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// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause
// nardump is like nix-store --dump, but in Go, writing a NAR
// file (tar-like, but focused on being reproducible) to stdout
// or to a hash with the --sri flag.
//
// It lets us calculate a Nix sha256 without the person running
// git-pull-oss.sh having Nix available.
package main
// For the format, see:
// See https://gist.github.com/jbeda/5c79d2b1434f0018d693
import (
"bufio"
"crypto/sha256"
"encoding/base64"
"encoding/binary"
"flag"
"fmt"
"io"
"io/fs"
"log"
"os"
"path"
"sort"
)
var sri = flag.Bool("sri", false, "print SRI")
func main() {
flag.Parse()
if flag.NArg() != 1 {
log.Fatal("usage: nardump <dir>")
}
arg := flag.Arg(0)
if err := os.Chdir(arg); err != nil {
log.Fatal(err)
}
if *sri {
hash := sha256.New()
if err := writeNAR(hash, os.DirFS(".")); err != nil {
log.Fatal(err)
}
fmt.Printf("sha256-%s\n", base64.StdEncoding.EncodeToString(hash.Sum(nil)))
return
}
bw := bufio.NewWriter(os.Stdout)
if err := writeNAR(bw, os.DirFS(".")); err != nil {
log.Fatal(err)
}
bw.Flush()
}
// writeNARError is a sentinel panic type that's recovered by writeNAR
// and converted into the wrapped error.
type writeNARError struct{ err error }
// narWriter writes NAR files.
type narWriter struct {
w io.Writer
fs fs.FS
}
// writeNAR writes a NAR file to w from the root of fs.
func writeNAR(w io.Writer, fs fs.FS) (err error) {
defer func() {
if e := recover(); e != nil {
if we, ok := e.(writeNARError); ok {
err = we.err
return
}
panic(e)
}
}()
nw := &narWriter{w: w, fs: fs}
nw.str("nix-archive-1")
return nw.writeDir(".")
}
func (nw *narWriter) writeDir(dirPath string) error {
ents, err := fs.ReadDir(nw.fs, dirPath)
if err != nil {
return err
}
sort.Slice(ents, func(i, j int) bool {
return ents[i].Name() < ents[j].Name()
})
nw.str("(")
nw.str("type")
nw.str("directory")
for _, ent := range ents {
nw.str("entry")
nw.str("(")
nw.str("name")
nw.str(ent.Name())
nw.str("node")
mode := ent.Type()
sub := path.Join(dirPath, ent.Name())
var err error
switch {
case mode.IsDir():
err = nw.writeDir(sub)
case mode.IsRegular():
err = nw.writeRegular(sub)
case mode&os.ModeSymlink != 0:
err = nw.writeSymlink(sub)
default:
return fmt.Errorf("unsupported file type %v at %q", sub, mode)
}
if err != nil {
return err
}
nw.str(")")
}
nw.str(")")
return nil
}
func (nw *narWriter) writeRegular(path string) error {
nw.str("(")
nw.str("type")
nw.str("regular")
fi, err := fs.Stat(nw.fs, path)
if err != nil {
return err
}
if fi.Mode()&0111 != 0 {
nw.str("executable")
nw.str("")
}
contents, err := fs.ReadFile(nw.fs, path)
if err != nil {
return err
}
nw.str("contents")
if err := writeBytes(nw.w, contents); err != nil {
return err
}
nw.str(")")
return nil
}
func (nw *narWriter) writeSymlink(path string) error {
nw.str("(")
nw.str("type")
nw.str("symlink")
nw.str("target")
// broken symlinks are valid in a nar
// given we do os.chdir(dir) and os.dirfs(".") above
// readlink now resolves relative links even if they are broken
link, err := os.Readlink(path)
if err != nil {
return err
}
nw.str(link)
nw.str(")")
return nil
}
func (nw *narWriter) str(s string) {
if err := writeString(nw.w, s); err != nil {
panic(writeNARError{err})
}
}
func writeString(w io.Writer, s string) error {
var buf [8]byte
binary.LittleEndian.PutUint64(buf[:], uint64(len(s)))
if _, err := w.Write(buf[:]); err != nil {
return err
}
if _, err := io.WriteString(w, s); err != nil {
return err
}
return writePad(w, len(s))
}
func writeBytes(w io.Writer, b []byte) error {
var buf [8]byte
binary.LittleEndian.PutUint64(buf[:], uint64(len(b)))
if _, err := w.Write(buf[:]); err != nil {
return err
}
if _, err := w.Write(b); err != nil {
return err
}
return writePad(w, len(b))
}
func writePad(w io.Writer, n int) error {
pad := n % 8
if pad == 0 {
return nil
}
var zeroes [8]byte
_, err := w.Write(zeroes[:8-pad])
return err
}
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