d2vm: flatten docker image using github.com/google/go-containerregistry

This allows to preserve files like /etc/hostname or /etc/resolv.conf that will otherwise be overriden by running the container to extract rootfs

wip img entrypoint script

Signed-off-by: Adphi <philippe.adrien.nousse@gmail.com>

docker_image_test.go

@@ -0,0 +1,171 @@
+package d2vm
+
+import (
+	"bytes"
+	"context"
+	"os"
+	"path/filepath"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"go.linka.cloud/d2vm/pkg/docker"
+	"go.linka.cloud/d2vm/pkg/exec"
+)
+
+func TestDockerImageAsRunSript(t *testing.T) {
+	tests := []struct {
+		name  string
+		image DockerImage
+		want  string
+	}{
+		{
+			name: "nothing",
+			image: DockerImage{
+				DockerImageConfig: DockerImageConfig{
+					User:       "",
+					WorkingDir: "",
+					Env:        nil,
+					Entrypoint: nil,
+					Cmd:        nil,
+				},
+			},
+			want: `
+#!/bin/sh
+
+
+
+
+`,
+		},
+		{
+			name: "tail -f /dev/null",
+			image: DockerImage{
+				DockerImageConfig: DockerImageConfig{
+					User: "root",
+					Cmd:  []string{"tail", "-f", "/dev/null"},
+				},
+			},
+			want: `
+#!/bin/sh
+
+
+
+su root -p -s /bin/sh -c '"tail" "-f" "/dev/null"'
+`,
+		},
+		{
+			name: "tail -f /dev/null inside home",
+			image: DockerImage{
+				DockerImageConfig: DockerImageConfig{
+					User:       "root",
+					WorkingDir: "/root",
+					Cmd:        []string{"tail", "-f", "/dev/null"},
+				},
+			},
+			want: `
+#!/bin/sh
+
+cd /root
+
+su root -p -s /bin/sh -c '"tail" "-f" "/dev/null"'
+`,
+		},
+		{
+			name: "subshell tail -f /dev/null",
+			image: DockerImage{
+				DockerImageConfig: DockerImageConfig{
+					User:       "root",
+					Entrypoint: []string{"/bin/sh", "-c"},
+					Cmd:        []string{"tail -f /dev/null"},
+				},
+			},
+			want: `
+#!/bin/sh
+
+
+
+su root -p -s /bin/sh -c '"/bin/sh" "-c" "tail -f /dev/null"'
+`,
+		},
+		{
+			name: "www-data with env",
+			image: DockerImage{
+				DockerImageConfig: DockerImageConfig{
+					User: "www-data",
+					Cmd:  []string{"tail", "-f", "/dev/null"},
+					Env:  []string{"ENV=PROD", "DB=mysql://user:password@localhost"},
+				},
+			},
+			want: `
+#!/bin/sh
+export ENV=PROD
+export DB=mysql://user:password@localhost
+
+
+
+su www-data -p -s /bin/sh -c '"tail" "-f" "/dev/null"'
+`,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var w bytes.Buffer
+			require.NoError(t, tt.image.AsRunScript(&w))
+			assert.Equal(t, tt.want, w.String())
+		})
+	}
+}
+
+func TestImageFlatten(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	const (
+		img        = "d2vm-flatten-test"
+		dockerfile = `FROM alpine
+
+COPY resolv.conf /etc/
+COPY hostname /etc/
+
+RUN rm -rf /etc/apk
+`
+	)
+	exec.Run = exec.RunStdout
+	tmp := filepath.Join(os.TempDir(), "d2vm-tests", "image-flatten")
+	require.NoError(t, os.MkdirAll(tmp, perm))
+	defer os.RemoveAll(tmp)
+
+	require.NoError(t, os.WriteFile(filepath.Join(tmp, "hostname"), []byte("d2vm-flatten-test"), perm))
+	require.NoError(t, os.WriteFile(filepath.Join(tmp, "resolv.conf"), []byte("nameserver 8.8.8.8"), perm))
+	require.NoError(t, os.WriteFile(filepath.Join(tmp, "Dockerfile"), []byte(dockerfile), perm))
+	require.NoError(t, docker.Cmd(ctx, "image", "build", "-t", img, tmp))
+	defer docker.Cmd(ctx, "image", "rm", img)
+
+	// imgTar := filepath.Join(tmp, img+".tar")
+	// require.NoError(t, docker.Cmd(ctx, "image", "save", img, "-o", imgTar))
+	//
+	imgTmp := filepath.Join(tmp, "image")
+
+	i, err := NewImage(ctx, img, imgTmp)
+	require.NoError(t, err)
+
+	rootfs := filepath.Join(tmp, "rootfs")
+	require.NoError(t, i.Flatten(ctx, rootfs))
+
+	b, err := os.ReadFile(filepath.Join(rootfs, "etc", "resolv.conf"))
+	require.NoError(t, err)
+	assert.Equal(t, "nameserver 8.8.8.8", string(b))
+
+	b, err = os.ReadFile(filepath.Join(rootfs, "etc", "hostname"))
+	require.NoError(t, err)
+	assert.Equal(t, "d2vm-flatten-test", string(b))
+
+	_, err = os.Stat(filepath.Join(rootfs, "etc", "apk"))
+	assert.Error(t, err)
+
+	require.NoError(t, i.Close())
+	_, err = os.Stat(imgTmp)
+	assert.Error(t, err)
+}