From 38450db74abdddfb3e366516f46e0e9c291002b1 Mon Sep 17 00:00:00 2001
From: Ophestra <cat@gensokyo.uk>
Date: Sun, 7 Jun 2026 21:12:15 +0900
Subject: [PATCH] internal/rosa: access backing storage through fs

This is more versatile than hardcoding the os.Root implementation.

Signed-off-by: Ophestra <cat@gensokyo.uk>
---
 cmd/mbf/main.go              |  2 +-
 internal/rosa/mirror.go      | 22 +++++++----
 internal/rosa/mirror_test.go | 77 ++++++++++++++++++++++++++++++++++++
 3 files changed, 92 insertions(+), 9 deletions(-)
 create mode 100644 internal/rosa/mirror_test.go

diff --git a/cmd/mbf/main.go b/cmd/mbf/main.go
index ae835500..8047e0c4 100644
--- a/cmd/mbf/main.go
+++ b/cmd/mbf/main.go
@@ -522,7 +522,7 @@ func main() {
 			if base, err := os.OpenRoot(cm.base); err != nil {
 				return err
 			} else {
-				h = rosa.NewMirror(msg, base, key)
+				h = rosa.NewMirror(msg, base.FS(), key)
 			}
 
 			server := http.Server{Addr: args[0], Handler: h}
diff --git a/internal/rosa/mirror.go b/internal/rosa/mirror.go
index 3f7822e5..09419396 100644
--- a/internal/rosa/mirror.go
+++ b/internal/rosa/mirror.go
@@ -204,7 +204,7 @@ func (r Remote) Status(
 // NewMirror returns an [http.Handler] for servicing mirror requests.
 func NewMirror(
 	msg message.Msg,
-	base *os.Root,
+	fsys fs.FS,
 	key ed25519.PrivateKey,
 ) http.Handler {
 	const identName = "ident"
@@ -224,7 +224,7 @@ func NewMirror(
 		}
 
 		ids := pkg.Encode((pkg.Checksum)(buf[:len(pkg.Checksum{})]))
-		if linkname, err := base.Readlink(filepath.Join(
+		if linkname, err := fs.ReadLink(fsys, filepath.Join(
 			"identifier",
 			ids,
 		)); err != nil {
@@ -239,7 +239,7 @@ func NewMirror(
 			(*pkg.Checksum)(buf[len(pkg.Checksum{}):]),
 			filepath.Base(linkname),
 		); err != nil {
-			http.Error(w, err.Error(), http.StatusBadRequest)
+			http.Error(w, err.Error(), http.StatusInternalServerError)
 			return
 		}
 		msg.Verbosef("serving artifact %s", ids)
@@ -276,7 +276,7 @@ func NewMirror(
 
 		checksums := pkg.Encode(buf)
 		rel := filepath.Join("checksum", checksums)
-		if _, err := base.Lstat(rel); err != nil {
+		if _, err := fs.Lstat(fsys, rel); err != nil {
 			if errors.Is(err, os.ErrNotExist) {
 				w.WriteHeader(http.StatusNotFound)
 				return
@@ -287,7 +287,7 @@ func NewMirror(
 		}
 		msg.Verbosef("serving outcome %s", pkg.Encode(buf))
 
-		fsys, err := fs.Sub(base.FS(), rel)
+		_fsys, err := fs.Sub(fsys, rel)
 		if err != nil {
 			msg.GetLogger().Println(err)
 			w.WriteHeader(http.StatusInternalServerError)
@@ -301,7 +301,7 @@ func NewMirror(
 			return
 		}
 		w.Header().Set("Content-Encoding", "gzip")
-		if err = pkg.Write(fsys, ".", gw); err != nil {
+		if err = pkg.Write(_fsys, ".", gw); err != nil {
 			msg.Verbose(err)
 		}
 		if err = gw.Close(); err != nil {
@@ -323,7 +323,7 @@ func NewMirror(
 		}
 
 		ids := pkg.Encode((pkg.Checksum)(buf[:len(pkg.Checksum{})]))
-		f, err := base.Open(filepath.Join(
+		f, err := fsys.Open(filepath.Join(
 			"status",
 			ids,
 		))
@@ -336,6 +336,12 @@ func NewMirror(
 			w.WriteHeader(http.StatusInternalServerError)
 			return
 		}
+		s, ok := f.(io.Seeker)
+		if !ok {
+			msg.GetLogger().Println("backing filesystem does not support seek")
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
 		msg.Verbosef("serving status %s", ids)
 
 		h := sha512.New384()
@@ -348,7 +354,7 @@ func NewMirror(
 		if _, err = w.Write(append(ed25519.Sign(key, buf[:]), buf[:]...)); err != nil {
 			msg.Verbose(err)
 			return
-		} else if _, err = f.Seek(0, io.SeekStart); err != nil {
+		} else if _, err = s.Seek(0, io.SeekStart); err != nil {
 			msg.GetLogger().Println(err)
 			return
 		} else if _, err = io.Copy(w, f); err != nil {
diff --git a/internal/rosa/mirror_test.go b/internal/rosa/mirror_test.go
new file mode 100644
index 00000000..a671cd31
--- /dev/null
+++ b/internal/rosa/mirror_test.go
@@ -0,0 +1,77 @@
+package rosa_test
+
+import (
+	"crypto/ed25519"
+	"io/fs"
+	"log"
+	"net/http/httptest"
+	"os"
+	"testing"
+	"testing/fstest"
+	"unique"
+
+	"hakurei.app/check"
+	"hakurei.app/fhs"
+	"hakurei.app/internal/pkg"
+	"hakurei.app/internal/rosa"
+	"hakurei.app/message"
+)
+
+func TestMirror(t *testing.T) {
+	t.Parallel()
+
+	pub, priv, err := ed25519.GenerateKey(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	base := check.MustAbs(t.TempDir())
+	msg := message.New(log.New(os.Stderr, "mirror: ", 0))
+	msg.SwapVerbose(testing.Verbose())
+
+	var c *pkg.Cache
+	c, err = pkg.Open(t.Context(), msg, 0, 0, 0, base)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(c.Close)
+
+	a := pkg.NewExec(
+		"", "",
+		nil, 0, false, false,
+		fhs.AbsRoot, nil, fhs.AbsRoot, nil,
+	)
+	id := c.Ident(a)
+	ids := pkg.Encode(id.Value())
+
+	var wantChecksum pkg.Checksum
+	if err = pkg.SumFS(&wantChecksum, fstest.MapFS{
+		".": {Mode: os.ModeDir | 0500},
+	}, "."); err != nil {
+		t.Fatal(err)
+	}
+	wantChecksums := pkg.Encode(wantChecksum)
+
+	server := httptest.NewServer(rosa.NewMirror(msg, fstest.MapFS{
+		"identifier/" + ids:         {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/" + wantChecksums)},
+		"checksum/" + wantChecksums: {Mode: os.ModeDir | 0500},
+	}, priv))
+	t.Cleanup(server.Close)
+
+	var extern pkg.External
+	extern, err = rosa.NewRemote("http://example.com:80", pub, server.Client())
+	if err != nil {
+		t.Fatal(err)
+	}
+	c.SetExternal(extern)
+
+	var got unique.Handle[pkg.Checksum]
+	if _, got, err = c.Cure(a); err != nil {
+		t.Fatal(err)
+	} else if got.Value() != wantChecksum {
+		t.Logf(
+			"Cure: checksum = %s, want %s",
+			pkg.Encode(got.Value()), pkg.Encode(wantChecksum),
+		)
+	}
+}