Migrating service initialization to use the Config object

[david-perez]

Since smithy-rs 0.57.0, with the introduction of #3095, the methods:

• builder_with_plugins on the service builder,
• builder_without_plugins on the service builder; and
• layer on the built service

are deprecated. They will be removed in a future release.

Instead, a ${serviceName}Config object is now generated, which serves as the central place to register plugins and layers.

Previously, you used builder_with_plugins to initialize the service builder with a set of plugins, or builder_without_plugins if you did not need any plugins. In both cases, you can now use the config builder object.

Before:

let http_plugins = HttpPlugins::new()
    .push(print_plugin)
    .instrument();

let authz_plugin = AuthorizationPlugin::new();

let app = PokemonService::builder_with_plugins(http_plugins, authz_plugin)
    .get_pokemon_species(get_pokemon_species)
    // <snip>
    .build()
    .expect("failed to build an instance of PokemonService");

Now:

let http_plugins = HttpPlugins::new()
    .push(print_plugin)
    .instrument();

let authz_plugin = AuthorizationPlugin::new();

let config = PokemonServiceConfig::builder()
    .http_plugin(plugins)
    .model_plugin(authz_plugin)
    .build();

let app = PokemonService::builder(config)
    .get_pokemon_species(get_pokemon_species)
    // <snip>
    .build()
    .expect("failed to build an instance of PokemonService");

Note you can also push multiple plugins directly onto PokemonServiceConfig:

let config = PokemonServiceConfig::builder()
    .http_plugin(print_plugin)
    .http_plugin(operation_extension_plugin)
    .model_plugin(authz_plugin)
    .build();

Similarly, you can now add layers onto PokemonServiceConfig. Before:

let app = PokemonService::builder_without_plugins()
    .get_pokemon_species(get_pokemon_species)
    // <snip>
    .build()
    .expect("failed to build an instance of PokemonService");

let app = app
    // Add server request IDs.
    .layer(&ServerRequestIdProviderLayer::new());

Now:

let config = PokemonServiceConfig::builder()
    // Add server request IDs.
    .layer(&ServerRequestIdProviderLayer::new())
    .build();

let app = PokemonService::builder(config)
    .get_pokemon_species(get_pokemon_species)
    // <snip>
    .build()
    .expect("failed to build an instance of PokemonService");

The layers get applied in the same place as before, namely, uniformly around routes inside the router.

The methods have not been removed, only deprecated, so you can continue using them until a future release. Therefore, in most cases your code should not break. However, there is a breaking change in the service builder: it now has one extra type parameter representing the layers, for a total of 4 generic type parameters. This may affect you if, for example, you have a variable binding using type ascription:

Example breaking code:

let builder: PokemonServiceBuilder<Body, _, _> = PokemonService::builder_with_plugins(http_plugins, IdentityPlugin);

Fix:

let builder: PokemonServiceBuilder<Body, _, _, _> = PokemonService::builder_with_plugins(http_plugins, IdentityPlugin);