Removing Internal Pubsub Types From Public API: A Guide

In software development, maintaining a clean and well-defined public API is crucial for ensuring the usability and maintainability of a library or service. A public API serves as the contract between the developers of a library and its users. It defines the functionalities and components that external users can rely on. In this article, we'll discuss the importance of removing internal-only types from a public API, focusing on the context of Google Cloud Pub/Sub and the Google Cloud Rust library. We'll explore the challenges, solutions, and best practices involved in this process, with the aim of providing a comprehensive guide for developers.

Understanding the Importance of a Clean Public API

A well-structured public API is fundamental for several reasons. Firstly, it enhances the user experience. When an API is clear and concise, developers can easily understand how to use it, reducing the learning curve and improving overall productivity. Secondly, a clean API promotes maintainability. By limiting the exposure of internal types and functionalities, developers can refactor and optimize the internal implementation without affecting external users. This is crucial for the long-term health and evolution of a library.

Furthermore, a public API acts as a promise to the users. Any changes to the public API can potentially break existing code that relies on it. Therefore, it's essential to carefully design the API and minimize the risk of introducing breaking changes. By removing internal types, we reduce the surface area of the API and the likelihood of accidental usage of internal components, which could lead to compatibility issues in the future.

In the context of Google Cloud Pub/Sub and the Google Cloud Rust library, maintaining a clean public API is particularly important. Google Cloud Pub/Sub is a powerful messaging service used in a wide range of applications. The Google Cloud Rust library provides a way to interact with Pub/Sub from Rust applications. A well-defined API ensures that developers can effectively leverage Pub/Sub's capabilities without being exposed to unnecessary internal details.

The Challenge: Exposing Internal Types

Sometimes, during the development process, internal types and components might inadvertently become exposed in the public API. This can happen for various reasons, such as the need to work around specific technical challenges or the lack of a clear separation between internal and external APIs. In the case mentioned, builders with the #[doc(hidden)] tag were exposed as a workaround for doctest failures. While this approach might solve the immediate problem, it's not a sustainable solution in the long run. The #[doc(hidden)] tag only hides the types from the documentation but doesn't prevent them from being used in code.

Exposing internal types can lead to several issues. Firstly, it can confuse users who might not understand the purpose of these types or how they are intended to be used. Secondly, it creates a dependency on internal implementation details, making it harder to refactor or change the internal code without breaking external applications. Thirdly, it increases the risk of users relying on these internal types, which could lead to unexpected behavior or compatibility issues in future versions.

Therefore, it's crucial to identify and remove these internal types from the public API. This involves a careful analysis of the API surface, identifying the types that should not be exposed, and finding alternative solutions that don't involve exposing internal details.

Identifying Internal-Only Types

The first step in removing internal-only types is to identify them. This requires a thorough understanding of the library's architecture and the intended use of each type. Internal-only types are typically those that are used internally within the library's implementation and are not meant to be used directly by external users. These types might represent internal data structures, helper functions, or implementation details that are not part of the public contract.

One common approach to identify internal types is to look for types that are marked with special annotations or attributes, such as #[doc(hidden)] in Rust. However, as mentioned earlier, this tag only hides the type from the documentation and doesn't prevent it from being used in code. Therefore, it's essential to go beyond documentation and analyze the code to understand the actual usage of each type.

Another approach is to consider the naming conventions used in the library. Internal types might have names that indicate their internal nature, such as prefixed with _ or internal. However, relying solely on naming conventions can be misleading, as developers might not always follow these conventions consistently. Therefore, it's crucial to combine naming analysis with code analysis and a deep understanding of the library's architecture.

In the specific case mentioned, the builders with the #[doc(hidden)] tag are a clear indication of internal types that should be removed from the public API. These builders were exposed as a workaround for doctest failures, which suggests that they are not intended for general use.

Solutions for Removing Internal Types

Once the internal types have been identified, the next step is to remove them from the public API. This can be achieved through several techniques, depending on the specific situation and the nature of the types. One common approach is to refactor the code to avoid exposing the internal types directly. This might involve creating new public types that encapsulate the functionality of the internal types or providing factory functions that create instances of the internal types without exposing their concrete implementation.

Another approach is to use the module system to hide internal types. In Rust, modules provide a way to control the visibility of types and functions. By placing internal types in a private module, they can be hidden from external users. This ensures that the internal types are not accessible from outside the module, effectively removing them from the public API.

In the specific case mentioned, the suggested solution is to fix this via a sidekick configuration. A sidekick configuration typically refers to a build system or a set of tools that help manage the build process and enforce certain rules. In this context, a sidekick configuration could be used to automatically identify and prevent the exposure of internal types in the public API. This might involve adding checks to the build process that verify the visibility of types and warn or fail the build if internal types are exposed.

The Importance of Sidekick Configuration

Using a sidekick configuration to prevent the exposure of internal types is a proactive approach that can significantly improve the maintainability and stability of a library. By automating the process of checking API visibility, developers can ensure that internal types are not accidentally exposed, reducing the risk of introducing breaking changes or confusing users.

A sidekick configuration can also help enforce coding standards and best practices related to API design. For example, it can be configured to warn against the use of certain patterns that might lead to the exposure of internal types, such as returning internal types from public functions or exposing internal types in public interfaces.

Furthermore, a sidekick configuration can provide valuable feedback during the development process. By running checks automatically as part of the build process, developers can quickly identify and fix issues related to API visibility, reducing the time and effort required to maintain a clean public API.

In the context of the Google Cloud Rust library, a sidekick configuration could be integrated into the build system to ensure that internal Pub/Sub types are not exposed in the public API. This would help maintain the quality and stability of the library, making it easier for developers to use Pub/Sub from Rust applications.

Best Practices for API Design

In addition to removing internal types, there are several other best practices that can help ensure a clean and well-defined public API. One important principle is to keep the API as small and focused as possible. This means only exposing the essential functionalities and types that are necessary for users to interact with the library. Avoid adding features or types that are not commonly used or that duplicate existing functionality.

Another best practice is to design the API with the user in mind. Consider how developers will use the API and strive to make it as intuitive and easy to use as possible. This might involve using clear and consistent naming conventions, providing comprehensive documentation, and offering examples and tutorials to help users get started.

It's also crucial to think about the evolution of the API over time. APIs are not static; they often need to be updated and extended to meet changing requirements. When designing an API, consider how it might need to evolve in the future and try to make it as flexible and extensible as possible. This might involve using abstract types and interfaces, providing extension points, and following the principles of the open/closed principle.

Furthermore, it's essential to communicate changes to the API clearly to users. When introducing new features or making breaking changes, provide detailed release notes and migration guides to help users adapt their code. This helps minimize disruption and ensures a smooth transition to new versions of the library.

Conclusion

Removing internal-only types from the public API is a crucial step in maintaining a clean, usable, and maintainable library. By carefully identifying and removing these types, developers can reduce the risk of exposing internal implementation details, prevent accidental usage of internal components, and improve the overall stability and quality of the API. Using a sidekick configuration to automate the process of checking API visibility is a proactive approach that can significantly enhance the maintainability of a library.

In the context of Google Cloud Pub/Sub and the Google Cloud Rust library, maintaining a clean public API is particularly important. A well-defined API ensures that developers can effectively leverage Pub/Sub's capabilities without being exposed to unnecessary internal details. By following best practices for API design and using tools like sidekick configurations, developers can create APIs that are easy to use, maintain, and evolve over time.

For more information on API design best practices, you can visit Microsoft's API Design Guide.