pull: cache summary and summary.sig

It allows an optimization to skip the download of the summary file
if its .sig file is unchanged.

Downloading the .sig file is much cheaper than downloading the summary
file from repositories with many branches.

https://bugzilla.gnome.org/show_bug.cgi?id=762973

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

src/libostree/ostree-repo-private.h

@@ -33,6 +33,8 @@ G_BEGIN_DECLS
 
 #define _OSTREE_OBJECT_SIZES_ENTRY_SIGNATURE "ay"
 
+#define _OSTREE_SUMMARY_CACHE_PATH "tmp/cache/summaries"
+
 /**
  * OstreeRepo:
  *
@@ -316,5 +318,23 @@ _ostree_repo_read_bare_fd (OstreeRepo           *self,
 gboolean
 _ostree_repo_update_mtime (OstreeRepo        *self,
                            GError           **error);
-                           
+
+/* Load the summary from the cache if the provided .sig file is the same as the
+   cached version.  */
+gboolean
+_ostree_repo_load_cache_summary_if_same_sig (OstreeRepo        *self,
+                                             const char        *remote,
+                                             GBytes            *summary_sig,
+                                             GBytes            **summary,
+                                             GCancellable      *cancellable,
+                                             GError           **error);
+
+gboolean
+_ostree_repo_cache_summary (OstreeRepo        *self,
+                            const char        *remote,
+                            GBytes            *summary,
+                            GBytes            *summary_sig,
+                            GCancellable      *cancellable,
+                            GError           **error);
+
 G_END_DECLS