Only verify OSTREE_MAX_METADATA_SIZE for HTTP fetches

There are use cases for libostree as a local content store
for content derived or delivered via other mechanisms (e.g. OCI
images, RPMs, etc.).  rpm-ostree today imports RPMs into OSTree
branches, and puts the RPM header value as commit metadata.
Some of these can be quite large because the header includes
permissions for each file.  Similarly, some OCI metadata is large.

Since there's no security issues with this, support committing
such content.

We still by default limit the size of metadata fetches, although
for good measure we make this configurable too via a new
`max-metadata-size` value.

Closes: https://github.com/ostreedev/ostree/issues/1721

Closes: #1744
Approved by: jlebon

src/libostree/ostree-repo-pull.c

@@ -150,6 +150,7 @@ typedef struct {
 
   gboolean          timestamp_check; /* Verify commit timestamps */
   int               maxdepth;
+  guint64           max_metadata_size;
   guint64           start_time;
 
   gboolean          is_mirror;
@@ -2193,7 +2194,7 @@ start_fetch (OtPullData *pull_data,
   if (expected_max_size_p)
     expected_max_size = *expected_max_size_p;
   else if (OSTREE_OBJECT_TYPE_IS_META (objtype))
-    expected_max_size = OSTREE_MAX_METADATA_SIZE;
+    expected_max_size = pull_data->max_metadata_size;
   else
     expected_max_size = 0;
 
@@ -3488,6 +3489,7 @@ 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
+ *   * 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
  *   * inherit-transaction (b): Don't initiate, finish or abort a transaction, useful to do multiple pulls in one transaction.
@@ -3543,6 +3545,9 @@ ostree_repo_pull_with_options (OstreeRepo             *self,
    */
   const char *the_ref_to_fetch = NULL;
 
+  /* Default */
+  pull_data->max_metadata_size = OSTREE_MAX_METADATA_SIZE;
+
   if (options)
     {
       int flags_i = OSTREE_REPO_PULL_FLAGS_NONE;
@@ -3570,6 +3575,7 @@ 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, "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 =
         g_variant_lookup (options, "n-network-retries", "u", &pull_data->n_network_retries);