Add response_content_type plugin for more easily setting content-type for responses

Author: jeremyevans

CHANGELOG

@@ -1,3 +1,7 @@
+=== master
+
+* Add response_content_type plugin for more easily setting content-type for responses (jeremyevans)
+
 === 3.94.0 (2025-07-14)
 
 * Add view_subdir_leading_slash plugin for using view subdirectory unless template name starts with slash (jeremyevans) (#395)

lib/roda/plugins/response_content_type.rb

@@ -0,0 +1,79 @@
+# frozen-string-literal: true
+
+#
+class Roda
+  module RodaPlugins
+    # The response_content_type extension adds response.content_type
+    # and response.content_type= methods for getting and setting the
+    # response content-type.
+    #
+    # When setting the content-type, you can pass either a string, which
+    # is used directly:
+    #
+    #   response.content_type = "text/html"
+    # 
+    # Or, if you have registered mime types when loading the plugin:
+    #
+    #  plugin :response_content_type, mime_types: {
+    #    plain: "text/plain",
+    #    html: "text/html",
+    #    pdf: "application/pdf"
+    #  }
+    #
+    # You can use a symbol:
+    #
+    #  response.content_type = :html
+    #
+    # If you would like to load all mime types supported by rack/mime,
+    # you can use the <tt>mime_types: :from_rack_mime</tt> option:
+    #
+    #  plugin :response_content_type, mime_types: :from_rack_mime
+    #
+    # Note that you are unlikely to be using all of these mime types,
+    # so doing this will likely result in unnecessary memory usage. It
+    # is recommended to use a hash with only the mime types your
+    # application actually uses.
+    #
+    # To prevent silent failures, if you attempt to set the response
+    # type with a symbol, and the symbol is not recognized, a KeyError
+    # is raised.
+    module ResponseContentType
+      def self.configure(app, opts=OPTS)
+        if mime_types = opts[:mime_types]
+          mime_types = if mime_types == :from_rack_mime
+            require "rack/mime"
+            h = {}
+            Rack::Mime::MIME_TYPES.each do |k, v|
+              h[k.slice(1,100).to_sym] = v
+            end
+            h
+          else
+            mime_types.dup
+          end
+          app.opts[:repsonse_content_types] = mime_types.freeze
+        else
+          app.opts[:repsonse_content_types] ||= {}
+        end
+      end
+
+      module ResponseMethods
+        # Return the content-type of the response. Will be nil if it has
+        # not yet been explicitly set.
+        def content_type
+          @headers[RodaResponseHeaders::CONTENT_TYPE]
+        end
+
+        # Set the content-type of the response. If given a string,
+        # it is used directly. If given a symbol, looks up the mime
+        # type with the given file extension. If the symbol is not
+        # a recognized mime type, raises KeyError.
+        def content_type=(mime_type)
+          mime_type = roda_class.opts[:repsonse_content_types].fetch(mime_type) if mime_type.is_a?(Symbol)
+          @headers[RodaResponseHeaders::CONTENT_TYPE] = mime_type
+        end
+      end
+    end
+
+    register_plugin(:response_content_type, ResponseContentType)
+  end
+end

spec/plugin/response_content_type_spec.rb

@@ -0,0 +1,67 @@
+require_relative "../spec_helper"
+
+describe "response_content_type plugin" do 
+  it "allows getting and setting content-type" do
+    app(:response_content_type) do |r|
+      r.get "a" do
+        response.content_type = "text/plain"
+        "a:#{response.content_type}"
+      end
+      ":#{response.content_type}"
+    end
+
+    _, h, b = req
+    h[RodaResponseHeaders::CONTENT_TYPE].must_equal 'text/html'
+    b.must_equal [":"]
+
+    _, h, b = req("/a")
+    h[RodaResponseHeaders::CONTENT_TYPE].must_equal 'text/plain'
+    b.must_equal ["a:text/plain"]
+  end
+
+  it "supports using symbols with plugin :mime_types option, and raises if an invalid symbol is provided" do
+    app(:bare) do
+      plugin :response_content_type, mime_types: {:txt => "text/plain"}
+      route do |r|
+        r.get "a" do
+          response.content_type = :bad
+        end
+        response.content_type = :txt
+        response.content_type
+      end
+    end
+
+    _, h, b = req
+    h[RodaResponseHeaders::CONTENT_TYPE].must_equal 'text/plain'
+    b.must_equal ["text/plain"]
+
+    proc{req("/a")}.must_raise KeyError
+  end
+
+  it "supports plugin mime_types: :from_rack_mime option" do
+    app(:bare) do
+      plugin :response_content_type, mime_types: :from_rack_mime
+      route do |r|
+        r.get String do |s|
+          response.content_type = s.to_sym
+          ""
+        end
+        response.content_type = :txt
+        response.content_type
+      end
+    end
+
+    2.times do
+      _, h, b = req
+      h[RodaResponseHeaders::CONTENT_TYPE].must_equal 'text/plain'
+      b.must_equal ["text/plain"]
+
+      header(RodaResponseHeaders::CONTENT_TYPE, "/pdf").must_equal "application/pdf"
+
+      proc{req("/invalid-mime-type")}.must_raise KeyError
+
+      # test when loading the plugin more than once
+      app.plugin :response_content_type
+    end
+  end
+end

www/pages/documentation.erb

@@ -121,6 +121,7 @@
       <li><a href="rdoc/classes/Roda/RodaPlugins/RedirectHttpToHttps.html">redirect_http_to_https</a>: Adds request method to redirect HTTP requests to the same location using HTTPS.</li>
       <li><a href="rdoc/classes/Roda/RodaPlugins/RequestAref.html">request_aref</a>: Adds configurable handling for [] and []= request methods.</li>
       <li><a href="rdoc/classes/Roda/RodaPlugins/RequestHeaders.html">request_headers</a>: Adds a headers method to the request object, for easier access to request headers.</li>
+      <li><a href="rdoc/classes/Roda/RodaPlugins/ResponseContentType.html">response_content_type</a>: More easily set content-type header for responses.</li>
       <li><a href="rdoc/classes/Roda/RodaPlugins/ResponseRequest.html">response_request</a>: Gives response object access to request object.</li>
       <li><a href="rdoc/classes/Roda/RodaPlugins/SinatraHelpers.html">sinatra_helpers</a>: Port of Sinatra::Helpers methods not covered by other plugins.</li>
       <li><a href="rdoc/classes/Roda/RodaPlugins/Status303.html">status_303</a>: Uses 303 as the default redirect status for non-GET requests by HTTP 1.1 clients.</li>