From 2245ffa0425fe66adf91772658f8c1be9f2b510d Mon Sep 17 00:00:00 2001
From: Alex Goodman <wagoodman@gmail.com>
Date: Mon, 14 May 2018 22:09:48 -0400
Subject: [PATCH] save an image filesystem layers

---
 main.go | 65 +++++++++++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 56 insertions(+), 9 deletions(-)

diff --git a/main.go b/main.go
index 7bae80c..d23ba4f 100644
--- a/main.go
+++ b/main.go
@@ -1,13 +1,60 @@
 package main
 
 import (
+	"bufio"
 	"encoding/json"
 	"fmt"
+	"io"
+	"os"
 
 	"github.com/docker/docker/client"
 	"golang.org/x/net/context"
 )
 
+func check(e error) {
+	if e != nil {
+		panic(e)
+	}
+}
+
+func saveImage(readCloser io.ReadCloser) {
+	defer readCloser.Close()
+
+	path := "image"
+	if _, err := os.Stat(path); os.IsNotExist(err) {
+		os.Mkdir(path, 0755)
+	}
+
+	fo, err := os.Create("image/cache.tar")
+	check(err)
+
+	defer func() {
+		if err := fo.Close(); err != nil {
+			panic(err)
+		}
+	}()
+	w := bufio.NewWriter(fo)
+
+	buf := make([]byte, 1024)
+	for {
+		n, err := readCloser.Read(buf)
+		if err != nil && err != io.EOF {
+			panic(err)
+		}
+		if n == 0 {
+			break
+		}
+
+		if _, err := w.Write(buf[:n]); err != nil {
+			panic(err)
+		}
+	}
+
+	if err = w.Flush(); err != nil {
+		panic(err)
+	}
+}
+
 func main() {
 	ctx := context.Background()
 	cli, err := client.NewEnvClient()
@@ -18,21 +65,20 @@ func main() {
 	// imageID := "golang:alpine"
 	imageID := "die-test:latest"
 
+	fmt.Println("Saving Image...")
+	readCloser, err := cli.ImageSave(ctx, []string{imageID})
+	check(err)
+	saveImage(readCloser)
+
 	for {
 		inspect, _, err := cli.ImageInspectWithRaw(ctx, imageID)
-		if err != nil {
-			panic(err)
-		}
+		check(err)
 
 		history, err := cli.ImageHistory(ctx, imageID)
-		if err != nil {
-			panic(err)
-		}
+		check(err)
 
 		historyStr, err := json.MarshalIndent(history, "", "  ")
-		if err != nil {
-			panic(err)
-		}
+		check(err)
 
 		layerStr := ""
 		for idx, layer := range inspect.RootFS.Layers {
@@ -53,4 +99,5 @@ func main() {
 			imageID = inspect.Parent
 		}
 	}
+	fmt.Println("See './image' for the cached image tar")
 }