discourse/app/controllers/groups_controller.rb

class GroupsController < ApplicationController

  def show
    render_serialized(find_group(:id), BasicGroupSerializer)
  end

  def counts
    group = find_group(:group_id)
    render json: {counts: { posts: group.posts_for(guardian).count,
                            members: group.users.count } }
  end

  def posts
    group = find_group(:group_id)
    posts = group.posts_for(guardian, params[:before_post_id]).limit(20)
    render_serialized posts.to_a, GroupPostSerializer
  end

  def members
    group = find_group(:group_id)

    limit = (params[:limit] || 50).to_i
    offset = params[:offset].to_i

    total = group.users.count
    members = group.users.order(:username_lower).limit(limit).offset(offset)

    render json: {
      members: serialize_data(members, GroupUserSerializer),
      meta: {
        total: total,
        limit: limit,
        offset: offset
      }
    }
  end

  private

    def find_group(param_name)
      name = params.require(param_name)
      group = Group.find_by("lower(name) = ?", name.downcase)
      guardian.ensure_can_see!(group)
      group
    end

end