Fixes forward scrubbing (#468)

The root cause was among the validation flags, where is_first_sei
was not updated correctly.

Author: bjornvolcker

lib/src/sv_auth.c

@@ -807,7 +807,7 @@ validate_authenticity(signed_video_t *self, bu_list_item_t *sei)
 
   // Determine if this GOP is valid, but has missing information. This happens if we have detected
   // missed BUs or if the GOP is incomplete.
-  if (valid == SV_AUTH_RESULT_OK && (num_missed > 0)) {  // && verify_success)) {
+  if (valid == SV_AUTH_RESULT_OK && (num_missed > 0)) {
     valid = SV_AUTH_RESULT_OK_WITH_MISSING_INFO;
     DEBUG_LOG("Successful validation, but detected missing Bitstream Units");
   }
@@ -1188,7 +1188,7 @@ maybe_validate_gop(signed_video_t *self, bu_info_t *bu)
     // If this is the first arrived SEI, but could still not validate the authenticity, signal to
     // the user that the Signed Video feature has been detected.
     svrc_t status = SV_OK;
-    if (validation_flags->is_first_sei) {
+    if (validation_flags->is_first_sei && bu->is_sv_sei) {
       latest->authenticity = SV_AUTH_RESULT_SIGNATURE_PRESENT;
       latest->public_key_has_changed = false;
       // Check if the data is golden. If it is, update the validation status accordingly.
@@ -1201,7 +1201,7 @@ maybe_validate_gop(signed_video_t *self, bu_info_t *bu)
       latest->number_of_pending_picture_nalus = bu_list_num_pending_items(bu_list);
       status = bu_list_update_status(bu_list, true);
       validation_flags->has_auth_result = true;
-      validation_flags->lost_start_of_gop = false;
+      validation_flags->is_first_sei = false;
     }
     return status;
   }
@@ -1225,6 +1225,8 @@ maybe_validate_gop(signed_video_t *self, bu_info_t *bu)
         latest->number_of_received_picture_nalus = 0;
         latest->number_of_pending_picture_nalus = -1;
         latest->public_key_has_changed = public_key_has_changed;
+        validation_flags->num_invalid = 0;
+        validation_flags->lost_start_of_gop = false;
         // Reset |in_validation|.
         update_sei_in_validation(self, true, NULL, NULL);
       }
@@ -1248,6 +1250,7 @@ maybe_validate_gop(signed_video_t *self, bu_info_t *bu)
       // The flag |is_first_validation| is used to ignore the first validation if we start the
       // validation in the middle of a stream. Now it is time to reset it.
       validation_flags->is_first_validation = !validation_flags->signing_present;
+      validation_flags->is_first_sei &= !bu->is_sv_sei;
 
       if (validation_flags->reset_first_validation) {
         validation_flags->is_first_validation = true;
@@ -1491,7 +1494,7 @@ add_bitstream_unit(signed_video_t *self, const uint8_t *bu_data, size_t bu_data_
       SV_THROW_IF(!self->legacy_sv, SV_MEMORY);
       sv_accumulated_validation_init(self->accumulated_validation);
     }
-    if (nalus_pending_registration && self->validation_flags.hash_algo_known) {
+    if (nalus_pending_registration && validation_flags->hash_algo_known) {
       SV_THROW(reregister_bu(self));
     }
     SV_THROW(maybe_validate_gop(self, &bu));

lib/src/sv_common.c

@@ -664,7 +664,6 @@ update_validation_flags(validation_flags_t *validation_flags, bu_info_t *bu)
 {
   if (!validation_flags || !bu) return;
 
-  validation_flags->is_first_sei = !validation_flags->signing_present && bu->is_sv_sei;
   // As soon as we receive a SEI, Signed Video is present.
   validation_flags->signing_present |= bu->is_sv_sei;
 }

lib/src/sv_internal.h

@@ -212,6 +212,7 @@ typedef struct {
   bool sei_in_sync;  // The SEIs are correctly associated with a (partial) GOP
   int num_lost_seis;  // Indicates how many SEIs has been lost since last the session got
   // the latest SEI. Note that this value can become negative if SEIs have changed order.
+  int num_invalid;  // Tracks invalid GOPs across multiple GOP validation.
   bool lost_start_of_gop;  // Tracks if an I-frame has been lost, which needs to be
   // handled as a special case if it happens for the first validation.
 } validation_flags_t;

tests/check/check_signed_video_auth.c

@@ -1220,10 +1220,6 @@ mimic_au_fast_forward_and_get_list(signed_video_t *sv, struct sv_setting setting
 
 START_TEST(fast_forward_stream_with_reset)
 {
-  // TODO: Remove when scrubbing forward works. Currently, the first SEI after a "fast
-  // forward" operation is validated as 'invalid' when it should not be validated at all.
-  // Disabling the test until it has been solved.
-  return;
   // Create a session.
   signed_video_t *sv = get_initialized_signed_video(settings[_i], false);
   ck_assert(sv);
@@ -1319,10 +1315,6 @@ mimic_au_fast_forward_on_late_seis_and_get_list(signed_video_t *sv, struct sv_se
 
 START_TEST(fast_forward_stream_with_delayed_seis)
 {
-  // TODO: Remove when scrubbing forward works. Currently, the first SEI after a "fast
-  // forward" operation is validated as 'invalid' when it should not be validated at all.
-  // Disabling the test until it has been solved.
-  return;
   // Create a new session.
   signed_video_t *sv = get_initialized_signed_video(settings[_i], false);
   ck_assert(sv);
@@ -2388,10 +2380,6 @@ END_TEST
 
 START_TEST(file_export_and_scrubbing_partial_gops)
 {
-  // TODO: Remove when scrubbing forward works. Currently, the first SEI after a "fast
-  // forward" operation is validated as 'invalid' when it should not be validated at all.
-  // Disabling the test until it has been solved.
-  return;
   // Device side
   struct sv_setting setting = settings[_i];
   const unsigned max_signing_frames = 4;