Custom decoder

By default, OCMAM uses the protopack library to decode the requested layer data.

To decode layer data using a custom decoder, use the schema_decoder field of the DataStoreServerSettings structure.

In this section, learn how to:

• Use a custom decoder for a specific layer
• Use a custom decoder for all layers
• Use a custom schema

Use a custom decoder for a specific layer

To decode a specific layer using a custom decoder:

1. Create the custom decoder for the layer.

   Example:

    struct RoadAttributeLayerDecoder
    {
        bool
        operator( )( const void* data,
                     const int size,
                     clientmap::decoder::LayerConfigurationPtr configuration,
                     clientmap::decoder::ClientMapTile& tile ) const
        {
            // Set the layer configuration.
            tile.road_attribute_layer_configuration
                = std::move( configuration );
   
            // The layer data may not be present (for example, if the users
            // request road attributes for a tile that does not contain any
            // roads). In this case, do not set the layer data and return.
            if ( data == nullptr || size <= 0 )
            {
                return true;
            }
   
            // Decode layer data.
            if ( !tile.arena )
            {
                tile.arena = std::make_shared<
                    clientmap::decoder::ClientMapTile::ArenaType >( );
            }
   
            auto* const road_attribute_layer = google::protobuf::Arena::Create<
                clientmap::decoder::RoadAttributeLayer >( tile.arena.get( ) );
   
            // Fill the `road_attribute_layer` instance with data.
            ...
   
            tile.road_attribute_layer = clientmap::decoder::LayerPtr<
                const clientmap::decoder::RoadAttributeLayer >(
                road_attribute_layer, tile.arena );
            return true;
        }
    };
   

   Note: operator( ) must be of the clientmap::decoder::AbstractSchemaDecoder::LayerDecoderType type.

2. Create a DefaultSchemaDecoder instance and configure it to use the custom decoder for the specific layer.

   Note: The layers for which custom decoders are not set are decoded using the protopack library by default.

   Example:

    auto decoder
        = std::make_shared< clientmap::decoder::DefaultSchemaDecoder >( );
   
    decoder->SetDecoder( clientmap::rendering::kRoadAttributeLayerName,
                         RoadAttributeLayerDecoder( ) );
   

3. Create a DataStoreServer instance that uses the DefaultSchemaDecoder instance.

   Example:

    olp::clientmap::datastore::DataStoreServerSettings server_settings;
    server_settings.schema_decoder = decoder;
    ...
   
    auto server
        = std::make_shared< olp::clientmap::datastore::DataStoreServer >(
            server_settings );
   

Use a custom decoder for all layers

To decode all layers using a custom decoder:

1. Create the custom decoder for all layers.

   Example:

    struct CustomLayerDecoder
    {
        bool
        operator( )( const void* data,
                     const int size,
                     clientmap::decoder::LayerConfigurationPtr configuration,
                     clientmap::decoder::ClientMapTile& tile ) const
        {
            ...
        }
    };
   

   Notes:

   • operator( ) must be of the clientmap::decoder::AbstractSchemaDecoder::LayerDecoderType type.
   • For each layer, operator( ) must set the correct layer data and layer configuration fields of the tile instance.

2. Create a DefaultSchemaDecoder instance and configure it to use the custom decoder for all layers.

   Example:

    auto decoder
        = std::make_shared< clientmap::decoder::DefaultSchemaDecoder >( );
   
    decoder->SetDecoder( CustomLayerDecoder( ) );
   

3. Create a DataStoreServer instance that uses the DefaultSchemaDecoder instance.

   Example:

    olp::clientmap::datastore::DataStoreServerSettings server_settings;
    server_settings.schema_decoder = decoder;
    ...
   
    auto server
        = std::make_shared< olp::clientmap::datastore::DataStoreServer >(
            server_settings );
   

Use a custom schema

To decode all layers using a custom schema:

1. Inherit the custom schema decoder from the clientmap::decoder::AbstractSchemaDecoder abstract class.

   Example:

    class CustomSchemaDecoder : public AbstractSchemaDecoder
    {
    public:
        ...
    };
   

2. Create a DataStoreServer instance that uses the custom schema decoder instance.

   Example:

    olp::clientmap::datastore::DataStoreServerSettings server_settings;
    server_settings.schema_decoder
        = std::make_shared< CustomSchemaDecoder >( );
    ...
   
    auto server
        = std::make_shared< olp::clientmap::datastore::DataStoreServer >(
            server_settings );