Note: This document covers API impact only. For more details, see the ABI compatibility page

Add a protocol method

Overview

Initial State {#init}

FIDL {#fidl-init}

protocol Example {
    ExistingMethod();
};

Dart {#dart-init}

class Server extends fidllib.Example {
  @override
  Future<void> existingMethod() async {}
}
void client(fidllib.ExampleProxy client) async {
  await client.existingMethod();
}

Go {#go-init}

type client struct {
    addMethod *lib.ExampleWithCtxInterface
}
func (c client) test() {
    c.addMethod.ExistingMethod(context.Background())
}
type server struct{}
// Assert that server implements the Example interface
var _ lib.ExampleWithCtx = &server{}
func (*server) ExistingMethod(fidl.Context) error {
    return nil
}

HLCPP {#hlcpp-init}

class Server : public fidl_test::Example {
  void ExistingMethod() final {}
};
void client(fidl_test::ExamplePtr client) { client->ExistingMethod(); }

LLCPP {#llcpp-init}

class Server final : public fidl_test::Example::Interface {
 public:
  void ExistingMethod(ExistingMethodCompleter::Sync& completer) final {}
};
void client(fidl::Client<fidl_test::Example> client) { client->ExistingMethod(); }

Rust {#rust-init}

struct ExampleFakeProxy;
impl fidl_lib::ExampleProxyInterface for ExampleFakeProxy {
    fn existing_method(&self) -> Result<(), fidl::Error> {
        Ok(())
    }
}
async fn example_service(chan: fasync::Channel) -> Result<(), fidl::Error> {
    let mut stream = fidl_lib::ExampleRequestStream::from_channel(chan);
    while let Some(req) = stream.try_next().await? {
        match req {
            fidl_lib::ExampleRequest::ExistingMethod { .. } => {}
        }
    }
    Ok(())
}

Update Source Code {#step-1}

Go {#go-1}

• Embed the protocol’s WithCtxTransitionBase struct into the server type.

  type client struct {
      addMethod *lib.ExampleWithCtxInterface
  }
  func (c client) test() {
      c.addMethod.ExistingMethod(context.Background())
  }
- type server struct{}
+ type server struct {
+     lib.ExampleWithCtxTransitionalBase
+ }
  // Assert that server implements the Example interface
  var _ lib.ExampleWithCtx = &server{}
  func (*server) ExistingMethod(fidl.Context) error {
      return nil
  }

Rust {#rust-1}

• Add #[allow(unreachable_patterns)] to the server’s request stream match.
• Add an underscore arm to the server’s request stream match.

  struct ExampleFakeProxy;
  impl fidl_lib::ExampleProxyInterface for ExampleFakeProxy {
      fn existing_method(&self) -> Result<(), fidl::Error> {
          Ok(())
      }
  }
  async fn example_service(chan: fasync::Channel) -> Result<(), fidl::Error> {
      let mut stream = fidl_lib::ExampleRequestStream::from_channel(chan);
      while let Some(req) = stream.try_next().await? {
+         #[allow(unreachable_patterns)]
          match req {
              fidl_lib::ExampleRequest::ExistingMethod { .. } => {}
+             _ => {}
          }
      }
      Ok(())
  }

Update FIDL Library {#step-2}

• Add the new method and mark it with the [Transitional] attribute.

  protocol Example {
      ExistingMethod();
+     [Transitional]
+     NewMethod();
  };

Update Source Code {#step-3}

Dart {#dart-3}

• Add the new method to protocol implementations.
• Start using the new method in client code.

  class Server extends fidllib.Example {
    @override
    Future<void> existingMethod() async {}
+ 
+   @override
+   Future<void> newMethod() async {}
  }
  void client(fidllib.ExampleProxy client) async {
    await client.existingMethod();
+   await client.newMethod();
  }

Go {#go-3}

• Implement the new method for the server type.
• Remove the protocol’s WithCtxTransitionBase struct from the server type.
• Start using the new method in client code.

  type client struct {
      addMethod *lib.ExampleWithCtxInterface
  }
  func (c client) test() {
      c.addMethod.ExistingMethod(context.Background())
+     c.addMethod.NewMethod(context.Background())
  }
- type server struct {
-     lib.ExampleWithCtxTransitionalBase
- }
+ type server struct{}
  // Assert that server implements the Example interface
  var _ lib.ExampleWithCtx = &server{}
  func (*server) ExistingMethod(fidl.Context) error {
      return nil
  }
+ func (*server) NewMethod(fidl.Context) error {
+     return nil
+ }
+

HLCPP {#hlcpp-3}

• Add the new method to protocol implementations.
• Start using the new method in client code.

  class Server : public fidl_test::Example {
    void ExistingMethod() final {}
+   void NewMethod() final {}
  };
- void client(fidl_test::ExamplePtr client) { client->ExistingMethod(); }
+ void client(fidl_test::ExamplePtr client) {
+   client->ExistingMethod();
+   client->NewMethod();
+ }

LLCPP {#llcpp-3}

• Add the new method to protocol implementations.
• Start using the new method in client code.

  class Server final : public fidl_test::Example::Interface {
   public:
    void ExistingMethod(ExistingMethodCompleter::Sync& completer) final {}
+   void NewMethod(NewMethodCompleter::Sync& completer) final {}
  };
- void client(fidl::Client<fidl_test::Example> client) { client->ExistingMethod(); }
+ void client(fidl::Client<fidl_test::Example> client) {
+   client->ExistingMethod();
+   client->NewMethod();
+ }

Rust {#rust-3}

• Add the new method to the protocol’s ProxyInterface implementation.
• Remove #[allow(unreachable_patterns)] from the server’s request stream match.
• Replace the underscore arm in the server’s request stream match with one that handles the new method.

  struct ExampleFakeProxy;
  impl fidl_lib::ExampleProxyInterface for ExampleFakeProxy {
      fn existing_method(&self) -> Result<(), fidl::Error> {
+         Ok(())
+     }
+     fn new_method(&self) -> Result<(), fidl::Error> {
          Ok(())
      }
  }
  async fn example_service(chan: fasync::Channel) -> Result<(), fidl::Error> {
      let mut stream = fidl_lib::ExampleRequestStream::from_channel(chan);
      while let Some(req) = stream.try_next().await? {
-         #[allow(unreachable_patterns)]
          match req {
              fidl_lib::ExampleRequest::ExistingMethod { .. } => {}
-             _ => {}
+             fidl_lib::ExampleRequest::NewMethod { .. } => {}
          }
      }
      Ok(())
  }

Update FIDL Library {#step-4}

• Remove the [Transitional] attribute from the new method.

  protocol Example {
      ExistingMethod();
-     [Transitional]
      NewMethod();
  };