wip layers

This commit is contained in:
Motiejus Jakštys 2021-05-24 00:11:57 +03:00
parent 273c337a23
commit 4d6476cca9
1 changed files with 85 additions and 1 deletions

View File

@ -1,7 +1,13 @@
package main
import (
"archive/tar"
"encoding/json"
"errors"
"fmt"
"io"
"os"
"strings"
goflags "github.com/jessevdk/go-flags"
)
@ -13,9 +19,87 @@ type cmdRootFS struct {
} `positional-args:"yes" required:"yes"`
}
const (
_manifestJSON = "manifest.json"
)
func (r *cmdRootFS) Execute(args []string) error {
if len(args) != 0 {
return errors.New("too many args")
}
return nil
in, err := os.Open(string(r.PositionalArgs.Infile))
if err != nil {
return err
}
defer in.Close()
out, err := os.Create(string(r.PositionalArgs.Outfile))
if err != nil {
return err
}
defer out.Close()
return r.rootfs(in, out)
}
type dockerManifestJSON []struct {
Config string `json:"Config"`
Layers []string `json:"Layers"`
}
// rootfs accepts a docker layer tarball and writes it to outfile.
// 1. create map[string]io.ReadSeeker for each layer.
// 2. parse manifest.json and get the layer order.
// 3. go through each layer in order and write:
// a) to an ordered slice: the file name.
// b) to an FS map: where does the file come from?
// I) layer name
// II) offset (0 being the first file in the layer)
// 4. go through
func (r *cmdRootFS) rootfs(in io.ReadSeeker, out io.Writer) error {
tr := tar.NewReader(in)
layerOffsets := map[string]int64{}
var manifest dockerManifestJSON
// phase 1: get layer offsets and manifest.json
for {
hdrIn, err := tr.Next()
if err == io.EOF {
break
}
if hdrIn.Typeflag != tar.TypeReg {
continue
}
switch {
case hdrIn.Name == _manifestJSON:
dec := json.NewDecoder(tr)
if err := dec.Decode(&manifest); err != nil {
return fmt.Errorf("decode manifest.json: %w", err)
}
case strings.HasSuffix(hdrIn.Name, "/layer.tar"):
here, err := in.Seek(0, io.SeekCurrent)
if err != nil {
return fmt.Errorf("seek: %w", err)
}
layers[hdrIn.Name] = here
}
}
// phase 1.5: enumerate layers
layers := make([]int64, len(layers))
for i, name := range manifest.Layers {
layers[i] = layerOffsets[name]
}
// phase 2: iterate through all layers and extract filenames
// to files and ordered
files := map[string]struct{
layer string
fmt.Printf("layers: %+v\n", layers)
return nil
//return tw.Close()
}