Gracefully handle non-contiguous Channel ids

Author: realityforge

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 ### Unreleased
 
+* Gracefully handle non-contiguous Channel ids.
+
 ### [v6.157](https://github.com/replicant4j/replicant/tree/v6.157) (2025-10-07) · [Full Changelog](https://github.com/replicant4j/replicant/compare/v6.156...v6.157)
 
 Changes in this release:

client/src/main/java/replicant/SystemSchema.java

@@ -67,13 +67,10 @@ public SystemSchema( final int id,
                             "' passed an array of entities where entity at index " + index + " does not " +
                             "have id matching index." );
       }
-      apiInvariant( () -> Arrays.stream( channels ).allMatch( Objects::nonNull ),
-                    () -> "Replicant-0055: SystemSchema named '" + ( null == name ? "?" : name ) +
-                          "' passed an array of channels that has a null element" );
       for ( int i = 0; i < channels.length; i++ )
       {
         final int index = i;
-        apiInvariant( () -> index == channels[ index ].getId(),
+        apiInvariant( () -> null == channels[ index ] || index == channels[ index ].getId(),
                       () -> "Replicant-0056: SystemSchema named '" + ( null == name ? "?" : name ) +
                             "' passed an array of channels where channel at index " + index + " does not " +
                             "have id matching index." );
@@ -173,6 +170,8 @@ public ChannelSchema getChannel( final int channelId )
     {
       apiInvariant( () -> channelId >= 0 && channelId < _channels.length,
                     () -> "Replicant-0058: SystemSchema.getChannel(id) passed an id that is out of range." );
+      apiInvariant( () -> null != _channels[channelId],
+                    () -> "Replicant-0008: SystemSchema.getChannel(id) attempted to access null channel." );
     }
     return _channels[ channelId ];
   }
@@ -183,6 +182,7 @@ public List<ChannelLinkSchema> getInwardChannelLinks( final int channelId, final
     return
       Stream
         .of( _channels )
+        .filter( Objects::nonNull )
         .flatMap( channelSchema ->
                     channelSchema
                       .getEntities()
@@ -202,6 +202,7 @@ public List<ChannelLinkSchema> getInwardChannelLinks( final int channelId )
     return
       Stream
         .of( _channels )
+        .filter( Objects::nonNull )
         .flatMap( channelSchema ->
                     channelSchema
                       .getEntities()

client/src/test/java/replicant/SystemSchemaTest.java

@@ -18,23 +18,23 @@ public void basicOperation()
     final EntitySchema entity2 =
       new EntitySchema( 1, ValueUtil.randomString(), String.class, ( i, d ) -> "", null, new ChannelLinkSchema[ 0 ] );
     final EntitySchema[] entities = new EntitySchema[]{ entity1, entity2 };
-    final ChannelSchema channel1 = new ChannelSchema( 0,
+    final ChannelSchema channel1 = new ChannelSchema( 1,
                                                       ValueUtil.randomString(),
                                                       null,
                                                       ChannelSchema.FilterType.NONE,
                                                       null,
                                                       false,
                                                       true,
                                                       Collections.emptyList() );
-    final ChannelSchema[] channels = { channel1 };
+    final ChannelSchema[] channels = { null, channel1 };
     final SystemSchema systemSchema = new SystemSchema( id, name, channels, entities );
     assertEquals( systemSchema.getId(), id );
     assertEquals( systemSchema.getName(), name );
     assertEquals( systemSchema.getEntityCount(), 2 );
     assertEquals( systemSchema.getEntity( 0 ), entity1 );
     assertEquals( systemSchema.getEntity( 1 ), entity2 );
-    assertEquals( systemSchema.getChannelCount(), 1 );
-    assertEquals( systemSchema.getChannel( 0 ), channel1 );
+    assertEquals( systemSchema.getChannelCount(), 2 );
+    assertEquals( systemSchema.getChannel( 1 ), channel1 );
     assertEquals( systemSchema.toString(), name );
   }
 
@@ -63,6 +63,7 @@ public void getEntity_BadIndex()
   @Test
   public void construct_nullEntity()
   {
+
     final IllegalStateException exception =
       expectThrows( IllegalStateException.class,
                     () -> new SystemSchema( ValueUtil.randomInt(),
@@ -73,19 +74,6 @@ public void construct_nullEntity()
                   "Replicant-0053: SystemSchema named 'X' passed an array of entities that has a null element" );
   }
 
-  @Test
-  public void construct_nullChannel()
-  {
-    final IllegalStateException exception =
-      expectThrows( IllegalStateException.class,
-                    () -> new SystemSchema( ValueUtil.randomInt(),
-                                            "X",
-                                            new ChannelSchema[]{ null },
-                                            new EntitySchema[]{} ) );
-    assertEquals( exception.getMessage(),
-                  "Replicant-0055: SystemSchema named 'X' passed an array of channels that has a null element" );
-  }
-
   @Test
   public void construct_badEntityIndex()
   {

client/src/test/java/replicant/diagnostic_messages.json

@@ -34,6 +34,11 @@
     "type": "INVARIANT",
     "messagePattern": "Unable to locate Connector by schemaId %s"
   },
+  {
+    "code": 8,
+    "type": "API_INVARIANT",
+    "messagePattern": "SystemSchema.getChannel(id) attempted to access null channel."
+  },
   {
     "code": 9,
     "type": "API_INVARIANT",
@@ -239,11 +244,6 @@
     "type": "API_INVARIANT",
     "messagePattern": "SystemSchema named '%s' passed an array of entities where entity at index %s does not have id matching index."
   },
-  {
-    "code": 55,
-    "type": "API_INVARIANT",
-    "messagePattern": "SystemSchema named '%s' passed an array of channels that has a null element"
-  },
   {
     "code": 56,
     "type": "API_INVARIANT",

server/src/main/java/replicant/server/transport/SchemaMetaData.java

@@ -17,11 +17,10 @@ public final class SchemaMetaData
 
   public SchemaMetaData( @Nonnull final String name, @Nonnull final ChannelMetaData... channels )
   {
-    assert Arrays.stream( channels ).allMatch( Objects::nonNull );
     for ( int i = 0; i < channels.length; i++ )
     {
       final ChannelMetaData channel = channels[ i ];
-      if ( i != channel.getChannelId() )
+      if ( null != channel && i != channel.getChannelId() )
       {
         final String message = "Channel at index " + i + " does not have channel id matching index: " + channel;
         throw new IllegalArgumentException( message );
@@ -30,7 +29,7 @@ public SchemaMetaData( @Nonnull final String name, @Nonnull final ChannelMetaDat
     _name = Objects.requireNonNull( name );
     _channels = channels;
     _instanceChannels =
-      Stream.of( channels ).filter( ChannelMetaData::isInstanceGraph ).toArray( ChannelMetaData[]::new );
+      Stream.of( channels ).filter( Objects::nonNull ).filter( ChannelMetaData::isInstanceGraph ).toArray( ChannelMetaData[]::new );
   }
 
   @Nonnull
@@ -56,6 +55,7 @@ public ChannelMetaData getChannelMetaData( @Nonnull final ChannelAddress address
   @Nonnull
   public ChannelMetaData getChannelMetaData( final int channelId )
   {
+    assert null != _channels[ channelId ];
     return _channels[ channelId ];
   }