1 files changed, 81 insertions, 0 deletions
diff --git a/storage/filesystem/dotgit/dotgit_rewrite_packed_refs.go b/storage/filesystem/dotgit/dotgit_rewrite_packed_refs.go
new file mode 100644
index 0000000..7f1c02c
--- /dev/null
+++ b/storage/filesystem/dotgit/dotgit_rewrite_packed_refs.go
@@ -0,0 +1,81 @@
+package dotgit
+
+import (
+	"io"
+	"os"
+	"runtime"
+
+	"gopkg.in/src-d/go-billy.v4"
+	"gopkg.in/src-d/go-git.v4/utils/ioutil"
+)
+
+func (d *DotGit) openAndLockPackedRefsMode() int {
+	if billy.CapabilityCheck(d.fs, billy.ReadAndWriteCapability) {
+		return os.O_RDWR
+	}
+
+	return os.O_RDONLY
+}
+
+func (d *DotGit) rewritePackedRefsWhileLocked(
+	tmp billy.File, pr billy.File) error {
+	// Try plain rename. If we aren't using the bare Windows filesystem as the
+	// storage layer, we might be able to get away with a rename over a locked
+	// file.
+	err := d.fs.Rename(tmp.Name(), pr.Name())
+	if err == nil {
+		return nil
+	}
+
+	// If we are in a filesystem that does not support rename (e.g. sivafs)
+	// a full copy is done.
+	if err == billy.ErrNotSupported {
+		return d.copyNewFile(tmp, pr)
+	}
+
+	if runtime.GOOS != "windows" {
+		return err
+	}
+
+	// Otherwise, Windows doesn't let us rename over a locked file, so
+	// we have to do a straight copy.  Unfortunately this could result
+	// in a partially-written file if the process fails before the
+	// copy completes.
+	return d.copyToExistingFile(tmp, pr)
+}
+
+func (d *DotGit) copyToExistingFile(tmp, pr billy.File) error {
+	_, err := pr.Seek(0, io.SeekStart)
+	if err != nil {
+		return err
+	}
+	err = pr.Truncate(0)
+	if err != nil {
+		return err
+	}
+	_, err = tmp.Seek(0, io.SeekStart)
+	if err != nil {
+		return err
+	}
+	_, err = io.Copy(pr, tmp)
+
+	return err
+}
+
+func (d *DotGit) copyNewFile(tmp billy.File, pr billy.File) (err error) {
+	prWrite, err := d.fs.Create(pr.Name())
+	if err != nil {
+		return err
+	}
+
+	defer ioutil.CheckClose(prWrite, &err)
+
+	_, err = tmp.Seek(0, io.SeekStart)
+	if err != nil {
+		return err
+	}
+
+	_, err = io.Copy(prWrite, tmp)
+
+	return err
+}