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Other Libraries

ActivityPub libraries for additional programming languages.

Elixir​

ActivityPub (Pleroma/Akkoma)​

The ActivityPub library used by Pleroma and Akkoma.

PropertyValue
Repositorygit.pleroma.social/pleroma/pleroma
Key Pathlib/pleroma/web/activity_pub/

Notable Patterns​

defmodule Pleroma.Web.ActivityPub.ObjectValidator do
  def validate(object, meta) do
    with {:ok, object} <- validate_type(object),
         {:ok, object} <- validate_actor(object),
         {:ok, object} <- validate_content(object) do
      {:ok, object, meta}
    end
  end
end

HTTPSignatures​

defmodule Pleroma.Signature do
  def sign(actor, headers) do
    # Build signing string
    # Sign with actor's private key
  end

  def validate(headers, public_key) do
    # Verify HTTP Signature
  end
end

C# / .NET​

FediNet​

ActivityPub library for .NET.

PropertyValue
Repositorygithub.com/rytmis/FediNet
NuGetFediNet
StatusExperimental

Example​

using FediNet.ActivityStreams;

var note = new Note
{
    Id = new Uri("https://example.com/notes/123"),
    Content = "Hello from .NET!",
    AttributedTo = new Uri("https://example.com/users/alice")
};

Java / Kotlin​

jActivityPub​

Java ActivityPub implementation.

PropertyValue
Repositorygithub.com/ibm-research/jActivityPub
StatusExperimental

Example​

import org.w3c.activitystreams.*;

Note note = new Note.Builder()
    .id("https://example.com/notes/123")
    .content("Hello from Java!")
    .attributedTo("https://example.com/users/alice")
    .build();

Swift​

ActivityPubSwift​

Swift ActivityPub library.

PropertyValue
StatusVarious experimental projects

Example Pattern​

struct Note: Codable {
    let context = "https://www.w3.org/ns/activitystreams"
    let type = "Note"
    let id: URL
    let content: String
    let attributedTo: URL

    enum CodingKeys: String, CodingKey {
        case context = "@context"
        case type, id, content, attributedTo
    }
}

Haskell​

No mature libraries, but reference implementations exist in various projects.

Pattern​

data Activity = Activity
    { activityContext :: Text
    , activityType :: Text
    , activityActor :: URI
    , activityObject :: Object
    }

instance ToJSON Activity where
    toJSON (Activity ctx typ actor obj) = object
        [ "@context" .= ctx
        , "type" .= typ
        , "actor" .= actor
        , "object" .= obj
        ]

Dart / Flutter​

flutter_activitypub​

Experimental Flutter client.

PropertyValue
StatusExperimental

Pattern​

class Actor {
  final String id;
  final String type;
  final String preferredUsername;
  final String inbox;
  final String outbox;

  Actor({
    required this.id,
    required this.type,
    required this.preferredUsername,
    required this.inbox,
    required this.outbox,
  });

  factory Actor.fromJson(Map<String, dynamic> json) {
    return Actor(
      id: json['id'],
      type: json['type'],
      preferredUsername: json['preferredUsername'],
      inbox: json['inbox'],
      outbox: json['outbox'],
    );
  }
}

Building Your Own​

If no library exists for your language:

1. Start with Types​

Define structures for:
- Actor (Person, Group, Service)
- Object (Note, Article, Image)
- Activity (Create, Follow, Like)
- Collection (OrderedCollection)

2. Implement HTTP Signatures​

1. Build signing string from headers
2. Sign with RSA-SHA256
3. Format as Signature header

3. WebFinger​

GET /.well-known/webfinger?resource=acct:{user}@{domain}
Return links to actor

4. Basic Endpoints​

GET /users/{username}        → Actor
POST /users/{username}/inbox → Receive activities
GET /users/{username}/outbox → Published activities

Community Resources​

See Also​