796ff086be
This will be required for making a standalone, Nixery-style image builder function usable from Nix. Change-Id: I5e36348bd4c32d249d56f6628cd046916691319f Reviewed-on: https://cl.tvl.fyi/c/depot/+/5601 Tested-by: BuildkiteCI Reviewed-by: sterni <sternenseemann@systemli.org>
104 lines
2.3 KiB
Go
104 lines
2.3 KiB
Go
// Copyright 2022 The TVL Contributors
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// SPDX-License-Identifier: Apache-2.0
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package builder
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// This file implements logic for walking through a directory and creating a
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// tarball of it.
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//
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// The tarball is written straight to the supplied reader, which makes it
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// possible to create an image layer from the specified store paths, hash it and
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// upload it in one reading pass.
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import (
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"archive/tar"
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"compress/gzip"
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"crypto/sha256"
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"fmt"
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"io"
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"os"
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"path/filepath"
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"github.com/google/nixery/layers"
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)
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// Create a new compressed tarball from each of the paths in the list
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// and write it to the supplied writer.
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//
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// The uncompressed tarball is hashed because image manifests must
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// contain both the hashes of compressed and uncompressed layers.
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func packStorePaths(l *layers.Layer, w io.Writer) (string, error) {
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shasum := sha256.New()
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gz := gzip.NewWriter(w)
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multi := io.MultiWriter(shasum, gz)
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t := tar.NewWriter(multi)
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for _, path := range l.Contents {
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err := filepath.Walk(path, tarStorePath(t))
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if err != nil {
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return "", err
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}
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}
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if err := t.Close(); err != nil {
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return "", err
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}
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if err := gz.Close(); err != nil {
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return "", err
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}
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return fmt.Sprintf("sha256:%x", shasum.Sum([]byte{})), nil
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}
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func tarStorePath(w *tar.Writer) filepath.WalkFunc {
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return func(path string, info os.FileInfo, err error) error {
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if err != nil {
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return err
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}
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// If the entry is not a symlink or regular file, skip it.
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if info.Mode()&os.ModeSymlink == 0 && !info.Mode().IsRegular() {
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return nil
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}
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// the symlink target is read if this entry is a symlink, as it
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// is required when creating the file header
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var link string
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if info.Mode()&os.ModeSymlink != 0 {
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link, err = os.Readlink(path)
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if err != nil {
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return err
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}
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}
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header, err := tar.FileInfoHeader(info, link)
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if err != nil {
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return err
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}
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// The name retrieved from os.FileInfo only contains the file's
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// basename, but the full path is required within the layer
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// tarball.
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header.Name = path
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if err = w.WriteHeader(header); err != nil {
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return err
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}
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// At this point, return if no file content needs to be written
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if !info.Mode().IsRegular() {
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return nil
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}
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f, err := os.Open(path)
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if err != nil {
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return err
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}
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if _, err := io.Copy(w, f); err != nil {
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return err
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}
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f.Close()
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return nil
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}
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}
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