deltas: Heuristically detect endianness for older deltas

If the average object size is greater than 4GiB, let's assume we're
dealing with opposite endianness.  I'm fairly confident no one is
going to be shipping peta- or exa- byte size ostree deltas, period.
Past the gigabyte scale you really want bittorrent or something.

Makefile-tests.am

@@ -85,6 +85,8 @@ insttest_DATA = tests/archive-test.sh \
 	tests/test-basic-user.sh \
 	tests/test-local-pull.sh \
 	tests/corrupt-repo-ref.js \
+	tests/pre-endian-deltas-repo-big.tar.xz \
+	tests/pre-endian-deltas-repo-little.tar.xz \
 	$(NULL)
 
 insttest_SCRIPTS += \

src/libostree/ostree-repo-static-delta-core.c

@@ -670,15 +670,22 @@ show_one_part (OstreeRepo                    *self,
 }
 
 OstreeDeltaEndianness
-_ostree_delta_get_endianness (GVariant *superblock)
+_ostree_delta_get_endianness (GVariant *superblock,
+                              gboolean *out_was_heuristic)
 {
   guint8 endianness_char;
   g_autoptr(GVariant) delta_meta = NULL;
   g_autoptr(GVariantDict) delta_metadict = NULL;
+  guint64 total_size = 0;
+  guint64 total_usize = 0;
+  guint total_objects = 0;
 
   delta_meta = g_variant_get_child_value (superblock, 0);
   delta_metadict = g_variant_dict_new (delta_meta);
 
+  if (out_was_heuristic)
+    *out_was_heuristic = FALSE;
+
   if (g_variant_dict_lookup (delta_metadict, "ostree.endianness", "y", &endianness_char))
     {
       switch (endianness_char)
@@ -691,13 +698,58 @@ _ostree_delta_get_endianness (GVariant *superblock)
           return OSTREE_DELTA_ENDIAN_INVALID;
         }
     }
-  return OSTREE_DELTA_ENDIAN_UNKNOWN;
+
+  if (out_was_heuristic)
+    *out_was_heuristic = TRUE;
+
+  { g_autoptr(GVariant) meta_entries = NULL;
+    guint n_parts;
+    guint i;
+
+    g_variant_get_child (superblock, 6, "@a" OSTREE_STATIC_DELTA_META_ENTRY_FORMAT, &meta_entries);
+    n_parts = g_variant_n_children (meta_entries);
+
+    for (i = 0; i < n_parts; i++)
+      {
+        g_autoptr(GVariant) objects = NULL;
+        guint64 size, usize;
+        guint n_objects;
+
+        g_variant_get_child (meta_entries, i, "(u@aytt@ay)", NULL, NULL, &size, &usize, &objects);
+        n_objects = (guint)(g_variant_get_size (objects) / OSTREE_STATIC_DELTA_OBJTYPE_CSUM_LEN);
+
+        total_objects += n_objects;
+        total_size += size;
+        total_usize += usize;
+      }
+
+    /* If the average object size is greater than 4GiB, let's assume
+     * we're dealing with opposite endianness.  I'm fairly confident
+     * no one is going to be shipping peta- or exa- byte size ostree
+     * deltas, period.  Past the gigabyte scale you really want
+     * bittorrent or something.
+     */
+    if ((total_size / total_objects) > G_MAXUINT32)
+      {
+        switch (G_BYTE_ORDER)
+          {
+          case G_BIG_ENDIAN:
+            return OSTREE_DELTA_ENDIAN_LITTLE;
+          case G_LITTLE_ENDIAN:
+            return OSTREE_DELTA_ENDIAN_BIG;
+          default:
+            g_assert_not_reached ();
+          }
+      }
+
+    return G_BYTE_ORDER;
+  }
 }
 
 gboolean
 _ostree_delta_needs_byteswap (GVariant *superblock)
 {
-  switch (_ostree_delta_get_endianness (superblock))
+  switch (_ostree_delta_get_endianness (superblock, NULL))
     {
     case OSTREE_DELTA_ENDIAN_BIG:
       return G_BYTE_ORDER == G_LITTLE_ENDIAN;
@@ -738,24 +790,28 @@ _ostree_repo_static_delta_dump (OstreeRepo                    *self,
 
   g_print ("Delta: %s\n", delta_id);
   { const char *endianness_description;
+    gboolean was_heuristic;
 
-    endianness = _ostree_delta_get_endianness (delta_superblock);
+    endianness = _ostree_delta_get_endianness (delta_superblock, &was_heuristic);
 
     switch (endianness)
       {
       case OSTREE_DELTA_ENDIAN_BIG:
-        endianness_description = "big";
+        if (was_heuristic)
+          endianness_description = "big (heuristic)";
+        else
+          endianness_description = "big";
         if (G_BYTE_ORDER == G_LITTLE_ENDIAN)
           swap_endian = TRUE;
         break;
       case OSTREE_DELTA_ENDIAN_LITTLE:
-        endianness_description = "little";
+        if (was_heuristic)
+          endianness_description = "little (heuristic)";
+        else
+          endianness_description = "little";
         if (G_BYTE_ORDER == G_BIG_ENDIAN)
           swap_endian = TRUE;
         break;
-      case OSTREE_DELTA_ENDIAN_UNKNOWN:
-        endianness_description = "unknown";
-        break;
       case OSTREE_DELTA_ENDIAN_INVALID:
         endianness_description = "invalid";
         break;

src/libostree/ostree-repo-static-delta-private.h

@@ -222,11 +222,10 @@ maybe_swap_endian_u64 (gboolean swap,
 typedef enum {
   OSTREE_DELTA_ENDIAN_BIG,
   OSTREE_DELTA_ENDIAN_LITTLE,
-  OSTREE_DELTA_ENDIAN_UNKNOWN,
   OSTREE_DELTA_ENDIAN_INVALID
 } OstreeDeltaEndianness;
 
-OstreeDeltaEndianness _ostree_delta_get_endianness (GVariant *superblock);
+OstreeDeltaEndianness _ostree_delta_get_endianness (GVariant *superblock, gboolean *out_was_heuristic);
 
 gboolean _ostree_delta_needs_byteswap (GVariant *superblock);
 

tests/test-delta.sh

@@ -128,6 +128,27 @@ assert_streq "${totalsize_orig}" "${totalsize_swapped}"
 
 echo 'ok generate + show endian swapped'
 
+tar xf ${SRCDIR}/pre-endian-deltas-repo-big.tar.xz
+mv pre-endian-deltas-repo{,-big}
+tar xf ${SRCDIR}/pre-endian-deltas-repo-little.tar.xz
+mv pre-endian-deltas-repo{,-little}
+legacy_origrev=$(${CMD_PREFIX} ostree --repo=pre-endian-deltas-repo-big rev-parse main^)
+legacy_newrev=$(${CMD_PREFIX} ostree --repo=pre-endian-deltas-repo-big rev-parse main)
+${CMD_PREFIX} ostree --repo=pre-endian-deltas-repo-big static-delta show ${legacy_origrev}-${legacy_newrev} > show-legacy-big.txt
+totalsize_legacy_big=$(grep 'Total Size:' show-legacy-big.txt)
+${CMD_PREFIX} ostree --repo=pre-endian-deltas-repo-big static-delta show ${legacy_origrev}-${legacy_newrev} > show-legacy-little.txt
+totalsize_legacy_little=$(grep 'Total Size:' show-legacy-little.txt)
+for f in show-legacy-{big,little}.txt; do
+    if grep 'Endianness:.*heuristic' $f; then
+	found_heuristic=yes
+	break
+    fi
+done
+assert_streq "${found_heuristic}" "yes"
+assert_streq "${totalsize_legacy_big}" "${totalsize_legacy_little}"
+
+echo 'ok heuristic endian detection'
+
 mkdir repo2 && ${CMD_PREFIX} ostree --repo=repo2 init --mode=archive-z2
 ${CMD_PREFIX} ostree --repo=repo2 pull-local repo ${newrev}
 ${CMD_PREFIX} ostree --repo=repo2 fsck