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// 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
}
}
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