1 files changed, 98 insertions, 0 deletions
diff --git a/object/store/packed/internal/reading/idx_open.go b/object/store/packed/internal/reading/idx_open.go
new file mode 100644
index 00000000..8f73c867
--- /dev/null
+++ b/object/store/packed/internal/reading/idx_open.go
@@ -0,0 +1,98 @@
+package reading
+
+import (
+	"fmt"
+	"os"
+	"syscall"
+
+	"codeberg.org/lindenii/furgit/internal/intconv"
+	objectid "codeberg.org/lindenii/furgit/object/id"
+)
+
+// openIndex returns one opened and parsed index, caching it by pack basename.
+func (store *Store) openIndex(candidate packCandidate) (*idxFile, error) {
+	store.idxMu.RLock()
+
+	index, ok := store.idxByPack[candidate.packName]
+	if ok {
+		store.idxMu.RUnlock()
+
+		return index, nil
+	}
+
+	store.idxMu.RUnlock()
+
+	index, err := openIdxFile(store.root, candidate.idxName, candidate.packName, store.algo)
+	if err != nil {
+		return nil, err
+	}
+
+	store.idxMu.Lock()
+
+	existing, ok := store.idxByPack[candidate.packName]
+	if ok {
+		store.idxMu.Unlock()
+
+		_ = index.close()
+
+		return existing, nil
+	}
+
+	store.idxByPack[candidate.packName] = index
+	store.idxMu.Unlock()
+
+	return index, nil
+}
+
+// openIdxFile maps and validates one idx v2 file.
+func openIdxFile(root *os.Root, idxName, packName string, algo objectid.Algorithm) (*idxFile, error) {
+	file, err := root.Open(idxName)
+	if err != nil {
+		return nil, err
+	}
+
+	info, err := file.Stat()
+	if err != nil {
+		_ = file.Close()
+
+		return nil, err
+	}
+
+	size := info.Size()
+	if size < 0 || size > int64(int(^uint(0)>>1)) {
+		_ = file.Close()
+
+		return nil, fmt.Errorf("objectstore/packed: idx %q has unsupported size", idxName)
+	}
+
+	fd, err := intconv.UintptrToInt(file.Fd())
+	if err != nil {
+		_ = file.Close()
+
+		return nil, err
+	}
+
+	data, err := syscall.Mmap(fd, 0, int(size), syscall.PROT_READ, syscall.MAP_PRIVATE)
+	if err != nil {
+		_ = file.Close()
+
+		return nil, err
+	}
+
+	index := &idxFile{
+		idxName:  idxName,
+		packName: packName,
+		algo:     algo,
+		file:     file,
+		data:     data,
+	}
+
+	err = index.parse()
+	if err != nil {
+		_ = index.close()
+
+		return nil, err
+	}
+
+	return index, nil
+}