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/server/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 } }