lemmy/crates/routes/src/webfinger.rs

use activitypub_federation::{
  config::Data,
  fetch::webfinger::{extract_webfinger_name, Webfinger, WebfingerLink, WEBFINGER_CONTENT_TYPE},
};
use actix_web::{web, web::Query, HttpResponse};
use lemmy_api_common::context::LemmyContext;
use lemmy_db_schema::{
  source::{community::Community, person::Person},
  traits::ApubActor,
  CommunityVisibility,
};
use lemmy_utils::{cache_header::cache_3days, error::LemmyResult};
use serde::Deserialize;
use std::collections::HashMap;
use url::Url;

#[derive(Deserialize)]
struct Params {
  resource: String,
}

pub fn config(cfg: &mut web::ServiceConfig) {
  cfg.route(
    ".well-known/webfinger",
    web::get().to(get_webfinger_response).wrap(cache_3days()),
  );
}

/// Responds to webfinger requests of the following format. There isn't any real documentation for
/// this, but it described in this blog post:
/// https://mastodon.social/.well-known/webfinger?resource=acct:gargron@mastodon.social
///
/// You can also view the webfinger response that Mastodon sends:
/// https://radical.town/.well-known/webfinger?resource=acct:felix@radical.town
async fn get_webfinger_response(
  info: Query<Params>,
  context: Data<LemmyContext>,
) -> LemmyResult<HttpResponse> {
  let name = extract_webfinger_name(&info.resource, &context)?;

  let links = if name == context.settings().hostname {
    // webfinger response for instance actor (required for mastodon authorized fetch)
    let url = Url::parse(&context.settings().get_protocol_and_hostname())?;
    vec![webfinger_link_for_actor(Some(url), "none", &context)]
  } else {
    // webfinger response for user/community
    let user_id: Option<Url> = Person::read_from_name(&mut context.pool(), name, false)
      .await
      .ok()
      .flatten()
      .map(|c| c.actor_id.into());
    let community_id: Option<Url> = Community::read_from_name(&mut context.pool(), name, false)
      .await
      .ok()
      .flatten()
      .and_then(|c| {
        if c.visibility == CommunityVisibility::Public {
          let id: Url = c.actor_id.into();
          Some(id)
        } else {
          None
        }
      });

    // Mastodon seems to prioritize the last webfinger item in case of duplicates. Put
    // community last so that it gets prioritized. For Lemmy the order doesn't matter.
    vec![
      webfinger_link_for_actor(user_id, "Person", &context),
      webfinger_link_for_actor(community_id, "Group", &context),
    ]
  }
  .into_iter()
  .flatten()
  .collect::<Vec<_>>();

  if links.is_empty() {
    Ok(HttpResponse::NotFound().finish())
  } else {
    let json = Webfinger {
      subject: info.resource.clone(),
      links,
      ..Default::default()
    };

    Ok(
      HttpResponse::Ok()
        .content_type(&WEBFINGER_CONTENT_TYPE)
        .json(json),
    )
  }
}

fn webfinger_link_for_actor(
  url: Option<Url>,
  kind: &str,
  context: &LemmyContext,
) -> Vec<WebfingerLink> {
  if let Some(url) = url {
    let type_key = "https://www.w3.org/ns/activitystreams#type"
      .parse()
      .expect("parse url");

    let mut vec = vec![
      WebfingerLink {
        rel: Some("http://webfinger.net/rel/profile-page".into()),
        kind: Some("text/html".into()),
        href: Some(url.clone()),
        ..Default::default()
      },
      WebfingerLink {
        rel: Some("self".into()),
        kind: Some("application/activity+json".into()),
        href: Some(url),
        properties: HashMap::from([(type_key, kind.into())]),
        ..Default::default()
      },
    ];

    // insert remote follow link
    if kind == "Person" {
      let template = format!(
        "{}/activitypub/externalInteraction?uri={{uri}}",
        context.settings().get_protocol_and_hostname()
      );
      vec.push(WebfingerLink {
        rel: Some("http://ostatus.org/schema/1.0/subscribe".into()),
        template: Some(template),
        ..Default::default()
      });
    }
    vec
  } else {
    vec![]
  }
}