internal/rosa: mirror service via external cache

This provides an authenticated implementation of the external cache.

Signed-off-by: Ophestra <cat@gensokyo.uk>

cmd/mbf/cache.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"net/http"
 	"os"
 	"path/filepath"
 	"testing"
@@ -9,6 +10,7 @@ import (
 	"hakurei.app/check"
 	"hakurei.app/container"
 	"hakurei.app/internal/pkg"
+	"hakurei.app/internal/rosa"
 	"hakurei.app/message"
 )
 
@@ -30,7 +32,7 @@ type cache struct {
 	// Loaded artifact of [rosa.QEMU].
 	qemu pkg.Artifact
 
-	base string
+	base, mirror string
 }
 
 // open opens the underlying [pkg.Cache].
@@ -86,6 +88,21 @@ func (cache *cache) open() (err error) {
 	}
 	done <- struct{}{}
 
+	if cache.mirror != "" {
+		var pub []byte
+		pub, err = os.ReadFile(base.Append("ed25519.pub").String())
+		if err != nil {
+			cache.c.Close()
+			return
+		}
+		var r rosa.Remote
+		if r, err = rosa.NewRemote(cache.mirror, pub, http.DefaultClient); err != nil {
+			cache.c.Close()
+			return err
+		}
+		cache.c.SetExternal(r)
+	}
+
 	if cache.qemu != nil {
 		var pathname *check.Absolute
 		pathname, _, err = cache.c.Cure(cache.qemu)

cmd/mbf/main.go

@@ -14,6 +14,7 @@ package main
 
 import (
 	"context"
+	"crypto/ed25519"
 	"crypto/sha512"
 	"errors"
 	"fmt"
@@ -47,6 +48,19 @@ import (
 	"hakurei.app/cmd/mbf/internal/pkgserver/ui"
 )
 
+// writeFileExcl is like [os.WriteFile], but sets [os.O_EXCL] instead.
+func writeFileExcl(name string, data []byte, perm os.FileMode) error {
+	f, err := os.OpenFile(name, os.O_WRONLY|os.O_CREATE|os.O_EXCL, perm)
+	if err != nil {
+		return err
+	}
+	_, err = f.Write(data)
+	if err1 := f.Close(); err1 != nil && err == nil {
+		err = err1
+	}
+	return err
+}
+
 func main() {
 	container.TryArgv0(nil)
 
@@ -186,6 +200,10 @@ func main() {
 		&cm.base,
 		"d", command.StringFlag("$MBF_CACHE_DIR"),
 		"Directory to store cured artifacts",
+	).Flag(
+		&cm.mirror,
+		"r", command.StringFlag("$MBF_REMOTE"),
+		"URL of mirror service",
 	).Flag(
 		&cm.idle,
 		"sched-idle", command.BoolFlag(false),
@@ -462,6 +480,70 @@ func main() {
 		},
 	)
 
+	c.NewCommand(
+		"keygen",
+		"Create keypair for local cache",
+		func([]string) error {
+			pub, priv, err := ed25519.GenerateKey(nil)
+			if err != nil {
+				return err
+			}
+
+			return errors.Join(writeFileExcl(filepath.Join(
+				cm.base,
+				"ed25519.pub",
+			), pub, 0444), writeFileExcl(filepath.Join(
+				cm.base,
+				"ed25519",
+			), priv, 0400))
+		},
+	)
+
+	c.NewCommand(
+		"serve",
+		"Export local cache as mirror",
+		func(args []string) error {
+			const shutdownTimeout = 15 * time.Second
+
+			if len(args) != 1 {
+				return errors.New("serve requires 1 argument")
+			}
+
+			var key ed25519.PrivateKey
+			if p, err := os.ReadFile(filepath.Join(cm.base, "ed25519")); err != nil {
+				return err
+			} else if len(p) != ed25519.PrivateKeySize {
+				return errors.New("invalid private key")
+			} else {
+				key = p
+			}
+
+			var h http.Handler
+			if base, err := os.OpenRoot(cm.base); err != nil {
+				return err
+			} else {
+				h = rosa.NewMirror(msg, base, key)
+			}
+
+			server := http.Server{Addr: args[0], Handler: h}
+			go func() {
+				<-ctx.Done()
+				cc, cancel := context.WithTimeout(context.Background(), shutdownTimeout)
+				defer cancel()
+				if err := server.Shutdown(cc); err != nil {
+					log.Fatal(err)
+				}
+			}()
+
+			msg.Verbosef("listening on %q", args[0])
+			err := server.ListenAndServe()
+			if errors.Is(err, http.ErrServerClosed) {
+				err = nil
+			}
+			return err
+		},
+	)
+
 	{
 		var (
 			flagGentoo   string