1 files changed, 82 insertions, 0 deletions
diff --git a/object/store/packed/pack.go b/object/store/packed/pack.go
new file mode 100644
index 00000000..c384d6a5
--- /dev/null
+++ b/object/store/packed/pack.go
@@ -0,0 +1,82 @@
+package packed
+
+import (
+	"encoding/binary"
+	"fmt"
+	"os"
+	"syscall"
+
+	"codeberg.org/lindenii/furgit/internal/intconv"
+	packfmt "codeberg.org/lindenii/furgit/packfile"
+)
+
+// packFile stores one mapped and validated .pack file.
+type packFile struct {
+	// name is the .pack basename.
+	name string
+	// file is the opened pack file descriptor.
+	file *os.File
+	// data is the mapped pack bytes.
+	data []byte
+}
+
+// openPackFile maps and validates one pack file.
+func openPackFile(name string, file *os.File, size int64) (*packFile, error) {
+	if size < 12 {
+		return nil, fmt.Errorf("objectstore/packed: pack %q too short", name)
+	}
+
+	if size > int64(int(^uint(0)>>1)) {
+		return nil, fmt.Errorf("objectstore/packed: pack %q has unsupported size", name)
+	}
+
+	fd, err := intconv.UintptrToInt(file.Fd())
+	if err != nil {
+		return nil, err
+	}
+
+	data, err := syscall.Mmap(fd, 0, int(size), syscall.PROT_READ, syscall.MAP_PRIVATE)
+	if err != nil {
+		return nil, err
+	}
+
+	if binary.BigEndian.Uint32(data[:4]) != packfmt.Signature {
+		_ = syscall.Munmap(data)
+
+		return nil, fmt.Errorf("objectstore/packed: pack %q invalid signature", name)
+	}
+
+	version := binary.BigEndian.Uint32(data[4:8])
+	if !packfmt.VersionSupported(version) {
+		_ = syscall.Munmap(data)
+
+		return nil, fmt.Errorf("objectstore/packed: pack %q unsupported version %d", name, version)
+	}
+
+	return &packFile{name: name, file: file, data: data}, nil
+}
+
+// close unmaps and closes one pack handle.
+func (pack *packFile) close() error {
+	var closeErr error
+
+	if pack.data != nil {
+		err := syscall.Munmap(pack.data)
+		if err != nil && closeErr == nil {
+			closeErr = err
+		}
+
+		pack.data = nil
+	}
+
+	if pack.file != nil {
+		err := pack.file.Close()
+		if err != nil && closeErr == nil {
+			closeErr = err
+		}
+
+		pack.file = nil
+	}
+
+	return closeErr
+}