separation of activitypub

crates/adapters/activitypub-base/src/activities.rs

@@ -0,0 +1,341 @@
+use activitypub_federation::{
+    config::Data,
+    fetch::object_id::ObjectId,
+    kinds::activity::{AcceptType, CreateType, DeleteType, FollowType, RejectType, UndoType, UpdateType},
+    traits::Activity,
+};
+use serde::{Deserialize, Serialize};
+use url::Url;
+
+use crate::actors::DbActor;
+use crate::data::FederationData;
+use crate::error::Error;
+use crate::repository::{FollowerStatus, FollowingStatus};
+
+// --- Follow ---
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct FollowActivity {
+    pub(crate) id: Url,
+    #[serde(rename = "type", default)]
+    pub(crate) kind: FollowType,
+    pub(crate) actor: ObjectId<DbActor>,
+    pub(crate) object: ObjectId<DbActor>,
+}
+
+#[async_trait::async_trait]
+impl Activity for FollowActivity {
+    type DataType = FederationData;
+    type Error = Error;
+
+    fn id(&self) -> &Url {
+        &self.id
+    }
+
+    fn actor(&self) -> &Url {
+        self.actor.inner()
+    }
+
+    async fn verify(&self, data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        let target_url = self.object.inner();
+        let target_domain = match (target_url.host_str(), target_url.port()) {
+            (Some(host), Some(port)) => format!("{}:{}", host, port),
+            (Some(host), None) => host.to_string(),
+            _ => return Err(Error::bad_request(anyhow::anyhow!("invalid follow target URL"))),
+        };
+        if target_domain != data.domain {
+            return Err(Error::bad_request(anyhow::anyhow!("follow target is not a local actor")));
+        }
+        Ok(())
+    }
+
+    async fn receive(self, data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        let _follower = self.actor.dereference(data).await?;
+        let local_actor = self.object.dereference(data).await?;
+
+        data.federation_repo
+            .add_follower(
+                local_actor.user_id,
+                self.actor.inner().as_str(),
+                FollowerStatus::Pending,
+                self.id.as_str(),
+            )
+            .await?;
+
+        tracing::info!(
+            follower = %self.actor.inner(),
+            local_user = %local_actor.user_id,
+            "follow request pending approval"
+        );
+        Ok(())
+    }
+}
+
+// --- Accept ---
+
+#[derive(Debug, Deserialize, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct AcceptActivity {
+    pub(crate) id: Url,
+    #[serde(rename = "type", default)]
+    pub(crate) kind: AcceptType,
+    pub(crate) actor: ObjectId<DbActor>,
+    pub(crate) object: FollowActivity,
+}
+
+#[async_trait::async_trait]
+impl Activity for AcceptActivity {
+    type DataType = FederationData;
+    type Error = Error;
+
+    fn id(&self) -> &Url {
+        &self.id
+    }
+
+    fn actor(&self) -> &Url {
+        self.actor.inner()
+    }
+
+    async fn verify(&self, _data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    async fn receive(self, data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        let local_user_id = crate::urls::extract_user_id_from_url(self.object.actor.inner())
+            .ok_or_else(|| Error::bad_request(anyhow::anyhow!("invalid actor URL in Follow")))?;
+        data.federation_repo
+            .update_following_status(local_user_id, self.actor.inner().as_str(), FollowingStatus::Accepted)
+            .await?;
+        tracing::info!(remote_actor = %self.actor.inner(), "follow accepted by remote");
+        Ok(())
+    }
+}
+
+// --- Reject ---
+
+#[derive(Debug, Deserialize, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct RejectActivity {
+    pub(crate) id: Url,
+    #[serde(rename = "type", default)]
+    pub(crate) kind: RejectType,
+    pub(crate) actor: ObjectId<DbActor>,
+    pub(crate) object: FollowActivity,
+}
+
+#[async_trait::async_trait]
+impl Activity for RejectActivity {
+    type DataType = FederationData;
+    type Error = Error;
+
+    fn id(&self) -> &Url {
+        &self.id
+    }
+
+    fn actor(&self) -> &Url {
+        self.actor.inner()
+    }
+
+    async fn verify(&self, _data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    async fn receive(self, data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        if let Some(user_id) = crate::urls::extract_user_id_from_url(self.object.actor.inner()) {
+            data.federation_repo
+                .remove_following(user_id, self.actor.inner().as_str())
+                .await?;
+        }
+        tracing::info!(actor = %self.actor.inner(), "follow rejected");
+        Ok(())
+    }
+}
+
+// --- Undo ---
+
+#[derive(Debug, Deserialize, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct UndoActivity {
+    pub(crate) id: Url,
+    #[serde(rename = "type", default)]
+    pub(crate) kind: UndoType,
+    pub(crate) actor: ObjectId<DbActor>,
+    pub(crate) object: FollowActivity,
+}
+
+#[async_trait::async_trait]
+impl Activity for UndoActivity {
+    type DataType = FederationData;
+    type Error = Error;
+
+    fn id(&self) -> &Url {
+        &self.id
+    }
+
+    fn actor(&self) -> &Url {
+        self.actor.inner()
+    }
+
+    async fn verify(&self, _data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    async fn receive(self, data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        if let Some(user_id) = crate::urls::extract_user_id_from_url(self.object.object.inner()) {
+            data.federation_repo
+                .remove_follower(user_id, self.actor.inner().as_str())
+                .await?;
+        }
+        data.object_handler
+            .on_actor_removed(self.actor.inner())
+            .await
+            .map_err(|e| Error::from(anyhow::anyhow!(e)))?;
+        tracing::info!(actor = %self.actor.inner(), "unfollowed");
+        Ok(())
+    }
+}
+
+// --- Create ---
+
+#[derive(Debug, Deserialize, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct CreateActivity {
+    pub(crate) id: Url,
+    #[serde(rename = "type", default)]
+    pub(crate) kind: CreateType,
+    pub(crate) actor: ObjectId<DbActor>,
+    pub(crate) object: serde_json::Value,
+}
+
+#[async_trait::async_trait]
+impl Activity for CreateActivity {
+    type DataType = FederationData;
+    type Error = Error;
+
+    fn id(&self) -> &Url {
+        &self.id
+    }
+
+    fn actor(&self) -> &Url {
+        self.actor.inner()
+    }
+
+    async fn verify(&self, _data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    async fn receive(self, data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        let ap_id = self.id.clone();
+        let actor_url = self.actor.inner().clone();
+        data.object_handler
+            .on_create(&ap_id, &actor_url, self.object)
+            .await
+            .map_err(|e| Error::from(anyhow::anyhow!(e)))?;
+        tracing::info!(actor = %actor_url, "received create activity");
+        Ok(())
+    }
+}
+
+// --- Delete ---
+
+#[derive(Debug, Deserialize, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct DeleteActivity {
+    pub(crate) id: Url,
+    #[serde(rename = "type", default)]
+    pub(crate) kind: DeleteType,
+    pub(crate) actor: ObjectId<DbActor>,
+    pub(crate) object: Url,
+}
+
+#[async_trait::async_trait]
+impl Activity for DeleteActivity {
+    type DataType = FederationData;
+    type Error = Error;
+
+    fn id(&self) -> &Url {
+        &self.id
+    }
+
+    fn actor(&self) -> &Url {
+        self.actor.inner()
+    }
+
+    async fn verify(&self, _data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    async fn receive(self, data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        let actor_url = self.actor.inner().clone();
+        data.object_handler
+            .on_delete(&self.object, &actor_url)
+            .await
+            .map_err(|e| Error::from(anyhow::anyhow!(e)))?;
+        tracing::info!(object = %self.object, "received delete activity");
+        Ok(())
+    }
+}
+
+// --- Update ---
+
+#[derive(Debug, Deserialize, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct UpdateActivity {
+    pub(crate) id: Url,
+    #[serde(rename = "type", default)]
+    pub(crate) kind: UpdateType,
+    pub(crate) actor: ObjectId<DbActor>,
+    pub(crate) object: serde_json::Value,
+}
+
+#[async_trait::async_trait]
+impl Activity for UpdateActivity {
+    type DataType = FederationData;
+    type Error = Error;
+
+    fn id(&self) -> &Url {
+        &self.id
+    }
+
+    fn actor(&self) -> &Url {
+        self.actor.inner()
+    }
+
+    async fn verify(&self, _data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        Ok(())
+    }
+
+    async fn receive(self, data: &Data<Self::DataType>) -> Result<(), Self::Error> {
+        let ap_id = self.id.clone();
+        let actor_url = self.actor.inner().clone();
+        data.object_handler
+            .on_update(&ap_id, &actor_url, self.object)
+            .await
+            .map_err(|e| Error::from(anyhow::anyhow!(e)))?;
+        tracing::info!(actor = %actor_url, "received update activity");
+        Ok(())
+    }
+}
+
+// --- Inbox dispatch enum ---
+
+#[derive(Debug, Deserialize, Serialize)]
+#[serde(tag = "type")]
+#[enum_delegate::implement(Activity)]
+pub enum InboxActivities {
+    #[serde(rename = "Follow")]
+    Follow(FollowActivity),
+    #[serde(rename = "Accept")]
+    Accept(AcceptActivity),
+    #[serde(rename = "Reject")]
+    Reject(RejectActivity),
+    #[serde(rename = "Undo")]
+    Undo(UndoActivity),
+    #[serde(rename = "Create")]
+    Create(CreateActivity),
+    #[serde(rename = "Delete")]
+    Delete(DeleteActivity),
+    #[serde(rename = "Update")]
+    Update(UpdateActivity),
+}

crates/adapters/activitypub-base/src/actor_handler.rs

@@ -0,0 +1,21 @@
+use activitypub_federation::{
+    axum::json::FederationJson, config::Data, protocol::context::WithContext, traits::Object,
+};
+use axum::extract::Path;
+
+use crate::actors::{get_local_actor, Person};
+use crate::data::FederationData;
+use crate::error::Error;
+
+pub async fn actor_handler(
+    Path(user_id_str): Path<String>,
+    data: Data<FederationData>,
+) -> Result<FederationJson<WithContext<Person>>, Error> {
+    let uuid = uuid::Uuid::parse_str(&user_id_str)
+        .map_err(|_| Error::bad_request(anyhow::anyhow!("invalid user id")))?;
+
+    let db_actor = get_local_actor(uuid, &data).await?;
+    let person = db_actor.into_json(&data).await?;
+
+    Ok(FederationJson(WithContext::new_default(person)))
+}

crates/adapters/activitypub-base/src/actors.rs

@@ -0,0 +1,230 @@
+use activitypub_federation::{
+    config::Data,
+    fetch::object_id::ObjectId,
+    http_signatures::generate_actor_keypair,
+    kinds::actor::PersonType,
+    protocol::{public_key::PublicKey, verification::verify_domains_match},
+    traits::{Actor, Object},
+};
+use chrono::{DateTime, Utc};
+use serde::{Deserialize, Serialize};
+use url::Url;
+
+use crate::data::FederationData;
+use crate::error::Error;
+use crate::repository::RemoteActor;
+
+#[derive(Debug, Clone)]
+pub struct DbActor {
+    pub user_id: uuid::Uuid,
+    pub username: String,
+    pub public_key_pem: String,
+    pub private_key_pem: Option<String>,
+    pub inbox_url: Url,
+    pub outbox_url: Url,
+    pub followers_url: Url,
+    pub following_url: Url,
+    pub ap_id: Url,
+    pub last_refreshed_at: DateTime<Utc>,
+}
+
+#[derive(Debug, Clone, Deserialize, Serialize)]
+#[serde(rename_all = "camelCase")]
+pub struct Person {
+    #[serde(rename = "type")]
+    kind: PersonType,
+    id: ObjectId<DbActor>,
+    preferred_username: String,
+    inbox: Url,
+    outbox: Url,
+    followers: Url,
+    following: Url,
+    public_key: PublicKey,
+    name: Option<String>,
+}
+
+pub async fn get_local_actor(
+    user_id: uuid::Uuid,
+    data: &Data<FederationData>,
+) -> Result<DbActor, Error> {
+    let user = data
+        .user_repo
+        .find_by_id(user_id)
+        .await
+        .map_err(Error::from)?
+        .ok_or_else(|| Error::not_found(anyhow::anyhow!("user not found: {}", user_id)))?;
+
+    let (public_key, private_key) = match data
+        .federation_repo
+        .get_local_actor_keypair(user_id)
+        .await?
+    {
+        Some(kp) => kp,
+        None => {
+            let kp = generate_actor_keypair()?;
+            data.federation_repo
+                .save_local_actor_keypair(
+                    user_id,
+                    kp.public_key.clone(),
+                    kp.private_key.clone(),
+                )
+                .await?;
+            (kp.public_key, kp.private_key)
+        }
+    };
+
+    let ap_id = crate::urls::actor_url(&data.base_url, user_id);
+    let inbox_url = Url::parse(&format!("{}/inbox", &ap_id)).expect("valid inbox url");
+    let outbox_url = Url::parse(&format!("{}/outbox", &ap_id)).expect("valid outbox url");
+    let followers_url = Url::parse(&format!("{}/followers", &ap_id)).expect("valid followers url");
+    let following_url = Url::parse(&format!("{}/following", &ap_id)).expect("valid following url");
+
+    Ok(DbActor {
+        user_id,
+        username: user.username,
+        public_key_pem: public_key,
+        private_key_pem: Some(private_key),
+        inbox_url,
+        outbox_url,
+        followers_url,
+        following_url,
+        ap_id,
+        last_refreshed_at: Utc::now(),
+    })
+}
+
+#[async_trait::async_trait]
+impl Object for DbActor {
+    type DataType = FederationData;
+    type Kind = Person;
+    type Error = Error;
+
+    fn id(&self) -> &Url {
+        &self.ap_id
+    }
+
+    fn last_refreshed_at(&self) -> Option<DateTime<Utc>> {
+        Some(self.last_refreshed_at)
+    }
+
+    async fn read_from_id(
+        object_id: Url,
+        data: &Data<Self::DataType>,
+    ) -> Result<Option<Self>, Self::Error> {
+        let user_id = match crate::urls::extract_user_id_from_url(&object_id) {
+            Some(id) => id,
+            None => return Ok(None),
+        };
+        let user = match data.user_repo.find_by_id(user_id).await {
+            Ok(Some(u)) => u,
+            _ => return Ok(None),
+        };
+
+        let keypair = data
+            .federation_repo
+            .get_local_actor_keypair(user_id)
+            .await?;
+
+        let (public_key, private_key) = match keypair {
+            Some(kp) => (kp.0, Some(kp.1)),
+            None => return Ok(None),
+        };
+
+        let ap_id = crate::urls::actor_url(&data.base_url, user_id);
+        let inbox_url = Url::parse(&format!("{}/inbox", &ap_id)).expect("valid url");
+        let outbox_url = Url::parse(&format!("{}/outbox", &ap_id)).expect("valid url");
+        let followers_url = Url::parse(&format!("{}/followers", &ap_id)).expect("valid url");
+        let following_url = Url::parse(&format!("{}/following", &ap_id)).expect("valid url");
+
+        Ok(Some(DbActor {
+            user_id,
+            username: user.username,
+            public_key_pem: public_key,
+            private_key_pem: private_key,
+            inbox_url,
+            outbox_url,
+            followers_url,
+            following_url,
+            ap_id,
+            last_refreshed_at: Utc::now(),
+        }))
+    }
+
+    async fn into_json(self, _data: &Data<Self::DataType>) -> Result<Self::Kind, Self::Error> {
+        let public_key = PublicKey {
+            id: format!("{}#main-key", &self.ap_id),
+            owner: self.ap_id.clone(),
+            public_key_pem: self.public_key_pem.clone(),
+        };
+
+        Ok(Person {
+            kind: Default::default(),
+            id: self.ap_id.clone().into(),
+            preferred_username: self.username.clone(),
+            inbox: self.inbox_url.clone(),
+            outbox: self.outbox_url.clone(),
+            followers: self.followers_url.clone(),
+            following: self.following_url.clone(),
+            public_key,
+            name: Some(self.username.clone()),
+        })
+    }
+
+    async fn verify(
+        json: &Self::Kind,
+        expected_domain: &Url,
+        _data: &Data<Self::DataType>,
+    ) -> Result<(), Self::Error> {
+        verify_domains_match(json.id.inner(), expected_domain)?;
+        Ok(())
+    }
+
+    async fn from_json(
+        json: Self::Kind,
+        data: &Data<Self::DataType>,
+    ) -> Result<Self, Self::Error> {
+        let actor = RemoteActor {
+            url: json.id.inner().to_string(),
+            handle: json.preferred_username.clone(),
+            inbox_url: json.inbox.to_string(),
+            shared_inbox_url: None,
+            display_name: json.name.clone(),
+        };
+        data.federation_repo.upsert_remote_actor(actor).await?;
+
+        let url_str = json.id.inner().to_string();
+        let user_id = uuid::Uuid::new_v5(&uuid::Uuid::NAMESPACE_URL, url_str.as_bytes());
+        let ap_id = json.id.inner().clone();
+        let inbox_url = json.inbox.clone();
+        let outbox_url = json.outbox.clone();
+        let followers_url = json.followers.clone();
+        let following_url = json.following.clone();
+
+        Ok(DbActor {
+            user_id,
+            username: json.preferred_username.clone(),
+            public_key_pem: json.public_key.public_key_pem,
+            private_key_pem: None,
+            inbox_url,
+            outbox_url,
+            followers_url,
+            following_url,
+            ap_id,
+            last_refreshed_at: Utc::now(),
+        })
+    }
+}
+
+impl Actor for DbActor {
+    fn public_key_pem(&self) -> &str {
+        &self.public_key_pem
+    }
+
+    fn private_key_pem(&self) -> Option<String> {
+        self.private_key_pem.clone()
+    }
+
+    fn inbox(&self) -> Url {
+        self.inbox_url.clone()
+    }
+}

crates/adapters/activitypub-base/src/content.rs

@@ -0,0 +1,34 @@
+use async_trait::async_trait;
+use url::Url;
+
+#[async_trait]
+pub trait ApObjectHandler: Send + Sync {
+    /// Returns (ap_id, serialized object) for all local content owned by this user.
+    /// Used by outbox (count) and backfill (delivery). Must only return locally-authored content.
+    async fn get_local_objects_for_user(
+        &self,
+        user_id: uuid::Uuid,
+    ) -> anyhow::Result<Vec<(Url, serde_json::Value)>>;
+
+    /// Incoming Create activity — persist remote content.
+    async fn on_create(
+        &self,
+        ap_id: &Url,
+        actor_url: &Url,
+        object: serde_json::Value,
+    ) -> anyhow::Result<()>;
+
+    /// Incoming Update activity — update existing remote content.
+    async fn on_update(
+        &self,
+        ap_id: &Url,
+        actor_url: &Url,
+        object: serde_json::Value,
+    ) -> anyhow::Result<()>;
+
+    /// Incoming Delete activity — remove specific remote content.
+    async fn on_delete(&self, ap_id: &Url, actor_url: &Url) -> anyhow::Result<()>;
+
+    /// Actor unfollowed/was removed — clean up all their remote content.
+    async fn on_actor_removed(&self, actor_url: &Url) -> anyhow::Result<()>;
+}

crates/adapters/activitypub-base/src/data.rs

@@ -0,0 +1,38 @@
+use std::sync::Arc;
+
+use crate::content::ApObjectHandler;
+use crate::repository::FederationRepository;
+use crate::user::ApUserRepository;
+
+#[derive(Clone)]
+pub struct FederationData {
+    pub(crate) federation_repo: Arc<dyn FederationRepository>,
+    pub(crate) user_repo: Arc<dyn ApUserRepository>,
+    pub(crate) object_handler: Arc<dyn ApObjectHandler>,
+    pub(crate) base_url: String,
+    pub(crate) domain: String,
+}
+
+impl FederationData {
+    pub fn new(
+        federation_repo: Arc<dyn FederationRepository>,
+        user_repo: Arc<dyn ApUserRepository>,
+        object_handler: Arc<dyn ApObjectHandler>,
+        base_url: String,
+    ) -> Self {
+        let domain = base_url
+            .trim_start_matches("https://")
+            .trim_start_matches("http://")
+            .split('/')
+            .next()
+            .unwrap_or("")
+            .to_string();
+        Self {
+            federation_repo,
+            user_repo,
+            object_handler,
+            base_url,
+            domain,
+        }
+    }
+}

crates/adapters/activitypub-base/src/error.rs

@@ -0,0 +1,48 @@
+use std::fmt::{Display, Formatter};
+
+use axum::http::StatusCode;
+
+#[derive(Debug)]
+pub struct Error(pub(crate) anyhow::Error, pub(crate) StatusCode);
+
+impl Error {
+    pub fn not_found(e: impl Into<anyhow::Error>) -> Self {
+        Self(e.into(), StatusCode::NOT_FOUND)
+    }
+
+    pub fn bad_request(e: impl Into<anyhow::Error>) -> Self {
+        Self(e.into(), StatusCode::BAD_REQUEST)
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        std::fmt::Display::fmt(&self.0, f)
+    }
+}
+
+impl<T> From<T> for Error
+where
+    T: Into<anyhow::Error>,
+{
+    fn from(t: T) -> Self {
+        Error(t.into(), StatusCode::INTERNAL_SERVER_ERROR)
+    }
+}
+
+impl axum::response::IntoResponse for Error {
+    fn into_response(self) -> axum::response::Response {
+        let status = self.1;
+        if status.is_server_error() {
+            tracing::error!(error = %self.0, status = status.as_u16(), "federation error");
+        } else {
+            tracing::debug!(error = %self.0, status = status.as_u16(), "federation response");
+        }
+        let body = if status.is_server_error() {
+            "internal server error".to_string()
+        } else {
+            self.0.to_string()
+        };
+        (status, body).into_response()
+    }
+}

crates/adapters/activitypub-base/src/federation.rs

@@ -0,0 +1,50 @@
+use activitypub_federation::config::{Data, FederationConfig, FederationMiddleware, UrlVerifier};
+use activitypub_federation::error::Error as FedError;
+use url::Url;
+
+use crate::data::FederationData;
+
+#[derive(Clone)]
+struct PermissiveVerifier;
+
+#[async_trait::async_trait]
+impl UrlVerifier for PermissiveVerifier {
+    async fn verify(&self, _url: &Url) -> Result<(), FedError> {
+        Ok(())
+    }
+}
+
+#[derive(Clone)]
+pub struct ApFederationConfig(pub FederationConfig<FederationData>);
+
+impl ApFederationConfig {
+    pub async fn new(data: FederationData, debug: bool) -> anyhow::Result<Self> {
+        let config = if debug {
+            FederationConfig::builder()
+                .domain(&data.domain)
+                .app_data(data)
+                .debug(true)
+                .http_signature_compat(true)
+                .url_verifier(Box::new(PermissiveVerifier))
+                .build()
+                .await?
+        } else {
+            FederationConfig::builder()
+                .domain(&data.domain)
+                .app_data(data)
+                .debug(false)
+                .http_signature_compat(true)
+                .build()
+                .await?
+        };
+        Ok(Self(config))
+    }
+
+    pub fn to_request_data(&self) -> Data<FederationData> {
+        self.0.to_request_data()
+    }
+
+    pub fn middleware(&self) -> FederationMiddleware<FederationData> {
+        FederationMiddleware::new(self.0.clone())
+    }
+}

crates/adapters/activitypub-base/src/followers_handler.rs

@@ -0,0 +1,71 @@
+use activitypub_federation::{axum::json::FederationJson, config::Data};
+use axum::extract::Path;
+use serde_json::json;
+
+use crate::data::FederationData;
+use crate::error::Error;
+use crate::repository::FollowerStatus;
+
+fn ordered_collection(id: String, total: usize, items: Vec<String>) -> serde_json::Value {
+    json!({
+        "@context": "https://www.w3.org/ns/activitystreams",
+        "type": "OrderedCollection",
+        "id": id,
+        "totalItems": total,
+        "orderedItems": items,
+    })
+}
+
+pub async fn followers_handler(
+    Path(user_id_str): Path<String>,
+    data: Data<FederationData>,
+) -> Result<FederationJson<serde_json::Value>, Error> {
+    let user_id = uuid::Uuid::parse_str(&user_id_str)
+        .map_err(|_| Error::bad_request(anyhow::anyhow!("invalid user id")))?;
+
+    data.user_repo
+        .find_by_id(user_id)
+        .await
+        .map_err(Error::from)?
+        .ok_or_else(|| Error::not_found(anyhow::anyhow!("user not found")))?;
+
+    let followers = data
+        .federation_repo
+        .get_followers(user_id)
+        .await
+        .map_err(Error::from)?;
+
+    let items: Vec<String> = followers
+        .into_iter()
+        .filter(|f| f.status == FollowerStatus::Accepted)
+        .map(|f| f.actor.url)
+        .collect();
+
+    let id = format!("{}/users/{}/followers", data.base_url, user_id_str);
+    Ok(FederationJson(ordered_collection(id, items.len(), items)))
+}
+
+pub async fn following_handler(
+    Path(user_id_str): Path<String>,
+    data: Data<FederationData>,
+) -> Result<FederationJson<serde_json::Value>, Error> {
+    let user_id = uuid::Uuid::parse_str(&user_id_str)
+        .map_err(|_| Error::bad_request(anyhow::anyhow!("invalid user id")))?;
+
+    data.user_repo
+        .find_by_id(user_id)
+        .await
+        .map_err(Error::from)?
+        .ok_or_else(|| Error::not_found(anyhow::anyhow!("user not found")))?;
+
+    let following = data
+        .federation_repo
+        .get_following(user_id)
+        .await
+        .map_err(Error::from)?;
+
+    let items: Vec<String> = following.into_iter().map(|a| a.url).collect();
+
+    let id = format!("{}/users/{}/following", data.base_url, user_id_str);
+    Ok(FederationJson(ordered_collection(id, items.len(), items)))
+}

crates/adapters/activitypub-base/src/inbox.rs

@@ -0,0 +1,20 @@
+use activitypub_federation::{
+    axum::inbox::{receive_activity, ActivityData},
+    config::Data,
+    protocol::context::WithContext,
+};
+
+use crate::activities::InboxActivities;
+use crate::actors::DbActor;
+use crate::data::FederationData;
+use crate::error::Error;
+
+pub async fn inbox_handler(
+    data: Data<FederationData>,
+    activity_data: ActivityData,
+) -> Result<(), Error> {
+    receive_activity::<WithContext<InboxActivities>, DbActor, FederationData>(
+        activity_data, &data,
+    )
+    .await
+}

crates/adapters/activitypub-base/src/lib.rs

@@ -0,0 +1,23 @@
+pub mod activities;
+pub mod actor_handler;
+pub mod actors;
+pub mod content;
+pub mod data;
+pub mod error;
+pub mod federation;
+pub mod followers_handler;
+pub mod inbox;
+pub mod outbox;
+pub mod repository;
+pub mod service;
+pub mod user;
+pub mod webfinger;
+pub(crate) mod urls;
+
+pub use content::ApObjectHandler;
+pub use data::FederationData;
+pub use error::Error;
+pub use federation::ApFederationConfig;
+pub use repository::{FederationRepository, Follower, FollowerStatus, FollowingStatus, RemoteActor};
+pub use service::ActivityPubService;
+pub use user::{ApUser, ApUserRepository};

crates/adapters/activitypub-base/src/outbox.rs

@@ -0,0 +1,48 @@
+use activitypub_federation::{axum::json::FederationJson, config::Data};
+use axum::extract::Path;
+use serde::{Deserialize, Serialize};
+
+use crate::data::FederationData;
+use crate::error::Error;
+
+#[derive(Serialize, Deserialize)]
+#[serde(rename_all = "camelCase")]
+pub struct OrderedCollection {
+    #[serde(rename = "@context")]
+    context: String,
+    #[serde(rename = "type")]
+    kind: String,
+    id: String,
+    total_items: u64,
+    ordered_items: Vec<serde_json::Value>,
+}
+
+pub async fn outbox_handler(
+    Path(user_id_str): Path<String>,
+    data: Data<FederationData>,
+) -> Result<FederationJson<OrderedCollection>, Error> {
+    let uuid = uuid::Uuid::parse_str(&user_id_str)
+        .map_err(|_| Error::bad_request(anyhow::anyhow!("invalid user id")))?;
+
+    data.user_repo
+        .find_by_id(uuid)
+        .await
+        .map_err(Error::from)?
+        .ok_or_else(|| Error::not_found(anyhow::anyhow!("user not found")))?;
+
+    let objects = data
+        .object_handler
+        .get_local_objects_for_user(uuid)
+        .await
+        .map_err(|e| Error::from(anyhow::anyhow!(e)))?;
+
+    let outbox_url = format!("{}/users/{}/outbox", data.base_url, user_id_str);
+
+    Ok(FederationJson(OrderedCollection {
+        context: "https://www.w3.org/ns/activitystreams".to_string(),
+        kind: "OrderedCollection".to_string(),
+        id: outbox_url,
+        total_items: objects.len() as u64,
+        ordered_items: vec![],
+    }))
+}

crates/adapters/activitypub-base/src/repository.rs

@@ -0,0 +1,50 @@
+use anyhow::Result;
+use async_trait::async_trait;
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum FollowerStatus {
+    Pending,
+    Accepted,
+    Rejected,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum FollowingStatus {
+    Pending,
+    Accepted,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct RemoteActor {
+    pub url: String,
+    pub handle: String,
+    pub inbox_url: String,
+    pub shared_inbox_url: Option<String>,
+    pub display_name: Option<String>,
+}
+
+#[derive(Debug, Clone)]
+pub struct Follower {
+    pub actor: RemoteActor,
+    pub status: FollowerStatus,
+}
+
+#[async_trait]
+pub trait FederationRepository: Send + Sync {
+    async fn add_follower(&self, local_user_id: uuid::Uuid, remote_actor_url: &str, status: FollowerStatus, follow_activity_id: &str) -> Result<()>;
+    async fn get_follower_follow_activity_id(&self, local_user_id: uuid::Uuid, remote_actor_url: &str) -> Result<Option<String>>;
+    async fn remove_follower(&self, local_user_id: uuid::Uuid, remote_actor_url: &str) -> Result<()>;
+    async fn get_followers(&self, local_user_id: uuid::Uuid) -> Result<Vec<Follower>>;
+    async fn update_follower_status(&self, local_user_id: uuid::Uuid, remote_actor_url: &str, status: FollowerStatus) -> Result<()>;
+    async fn add_following(&self, local_user_id: uuid::Uuid, actor: RemoteActor, follow_activity_id: &str) -> Result<()>;
+    async fn get_follow_activity_id(&self, local_user_id: uuid::Uuid, remote_actor_url: &str) -> Result<Option<String>>;
+    async fn remove_following(&self, local_user_id: uuid::Uuid, actor_url: &str) -> Result<()>;
+    async fn get_following(&self, local_user_id: uuid::Uuid) -> Result<Vec<RemoteActor>>;
+    async fn count_following(&self, local_user_id: uuid::Uuid) -> Result<usize>;
+    async fn upsert_remote_actor(&self, actor: RemoteActor) -> Result<()>;
+    async fn get_remote_actor(&self, actor_url: &str) -> Result<Option<RemoteActor>>;
+    async fn get_local_actor_keypair(&self, user_id: uuid::Uuid) -> Result<Option<(String, String)>>;
+    async fn save_local_actor_keypair(&self, user_id: uuid::Uuid, public_key: String, private_key: String) -> Result<()>;
+    async fn get_pending_followers(&self, local_user_id: uuid::Uuid) -> Result<Vec<RemoteActor>>;
+    async fn update_following_status(&self, local_user_id: uuid::Uuid, remote_actor_url: &str, status: FollowingStatus) -> Result<()>;
+}

crates/adapters/activitypub-base/src/service.rs

@@ -0,0 +1,470 @@
+use std::sync::Arc;
+
+use activitypub_federation::{
+    activity_sending::SendActivityTask,
+    fetch::{object_id::ObjectId, webfinger::webfinger_resolve_actor},
+    protocol::context::WithContext,
+    traits::Actor,
+};
+use axum::{routing::get, routing::post, Router};
+use url::Url;
+
+use crate::{
+    activities::{AcceptActivity, CreateActivity, FollowActivity, RejectActivity, UndoActivity},
+    actor_handler::actor_handler,
+    actors::{get_local_actor, DbActor},
+    content::ApObjectHandler,
+    data::FederationData,
+    federation::ApFederationConfig,
+    followers_handler::{followers_handler, following_handler},
+    inbox::inbox_handler,
+    outbox::outbox_handler,
+    repository::{FederationRepository, FollowerStatus, RemoteActor},
+    user::ApUserRepository,
+    urls::activity_url,
+    webfinger::webfinger_handler,
+};
+
+pub(crate) async fn send_with_retry(
+    sends: Vec<SendActivityTask>,
+    data: &activitypub_federation::config::Data<FederationData>,
+) -> Vec<anyhow::Error> {
+    let mut failures = vec![];
+    for send in sends {
+        let mut delay = std::time::Duration::from_secs(1);
+        for attempt in 1..=3u32 {
+            match send.clone().sign_and_send(data).await {
+                Ok(()) => break,
+                Err(e) if attempt < 3 => {
+                    tracing::warn!(attempt, error = %e, "delivery failed, retrying");
+                    tokio::time::sleep(delay).await;
+                    delay *= 2;
+                }
+                Err(e) => {
+                    tracing::error!(attempt, error = %e, "delivery failed permanently");
+                    failures.push(anyhow::anyhow!(e));
+                }
+            }
+        }
+    }
+    failures
+}
+
+pub struct ActivityPubService {
+    federation_config: ApFederationConfig,
+    base_url: String,
+}
+
+impl ActivityPubService {
+    pub async fn new(
+        repo: Arc<dyn FederationRepository>,
+        user_repo: Arc<dyn ApUserRepository>,
+        object_handler: Arc<dyn ApObjectHandler>,
+        base_url: String,
+        debug: bool,
+    ) -> anyhow::Result<Self> {
+        let data = FederationData::new(repo, user_repo, object_handler, base_url.clone());
+        let federation_config = ApFederationConfig::new(data, debug).await?;
+        Ok(Self { federation_config, base_url })
+    }
+
+    pub fn federation_config(&self) -> &ApFederationConfig {
+        &self.federation_config
+    }
+
+    pub fn request_data(&self) -> activitypub_federation::config::Data<FederationData> {
+        self.federation_config.to_request_data()
+    }
+
+    pub async fn actor_json(&self, user_id_str: &str) -> anyhow::Result<String> {
+        use activitypub_federation::traits::Object;
+        let uuid = uuid::Uuid::parse_str(user_id_str)?;
+        let data = self.federation_config.to_request_data();
+        let actor = get_local_actor(uuid, &data)
+            .await
+            .map_err(|e| anyhow::anyhow!("{e}"))?;
+        let person = actor.into_json(&data).await
+            .map_err(|e| anyhow::anyhow!("{e}"))?;
+        Ok(serde_json::to_string(&WithContext::new_default(person))?)
+    }
+
+    pub fn router(&self) -> Router {
+        Router::new()
+            .route("/.well-known/webfinger", get(webfinger_handler))
+            .route("/users/{user_id}", get(actor_handler))
+            .route("/users/{user_id}/inbox", post(inbox_handler))
+            .route("/users/{user_id}/outbox", get(outbox_handler))
+            .route("/users/{user_id}/followers", get(followers_handler))
+            .route("/users/{user_id}/following", get(following_handler))
+            .layer(self.federation_config.middleware())
+    }
+
+    pub async fn follow(&self, local_user_id: uuid::Uuid, handle: &str) -> anyhow::Result<()> {
+        let data = self.federation_config.to_request_data();
+
+        let remote_actor: DbActor = webfinger_resolve_actor(handle, &data)
+            .await
+            .map_err(|e| anyhow::anyhow!("{e}"))?;
+
+        let local_actor = get_local_actor(local_user_id, &data)
+            .await
+            .map_err(|e| anyhow::anyhow!("{e}"))?;
+
+        let follow_id = activity_url(&self.base_url).map_err(|e| anyhow::anyhow!("{e}"))?;
+        let follow_id_str = follow_id.to_string();
+        let follow = FollowActivity {
+            id: follow_id,
+            kind: Default::default(),
+            actor: ObjectId::from(local_actor.ap_id.clone()),
+            object: ObjectId::from(remote_actor.ap_id.clone()),
+        };
+        let follow_with_ctx = WithContext::new_default(follow);
+
+        let sends = SendActivityTask::prepare(
+            &follow_with_ctx,
+            &local_actor,
+            vec![remote_actor.inbox()],
+            &data,
+        )
+        .await?;
+        let failures = send_with_retry(sends, &data).await;
+        if !failures.is_empty() {
+            tracing::warn!(count = failures.len(), "some activity deliveries failed permanently");
+        }
+
+        let remote = RemoteActor {
+            url: remote_actor.ap_id.to_string(),
+            handle: remote_actor.username.clone(),
+            inbox_url: remote_actor.inbox_url.to_string(),
+            shared_inbox_url: None,
+            display_name: Some(remote_actor.username.clone()),
+        };
+        data.federation_repo
+            .add_following(local_user_id, remote, &follow_id_str)
+            .await?;
+
+        Ok(())
+    }
+
+    pub async fn unfollow(&self, local_user_id: uuid::Uuid, actor_url_str: &str) -> anyhow::Result<()> {
+        let data = self.federation_config.to_request_data();
+
+        let remote = data
+            .federation_repo
+            .get_remote_actor(actor_url_str)
+            .await?
+            .ok_or_else(|| anyhow::anyhow!("remote actor not found: {}", actor_url_str))?;
+
+        let local_actor = get_local_actor(local_user_id, &data)
+            .await
+            .map_err(|e| anyhow::anyhow!("{e}"))?;
+
+        let remote_ap_id = Url::parse(actor_url_str)?;
+        let inbox = Url::parse(&remote.inbox_url)?;
+
+        let follow_activity_id_str = data
+            .federation_repo
+            .get_follow_activity_id(local_user_id, actor_url_str)
+            .await?;
+        let follow_id = match follow_activity_id_str {
+            Some(id) => Url::parse(&id)?,
+            None => activity_url(&self.base_url).map_err(|e| anyhow::anyhow!("{e}"))?,
+        };
+        let follow = FollowActivity {
+            id: follow_id,
+            kind: Default::default(),
+            actor: ObjectId::from(local_actor.ap_id.clone()),
+            object: ObjectId::from(remote_ap_id),
+        };
+
+        let undo_id = activity_url(&self.base_url).map_err(|e| anyhow::anyhow!("{e}"))?;
+        let undo = UndoActivity {
+            id: undo_id,
+            kind: Default::default(),
+            actor: ObjectId::from(local_actor.ap_id.clone()),
+            object: follow,
+        };
+
+        let sends = SendActivityTask::prepare(
+            &WithContext::new_default(undo),
+            &local_actor,
+            vec![inbox],
+            &data,
+        )
+        .await?;
+        let failures = send_with_retry(sends, &data).await;
+        if !failures.is_empty() {
+            tracing::warn!(count = failures.len(), "some activity deliveries failed permanently");
+        }
+
+        data.federation_repo
+            .remove_following(local_user_id, actor_url_str)
+            .await?;
+
+        data.object_handler
+            .on_actor_removed(&Url::parse(actor_url_str)?)
+            .await?;
+
+        Ok(())
+    }
+
+    pub async fn accept_follower(
+        &self,
+        local_user_id: uuid::Uuid,
+        remote_actor_url: &str,
+    ) -> anyhow::Result<()> {
+        let data = self.federation_config.to_request_data();
+        let local_actor = get_local_actor(local_user_id, &data)
+            .await
+            .map_err(|e| anyhow::anyhow!("{e}"))?;
+
+        let remote_actor = data
+            .federation_repo
+            .get_remote_actor(remote_actor_url)
+            .await?
+            .ok_or_else(|| anyhow::anyhow!("remote actor not found"))?;
+
+        let follow_id_str = data
+            .federation_repo
+            .get_follower_follow_activity_id(local_user_id, remote_actor_url)
+            .await?
+            .ok_or_else(|| anyhow::anyhow!("follow activity id not found for {}", remote_actor_url))?;
+        let follow_id = Url::parse(&follow_id_str)?;
+        let follow = FollowActivity {
+            id: follow_id,
+            kind: Default::default(),
+            actor: ObjectId::from(Url::parse(remote_actor_url)?),
+            object: ObjectId::from(local_actor.ap_id.clone()),
+        };
+        let accept = AcceptActivity {
+            id: activity_url(&self.base_url).map_err(|e| anyhow::anyhow!("{e}"))?,
+            kind: Default::default(),
+            actor: ObjectId::from(local_actor.ap_id.clone()),
+            object: follow,
+        };
+
+        data.federation_repo
+            .update_follower_status(local_user_id, remote_actor_url, FollowerStatus::Accepted)
+            .await?;
+
+        let inbox = Url::parse(&remote_actor.inbox_url)?;
+        let sends = SendActivityTask::prepare(
+            &WithContext::new_default(accept),
+            &local_actor,
+            vec![inbox.clone()],
+            &data,
+        )
+        .await?;
+        let failures = send_with_retry(sends, &data).await;
+        if !failures.is_empty() {
+            tracing::warn!("failed to deliver Accept activity, but follower is marked accepted locally");
+        }
+
+        self.spawn_backfill(local_user_id, remote_actor.inbox_url.clone());
+
+        Ok(())
+    }
+
+    pub async fn reject_follower(
+        &self,
+        local_user_id: uuid::Uuid,
+        remote_actor_url: &str,
+    ) -> anyhow::Result<()> {
+        let data = self.federation_config.to_request_data();
+        let local_actor = get_local_actor(local_user_id, &data)
+            .await
+            .map_err(|e| anyhow::anyhow!("{e}"))?;
+
+        let remote_actor = data
+            .federation_repo
+            .get_remote_actor(remote_actor_url)
+            .await?
+            .ok_or_else(|| anyhow::anyhow!("remote actor not found"))?;
+
+        let follow_id = activity_url(&self.base_url).map_err(|e| anyhow::anyhow!("{e}"))?;
+        let follow = FollowActivity {
+            id: follow_id,
+            kind: Default::default(),
+            actor: ObjectId::from(Url::parse(remote_actor_url)?),
+            object: ObjectId::from(local_actor.ap_id.clone()),
+        };
+        let reject = RejectActivity {
+            id: activity_url(&self.base_url).map_err(|e| anyhow::anyhow!("{e}"))?,
+            kind: Default::default(),
+            actor: ObjectId::from(local_actor.ap_id.clone()),
+            object: follow,
+        };
+
+        let inbox = Url::parse(&remote_actor.inbox_url)?;
+        let sends = SendActivityTask::prepare(
+            &WithContext::new_default(reject),
+            &local_actor,
+            vec![inbox],
+            &data,
+        )
+        .await?;
+        let failures = send_with_retry(sends, &data).await;
+        if !failures.is_empty() {
+            tracing::warn!(count = failures.len(), "some activity deliveries failed permanently");
+        }
+
+        data.federation_repo
+            .remove_follower(local_user_id, remote_actor_url)
+            .await?;
+
+        Ok(())
+    }
+
+    pub async fn get_pending_followers(&self, local_user_id: uuid::Uuid) -> anyhow::Result<Vec<RemoteActor>> {
+        let data = self.federation_config.to_request_data();
+        data.federation_repo.get_pending_followers(local_user_id).await
+    }
+
+    pub async fn get_accepted_followers(&self, local_user_id: uuid::Uuid) -> anyhow::Result<Vec<RemoteActor>> {
+        let data = self.federation_config.to_request_data();
+        let followers = data.federation_repo.get_followers(local_user_id).await?;
+        Ok(followers
+            .into_iter()
+            .filter(|f| f.status == FollowerStatus::Accepted)
+            .map(|f| f.actor)
+            .collect())
+    }
+
+    pub async fn count_accepted_followers(&self, local_user_id: uuid::Uuid) -> anyhow::Result<usize> {
+        let data = self.federation_config.to_request_data();
+        let followers = data.federation_repo.get_followers(local_user_id).await?;
+        Ok(followers.into_iter().filter(|f| f.status == FollowerStatus::Accepted).count())
+    }
+
+    pub async fn get_following(&self, local_user_id: uuid::Uuid) -> anyhow::Result<Vec<RemoteActor>> {
+        let data = self.federation_config.to_request_data();
+        data.federation_repo.get_following(local_user_id).await
+    }
+
+    pub async fn count_following(&self, local_user_id: uuid::Uuid) -> anyhow::Result<usize> {
+        let data = self.federation_config.to_request_data();
+        data.federation_repo.count_following(local_user_id).await
+    }
+
+    pub async fn remove_follower(&self, local_user_id: uuid::Uuid, actor_url: &str) -> anyhow::Result<()> {
+        let data = self.federation_config.to_request_data();
+        data.federation_repo.remove_follower(local_user_id, actor_url).await
+    }
+
+    /// Broadcast a single object to all accepted followers as a Create activity.
+    /// Called by project-specific event handlers when new content is created.
+    pub async fn broadcast_to_followers(
+        &self,
+        local_user_id: uuid::Uuid,
+        ap_id: Url,
+        object: serde_json::Value,
+    ) -> anyhow::Result<()> {
+        let data = self.federation_config.to_request_data();
+        let local_actor = get_local_actor(local_user_id, &data)
+            .await
+            .map_err(|e| anyhow::anyhow!("{e}"))?;
+
+        let followers = data.federation_repo.get_followers(local_user_id).await?;
+        let accepted: Vec<_> = followers
+            .into_iter()
+            .filter(|f| f.status == FollowerStatus::Accepted)
+            .collect();
+
+        if accepted.is_empty() {
+            return Ok(());
+        }
+
+        let create = CreateActivity {
+            id: ap_id.clone(),
+            kind: Default::default(),
+            actor: ObjectId::from(local_actor.ap_id.clone()),
+            object,
+        };
+        let create_with_ctx = WithContext::new_default(create);
+
+        let inboxes: Vec<Url> = accepted
+            .iter()
+            .filter_map(|f| Url::parse(&f.actor.inbox_url).ok())
+            .collect();
+
+        let sends = SendActivityTask::prepare(&create_with_ctx, &local_actor, inboxes, &data).await?;
+        let failures = send_with_retry(sends, &data).await;
+        if !failures.is_empty() {
+            tracing::warn!(count = failures.len(), "some activity deliveries failed permanently");
+        }
+
+        Ok(())
+    }
+
+    fn spawn_backfill(&self, owner_user_id: uuid::Uuid, follower_inbox_url: String) {
+        let config = self.federation_config.clone();
+        let base_url = self.base_url.clone();
+        tokio::spawn(async move {
+            if let Err(e) = ActivityPubService::run_backfill(config, base_url, owner_user_id, follower_inbox_url).await {
+                tracing::warn!(error = %e, "backfill: task failed");
+            }
+        });
+    }
+
+    async fn run_backfill(
+        config: ApFederationConfig,
+        base_url: String,
+        owner_user_id: uuid::Uuid,
+        follower_inbox_url: String,
+    ) -> anyhow::Result<()> {
+        const BATCH_SIZE: usize = 20;
+
+        let data = config.to_request_data();
+        let local_actor = get_local_actor(owner_user_id, &data)
+            .await
+            .map_err(|e| anyhow::anyhow!("{e}"))?;
+        let inbox = Url::parse(&follower_inbox_url)?;
+
+        let mut objects = data.object_handler.get_local_objects_for_user(owner_user_id).await?;
+        objects.reverse(); // oldest first → chronological feed
+
+        let total = objects.len();
+        let mut success_count = 0usize;
+        let mut failure_count = 0usize;
+
+        for chunk in objects.chunks(BATCH_SIZE) {
+            for (ap_id, object_json) in chunk {
+                // Use a stable Create activity ID derived from the object's ap_id
+                let create_id = Url::parse(&format!("{}/activities/create/{}", base_url,
+                    uuid::Uuid::new_v5(&uuid::Uuid::NAMESPACE_URL, ap_id.as_str().as_bytes())
+                ))?;
+
+                let create = CreateActivity {
+                    id: create_id,
+                    kind: Default::default(),
+                    actor: ObjectId::from(local_actor.ap_id.clone()),
+                    object: object_json.clone(),
+                };
+
+                let sends = SendActivityTask::prepare(
+                    &WithContext::new_default(create),
+                    &local_actor,
+                    vec![inbox.clone()],
+                    &data,
+                ).await?;
+                let failures = send_with_retry(sends, &data).await;
+                if failures.is_empty() {
+                    success_count += 1;
+                } else {
+                    failure_count += 1;
+                }
+            }
+            tokio::time::sleep(std::time::Duration::from_millis(100)).await;
+        }
+
+        tracing::info!(
+            user_id = %owner_user_id,
+            follower = %follower_inbox_url,
+            sent = success_count,
+            failed = failure_count,
+            total = total,
+            "backfill complete"
+        );
+        Ok(())
+    }
+}

crates/adapters/activitypub-base/src/urls.rs

@@ -0,0 +1,20 @@
+use url::Url;
+
+use crate::error::Error;
+
+pub fn extract_user_id_from_url(url: &Url) -> Option<uuid::Uuid> {
+    let path = url.path();
+    path.strip_prefix("/users/")
+        .and_then(|s| s.split('/').next())
+        .and_then(|s| uuid::Uuid::parse_str(s).ok())
+}
+
+pub fn activity_url(base_url: &str) -> Result<Url, Error> {
+    Url::parse(&format!("{}/activities/{}", base_url, uuid::Uuid::new_v4()))
+        .map_err(|e| Error::bad_request(anyhow::anyhow!(e)))
+}
+
+pub fn actor_url(base_url: &str, user_id: uuid::Uuid) -> Url {
+    Url::parse(&format!("{}/users/{}", base_url, user_id))
+        .expect("base_url is always a valid URL prefix")
+}

crates/adapters/activitypub-base/src/user.rs

@@ -0,0 +1,13 @@
+use async_trait::async_trait;
+
+#[derive(Debug, Clone)]
+pub struct ApUser {
+    pub id: uuid::Uuid,
+    pub username: String,
+}
+
+#[async_trait]
+pub trait ApUserRepository: Send + Sync {
+    async fn find_by_id(&self, id: uuid::Uuid) -> anyhow::Result<Option<ApUser>>;
+    async fn find_by_username(&self, username: &str) -> anyhow::Result<Option<ApUser>>;
+}

crates/adapters/activitypub-base/src/webfinger.rs

@@ -0,0 +1,42 @@
+use activitypub_federation::{
+    config::Data,
+    fetch::webfinger::{build_webfinger_response, extract_webfinger_name, Webfinger},
+};
+use axum::{
+    extract::Query,
+    http::header,
+    response::{IntoResponse, Response},
+};
+use serde::Deserialize;
+
+use crate::data::FederationData;
+use crate::error::Error;
+
+#[derive(Deserialize)]
+pub struct WebfingerQuery {
+    resource: String,
+}
+
+pub async fn webfinger_handler(
+    Query(query): Query<WebfingerQuery>,
+    data: Data<FederationData>,
+) -> Result<Response, Error> {
+    let name = extract_webfinger_name(&query.resource, &data)?;
+
+    let user = data
+        .user_repo
+        .find_by_username(name)
+        .await
+        .map_err(Error::from)?
+        .ok_or_else(|| Error::not_found(anyhow::anyhow!("user not found")))?;
+
+    let ap_id = crate::urls::actor_url(&data.base_url, user.id);
+
+    let wf: Webfinger = build_webfinger_response(query.resource, ap_id);
+    let body = serde_json::to_string(&wf)
+        .map_err(|e| Error::from(anyhow::anyhow!(e)))?;
+    Ok((
+        [(header::CONTENT_TYPE, "application/jrd+json")],
+        body,
+    ).into_response())
+}