internal/rosa: mirror response write methods

For the fs.FS implementation and static publishing.

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

internal/rosa/mirror_test.go

@@ -4,6 +4,7 @@ import (
 	"crypto/ed25519"
 	"io/fs"
 	"log"
+	"net/http"
 	"net/http/httptest"
 	"os"
 	"testing"
@@ -52,14 +53,16 @@ func TestMirror(t *testing.T) {
 	}
 	wantChecksums := pkg.Encode(wantChecksum)
 
-	server := httptest.NewServer(rosa.NewMirror(msg, fstest.MapFS{
+	var mux http.ServeMux
+	rosa.NewMirror(msg, fstest.MapFS{
 		"identifier/" + ids:         {Mode: fs.ModeSymlink | 0777, Data: []byte("../checksum/" + wantChecksums)},
 		"checksum/" + wantChecksums: {Mode: os.ModeDir | 0500},
-	}, priv))
+	}, priv).Register(&mux)
+	server := httptest.NewServer(&mux)
 	t.Cleanup(server.Close)
 
 	var extern pkg.External
-	extern, err = rosa.NewRemote("http://example.com:80", pub, server.Client())
+	extern, err = rosa.NewRemote(server.Client(), "http://example.com:80", pub)
 	if err != nil {
 		t.Fatal(err)
 	}