inits/pkg/cmd/dynlay/dynlay.go

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package dynlay
import (
"fmt"
"io"
"log"
"net/http"
"os"
"os/exec"
"path/filepath"
"github.com/antage/mntent"
"github.com/spf13/cobra"
)
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var urlPrefix = "https://dkl.novit.io/dist/layers"
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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
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target := "/" + path
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fmt.Println("linking", 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)
}
}