[ostree] pull: add support for tombstone commits

[Giuseppe Scrivano <gscrivano src gnome org>]

commit 76c5cc07db1a8ac4bd37ecc5f50c84ac4b42e886
Author: Giuseppe Scrivano <gscrivan redhat com>
Date:   Wed Oct 28 10:07:51 2015 +0100

    pull: add support for tombstone commits
    
    Add a new object type: OSTREE_OBJECT_TYPE_TOMBSTONE_COMMIT that is
    used when a commit was intentionally removed.
    
    If the remote repository doesn't use tombstone commits, do not fail on
    a missing commit (change 0b795785dd81cd1e8c2c5960f0959740bce72a51).
    
    When the remote repository uses tombstones, if a commit cannot be
    found, check if the tombstone file is present and fail if it is not
    present.
    
    Signed-off-by: Giuseppe Scrivano <gscrivan redhat com>

 src/libostree/ostree-core.c      |    2 ++
 src/libostree/ostree-core.h      |   14 ++++++++------
 src/libostree/ostree-repo-pull.c |   18 +++++++++++++++++-
 3 files changed, 27 insertions(+), 7 deletions(-)
---
diff --git a/src/libostree/ostree-core.c b/src/libostree/ostree-core.c
index 8fe9d76..5f24e7c 100644
--- a/src/libostree/ostree-core.c
+++ b/src/libostree/ostree-core.c
@@ -975,6 +975,8 @@ ostree_object_type_to_string (OstreeObjectType objtype)
       return "dirmeta";
     case OSTREE_OBJECT_TYPE_COMMIT:
       return "commit";
+    case OSTREE_OBJECT_TYPE_TOMBSTONE_COMMIT:
+      return "tombstone-commit";
     default:
       g_assert_not_reached ();
       return NULL;
diff --git a/src/libostree/ostree-core.h b/src/libostree/ostree-core.h
index 711c699..637f817 100644
--- a/src/libostree/ostree-core.h
+++ b/src/libostree/ostree-core.h
@@ -56,15 +56,17 @@ G_BEGIN_DECLS
  * @OSTREE_OBJECT_TYPE_DIR_TREE: List of children (trees or files), and metadata
  * @OSTREE_OBJECT_TYPE_DIR_META: Directory metadata
  * @OSTREE_OBJECT_TYPE_COMMIT: Toplevel object, refers to tree and dirmeta for root
+ * @OSTREE_OBJECT_TYPE_COMMIT_TOMBSTONE: Toplevel object, refers to a deleted commit
  *
  * Enumeration for core object types; %OSTREE_OBJECT_TYPE_FILE is for
  * content, the other types are metadata.
  */
 typedef enum {
-  OSTREE_OBJECT_TYPE_FILE = 1,      /* .file */
-  OSTREE_OBJECT_TYPE_DIR_TREE = 2,  /* .dirtree */
-  OSTREE_OBJECT_TYPE_DIR_META = 3,  /* .dirmeta */
-  OSTREE_OBJECT_TYPE_COMMIT = 4     /* .commit */
+  OSTREE_OBJECT_TYPE_FILE = 1,                /* .file */
+  OSTREE_OBJECT_TYPE_DIR_TREE = 2,            /* .dirtree */
+  OSTREE_OBJECT_TYPE_DIR_META = 3,            /* .dirmeta */
+  OSTREE_OBJECT_TYPE_COMMIT = 4,              /* .commit */
+  OSTREE_OBJECT_TYPE_TOMBSTONE_COMMIT = 5,    /* .commit-tombstone */
 } OstreeObjectType;
 
 /**
@@ -73,14 +75,14 @@ typedef enum {
  *
  * Returns: %TRUE if object type is metadata
  */
-#define OSTREE_OBJECT_TYPE_IS_META(t) (t >= 2 && t <= 4)
+#define OSTREE_OBJECT_TYPE_IS_META(t) (t >= 2 && t <= 5)
 
 /**
  * OSTREE_OBJECT_TYPE_LAST:
  *
  * Last valid object type; use this to validate ranges.
  */
-#define OSTREE_OBJECT_TYPE_LAST OSTREE_OBJECT_TYPE_COMMIT
+#define OSTREE_OBJECT_TYPE_LAST OSTREE_OBJECT_TYPE_TOMBSTONE_COMMIT
 
 /**
  * OSTREE_DIRMETA_GVARIANT_FORMAT:
diff --git a/src/libostree/ostree-repo-pull.c b/src/libostree/ostree-repo-pull.c
index 41cc46b..7ba3ef6 100644
--- a/src/libostree/ostree-repo-pull.c
+++ b/src/libostree/ostree-repo-pull.c
@@ -58,6 +58,7 @@ typedef struct {
   
   gboolean          gpg_verify;
   gboolean          gpg_verify_summary;
+  gboolean          has_tombstone_commits;
 
   GBytes           *summary_data;
   GBytes           *summary_data_sig;
@@ -795,12 +796,23 @@ meta_fetch_on_complete (GObject           *object,
                    pull_data->maxdepth != 0)
             {
               g_clear_error (&local_error);
+              /* If the remote repo supports tombstone commits, check if the commit was intentionally
+                 deleted.  */
+              if (pull_data->has_tombstone_commits)
+                {
+                  enqueue_one_object_request (pull_data, checksum, OSTREE_OBJECT_TYPE_TOMBSTONE_COMMIT,
+                                              FALSE, FALSE);
+                }
             }
         }
 
       goto out;
     }
 
+  /* Tombstone commits are always empty, so skip all processing here */
+  if (objtype == OSTREE_OBJECT_TYPE_TOMBSTONE_COMMIT)
+    goto out;
+
   fd = openat (pull_data->tmpdir_dfd, temp_path, O_RDONLY | O_CLOEXEC);
   if (fd == -1)
     {
@@ -1854,7 +1866,11 @@ ostree_repo_pull_with_options (OstreeRepo             *self,
 
       if (!ostree_repo_mode_from_string (remote_mode_str, &pull_data->remote_mode, error))
         goto out;
-    
+
+      if (!ot_keyfile_get_boolean_with_default (remote_config, "core", "tombstone-commits", FALSE,
+                                                &pull_data->has_tombstone_commits, error))
+        goto out;
+
       if (pull_data->remote_mode != OSTREE_REPO_MODE_ARCHIVE_Z2)
         {
           g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,