gboolean
_ostree_static_delta_part_open (GInputStream   *part_in,
                                GBytes         *inline_part_bytes,
                                OstreeStaticDeltaOpenFlags flags,
                                const char     *expected_checksum,
                                GVariant    **out_part,
                                GCancellable *cancellable,
                                GError      **error)
{
  gboolean ret = FALSE;
  const gboolean trusted = (flags & OSTREE_STATIC_DELTA_OPEN_FLAGS_VARIANT_TRUSTED) > 0;
  const gboolean skip_checksum = (flags & OSTREE_STATIC_DELTA_OPEN_FLAGS_SKIP_CHECKSUM) > 0;
  gsize bytes_read;
  guint8 comptype;
  g_autoptr(GChecksum) checksum = NULL;
  g_autoptr(GInputStream) checksum_in = NULL;
  g_autoptr(GVariant) ret_part = NULL;
  GInputStream *source_in;

  /* We either take a fd or a GBytes reference */
  g_return_val_if_fail (G_IS_FILE_DESCRIPTOR_BASED (part_in) || inline_part_bytes != NULL, FALSE);
  g_return_val_if_fail (skip_checksum || expected_checksum != NULL, FALSE);

  if (!skip_checksum)
    {
      checksum = g_checksum_new (G_CHECKSUM_SHA256);
      checksum_in = (GInputStream*)ostree_checksum_input_stream_new (part_in, checksum);
      source_in = checksum_in;
    }
  else
    {
      source_in = part_in;
    }

  { guint8 buf[1];
    /* First byte is compression type */
    if (!g_input_stream_read_all (source_in, buf, sizeof(buf), &bytes_read,
                                  cancellable, error))
      {
        g_prefix_error (error, "Reading initial compression flag byte: ");
      goto out;
      }
    comptype = buf[0];
  }

  switch (comptype)
    {
    case 0:
      if (!inline_part_bytes)
        {
          int part_fd = g_file_descriptor_based_get_fd ((GFileDescriptorBased*)part_in);

          /* No compression, no checksums - a fast path */
          if (!ot_util_variant_map_fd (part_fd, 1, G_VARIANT_TYPE (OSTREE_STATIC_DELTA_PART_PAYLOAD_FORMAT_V0),
                                       trusted, &ret_part, error))
            goto out;
        }
      else
        {
          g_autoptr(GBytes) content_bytes = g_bytes_new_from_bytes (inline_part_bytes, 1,
                                                                    g_bytes_get_size (inline_part_bytes) - 1);
          ret_part = g_variant_new_from_bytes (G_VARIANT_TYPE (OSTREE_STATIC_DELTA_PART_PAYLOAD_FORMAT_V0),
                                               content_bytes, trusted);
          g_variant_ref_sink (ret_part);
        }

      if (!skip_checksum)
        g_checksum_update (checksum, g_variant_get_data (ret_part),
                           g_variant_get_size (ret_part));
      
      break;
    case 'x':
      {
        g_autofree char *tmppath = g_strdup ("/var/tmp/ostree-delta-XXXXXX");
        g_autoptr(GConverter) decomp = (GConverter*) _ostree_lzma_decompressor_new ();
        g_autoptr(GInputStream) convin = g_converter_input_stream_new (source_in, decomp);
        g_autoptr(GOutputStream) unpacked_out = NULL;
        glnx_fd_close int unpacked_fd = -1;
        gssize n_bytes_written;

        unpacked_fd = g_mkstemp_full (tmppath, O_RDWR | O_CLOEXEC, 0640);
        if (unpacked_fd < 0)
          {
            glnx_set_error_from_errno (error);
            goto out;
          }
        
        /* Now make it autocleanup on process exit - in the future, we
         * should consider caching unpacked deltas as well.
         */
        if (unlink (tmppath) < 0)
          {
            glnx_set_error_from_errno (error);
            goto out;
          }
        
        unpacked_out = g_unix_output_stream_new (unpacked_fd, FALSE);

        n_bytes_written = g_output_stream_splice (unpacked_out, convin,
                                                  G_OUTPUT_STREAM_SPLICE_CLOSE_SOURCE |
                                                  G_OUTPUT_STREAM_SPLICE_CLOSE_TARGET,
                                                  cancellable, error);
        if (n_bytes_written < 0)
          goto out;

        if (!ot_util_variant_map_fd (unpacked_fd, 0, G_VARIANT_TYPE (OSTREE_STATIC_DELTA_PART_PAYLOAD_FORMAT_V0),
                                     trusted, &ret_part, error))
          goto out;
      }
      break;
    default:
      g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
                   "Invalid compression type '%u'", comptype);
      goto out;
    }

  if (checksum)
    {
      const char *actual_checksum = g_checksum_get_string (checksum);
      g_assert (expected_checksum != NULL);
      if (strcmp (actual_checksum, expected_checksum) != 0)
        {
          g_set_error (error, G_IO_ERROR, G_IO_ERROR_FAILED,
                       "Checksum mismatch in static delta part; expected=%s actual=%s",
                       expected_checksum, actual_checksum);
          goto out;
        }
    }
        
  ret = TRUE;
  *out_part = g_steal_pointer (&ret_part);
 out:
  return ret;
}
gboolean
_ostree_static_delta_part_open (GInputStream   *part_in,
                                GBytes         *inline_part_bytes,
                                OstreeStaticDeltaOpenFlags flags,
                                const char     *expected_checksum,
                                GVariant    **out_part,
                                GCancellable *cancellable,
                                GError      **error)
{
  const gboolean trusted = (flags & OSTREE_STATIC_DELTA_OPEN_FLAGS_VARIANT_TRUSTED) > 0;
  const gboolean skip_checksum = (flags & OSTREE_STATIC_DELTA_OPEN_FLAGS_SKIP_CHECKSUM) > 0;
  gsize bytes_read;
  guint8 comptype;
  g_autoptr(GChecksum) checksum = NULL;
  g_autoptr(GInputStream) checksum_in = NULL;
  GInputStream *source_in;

  /* We either take a fd or a GBytes reference */
  g_return_val_if_fail (G_IS_FILE_DESCRIPTOR_BASED (part_in) || inline_part_bytes != NULL, FALSE);
  g_return_val_if_fail (skip_checksum || expected_checksum != NULL, FALSE);

  if (!skip_checksum)
    {
      checksum = g_checksum_new (G_CHECKSUM_SHA256);
      checksum_in = (GInputStream*)ostree_checksum_input_stream_new (part_in, checksum);
      source_in = checksum_in;
    }
  else
    {
      source_in = part_in;
    }

  { guint8 buf[1];
    /* First byte is compression type */
    if (!g_input_stream_read_all (source_in, buf, sizeof(buf), &bytes_read,
                                  cancellable, error))
      return glnx_prefix_error (error, "Reading initial compression flag byte");
    comptype = buf[0];
  }

  g_autoptr(GVariant) ret_part = NULL;
  switch (comptype)
    {
    case 0:
      if (!inline_part_bytes)
        {
          int part_fd = g_file_descriptor_based_get_fd ((GFileDescriptorBased*)part_in);

          /* No compression, no checksums - a fast path */
          if (!ot_util_variant_map_fd (part_fd, 1, G_VARIANT_TYPE (OSTREE_STATIC_DELTA_PART_PAYLOAD_FORMAT_V0),
                                       trusted, &ret_part, error))
            return FALSE;
        }
      else
        {
          g_autoptr(GBytes) content_bytes = g_bytes_new_from_bytes (inline_part_bytes, 1,
                                                                    g_bytes_get_size (inline_part_bytes) - 1);
          ret_part = g_variant_new_from_bytes (G_VARIANT_TYPE (OSTREE_STATIC_DELTA_PART_PAYLOAD_FORMAT_V0),
                                               content_bytes, trusted);
          g_variant_ref_sink (ret_part);
        }

      if (!skip_checksum)
        g_checksum_update (checksum, g_variant_get_data (ret_part),
                           g_variant_get_size (ret_part));

      break;
    case 'x':
      {
        g_autoptr(GConverter) decomp = (GConverter*) _ostree_lzma_decompressor_new ();
        g_autoptr(GInputStream) convin = g_converter_input_stream_new (source_in, decomp);
        g_autoptr(GBytes) buf = ot_map_anonymous_tmpfile_from_content (convin, cancellable, error);
        if (!buf)
          return FALSE;

        ret_part = g_variant_new_from_bytes (G_VARIANT_TYPE (OSTREE_STATIC_DELTA_PART_PAYLOAD_FORMAT_V0),
                                             buf, FALSE);
      }
      break;
    default:
      return glnx_throw (error, "Invalid compression type '%u'", comptype);
    }

  if (checksum)
    {
      const char *actual_checksum = g_checksum_get_string (checksum);
      g_assert (expected_checksum != NULL);
      if (strcmp (actual_checksum, expected_checksum) != 0)
        return glnx_throw (error, "Checksum mismatch in static delta part; expected=%s actual=%s",
                           expected_checksum, actual_checksum);
    }

  *out_part = g_steal_pointer (&ret_part);
  return TRUE;
}