internal/rosa: populate mirror snapshot

This produces the same structure served by the dynamic server.

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

internal/rosa/mirror.go

@@ -14,6 +14,7 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"syscall"
 	"unique"
 
 	"hakurei.app/internal/pkg"
@@ -211,6 +212,114 @@ type Mirror struct {
 	msg message.Msg
 }
 
+// Populate fills an empty root with a static mirror snapshot.
+func (m Mirror) Populate(root *os.Root) error {
+	if dents, err := fs.ReadDir(root.FS(), "."); err != nil {
+		return err
+	} else if len(dents) > 0 {
+		return syscall.ENOTEMPTY
+	}
+
+	for _, name := range []string{
+		dirArtifact,
+		dirOutcome,
+		dirStatus,
+	} {
+		if err := root.Mkdir(name, 0755); err != nil {
+			return err
+		}
+	}
+	var w *os.File
+
+	if dents, err := fs.ReadDir(m.fsys, "identifier"); err != nil {
+		return err
+	} else {
+		for _, dent := range dents {
+			name := dent.Name()
+			var buf [2 * len(pkg.Checksum{})]byte
+			if err = pkg.Decode(
+				(*pkg.Checksum)(buf[:len(pkg.Checksum{})]),
+				name,
+			); err != nil {
+				return err
+			}
+
+			if w, err = root.OpenFile(
+				filepath.Join(dirArtifact, name),
+				syscall.O_WRONLY|syscall.O_CREAT|syscall.O_EXCL,
+				0444,
+			); err != nil {
+				return err
+			}
+			err = m.writeArtifact(&buf, w, nil)
+			if err = errors.Join(err, w.Close()); err != nil {
+				return err
+			}
+		}
+	}
+
+	if dents, err := fs.ReadDir(m.fsys, "checksum"); err != nil {
+		return err
+	} else {
+		for _, dent := range dents {
+			name := dent.Name()
+			var buf pkg.Checksum
+			if err = pkg.Decode(&buf, name); err != nil {
+				return err
+			}
+
+			var fsys fs.FS
+			fsys, err = fs.Sub(m.fsys, filepath.Join("checksum", name))
+			if err != nil {
+				return err
+			}
+
+			if w, err = root.OpenFile(
+				filepath.Join(dirOutcome, name),
+				syscall.O_WRONLY|syscall.O_CREAT|syscall.O_EXCL,
+				0444,
+			); err != nil {
+				return err
+			}
+
+			m.msg.Verbosef("exporting outcome %s", name)
+			err = pkg.Write(fsys, ".", w)
+			if err = errors.Join(err, w.Close()); err != nil {
+				return err
+			}
+		}
+	}
+
+	if dents, err := fs.ReadDir(m.fsys, "status"); err != nil {
+		return err
+	} else {
+		for _, dent := range dents {
+			name := dent.Name()
+			var buf [2 * len(pkg.Checksum{})]byte
+			if err = pkg.Decode(
+				(*pkg.Checksum)(buf[:len(pkg.Checksum{})]),
+				name,
+			); err != nil {
+				return err
+			}
+
+			if w, err = root.OpenFile(
+				filepath.Join(dirStatus, name),
+				syscall.O_WRONLY|syscall.O_CREAT|syscall.O_EXCL,
+				0444,
+			); err != nil {
+				return err
+			}
+			err = m.writeStatus(&buf, w, nil)
+			if err = errors.Join(err, w.Close()); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
 // NewMirror returns a populated [Mirror] for servicing mirror requests.
 func NewMirror(
 	msg message.Msg,