go-fed-activity/pub

pub

Implements the Social and Federating Protocols in the ActivityPub specification.

Reference & Tutorial

The go-fed website contains tutorials and reference materials, in addition to the rest of this README.

How To Use

go get github.com/go-fed/activity

The root of all ActivityPub behavior is the Actor, which requires you to implement a few interfaces:

import (
  "github.com/go-fed/activity/pub"
)

type myActivityPubApp struct { /* ... */ }
type myAppsDatabase struct { /* ... */ }
type myAppsClock struct { /* ... */ }

var (
  // Your app will implement pub.CommonBehavior, and either
  // pub.SocialProtocol, pub.FederatingProtocol, or both.
  myApp = &myActivityPubApp{}
  myCommonBehavior pub.CommonBehavior = myApp
  mySocialProtocol pub.SocialProtocol = myApp
  myFederatingProtocol pub.FederatingProtocol = myApp
  // Your app's database implementation.
  myDatabase pub.Database = &myAppsDatabase{}
  // Your app's clock.
  myClock pub.Clock = &myAppsClock{}
)

// Only support the C2S Social protocol
actor := pub.NewSocialActor(
  myCommonBehavior,
  mySocialProtocol,
  myDatabase,
  myClock)
// OR
//
// Only support S2S Federating protocol
actor = pub.NewFederatingActor(
  myCommonBehavior,
  myFederatingProtocol,
  myDatabase,
  myClock)
// OR
//
// Support both C2S Social and S2S Federating protocol.
actor = pub.NewActor(
  myCommonBehavior,
  mySocialProtocol,
  myFederatingProtocol,
  myDatabase,
  myClock)

Next, hook the Actor into your web server:

// The application's actor
var actor pub.Actor
var outboxHandler http.HandlerFunc = func(w http.ResponseWriter, r *http.Request) {
  c := context.Background()
  // Populate c with request-specific information
  if handled, err := actor.PostOutbox(c, w, r); err != nil {
    // Write to w
    return
  } else if handled {
    return
  } else if handled, err = actor.GetOutbox(c, w, r); err != nil {
    // Write to w
    return
  } else if handled {
    return
  }
  // else:
  //
  // Handle non-ActivityPub request, such as serving a webpage.
}
var inboxHandler http.HandlerFunc = func(w http.ResponseWriter, r *http.Request) {
  c := context.Background()
  // Populate c with request-specific information
  if handled, err := actor.PostInbox(c, w, r); err != nil {
    // Write to w
    return
  } else if handled {
    return
  } else if handled, err = actor.GetInbox(c, w, r); err != nil {
    // Write to w
    return
  } else if handled {
    return
  }
  // else:
  //
  // Handle non-ActivityPub request, such as serving a webpage.
}
// Add the handlers to a HTTP server
serveMux := http.NewServeMux()
serveMux.HandleFunc("/actor/outbox", outboxHandler)
serveMux.HandleFunc("/actor/inbox", inboxHandler)
var server http.Server
server.Handler = serveMux

To serve ActivityStreams data:

myHander := pub.NewActivityStreamsHandler(myDatabase, myClock)
var activityStreamsHandler http.HandlerFunc = func(w http.ResponseWriter, r *http.Request) {
  c := context.Background()
  // Populate c with request-specific information
  if handled, err := myHandler(c, w, r); err != nil {
    // Write to w
    return
  } else if handled {
    return
  }
  // else:
  //
  // Handle non-ActivityPub request, such as serving a webpage.
}
serveMux.HandleFunc("/some/data/like/a/note", activityStreamsHandler)

Dependency Injection

Package pub relies on dependency injection to provide out-of-the-box support for ActivityPub. The interfaces to be satisfied are:

• CommonBehavior - Behavior needed regardless of which Protocol is used.
• SocialProtocol - Behavior needed for the Social Protocol.
• FederatingProtocol - Behavior needed for the Federating Protocol.
• Database - The data store abstraction, not tied to the database/sql package.
• Clock - The server's internal clock.
• Transport - Responsible for the network that serves requests and deliveries of ActivityStreams data. A HttpSigTransport type is provided.

These implementations form the core of an application's behavior without worrying about the particulars and pitfalls of the ActivityPub protocol. Implementing these interfaces gives you greater assurance about being ActivityPub compliant.

Application Logic

The SocialProtocol and FederatingProtocol are responsible for returning callback functions compatible with streams.TypeResolver. They also return SocialWrappedCallbacks and FederatingWrappedCallbacks, which are nothing more than a bundle of default behaviors for types like Create, Update, and so on.

Applications will want to focus on implementing their specific behaviors in the callbacks, and have fine-grained control over customization:

// Implements the FederatingProtocol interface.
//
// This illustration can also be applied for the Social Protocol.
func (m *myAppsFederatingProtocol) Callbacks(c context.Context) (wrapped pub.FederatingWrappedCallbacks, other []interface{}) {
  // The context 'c' has request-specific logic and can be used to apply complex
  // logic building the right behaviors, if desired.
  //
  // 'c' will later be passed through to the callbacks created below.
  wrapped = pub.FederatingWrappedCallbacks{
    Create: func(ctx context.Context, create vocab.ActivityStreamsCreate) error {
      // This function is wrapped by default behavior.
      //
      // More application specific logic can be written here.
      //
      // 'ctx' will have request-specific information from the HTTP handler. It
      // is the same as the 'c' passed to the Callbacks method.
      // 'create' has, at this point, already triggered the recommended
      // ActivityPub side effect behavior. The application can process it
      // further as needed.
      return nil
    },
  }
  // The 'other' must contain functions that satisfy the signature pattern
  // required by streams.JSONResolver.
  //
  // If they are not, at runtime errors will be returned to indicate this.
  other = []interface{}{
    // The FederatingWrappedCallbacks has default behavior for an "Update" type,
    // but since we are providing this behavior in "other" and not in the
    // FederatingWrappedCallbacks.Update member, we will entirely replace the
    // default behavior provided by go-fed. Be careful that this still
    // implements ActivityPub properly.
    func(ctx context.Context, update vocab.ActivityStreamsUpdate) error {
      // This function is NOT wrapped by default behavior.
      //
      // Application specific logic can be written here.
      //
      // 'ctx' will have request-specific information from the HTTP handler. It
      // is the same as the 'c' passed to the Callbacks method.
      // 'update' will NOT trigger the recommended ActivityPub side effect
      // behavior. The application should do so in addition to any other custom
      // side effects required.
      return nil
    },
    // The "Listen" type has no default suggested behavior in ActivityPub, so
    // this just makes this application able to handle "Listen" activities.
    func(ctx context.Context, listen vocab.ActivityStreamsListen) error {
      // This function is NOT wrapped by default behavior. There's not a
      // FederatingWrappedCallbacks.Listen member to wrap.
      //
      // Application specific logic can be written here.
      //
      // 'ctx' will have request-specific information from the HTTP handler. It
      // is the same as the 'c' passed to the Callbacks method.
      // 'listen' can be processed with side effects as the application needs.
      return nil
    },
  }
  return
}

The pub package supports applications that grow into more custom solutions by overriding the default behaviors as needed.

ActivityStreams Extensions: Future-Proofing An Application

Package pub relies on the streams.TypeResolver and streams.JSONResolver code generated types. As new ActivityStreams extensions are developed and their code is generated, pub will automatically pick up support for these extensions.

The steps to rapidly implement a new extension in a pub application are:

1. Generate an OWL definition of the ActivityStreams extension. This definition could be the same one defining the vocabulary at the @context IRI.
2. Run astool to autogenerate the golang types in the streams package.
3. Implement the application's callbacks in the FederatingProtocol.Callbacks or SocialProtocol.Callbacks for the new behaviors needed.
4. Build the application, which builds pub, with the newly generated streams code. No code changes in pub are required.

Whether an author of an ActivityStreams extension or an application developer, these quick steps should reduce the barrier to adopion in a statically-typed environment.

DelegateActor

For those that need a near-complete custom ActivityPub solution, or want to have that possibility in the future after adopting go-fed, the DelegateActor interface can be used to obtain an Actor:

// Use custom ActivityPub implementation
actor = pub.NewCustomActor(
  myDelegateActor,
  isSocialProtocolEnabled,
  isFederatedProtocolEnabled,
  myAppsClock)

It does not guarantee that an implementation adheres to the ActivityPub specification. It acts as a stepping stone for applications that want to build up to a fully custom solution and not be locked into the pub package implementation.