Enable frozen string literals.

Make all string literals immutable by default.

app/logical/danbooru/helpers.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Danbooru
   module Helpers
     module_function

app/logical/danbooru/http.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 require "danbooru/http/application_client"
 require "danbooru/http/html_adapter"
 require "danbooru/http/xml_adapter"

app/logical/danbooru/http/application_client.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # An extension to HTTP::Client that lets us write Rack-style middlewares that
 # hook into the request/response cycle and override how requests are made. This
 # works by extending http.rb's concept of features (HTTP::Feature) to give them

app/logical/danbooru/http/cache.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Danbooru
   class Http
     class Cache < HTTP::Feature

app/logical/danbooru/http/html_adapter.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Danbooru
   class Http
     class HtmlAdapter < HTTP::MimeType::Adapter

app/logical/danbooru/http/logger.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Danbooru
   class Http
     class Logger < HTTP::Feature

app/logical/danbooru/http/redirector.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # A HTTP::Feature that automatically follows HTTP redirects.
 #
 # @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Redirections

app/logical/danbooru/http/retriable.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # A HTTP::Feature that automatically retries requests that return a 429 error
 # or a Retry-After header.
 #

app/logical/danbooru/http/session.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Danbooru
   class Http
     class Session < HTTP::Feature

app/logical/danbooru/http/spoof_referrer.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Danbooru
   class Http
     class SpoofReferrer < HTTP::Feature

app/logical/danbooru/http/unpolish_cloudflare.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # Detect sites using Cloudflare Polish and bypass it by adding a random
 # cache-busting URL param.
 #

app/logical/danbooru/http/xml_adapter.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Danbooru
   class Http
     class XmlAdapter < HTTP::MimeType::Adapter

app/logical/danbooru/ip_address.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 # A wrapper around the IPAddress gem that adds some extra utility methods.
 #
 # @see https://github.com/ipaddress-gem/ipaddress

app/logical/danbooru/message_verifier.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Danbooru
   class MessageVerifier
     attr_reader :purpose, :secret, :verifier