1 files changed, 104 insertions, 0 deletions
diff --git a/tools/nixery/builder/archive.go b/tools/nixery/builder/archive.go
new file mode 100644
index 000000000000..8763e4cb8566
--- /dev/null
+++ b/tools/nixery/builder/archive.go
@@ -0,0 +1,104 @@
+// Copyright 2022 The TVL Contributors
+// SPDX-License-Identifier: Apache-2.0
+package builder
+
+// This file implements logic for walking through a directory and creating a
+// tarball of it.
+//
+// The tarball is written straight to the supplied reader, which makes it
+// possible to create an image layer from the specified store paths, hash it and
+// upload it in one reading pass.
+import (
+	"archive/tar"
+	"compress/gzip"
+	"crypto/sha256"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+
+	"github.com/google/nixery/layers"
+)
+
+// Create a new compressed tarball from each of the paths in the list
+// and write it to the supplied writer.
+//
+// The uncompressed tarball is hashed because image manifests must
+// contain both the hashes of compressed and uncompressed layers.
+func packStorePaths(l *layers.Layer, w io.Writer) (string, error) {
+	shasum := sha256.New()
+	gz := gzip.NewWriter(w)
+	multi := io.MultiWriter(shasum, gz)
+	t := tar.NewWriter(multi)
+
+	for _, path := range l.Contents {
+		err := filepath.Walk(path, tarStorePath(t))
+		if err != nil {
+			return "", err
+		}
+	}
+
+	if err := t.Close(); err != nil {
+		return "", err
+	}
+
+	if err := gz.Close(); err != nil {
+		return "", err
+	}
+
+	return fmt.Sprintf("sha256:%x", shasum.Sum([]byte{})), nil
+}
+
+func tarStorePath(w *tar.Writer) filepath.WalkFunc {
+	return func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		// If the entry is not a symlink or regular file, skip it.
+		if info.Mode()&os.ModeSymlink == 0 && !info.Mode().IsRegular() {
+			return nil
+		}
+
+		// the symlink target is read if this entry is a symlink, as it
+		// is required when creating the file header
+		var link string
+		if info.Mode()&os.ModeSymlink != 0 {
+			link, err = os.Readlink(path)
+			if err != nil {
+				return err
+			}
+		}
+
+		header, err := tar.FileInfoHeader(info, link)
+		if err != nil {
+			return err
+		}
+
+		// The name retrieved from os.FileInfo only contains the file's
+		// basename, but the full path is required within the layer
+		// tarball.
+		header.Name = path
+		if err = w.WriteHeader(header); err != nil {
+			return err
+		}
+
+		// At this point, return if no file content needs to be written
+		if !info.Mode().IsRegular() {
+			return nil
+		}
+
+		f, err := os.Open(path)
+		if err != nil {
+			return err
+		}
+
+		if _, err := io.Copy(w, f); err != nil {
+			return err
+		}
+
+		f.Close()
+
+		return nil
+	}
+}