Deflake 'uploading signed devices gets propagated over federation'

This test started to fail after implementing
element-hq/synapse#18899. The failure
appeared to be due to the test not waiting for signatures to
propagate over federation. The  loop
would exit as soon as it saw a 'signatures' key. But the
value was an empty dict.

A few moments later, the dict would be populated with the key
we were waiting for. But while that was being sent over federation,
the test would fail and exit abruptly.

This commit changes the  loop to actually
check for the signature we're waiting for, instead of exiting
upon seeing the 'signatures' key. This seems like it would be
less flaky in general, and prevents the test from failing in
this case.

Author: anoadragon453

tests/41end-to-end-keys/08-cross-signing.pl

@@ -29,7 +29,7 @@
                       => "nqOvzeuGWT/sRx3h7+MHoInYj3Uk2LD/unI9kDYcHwk",
               },
           },
-      })->then( sub {
+      })->then( sub {#get_media_config_for_user
          matrix_get_e2e_keys( $user, $user_id );
       })->then( sub {
          my ( $content ) = @_;
@@ -587,6 +587,8 @@
 
       my $user2_id = $user2->user_id;
       my $user2_device = $user2->device_id;
+      my $user2_device_key_id_hash = "EmkqvokUn8p+vQAGZitOk4PWjp7Ukp3txV2TbMPEiBQ";
+      my $user2_device_key_id = "ed25519:$user2_device_key_id_hash";
 
       my $room_id;
 
@@ -597,8 +599,7 @@
          "user_id" => $user2_id,
          "usage" => ["self_signing"],
          "keys" => {
-            "ed25519:EmkqvokUn8p+vQAGZitOk4PWjp7Ukp3txV2TbMPEiBQ"
-                => "EmkqvokUn8p+vQAGZitOk4PWjp7Ukp3txV2TbMPEiBQ",
+            $user2_device_key_id => $user2_device_key_id_hash,
          },
       };
       sign_json(
@@ -668,10 +669,10 @@
       })->then( sub {
          sign_json(
             $device, secret_key => $self_signing_secret_key,
-            origin => $user2_id, key_id => "ed25519:EmkqvokUn8p+vQAGZitOk4PWjp7Ukp3txV2TbMPEiBQ"
+            origin => $user2_id, key_id => $user2_device_key_id
          );
          log_if_fail "sent signature", $device;
-         $cross_signature = $device->{signatures}->{$user2_id}->{"ed25519:EmkqvokUn8p+vQAGZitOk4PWjp7Ukp3txV2TbMPEiBQ"};
+         $cross_signature = $device->{signatures}->{$user2_id}->{$user2_device_key_id};
          matrix_upload_signatures( $user2, {
              $user2_id => {
                  $user2_device => $device
@@ -690,11 +691,19 @@
             # On server0, user1 syncs until they see user2's device. This is racey: the
             # sync may complete before the signatures have uploaded, propagated over
             # federation to server 1 and then over replication to the sync worker.
+            #
+            # Thus we check for the expected signatures inside this function.
             matrix_get_e2e_keys( $user1, $user2_id )->then( sub {
                my ( $content ) = @_;
                log_if_fail "key query content2", $content;
-               $content->{device_keys}{$user2_id}{$user2_device}{"signatures"}
+               my $sigs = $content->{device_keys}{$user2_id}{$user2_device}{"signatures"}
                   or die "No 'signatures' key present";
+               
+               exists $sigs->{$user2_id}
+                  && exists $sigs->{$user2_id}{$user2_device_key_id}
+                  && $sigs->{$user2_id}{$user2_device_key_id} eq $cross_signature
+                  or die "Expected cross-signature not visible";
+
                Future->done( $content );
             });
          };
@@ -703,15 +712,6 @@
 
          log_if_fail "key query content3", $content;
 
-         # Check that fetching the devices again returns the new signature
-         assert_json_keys( $content->{device_keys}->{$user2_id}->{$user2_device}, "signatures" );
-
-         assert_deeply_eq( $content->{device_keys}->{$user2_id}->{$user2_device}->{signatures}, {
-            $user2_id => {
-               "ed25519:EmkqvokUn8p+vQAGZitOk4PWjp7Ukp3txV2TbMPEiBQ" => $cross_signature
-            },
-         } );
-
          # Check that we still see the master key when querying the devices.
          assert_json_keys( $content->{master_keys}, $user2_id );
          assert_json_keys( $content->{master_keys}->{$user2_id}, "keys");