lib/pull: Add timestamp-check-from-rev

The way `timestamp-check` works might be too restrictive in some
situations. Essentially, we need to support the case where users want to
pull an older commit than the current tip, but while still guaranteeing
that it is newer than some even older commit.

This will be used in Fedora CoreOS. For more information see:
https://github.com/coreos/rpm-ostree/pull/2094
https://github.com/coreos/fedora-coreos-tracker/issues/481

src/libostree/ostree-repo-pull-private.h

@@ -114,6 +114,7 @@ typedef struct {
   guint             n_imported_content;
 
   gboolean          timestamp_check; /* Verify commit timestamps */
+  char             *timestamp_check_from_rev;
   int               maxdepth;
   guint64           max_metadata_size;
   guint64           start_time;

src/libostree/ostree-repo-pull.c

@@ -1593,6 +1593,7 @@ scan_commit_object (OtPullData                 *pull_data,
                                      commit, error))
     return glnx_prefix_error (error, "Commit %s", checksum);
 
+  guint64 new_ts = ostree_commit_get_timestamp (commit);
   if (pull_data->timestamp_check)
     {
       /* We don't support timestamp checking while recursing right now */
@@ -1611,11 +1612,22 @@ scan_commit_object (OtPullData                 *pull_data,
             return glnx_prefix_error (error, "Reading %s for timestamp-check", ref->ref_name);
 
           guint64 orig_ts = ostree_commit_get_timestamp (orig_commit);
-          guint64 new_ts = ostree_commit_get_timestamp (commit);
           if (!_ostree_compare_timestamps (orig_rev, orig_ts, checksum, new_ts, error))
             return FALSE;
         }
     }
+  if (pull_data->timestamp_check_from_rev)
+    {
+      g_autoptr(GVariant) commit = NULL;
+      if (!ostree_repo_load_commit (pull_data->repo, pull_data->timestamp_check_from_rev,
+                                    &commit, NULL, error))
+        return glnx_prefix_error (error, "Reading %s for timestamp-check-from-rev",
+                                  pull_data->timestamp_check_from_rev);
+
+      guint64 ts = ostree_commit_get_timestamp (commit);
+      if (!_ostree_compare_timestamps (pull_data->timestamp_check_from_rev, ts, checksum, new_ts, error))
+        return FALSE;
+    }
 
   /* If we found a legacy transaction flag, assume all commits are partial */
   gboolean is_partial = commitstate_is_partial (pull_data, commitstate);
@@ -3270,6 +3282,7 @@ initiate_request (OtPullData                 *pull_data,
  *   * require-static-deltas (b): Require static deltas
  *   * override-commit-ids (as): Array of specific commit IDs to fetch for refs
  *   * timestamp-check (b): Verify commit timestamps are newer than current (when pulling via ref); Since: 2017.11
+ *   * timestamp-check-from-rev (s): Verify that all fetched commit timestamps are newer than timestamp of given rev; Since: 2020.4
  *   * metadata-size-restriction (t): Restrict metadata objects to a maximum number of bytes; 0 to disable.  Since: 2018.9
  *   * dry-run (b): Only print information on what will be downloaded (requires static deltas)
  *   * override-url (s): Fetch objects from this URL if remote specifies no metalink in options
@@ -3372,6 +3385,7 @@ ostree_repo_pull_with_options (OstreeRepo             *self,
       (void) g_variant_lookup (options, "update-frequency", "u", &update_frequency);
       (void) g_variant_lookup (options, "localcache-repos", "^a&s", &opt_localcache_repos);
       (void) g_variant_lookup (options, "timestamp-check", "b", &pull_data->timestamp_check);
+      (void) g_variant_lookup (options, "timestamp-check-from-rev", "s", &pull_data->timestamp_check_from_rev);
       (void) g_variant_lookup (options, "max-metadata-size", "t", &pull_data->max_metadata_size);
       (void) g_variant_lookup (options, "append-user-agent", "s", &pull_data->append_user_agent);
       opt_n_network_retries_set =
@@ -4259,6 +4273,18 @@ ostree_repo_pull_with_options (OstreeRepo             *self,
                             g_steal_pointer (&checksum));
     }
 
+  /* Resolve refs to a checksum if necessary */
+  if (pull_data->timestamp_check_from_rev &&
+      !ostree_validate_checksum_string (pull_data->timestamp_check_from_rev, NULL))
+    {
+      g_autofree char *from_rev = NULL;
+      if (!ostree_repo_resolve_rev (pull_data->repo, pull_data->timestamp_check_from_rev, FALSE,
+                                    &from_rev, error))
+        goto out;
+      g_free (pull_data->timestamp_check_from_rev);
+      pull_data->timestamp_check_from_rev = g_steal_pointer (&from_rev);
+    }
+
   g_hash_table_unref (requested_refs_to_fetch);
   requested_refs_to_fetch = g_steal_pointer (&updated_requested_refs_to_fetch);
   if (g_hash_table_size (requested_refs_to_fetch) == 1)
@@ -4604,6 +4630,7 @@ ostree_repo_pull_with_options (OstreeRepo             *self,
   g_clear_pointer (&pull_data->fetched_detached_metadata, (GDestroyNotify) g_hash_table_unref);
   g_clear_pointer (&pull_data->summary_deltas_checksums, (GDestroyNotify) g_hash_table_unref);
   g_clear_pointer (&pull_data->ref_original_commits, (GDestroyNotify) g_hash_table_unref);
+  g_free (pull_data->timestamp_check_from_rev);
   g_clear_pointer (&pull_data->verified_commits, (GDestroyNotify) g_hash_table_unref);
   g_clear_pointer (&pull_data->ref_keyring_map, (GDestroyNotify) g_hash_table_unref);
   g_clear_pointer (&pull_data->requested_content, (GDestroyNotify) g_hash_table_unref);