preliminary unit tests

lxcconfig/BUILD

@@ -1,4 +1,4 @@
-load("@io_bazel_rules_go//go:def.bzl", "go_library")
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
 
 go_library(
     name = "go_default_library",
@@ -6,3 +6,13 @@ go_library(
     importpath = "github.com/motiejus/code/undocker/lxcconfig",
     visibility = ["//visibility:public"],
 )
+
+go_test(
+    name = "go_default_test",
+    srcs = ["lxcconfig_test.go"],
+    embed = [":go_default_library"],
+    deps = [
+        "@com_github_stretchr_testify//assert:go_default_library",
+        "@com_github_stretchr_testify//require:go_default_library",
+    ],
+)

lxcconfig/lxcconfig.go

@@ -7,32 +7,89 @@ import (
 	"fmt"
 	"io"
 	"strings"
+	"text/template"
 )
 
-const _manifestJSON = "manifest.json"
+const (
+	_json         = ".json"
+	_manifestJSON = "manifest.json"
+)
+
+var (
+	_lxcTemplate = template.Must(
+		template.New("lxcconfig").Parse("" +
+			"lxc.include = LXC_TEMPLATE_CONFIG/common.conf\n" +
+			"lxc.architecture = {{ .Architecture }}\n" +
+			"lxc.execute.cmd = '{{ .Cmd }}'\n" +
+			"{{ if .Cwd }}lxc.init.cwd = {{ .Cwd }}\n{{ end }}" +
+			"{{ range .Env }}lxc.environment = {{ . }}\n{{ end }}"))
+	errBadManifest = errors.New("bad or missing manifest.json")
+)
+
+type (
+	// lxcConfig is passed to _lxcTemplate
+	lxcConfig struct {
+		Architecture string
+		Cmd          string
+		Cwd          string
+		Env          []string
+	}
 
 	// dockerManifest is manifest.json
-type dockerManifest []struct {
+	dockerManifest []struct {
 		Config string `json:"Config"`
 	}
 
 	// dockerConfig returns interesting configs for the container. user/group are
 	// skipped, since Docker allows specifying them by name, which would require
 	// peeking into the container image's /etc/passwd to resolve the names to ints.
-type dockerConfig struct {
+	dockerConfig struct {
 		Architecture string             `json:"architecture"`
-	Config       struct {
-		Entrypoint []string `json:"Entrypoint"`
-		Cmd        []string `json:"Cmd"`
-		Env        []string `json:"Env"`
-		WorkingDir string   `json:"WorkingDir"`
-	} `json:"config"`
+		Config       dockerConfigConfig `json:"config"`
 	}
 
-var (
-	errBadManifest = errors.New("bad or missing manifest.json")
+	dockerConfigConfig struct {
+		Entrypoint []string `json:"Entrypoint"`
+		Cmd        []string `json:"Cmd"`
+		WorkingDir string   `json:"WorkingDir"`
+		Env        []string `json:"Env"`
+	}
 )
 
+// LXCConfig accepts a Docker container image and returns lxc configuration.
+func LXCConfig(in io.ReadSeeker, wr io.Writer) error {
+	dockerCfg, err := getDockerConfig(in)
+	if err != nil {
+		return err
+	}
+	lxcCfg := docker2lxc(dockerCfg)
+	return lxcCfg.WriteTo(wr)
+}
+
+func docker2lxc(d dockerConfig) lxcConfig {
+	// cmd/entrypoint logic is copied from lxc-oci template
+	ep := strings.Join(d.Config.Entrypoint, " ")
+	cmd := strings.Join(d.Config.Cmd, " ")
+	if len(ep) == 0 {
+		ep = cmd
+		if len(ep) == 0 {
+			ep = "/bin/sh"
+		}
+	} else if len(cmd) != 0 {
+		ep = ep + " " + cmd
+	}
+	return lxcConfig{
+		Architecture: d.Architecture,
+		Cmd:          ep,
+		Env:          d.Config.Env,
+		Cwd:          d.Config.WorkingDir,
+	}
+}
+
+func (l lxcConfig) WriteTo(wr io.Writer) error {
+	return _lxcTemplate.Execute(wr, l)
+}
+
 func getDockerConfig(in io.ReadSeeker) (dockerConfig, error) {
 	tr := tar.NewReader(in)
 	// get offsets to all json files in the archive
@@ -45,7 +102,7 @@ func getDockerConfig(in io.ReadSeeker) (dockerConfig, error) {
 		if hdr.Typeflag != tar.TypeReg {
 			continue
 		}
-		if !strings.HasSuffix(".json", hdr.Name) {
+		if !strings.HasSuffix(_json, hdr.Name) {
 			continue
 		}
 		here, err := in.Seek(0, io.SeekCurrent)

lxcconfig/lxcconfig_test.go

@@ -0,0 +1,58 @@
+package lxcconfig
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestLXCConfig(t *testing.T) {
+	tests := []struct {
+		name   string
+		docker dockerConfig
+		want   string
+	}{
+		{
+			name: "just architecture",
+			docker: dockerConfig{
+				Architecture: "amd64",
+			},
+			want: `lxc.include = LXC_TEMPLATE_CONFIG/common.conf
+lxc.architecture = amd64
+lxc.execute.cmd = '/bin/sh'
+`,
+		},
+		{
+			name: "all fields",
+			docker: dockerConfig{
+				Architecture: "amd64",
+				Config: dockerConfigConfig{
+					Entrypoint: []string{"/entrypoint.sh"},
+					Cmd:        []string{"/bin/sh", "-c", "echo foo"},
+					WorkingDir: "/x",
+					Env: []string{
+						`LONGNAME="Foo Bar"`,
+						"SHELL=/bin/tcsh",
+					},
+				},
+			},
+			want: `lxc.include = LXC_TEMPLATE_CONFIG/common.conf
+lxc.architecture = amd64
+lxc.execute.cmd = '/entrypoint.sh /bin/sh -c echo foo'
+lxc.init.cwd = /x
+lxc.environment = LONGNAME="Foo Bar"
+lxc.environment = SHELL=/bin/tcsh
+`,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var buf bytes.Buffer
+			require.NoError(t, docker2lxc(tt.docker).WriteTo(&buf))
+			assert.Equal(t, tt.want, string(buf.Bytes()))
+		})
+	}
+}

rootfs/rootfs.go

@@ -36,9 +36,9 @@ type dockerManifestJSON []struct {
 //       I) layer name
 //       II) offset (0 being the first file in the layer)
 // 4. go through
-func RootFS(in io.ReadSeeker, out io.Writer) (err error) {
+func RootFS(in io.ReadSeeker, wr io.Writer) (err error) {
 	tr := tar.NewReader(in)
-	tw := tar.NewWriter(out)
+	tw := tar.NewWriter(wr)
 	defer func() { err = multierr.Append(err, tw.Close()) }()
 
 	// layerOffsets maps a layer name (a9b123c0daa/layer.tar) to it's offset