API pagination for all collections using Link header

app/controllers/api/v1/accounts_controller.rb

@@ -4,7 +4,7 @@ class Api::V1::AccountsController < ApiController
   before_action :require_user!, except: [:show, :following, :followers, :statuses]
   before_action :set_account, except: [:verify_credentials, :suggestions]
 
-  respond_to    :json
+  respond_to :json
 
   def show
   end
@@ -15,12 +15,26 @@ class Api::V1::AccountsController < ApiController
   end
 
   def following
-    @accounts = @account.following.with_counters.limit(40)
+    results   = Follow.where(account: @account).paginate_by_max_id(DEFAULT_ACCOUNTS_LIMIT, params[:max_id], params[:since_id])
+    @accounts = Account.where(id: results.map(&:account_id)).with_counters.to_a
+
+    next_path = following_api_v1_account_url(max_id: results.last.id)    if results.size == DEFAULT_ACCOUNTS_LIMIT
+    prev_path = following_api_v1_account_url(since_id: results.first.id) if results.size > 0
+
+    set_pagination_headers(next_path, prev_path)
+
     render action: :index
   end
 
   def followers
-    @accounts = @account.followers.with_counters.limit(40)
+    results   = Follow.where(target_account: @account).paginate_by_max_id(DEFAULT_ACCOUNTS_LIMIT, params[:max_id], params[:since_id])
+    @accounts = Account.where(id: results.map(&:account_id)).with_counters.to_a
+
+    next_path = following_api_v1_account_url(max_id: results.last.id)    if results.size == DEFAULT_ACCOUNTS_LIMIT
+    prev_path = following_api_v1_account_url(since_id: results.first.id) if results.size > 0
+
+    set_pagination_headers(next_path, prev_path)
+
     render action: :index
   end
 
@@ -35,8 +49,14 @@ class Api::V1::AccountsController < ApiController
   end
 
   def statuses
-    @statuses = @account.statuses.with_includes.with_counters.paginate_by_max_id(20, params[:max_id], params[:since_id]).to_a
+    @statuses = @account.statuses.with_includes.with_counters.paginate_by_max_id(DEFAULT_STATUSES_LIMIT, params[:max_id], params[:since_id]).to_a
+
     set_maps(@statuses)
+
+    next_path = statuses_api_v1_account_url(max_id: @statuses.last.id)    if @statuses.size == DEFAULT_STATUSES_LIMIT
+    prev_path = statuses_api_v1_account_url(since_id: @statuses.first.id) if @statuses.size > 0
+
+    set_pagination_headers(next_path, prev_path)
   end
 
   def follow

app/controllers/api/v1/follows_controller.rb

@@ -2,7 +2,7 @@ class Api::V1::FollowsController < ApiController
   before_action -> { doorkeeper_authorize! :follow }
   before_action :require_user!
 
-  respond_to    :json
+  respond_to :json
 
   def create
     raise ActiveRecord::RecordNotFound if params[:uri].blank?

app/controllers/api/v1/media_controller.rb

@@ -2,7 +2,7 @@ class Api::V1::MediaController < ApiController
   before_action -> { doorkeeper_authorize! :write }
   before_action :require_user!
 
-  respond_to    :json
+  respond_to :json
 
   def create
     @media = MediaAttachment.create!(account: current_user.account, file: params[:file])

app/controllers/api/v1/statuses_controller.rb

@@ -15,12 +15,26 @@ class Api::V1::StatusesController < ApiController
   end
 
   def reblogged_by
-    @accounts = @status.reblogged_by(40)
+    results   = @status.reblogs.paginate_by_max_id(DEFAULT_ACCOUNTS_LIMIT, params[:max_id], params[:since_id])
+    @accounts = Account.where(id: results.map(&:account_id)).with_counters.to_a
+
+    next_path = reblogged_by_api_v1_status_url(max_id: results.last.id)    if results.size == DEFAULT_ACCOUNTS_LIMIT
+    prev_path = reblogged_by_api_v1_status_url(since_id: results.first.id) if results.size > 0
+
+    set_pagination_headers(next_path, prev_path)
+
     render action: :accounts
   end
 
   def favourited_by
-    @accounts = @status.favourited_by(40)
+    results   = @status.favourites.paginate_by_max_id(DEFAULT_ACCOUNTS_LIMIT, params[:max_id], params[:since_id])
+    @accounts = Account.where(id: results.map(&:account_id)).with_counters.to_a
+
+    next_path = favourited_by_api_v1_status_url(max_id: results.last.id)    if results.size == DEFAULT_ACCOUNTS_LIMIT
+    prev_path = favourited_by_api_v1_status_url(since_id: results.first.id) if results.size > 0
+
+    set_pagination_headers(next_path, prev_path)
+
     render action: :accounts
   end
 

app/controllers/api/v1/timelines_controller.rb

@@ -5,32 +5,54 @@ class Api::V1::TimelinesController < ApiController
   respond_to :json
 
   def home
-    @statuses = Feed.new(:home, current_account).get(20, params[:max_id], params[:since_id]).to_a
+    @statuses = Feed.new(:home, current_account).get(DEFAULT_STATUSES_LIMIT, params[:max_id], params[:since_id]).to_a
+
     set_maps(@statuses)
+
+    next_path = api_v1_home_timeline_url(max_id: @statuses.last.id)    if @statuses.size == DEFAULT_STATUSES_LIMIT
+    prev_path = api_v1_home_timeline_url(since_id: @statuses.first.id) if @statuses.size > 0
+
+    set_pagination_headers(next_path, prev_path)
+
     render action: :index
   end
 
   def mentions
-    @statuses = Feed.new(:mentions, current_account).get(20, params[:max_id], params[:since_id]).to_a
+    @statuses = Feed.new(:mentions, current_account).get(DEFAULT_STATUSES_LIMIT, params[:max_id], params[:since_id]).to_a
+
     set_maps(@statuses)
+
+    next_path = api_v1_mentions_timeline_url(max_id: @statuses.last.id)    if @statuses.size == DEFAULT_STATUSES_LIMIT
+    prev_path = api_v1_mentions_timeline_url(since_id: @statuses.first.id) if @statuses.size > 0
+
+    set_pagination_headers(next_path, prev_path)
+
     render action: :index
   end
 
   def public
-    @statuses = Status.as_public_timeline(current_account).paginate_by_max_id(20, params[:max_id], params[:since_id]).to_a
+    @statuses = Status.as_public_timeline(current_account).paginate_by_max_id(DEFAULT_STATUSES_LIMIT, params[:max_id], params[:since_id]).to_a
+
     set_maps(@statuses)
+
+    next_path = api_v1_public_timeline_url(max_id: @statuses.last.id)    if @statuses.size == DEFAULT_STATUSES_LIMIT
+    prev_path = api_v1_public_timeline_url(since_id: @statuses.first.id) if @statuses.size > 0
+
+    set_pagination_headers(next_path, prev_path)
+
     render action: :index
   end
 
   def tag
-    @tag = Tag.find_by(name: params[:id].downcase)
-
-    if @tag.nil?
-      @statuses = []
-    else
-      @statuses = Status.as_tag_timeline(@tag, current_account).paginate_by_max_id(20, params[:max_id], params[:since_id]).to_a
-      set_maps(@statuses)
-    end
+    @tag      = Tag.find_by(name: params[:id].downcase)
+    @statuses = @tag.nil? ? [] : Status.as_tag_timeline(@tag, current_account).paginate_by_max_id(DEFAULT_STATUSES_LIMIT, params[:max_id], params[:since_id]).to_a
+
+    set_maps(@statuses)
+
+    next_path = api_v1_hashtag_timeline_url(params[:id], max_id: @statuses.last.id)    if @statuses.size == DEFAULT_STATUSES_LIMIT
+    prev_path = api_v1_hashtag_timeline_url(params[:id], since_id: @statuses.first.id) if @statuses.size > 0
+
+    set_pagination_headers(next_path, prev_path)
 
     render action: :index
   end

app/controllers/api_controller.rb

 class ApiController < ApplicationController
+  DEFAULT_STATUSES_LIMIT = 20
+  DEFAULT_ACCOUNTS_LIMIT = 40
+
   protect_from_forgery with: :null_session
 
   skip_before_action :verify_authenticity_token
@@ -54,6 +57,13 @@ class ApiController < ApplicationController
     response.headers['Access-Control-Allow-Headers']  = 'Origin, X-Requested-With, Content-Type, Accept, Authorization'
   end
 
+  def set_pagination_headers(next_path = nil, prev_path = nil)
+    links = []
+    links << [next_path, [['rel', 'next']]] if next_path
+    links << [prev_path, [['rel', 'prev']]] if prev_path
+    response.headers['Link'] = LinkHeader.new(links)
+  end
+
   def current_resource_owner
     User.find(doorkeeper_token.resource_owner_id) if doorkeeper_token
   end

app/models/account.rb

@@ -133,36 +133,38 @@ class Account < ApplicationRecord
     []
   end
 
-  def self.find_local!(username)
-    find_remote!(username, nil)
-  end
+  class << self
+    def find_local!(username)
+      find_remote!(username, nil)
+    end
 
-  def self.find_remote!(username, domain)
-    where(arel_table[:username].matches(username)).where(domain.nil? ? { domain: nil } : arel_table[:domain].matches(domain)).take!
-  end
+    def find_remote!(username, domain)
+      where(arel_table[:username].matches(username)).where(domain.nil? ? { domain: nil } : arel_table[:domain].matches(domain)).take!
+    end
 
-  def self.find_local(username)
-    find_local!(username)
-  rescue ActiveRecord::RecordNotFound
-    nil
-  end
+    def find_local(username)
+      find_local!(username)
+    rescue ActiveRecord::RecordNotFound
+      nil
+    end
 
-  def self.find_remote(username, domain)
-    find_remote!(username, domain)
-  rescue ActiveRecord::RecordNotFound
-    nil
-  end
+    def find_remote(username, domain)
+      find_remote!(username, domain)
+    rescue ActiveRecord::RecordNotFound
+      nil
+    end
 
-  def self.following_map(target_account_ids, account_id)
-    Follow.where(target_account_id: target_account_ids).where(account_id: account_id).map { |f| [f.target_account_id, true] }.to_h
-  end
+    def following_map(target_account_ids, account_id)
+      Follow.where(target_account_id: target_account_ids).where(account_id: account_id).map { |f| [f.target_account_id, true] }.to_h
+    end
 
-  def self.followed_by_map(target_account_ids, account_id)
-    Follow.where(account_id: target_account_ids).where(target_account_id: account_id).map { |f| [f.account_id, true] }.to_h
-  end
+    def followed_by_map(target_account_ids, account_id)
+      Follow.where(account_id: target_account_ids).where(target_account_id: account_id).map { |f| [f.account_id, true] }.to_h
+    end
 
-  def self.blocking_map(target_account_ids, account_id)
-    Block.where(target_account_id: target_account_ids).where(account_id: account_id).map { |b| [b.target_account_id, true] }.to_h
+    def blocking_map(target_account_ids, account_id)
+      Block.where(target_account_id: target_account_ids).where(account_id: account_id).map { |b| [b.target_account_id, true] }.to_h
+    end
   end
 
   before_create do

app/models/concerns/paginable.rb

@@ -2,11 +2,11 @@ module Paginable
   extend ActiveSupport::Concern
 
   included do
-    def self.paginate_by_max_id(limit, max_id = nil, since_id = nil)
-      query = order('id desc').limit(limit)
+    scope :paginate_by_max_id, -> (limit, max_id = nil, since_id = nil) {
+      query = order(arel_table[:id].desc).limit(limit)
       query = query.where(arel_table[:id].lt(max_id)) unless max_id.blank?
       query = query.where(arel_table[:id].gt(since_id)) unless since_id.blank?
       query
-    end
+    }
   end
 end

app/models/favourite.rb

 class Favourite < ApplicationRecord
+  include Paginable
   include Streamable
 
   belongs_to :account, inverse_of: :favourites

app/models/feed.rb

@@ -12,11 +12,13 @@ class Feed
     # If we're after most recent items and none are there, we need to precompute the feed
     if unhydrated.empty? && max_id == '+inf' && since_id == '-inf'
       RegenerationWorker.perform_async(@account.id, @type)
-      Status.send("as_#{@type}_timeline", @account).paginate_by_max_id(limit, nil, nil)
+      @statuses = Status.send("as_#{@type}_timeline", @account).paginate_by_max_id(limit, nil, nil)
     else
       status_map = Status.where(id: unhydrated).with_includes.with_counters.map { |status| [status.id, status] }.to_h
-      unhydrated.map { |id| status_map[id] }.compact
+      @statuses = unhydrated.map { |id| status_map[id] }.compact
     end
+
+    @statuses
   end
 
   private

app/models/follow.rb

 class Follow < ApplicationRecord
+  include Paginable
   include Streamable
 
   belongs_to :account

app/models/status.rb

@@ -78,14 +78,6 @@ class Status < ApplicationRecord
     ids.map { |id| statuses[id].first }
   end
 
-  def reblogged_by(limit)
-    Account.where(id: reblogs.limit(limit).pluck(:account_id)).with_counters
-  end
-
-  def favourited_by(limit)
-    Account.where(id: favourites.limit(limit).pluck(:account_id)).with_counters
-  end
-
   class << self
     def as_home_timeline(account)
       where(account: [account] + account.following).with_includes.with_counters

config/routes.rb

@@ -67,14 +67,10 @@ Rails.application.routes.draw do
         end
       end
 
-      resources :timelines, only: [] do
-        collection do
-          get :home
-          get :mentions
-          get :public
-          get '/tag/:id', action: :tag
-        end
-      end
+      get '/timelines/home',     to: 'timelines#home', as: :home_timeline
+      get '/timelines/mentions', to: 'timelines#mentions', as: :mentions_timeline
+      get '/timelines/public',   to: 'timelines#public', as: :public_timeline
+      get '/timelines/tag/:id',  to: 'timelines#tag', as: :hashtag_timeline
 
       resources :follows,  only: [:create]
       resources :media,    only: [:create]