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// The code in this file creates a Docker image layer containing the binary of the
// application itself.
package main
import (
"archive/tar"
"bytes"
"compress/gzip"
"crypto/sha256"
"encoding/json"
"fmt"
"io/ioutil"
"log"
"os"
"time"
)
// This function creates a Docker-image digest (i.e. SHA256 hash with
// algorithm-specification prefix)
func Digest(b []byte) string {
hash := sha256.New()
hash.Write(b)
return fmt.Sprintf("sha256:%x", hash.Sum(nil))
}
func GetImageOfCurrentExecutable() Image {
binary := getCurrentBinary()
tarArchive := createTarArchive(&map[string][]byte{
"/main": binary,
})
configJson, configElem := createConfig([]string{Digest(tarArchive)})
compressed := gzipArchive("Quinistry image", tarArchive)
manifest := createManifest(&configElem, &compressed)
manifestJson, _ := json.Marshal(manifest)
return Image{
Layer: compressed,
LayerDigest: Digest(compressed),
Manifest: manifestJson,
ManifestDigest: Digest(manifestJson),
Config: configJson,
ConfigDigest: Digest(configJson),
}
}
func getCurrentBinary() []byte {
path, _ := os.Executable()
file, _ := ioutil.ReadFile(path)
return file
}
func createTarArchive(files *map[string][]byte) []byte {
buf := new(bytes.Buffer)
w := tar.NewWriter(buf)
for name, file := range *files {
hdr := &tar.Header{
Name: name,
// Everything is executable \o/
Mode: 0755,
Size: int64(len(file)),
}
w.WriteHeader(hdr)
w.Write(file)
}
if err := w.Close(); err != nil {
log.Fatalln(err)
os.Exit(1)
}
return buf.Bytes()
}
func gzipArchive(name string, archive []byte) []byte {
buf := new(bytes.Buffer)
w := gzip.NewWriter(buf)
w.Name = name
w.Write(archive)
if err := w.Close(); err != nil {
log.Fatalln(err)
os.Exit(1)
}
return buf.Bytes()
}
func createConfig(layerDigests []string) (configJson []byte, elem Element) {
now := time.Now()
imageConfig := &ImageConfig{
Cmd: []string{"/main"},
Env: []string{"PATH=/"},
}
rootFs := RootFs{
DiffIds: layerDigests,
Type: "layers",
}
history := []History{
{
Created: now,
CreatedBy: "Quinistry magic",
},
}
config := Config{
Created: now,
Author: "tazjin",
Architecture: "amd64",
Os: "linux",
Config: imageConfig,
RootFs: rootFs,
History: history,
}
configJson, _ = json.Marshal(config)
elem = Element{
MediaType: ImageConfigMediaType,
Size: len(configJson),
Digest: Digest(configJson),
}
return
}
func createManifest(config *Element, layer *[]byte) Manifest {
layers := []Element{
{
MediaType: LayerMediaType,
Size: len(*layer),
// Layers must contain the digest of the *gzipped* layer.
Digest: Digest(*layer),
},
}
return Manifest{
SchemaVersion: 2,
MediaType: ManifestMediaType,
Config: *config,
Layers: layers,
}
}
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