static-delta: Change `show` to display from/to commits

When writing a delta to a file this may not always be recorded
in the filename, and it's useful data.

Ref: https://mail.gnome.org/archives/ostree-list/2019-February/msg00000.html

This also required teaching `show` to accept a file path.

Note...for some reason `test-deltas.sh` breaks when run from
a tty - we get `SIGTTIN` which implies something is reading from
the tty but it wasn't obvious to me what.

Closes: #1823
Approved by: jlebon

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

@@ -725,16 +725,25 @@ _ostree_repo_static_delta_dump (OstreeRepo                    *self,
                                 GCancellable                  *cancellable,
                                 GError                       **error)
 {
+  glnx_autofd int superblock_fd = -1;
+
+  if (strchr (delta_id, '/'))
+    {
+      if (!glnx_openat_rdonly (AT_FDCWD, delta_id, TRUE, &superblock_fd, error))
+        return FALSE;
+    }
+  else
+    {
       g_autofree char *from = NULL;
       g_autofree char *to = NULL;
       if (!_ostree_parse_delta_name (delta_id, &from, &to, error))
         return FALSE;
 
       g_autofree char *superblock_path = _ostree_get_relative_static_delta_superblock_path (from, to);
-
-  glnx_autofd int superblock_fd = -1;
       if (!glnx_openat_rdonly (self->repo_dir_fd, superblock_path, TRUE, &superblock_fd, error))
         return FALSE;
+    }
+
   g_autoptr(GVariant) delta_superblock = NULL;
   if (!ot_variant_read_fd (superblock_fd, 0,
                            (GVariantType*)OSTREE_STATIC_DELTA_SUPERBLOCK_FORMAT,
@@ -742,6 +751,26 @@ _ostree_repo_static_delta_dump (OstreeRepo                    *self,
     return FALSE;
 
   g_print ("Delta: %s\n", delta_id);
+  g_autoptr(GVariant) from_commit_v = NULL;
+  g_variant_get_child (delta_superblock, 2, "@ay", &from_commit_v);
+  g_autofree char *from_commit = NULL;
+  if (g_variant_n_children (from_commit_v) > 0)
+    {
+      if (!ostree_checksum_bytes_peek_validate (from_commit_v, error))
+        return FALSE;
+      from_commit = ostree_checksum_from_bytes_v (from_commit_v);
+      g_print ("From: %s\n", from_commit);
+    }
+  else
+    {
+      g_print ("From <scratch>\n");
+    }
+  g_autoptr(GVariant) to_commit_v = NULL;
+  g_variant_get_child (delta_superblock, 3, "@ay", &to_commit_v);
+  if (!ostree_checksum_bytes_peek_validate (to_commit_v, error))
+    return FALSE;
+  g_autofree char *to_commit = ostree_checksum_from_bytes_v (to_commit_v);
+  g_print ("To: %s\n", to_commit);
 
   gboolean swap_endian = FALSE;
   OstreeDeltaEndianness endianness;
@@ -777,6 +806,7 @@ _ostree_repo_static_delta_dump (OstreeRepo                    *self,
 
     g_print ("Endianness: %s\n", endianness_description);
   }
+
   guint64 ts;
   g_variant_get_child (delta_superblock, 1, "t", &ts);
   g_print ("Timestamp: %" G_GUINT64_FORMAT "\n", GUINT64_FROM_BE (ts));
@@ -821,7 +851,7 @@ _ostree_repo_static_delta_dump (OstreeRepo                    *self,
 
   for (guint i = 0; i < n_parts; i++)
     {
-      if (!show_one_part (self, swap_endian, from, to, meta_entries, i,
+      if (!show_one_part (self, swap_endian, from_commit, to_commit, meta_entries, i,
                           &total_size, &total_usize,
                           cancellable, error))
         return FALSE;

tests/test-delta.sh

@@ -135,6 +135,8 @@ rm temp-repo -rf
 echo 'ok generate'
 
 ${CMD_PREFIX} ostree --repo=repo static-delta show ${origrev}-${newrev} > show.txt
+assert_file_has_content show.txt "From: ${origrev}"
+assert_file_has_content show.txt "To: ${newrev}"
 assert_file_has_content show.txt 'Endianness: \(little\|big\)'
 
 echo 'ok show'