Initial basic static delta code drop

This has a very basic level of functionality (deltas can be generated,
and applied offline).  There is only some stubbed out pull code to
fetch them via HTTP.

But, better to commit this now and improve it from a known starting
point, rather than have it languish in a branch.

src/libotutil/ot-variant-utils.c

@@ -23,8 +23,10 @@
 #include "config.h"
 
 #include <gio/gio.h>
+#include <gio/gfiledescriptorbased.h>
 
 #include <string.h>
+#include <sys/mman.h>
 
 #include "otutil.h"
 
@@ -149,6 +151,55 @@ ot_util_variant_map (GFile              *src,
   return ret;
 }
 
+typedef struct {
+  gpointer addr;
+  gsize len;
+} VariantMapData;
+
+static void
+variant_map_data_destroy (gpointer data)
+{
+  VariantMapData *mdata = data;
+  (void) munmap (mdata->addr, mdata->len);
+}
+
+gboolean
+ot_util_variant_map_fd (GFileDescriptorBased  *stream,
+                        goffset                start,
+                        const GVariantType    *type,
+                        gboolean               trusted,
+                        GVariant             **out_variant,
+                        GError               **error)
+{
+  gboolean ret = FALSE;
+  gpointer map;
+  struct stat stbuf;
+  VariantMapData *mdata = NULL;
+  gsize len;
+
+  if (!gs_stream_fstat (stream, &stbuf, NULL, error))
+    goto out;
+
+  len = stbuf.st_size - start;
+  map = mmap (NULL, len, PROT_READ, MAP_PRIVATE, 
+              g_file_descriptor_based_get_fd (stream), start);
+  if (!map)
+    {
+      ot_util_set_error_from_errno (error, errno);
+      goto out;
+    }
+
+  mdata = g_new (VariantMapData, 1);
+  mdata->addr = map;
+  mdata->len = len;
+
+  ret = TRUE;
+  *out_variant = g_variant_new_from_data (type, map, len, trusted,
+                                          variant_map_data_destroy, mdata);
+ out:
+  return ret;
+}
+
 /**
  * Read all input from @src, allocating a new #GVariant from it into
  * output variable @out_variant.  @src will be closed as a result.
@@ -219,3 +270,17 @@ ot_util_variant_builder_from_variant (GVariant            *variant,
   return builder;
 }
 
+GVariant *
+ot_variant_new_from_bytes (const GVariantType  *type,
+                           GBytes        *bytes,
+                           gboolean       trusted)
+{
+#if GLIB_VERSION_MIN_REQUIRED >= GLIB_VERSION_2_36
+  return g_variant_new_from_bytes (type, bytes, trusted);
+#else
+  gsize size;
+  gconstpointer data = g_bytes_get_data (bytes, &size);
+  return g_variant_new_from_data (type, data, size, trusted,
+                                  (GDestroyNotify)g_bytes_unref, bytes);
+#endif
+}

src/libotutil/ot-variant-utils.h

@@ -46,6 +46,13 @@ gboolean ot_util_variant_map (GFile *src,
                               GVariant **out_variant,
                               GError  **error);
 
+gboolean ot_util_variant_map_fd (GFileDescriptorBased *stream,
+                                 goffset              offset,
+                                 const GVariantType  *type,
+                                 gboolean             trusted,
+                                 GVariant           **out_variant,
+                                 GError             **error);
+
 gboolean ot_util_variant_from_stream (GInputStream         *src,
                                       const GVariantType   *type,
                                       gboolean              trusted,
@@ -58,5 +65,10 @@ GInputStream *ot_variant_read (GVariant             *variant);
 GVariantBuilder *ot_util_variant_builder_from_variant (GVariant            *variant,
                                                        const GVariantType  *type);
 
+GVariant *
+ot_variant_new_from_bytes (const GVariantType  *type,
+                           GBytes        *bytes,
+                           gboolean       trusted);
+
 G_END_DECLS