❗❗ Please note - this project is incomplete and not ready for production use. The information here describes the design and technical goals of ActivityPubSharp, not the currently implemented functionality. Please see the issues tracker for detailed status.
ActivityPubSharp is a toolkit of modular packages that support the use of ActivityPub in .NET applications. Low-level APIs offer raw - but safe - access to strongly-typed models, while high-level interfaces support ergonomic and standards-compliant use of the protocol. Special utility types and integrated JSON-LD converters further abstract ActivityPub's rougher edges, bringing the user experience up to par with more traditional APIs. For more information, see the introduction post - What is ActivityPubSharp?
Modularity and Abstraction are keys goals of this project. It should be simple to integrate this library at any appropriate level of abstraction. Low-level apps can utilize the strongly-typed models and utility types, but bring their own parser, logic, and other components. Mid-level apps may want to use the HTTP client or abstract server logic. On the other hand, high-level apps will likely desire framework integration and custom middleware.
To support these varying use cases, ActivityPubSharp is split into multiple separate NuGet packages. While separate and self-contained, these packages are designed to work together and will seamlessly integrate through Dependency Injection. A typical use case will include the highest-level "main" package needed for the application, and then as many "secondary" packages as desired for extra functionality.
| Package | Description | Use Case |
|---|---|---|
| ActivityPubSharp.Types | Serializable type definitions for ActivityPub types. Includes utility classes to handle polymorphic properties. | You only need the ActivityPub object types, and nothing else. |
| ActivityPubSharp.Types.Proposed | Extended type definitions for proposed extensions to ActivityStreams. | You need to use the unreleased ActivityStreams extensions. |
| ActivityPubSharp.Types.Mastodon | Extended type definitions for integration with Mastodon. | You are communicating with a Mastodon server. |
| ActivityPubSharp.Types.W3ID | Extended type definitions for W3ID Security. This only includes the types - actual security logic is handled by ActivityPubSharp.Auth. | You need to secure communications using W3ID security. |
| ActivityPubSharp.Types.Schema | Extended type definitions for schema.org. | You integrate with an application that expects a schema, or you want to use a related technology like Microdata. |
| ActivityPubSharp.Auth | Authentication schemes used by common ActivityPub implementations. | You will communicate with an external host which requires signatures or other authentication. |
| ActivityPubSharp.Client | Implementation of the Client conformance class. Supports the client side of Client to Server interactions. | You are implementing (at least) the Client conformance class. |
| ActivityPubSharp.Server | Implementation of the Server conformance class. Supports the server side of Client to Server interactions. | You are implementing (at least) the Server conformance class. |
| ActivityPubSharp.Federation | Implementation of the Federated Server conformance class. Supports Server to Server interactions. | You are implementing (at least) the Federated Server conformance class. |
| ActivityPubSharp.AspNetCore | Extends Server package with bindings and middleware for ASP.NET Core. | You are implementing a server that will utilize ASP.NET. |
| ActivityPubSharp | Meta-package that includes all others. | You want ActivityPub with minimal effort, and can accept the library authors' default implementations and 3rd-party bindings. |
As the name suggests, ActivityPubSharp is focused on ActivityPub rather than any other ActivityStreams-based standard. While ActivityStreams is implemented as an underlying component of ActivityPub, it alone is not a supported use case. If there is ever a conflict between specifications, then the ActivityPub spec will be considered authoritative.
At present, ActivityPubSharp intends to offer only a subset of JSON-LD support. The included serializers support all features that are necessary for ActivityPub and integration with mainstream fediverse software, but that is all. Attempting to parse other forms of linked data may fail catastrophically. In the future, it will be possible to inject a user-provided compaction/normalization layer through DI. This should be sufficient for all most use cases.
ActivityPubSharp utilizes Dependency Injection to easily support unique or extended use cases.
For example, included services all utilize the IJsonLdSerializer interface which enables user code to replace or modify the default JSON support.
Most default implementations expose configuration objects that are compatible with the Options Pattern.
User-accessible DI services and and options are described in the README for each individual package.
- .NET 7 (newer should work, but is untested)
- Any platform - no native code is used
- Minimal dependencies - software supply chain risks are an underappreciated threat. ActivityPubSharp keeps minimal dependencies to reduce the supply chain footprint.
- Modern .NET - ActivityPubSharp has set .NET 7 as the minimum supported version. This unfortunately excludes some projects, but is critical for System.Text.Json support.
- Ergonomic and Conventional APIs - mid/high level APIs should feel and function like typical .NET APIs. An important goal (and difficult challenge) of this project is abstracting ActivityPub's dynamic nature to better fit with C#'s strongly-typed model.