Finish the API endpoint for cover upload

src/handlers/upload_handler.cr

@@ -0,0 +1,28 @@
+require "kemal"
+require "../util"
+
+class UploadHandler < Kemal::Handler
+  def initialize(@upload_dir : String)
+  end
+
+  def call(env)
+    unless request_path_startswith(env, [UPLOAD_URL_PREFIX]) &&
+           env.request.method == "GET"
+      return call_next env
+    end
+
+    pp env.request.path
+
+    ary = env.request.path.split(File::SEPARATOR).select { |part| !part.empty? }
+    ary[0] = @upload_dir
+    path = File.join ary
+
+    pp path
+
+    if File.exists? path
+      send_file env, path
+    else
+      env.response.status_code = 404
+    end
+  end
+end