device: Add API for perstistent data storage

API consumers should fetch the persistent data when they are done and
store it to disk. It is undefined when this data is updated by the
driver, but in general, it should only be updated once the first time
a device is used.

doc/libfprint-2-sections.txt

@@ -40,6 +40,8 @@ fp_device_has_feature
 fp_device_has_storage
 fp_device_supports_identify
 fp_device_supports_capture
+fp_device_get_persistent_data
+fp_device_set_persistent_data
 fp_device_is_open
 fp_device_open
 fp_device_close

libfprint/fp-device-private.h

@@ -61,6 +61,7 @@ typedef struct
   FpDeviceFeature features;
 
   guint64         driver_data;
+  GVariant       *persistent_data;
 
   gint            nr_enroll_stages;
   GSList         *sources;

libfprint/fp-device.c

@@ -54,6 +54,7 @@ enum {
   PROP_FPI_UDEV_DATA_SPIDEV,
   PROP_FPI_UDEV_DATA_HIDRAW,
   PROP_FPI_DRIVER_DATA,
+  PROP_FPI_PERSISTENT_DATA,
   N_PROPS
 };
 
@@ -235,6 +236,8 @@ fp_device_finalize (GObject *object)
   g_clear_pointer (&priv->udev_data.spidev_path, g_free);
   g_clear_pointer (&priv->udev_data.hidraw_path, g_free);
 
+  g_clear_pointer (&priv->persistent_data, g_variant_unref);
+
   G_OBJECT_CLASS (fp_device_parent_class)->finalize (object);
 }
 
@@ -304,6 +307,10 @@ fp_device_get_property (GObject    *object,
         g_value_set_string (value, NULL);
       break;
 
+    case PROP_FPI_PERSISTENT_DATA:
+      g_value_set_variant (value, priv->persistent_data);
+      break;
+
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
     }
@@ -354,6 +361,11 @@ fp_device_set_property (GObject      *object,
       priv->driver_data = g_value_get_uint64 (value);
       break;
 
+    case PROP_FPI_PERSISTENT_DATA:
+      g_clear_pointer (&priv->persistent_data, g_variant_unref);
+      priv->persistent_data = g_value_dup_variant (value);
+      break;
+
     default:
       G_OBJECT_WARN_INVALID_PROPERTY_ID (object, prop_id, pspec);
     }
@@ -594,6 +606,21 @@ fp_device_class_init (FpDeviceClass *klass)
                          0,
                          G_PARAM_STATIC_STRINGS | G_PARAM_WRITABLE | G_PARAM_CONSTRUCT_ONLY);
 
+  /**
+   * FpDevice::fpi-persistent-data: (skip)
+   *
+   * This property is only for internal purposes.
+   *
+   * Stability: private
+   */
+  properties[PROP_FPI_PERSISTENT_DATA] =
+    g_param_spec_variant ("fpi-persistent-data",
+                          "Persistent Driver Data",
+                          "Private: Previously stored data for the device",
+                          G_VARIANT_TYPE_ANY,
+                          NULL,
+                          G_PARAM_STATIC_STRINGS | G_PARAM_READWRITE);
+
   g_object_class_install_properties (object_class, N_PROPS, properties);
 }
 
@@ -739,6 +766,139 @@ fp_device_get_temperature (FpDevice *device)
   return priv->temp_current;
 }
 
+/**
+ * fp_device_get_persistent_data:
+ * @device: A #FpDevice
+ * @data: (array length=length) (transfer full) (out): Return location for data pointer
+ * @length: (transfer full) (out): Length of @data
+ * @error: Return location for error
+ *
+ * Retrieves persistent data that should be stored for this device. Storage
+ * needs to be device specific, i.e. device ID and driver must match when
+ * restored.
+ *
+ * Returns: (type void): %TRUE on success
+ */
+gboolean
+fp_device_get_persistent_data (FpDevice *device,
+                               guchar  **data,
+                               gsize    *length,
+                               GError  **error)
+{
+  g_autoptr(GVariant) res = NULL;
+  FpDevicePrivate *priv = fp_device_get_instance_private (device);
+
+  g_assert (data);
+  g_assert (length);
+
+  if (priv->persistent_data == NULL)
+    {
+      *data = NULL;
+      *length = 0;
+
+      return TRUE;
+    }
+
+  /* Version + variant from driver */
+  res = g_variant_new ("(issv)",
+                       1,
+                       fp_device_get_driver (device),
+                       priv->device_id,
+                       priv->persistent_data);
+
+  *length = g_variant_get_size (res);
+  *data = g_malloc (*length);
+  g_variant_store (res, *data);
+
+  return TRUE;
+}
+
+/**
+ * fp_device_get_persistent_data:
+ * @device: A #FpDevice
+ * @data: (array length=length) (transfer none): Persistent Data
+ * @length: (transfer none): Length of @data
+ * @error: Return location for error
+ *
+ * Load persistent data from storage. This function should be called after
+ * a device was discovered and before it is opened for the first time. It is
+ * an error to call it if data has already been set (or generated by the
+ * driver).
+ *
+ * Note that the driver may update the data. The API user should retrieve the
+ * value when done with the device and store it in a persistent location.
+ *
+ * Returns: (type void): %TRUE on success
+ */
+gboolean
+fp_device_set_persistent_data (FpDevice *device,
+                               guchar   *data,
+                               gsize     length,
+                               GError  **error)
+{
+  g_autoptr(GVariant) stored = NULL;
+  g_autoptr(GVariant) loaded = NULL;
+  FpDevicePrivate *priv = fp_device_get_instance_private (device);
+  guchar *copy;
+  gint version;
+  const gchar *device_id;
+  const gchar *driver;
+
+  if (priv->is_open)
+    {
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_NOT_SUPPORTED,
+                   "Data can only be set right after device creation");
+      return FALSE;
+    }
+
+  if (priv->persistent_data)
+    {
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_EXISTS,
+                   "Data has already been set");
+      return FALSE;
+    }
+
+  if (length == 0)
+    {
+      g_clear_pointer (&priv->persistent_data, g_variant_unref);
+      g_object_notify_by_pspec (G_OBJECT (device), properties[PROP_FPI_PERSISTENT_DATA]);
+      return TRUE;
+    }
+  g_assert (data);
+
+  copy = g_memdup (data, length);
+  stored = g_variant_new_from_data (G_VARIANT_TYPE ("(issv)"), copy, length, FALSE, g_free, copy);
+
+  if (!stored)
+    {
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_INVALID_DATA,
+                   "Data could not be parsed");
+      return FALSE;
+    }
+
+  g_variant_get (stored, "(issv)", &version, &driver, &device_id, &loaded);
+  if (version != 1)
+    {
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_INVALID_DATA,
+                   "Unknown data storage version");
+      return FALSE;
+    }
+
+  if (g_strcmp0 (device_id, priv->device_id) != 0 ||
+      g_strcmp0 (driver, fp_device_get_driver (device)) != 0)
+    {
+      g_set_error (error, G_IO_ERROR, G_IO_ERROR_INVALID_DATA,
+                   "Driver or device ID mismatch!");
+      return FALSE;
+    }
+
+  g_clear_pointer (&priv->persistent_data, g_variant_unref);
+  priv->persistent_data = g_steal_pointer (&loaded);
+  g_object_notify_by_pspec (G_OBJECT (device), properties[PROP_FPI_PERSISTENT_DATA]);
+
+  return TRUE;
+}
+
 /**
  * fp_device_supports_identify:
  * @device: A #FpDevice

libfprint/fp-device.h

@@ -230,6 +230,15 @@ FpDeviceFeature     fp_device_get_features (FpDevice *device);
 gboolean            fp_device_has_feature (FpDevice       *device,
                                            FpDeviceFeature feature);
 
+gboolean fp_device_get_persistent_data (FpDevice *device,
+                                        guchar  **data,
+                                        gsize    *length,
+                                        GError  **error);
+gboolean fp_device_set_persistent_data (FpDevice *device,
+                                        guchar   *data,
+                                        gsize     length,
+                                        GError  **error);
+
 /* Opening the device */
 void fp_device_open (FpDevice           *device,
                      GCancellable       *cancellable,

tests/test-fp-device.c

@@ -232,6 +232,53 @@ test_device_has_storage (void)
   G_GNUC_END_IGNORE_DEPRECATIONS
 }
 
+static void
+test_device_persistent_data (void)
+{
+  g_autoptr(FptContext) tctx = fpt_context_new_with_virtual_device (FPT_VIRTUAL_DEVICE_IMAGE);
+  g_autoptr(GVariant) initial = NULL;
+  g_autoptr(GVariant) loaded = NULL;
+  g_autoptr(GError) error = NULL;
+  guint8 *data = (guint8 *) 0xdeadbeef;
+  gsize length = 1;
+
+  initial = g_variant_ref_sink (g_variant_new ("(s)", "stored data"));
+
+  g_assert_true (fp_device_get_persistent_data (tctx->device, &data, &length, &error));
+  g_assert_cmpint (length, ==, 0);
+  g_assert_null (data);
+  g_assert_no_error (error);
+
+  /* Use the fact that this is a property that we can poke from the outside. */
+  g_object_set (tctx->device, "fpi-persistent-data", initial, NULL);
+
+  /* Works now */
+  g_assert_true (fp_device_get_persistent_data (tctx->device, &data, &length, &error));
+  g_assert_cmpint (length, !=, 0);
+  g_assert_nonnull (data);
+  g_assert_no_error (error);
+
+  /* We can't load the data, as data has been set already. */
+  g_assert_false (fp_device_set_persistent_data (tctx->device, data, length, &error));
+  g_assert_error (error, G_IO_ERROR, G_IO_ERROR_EXISTS);
+  g_clear_pointer (&error, g_error_free);
+
+  /* Abuse that we can "load" again if the data is set to NULL.
+   * This is an implementation detail and just a lack of error checking. */
+  g_object_set (tctx->device, "fpi-persistent-data", NULL, NULL);
+
+  /* Incomplete data, causes parsing error */
+  g_assert_false (fp_device_set_persistent_data (tctx->device, data, 5, &error));
+  g_assert_error (error, G_IO_ERROR, G_IO_ERROR_INVALID_DATA);
+  g_clear_pointer (&error, g_error_free);
+
+  g_assert_true (fp_device_set_persistent_data (tctx->device, data, length, &error));
+  g_assert_no_error (error);
+
+  g_object_get (tctx->device, "fpi-persistent-data", &loaded, NULL);
+  g_assert_cmpvariant (initial, loaded);
+}
+
 int
 main (int argc, char *argv[])
 {
@@ -252,6 +299,7 @@ main (int argc, char *argv[])
   g_test_add_func ("/device/sync/supports_identify", test_device_supports_identify);
   g_test_add_func ("/device/sync/supports_capture", test_device_supports_capture);
   g_test_add_func ("/device/sync/has_storage", test_device_has_storage);
+  g_test_add_func ("/device/persistent_data", test_device_persistent_data);
 
   return g_test_run ();
 }