarhash,
+			}).Info("created image layer")
+
+			go cacheLayer(ctx, s, l.Hash(), *entry)
+			entries = append(entries, *entry)
+		}
+	}
+
+	// Symlink layer (built in the first Nix build) needs to be
+	// included here manually:
+	slkey := result.SymlinkLayer.TarHash
+	entry, err := uploadHashLayer(ctx, s, slkey, func(w io.Writer) error {
+		f, err := os.Open(result.SymlinkLayer.Path)
+		if err != nil {
+			log.WithError(err).WithFields(log.Fields{
+				"image": image.Name,
+				"tag":   image.Tag,
+				"layer": slkey,
+			}).Error("failed to open symlink layer")
+
+			return err
+		}
+		defer f.Close()
+
+		gz := gzip.NewWriter(w)
+		_, err = io.Copy(gz, f)
+		if err != nil {
+			log.WithError(err).WithFields(log.Fields{
+				"image": image.Name,
+				"tag":   image.Tag,
+				"layer": slkey,
+			}).Error("failed to upload symlink layer")
+
+			return err
+		}
+
+		return gz.Close()
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	entry.TarHash = "sha256:" + result.SymlinkLayer.TarHash
+	go cacheLayer(ctx, s, slkey, *entry)
+	entries = append(entries, *entry)
+
+	return entries, nil
+}
+
+// layerWriter is the type for functions that can write a layer to the
+// multiwriter used for uploading & hashing.
+//
+// This type exists to avoid duplication between the handling of
+// symlink layers and store path layers.
+type layerWriter func(w io.Writer) error
+
+// byteCounter is a special io.Writer that counts all bytes written to
+// it and does nothing else.
+//
+// This is required because the ad-hoc writing of tarballs leaves no
+// single place to count the final tarball size otherwise.
+type byteCounter struct {
+	count int64
+}
+
+func (b *byteCounter) Write(p []byte) (n int, err error) {
+	b.count += int64(len(p))
+	return len(p), nil
+}
+
+// Upload a layer tarball to the storage bucket, while hashing it at
+// the same time. The supplied function is expected to provide the
+// layer data to the writer.
+//
+// The initial upload is performed in a 'staging' folder, as the
+// SHA256-hash is not yet available when the upload is initiated.
+//
+// After a successful upload, the file is moved to its final location
+// in the bucket and the build cache is populated.
+//
+// The return value is the layer's SHA256 hash, which is used in the
+// image manifest.
+func uploadHashLayer(ctx context.Context, s *State, key string, lw layerWriter) (*manifest.Entry, error) {
+	path := "staging/" + key
+	sha256sum, size, err := s.Storage.Persist(ctx, path, manifest.LayerType, func(sw io.Writer) (string, int64, error) {
+		// Sets up a "multiwriter" that simultaneously runs both hash
+		// algorithms and uploads to the storage backend.
+		shasum := sha256.New()
+		counter := &byteCounter{}
+		multi := io.MultiWriter(sw, shasum, counter)
+
+		err := lw(multi)
+		sha256sum := fmt.Sprintf("%x", shasum.Sum([]byte{}))
+
+		return sha256sum, counter.count, err
+	})
+
+	if err != nil {
+		log.WithError(err).WithFields(log.Fields{
+			"layer":   key,
+			"backend": s.Storage.Name(),
+		}).Error("failed to create and store layer")
+
+		return nil, err
+	}
+
+	// Hashes are now known and the object is in the bucket, what
+	// remains is to move it to the correct location and cache it.
+	err = s.Storage.Move(ctx, "staging/"+key, "layers/"+sha256sum)
+	if err != nil {
+		log.WithError(err).WithField("layer", key).
+			Error("failed to move layer from staging")
+
+		return nil, err
+	}
+
+	log.WithFields(log.Fields{
+		"layer":  key,
+		"sha256": sha256sum,
+		"size":   size,
+	}).Info("created and persisted layer")
+
+	entry := manifest.Entry{
+		Digest: "sha256:" + sha256sum,
+		Size:   size,
+	}
+
+	return &entry, nil
+}
+
+func BuildImage(ctx context.Context, s *State, image *Image) (*BuildResult, error) {
+	key := s.Cfg.Pkgs.CacheKey(image.Packages, image.Tag)
+	if key != "" {
+		if m, c := manifestFromCache(ctx, s, key); c {
+			return &BuildResult{
+				Manifest: m,
+			}, nil
+		}
+	}
+
+	imageResult, err := prepareImage(s, image)
+	if err != nil {
+		return nil, err
+	}
+
+	if imageResult.Error != "" {
+		return &BuildResult{
+			Error: imageResult.Error,
+			Pkgs:  imageResult.Pkgs,
+		}, nil
+	}
+
+	layers, err := prepareLayers(ctx, s, image, imageResult)
+	if err != nil {
+		return nil, err
+	}
+
+	// If the requested packages include a shell,
+	// set cmd accordingly.
+	cmd := ""
+	for _, pkg := range image.Packages {
+		if pkg == "bashInteractive" {
+			cmd = "bash"
+		}
+	}
+	m, c := manifest.Manifest(image.Arch.imageArch, layers, cmd)
+
+	lw := func(w io.Writer) error {
+		r := bytes.NewReader(c.Config)
+		_, err := io.Copy(w, r)
+		return err
+	}
+
+	if _, err = uploadHashLayer(ctx, s, c.SHA256, lw); err != nil {
+		log.WithError(err).WithFields(log.Fields{
+			"image": image.Name,
+			"tag":   image.Tag,
+		}).Error("failed to upload config")
+
+		return nil, err
+	}
+
+	if key != "" {
+		go cacheManifest(ctx, s, key, m)
+	}
+
+	result := BuildResult{
+		Manifest: m,
+	}
+	return &result, nil
+}