dynlay

pkg/cmd/dynlay/dynlay.go

@@ -0,0 +1,190 @@
+package dynlay
+
+import (
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"os"
+	"os/exec"
+	"path/filepath"
+
+	"github.com/antage/mntent"
+	"github.com/spf13/cobra"
+)
+
+var urlPrefix = "https://dkl.novit.nc/dist/layers"
+
+func Command() (c *cobra.Command) {
+	c = &cobra.Command{
+		Use:   "dynlay <layer> <version>",
+		Short: "set dynamic layer",
+		Args:  cobra.ExactArgs(2),
+
+		Run: run,
+	}
+
+	c.Flags().StringVar(&urlPrefix, "url-prefix", urlPrefix, "Layer URL prefix")
+
+	return c
+}
+
+func run(_ *cobra.Command, args []string) {
+	layer, version := args[0], args[1]
+
+	layDir := filepath.Join("/opt/dynlay", layer)
+
+	err := os.MkdirAll(layDir, 0755)
+	fail(err)
+
+	layPath := filepath.Join(layDir, version)
+
+	// fetch if not exist
+	_, err = os.Stat(layPath)
+	if os.IsNotExist(err) {
+		fetch(layPath, urlPrefix+"/"+layer+"/"+version)
+	}
+
+	mounted := map[string]bool{}
+	{
+		mounts, err := mntent.Parse("/etc/mtab")
+		fail(err)
+		for _, mount := range mounts {
+			mounted[mount.Directory] = true
+		}
+	}
+
+	// mount
+	mountPath := filepath.Join("/run/dynlay", layer, version)
+
+	if !mounted[mountPath] {
+		err = os.MkdirAll(mountPath, 0755)
+		fail(err)
+
+		cmd := exec.Command("mount", "-t", "squashfs", layPath, mountPath)
+		cmd.Stdout = os.Stdout
+		cmd.Stderr = os.Stderr
+		err = cmd.Run()
+		if err != nil {
+			os.Remove(mountPath)
+			fail(err)
+		}
+	}
+
+	// update links
+	existing := map[string]bool{}
+	{
+		paths, err := linkableFrom(mountPath)
+		fail(err)
+
+		for _, path := range paths {
+			existing[path] = true
+
+			fmt.Println("linking", path)
+
+			target := "/" + path
+			os.Remove(target)
+
+			os.MkdirAll(filepath.Dir(target), 0755)
+
+			err := os.Symlink(filepath.Join(mountPath, path), target)
+			if err != nil {
+				log.Print("warning: symlink of ", path, " failed: ", err)
+			}
+		}
+	}
+
+	// remove expired links
+	basePaths, err := filepath.Glob(filepath.Join(filepath.Dir(mountPath), "*"))
+	fail(err)
+
+	for _, base := range basePaths {
+		if base == mountPath {
+			continue
+		}
+
+		stat, err := os.Stat(base)
+		fail(err)
+
+		if !stat.IsDir() {
+			continue
+		}
+
+		paths, err := linkableFrom(base)
+		fail(err)
+
+		for _, path := range paths {
+			if existing[path] {
+				continue
+			}
+
+			_, err := os.Stat("/" + path)
+			if os.IsNotExist(err) {
+				continue
+			}
+
+			fmt.Print("unlinking ", path, " (from ", filepath.Base(base), ")\n")
+
+			err = os.Remove("/" + path)
+			if err != nil {
+				log.Print("warning: failed to unlink ", path, ": ", err)
+			}
+		}
+
+		if mounted[base] {
+			cmd := exec.Command("umount", "-l", base)
+			cmd.Stdout = os.Stdout
+			cmd.Stderr = os.Stderr
+			cmd.Run()
+		}
+
+		os.Remove(base)
+	}
+}
+
+func linkableFrom(dir string) (paths []string, err error) {
+	err = filepath.Walk(dir, func(path string, info os.FileInfo, err error) error {
+		if err != nil {
+			return err
+		}
+
+		if info.IsDir() {
+			return nil
+		}
+
+		path, err = filepath.Rel(dir, path)
+		paths = append(paths, path)
+		return nil
+	})
+	return
+}
+
+func fetch(outPath string, url string) {
+	f, err := os.Create(outPath + ".part")
+	fail(err)
+
+	defer f.Close()
+
+	log.Print("fetching ", url)
+	resp, err := http.Get(url)
+	fail(err)
+
+	if resp.StatusCode != 200 {
+		log.Fatal("GET failed on ", url, ": ", resp.Status)
+	}
+
+	_, err = io.Copy(f, resp.Body)
+	fail(err)
+
+	f.Close()
+
+	os.Rename(outPath+".part", outPath)
+}
+
+func fail(err error) {
+	if err != nil {
+		log.SetFlags(log.Flags() | log.Lshortfile)
+		log.Output(2, err.Error())
+		os.Exit(-1)
+	}
+}