Add support for pulling from remote archives

This necessitated a large set of changes.

We now support an "archive" mode for repositories.  In this mode,
files are stored "packed" rather than hard linked.  This allows one to
e.g. store an OSTree repository with root-owned files as non-root.  It
is also used as the basis for serving repositories via HTTP.

While doing this I realized that GVariant is endianness-dependent; I
decided to just store all data in big endian.

src/libostree/ostree-core.h

@@ -39,6 +39,7 @@ typedef enum {
   OSTREE_SERIALIZED_DIRMETA_VARIANT = 3,
   OSTREE_SERIALIZED_XATTR_VARIANT = 4
 } OstreeSerializedVariantType;
+#define OSTREE_SERIALIZED_VARIANT_LAST 4
 
 #define OSTREE_SERIALIZED_VARIANT_FORMAT "(uv)"
 
@@ -83,13 +84,54 @@ typedef enum {
  */
 #define OSTREE_COMMIT_GVARIANT_FORMAT "(ua{sv}ssstss)"
 
-GVariant *ostree_get_xattrs_for_path (const char *path,
-                                        GError    **error);
+gboolean ostree_validate_checksum_string (const char *sha256,
+                                          GError    **error);
+
+char *ostree_get_relative_object_path (const char *checksum,
+                                       OstreeObjectType type,
+                                       gboolean         archive);
+
+GVariant *ostree_get_xattrs_for_path (const char   *path,
+                                      GError     **error);
+
+gboolean ostree_set_xattrs (const char *path, GVariant *xattrs, GError **error);
+
+gboolean ostree_parse_metadata_file (const char                  *path,
+                                     OstreeSerializedVariantType *out_type,
+                                     GVariant                   **out_variant,
+                                     GError                     **error);
 
 gboolean ostree_stat_and_checksum_file (int dirfd, const char *path,
-                                          GChecksum **out_checksum,
-                                          struct stat *out_stbuf,
-                                          GError **error);
+                                        OstreeObjectType type,
+                                        GChecksum **out_checksum,
+                                        struct stat *out_stbuf,
+                                        GError **error);
+
+/* Packed files:
+ *
+ * guint32 metadata_length [metadata gvariant] [content]
+ *
+ * metadata variant:
+ * u - Version
+ * u - uid
+ * u - gid
+ * u - mode
+ * a(ayay) - xattrs
+ * t - content length
+ *
+ * And then following the end of the variant is the content.  If
+ * symlink, then this is the target; if device, then device ID as
+ * network byte order uint32.
+ */
+#define OSTREE_PACK_FILE_VARIANT_FORMAT "(uuuua(ayay)t)"
+
+gboolean  ostree_pack_object (GOutputStream     *output,
+                              GFile             *path,
+                              OstreeObjectType  objtype,
+                              GCancellable     *cancellable,
+                              GError          **error);
+
+void ostree_checksum_update_stat (GChecksum *checksum, guint32 uid, guint32 gid, guint32 mode);
 
 
 #endif /* _OSTREE_REPO */