mruby.handler

    paths:
      "/":
        proxy.reverse.url: http://localhost:5001
        proxy.preserve-host: ON
        mruby.handler: |
          require "/srv/www/rewrite_rules.rb"
          lambda do |env|
            RewriteRules.rewrite(env) do
              rewrite '/favicon.ico', '/images/favicon.ico', :break
              rewrite '/apple-touch-icon.png', '/images/apple-touch-icon.png', :break

              rewrite %r{^/2005/colors-canvas\.xhtml$}, '/2005/colors-canvas.html', :permanent
              rewrite %r{^/2005/colors-canvas$}, '/2005/colors-canvas.html', :permanent

              rewrite %r{^/logs/latest$}, '/', :permanent
              rewrite %r{^/logs/latest.rdf$}, '/feed', :permanent
              rewrite %r{^/logs/latest.atom$}, '/feed', :permanent
              rewrite %r{^/latest\.rdf$}, '/feed', :permanent
              rewrite %r{^/blog/index\.(rdf|atom)$}, '/feed', :permanent
              rewrite %r{^/logs(/.+?)(\.(rdf|atom))$}, '/feed', :permanent

              rewrite %r{^/logs(/.+?)(\.(x?html|xml|txt))?$}, '\1', :permanent
              rewrite %r{^/blog(/.+?)(\.(x?html|xml|txt))?$}, '\1', :permanent
              rewrite %r{^/photo$}, '/photo/', :permanent

              rewrite %r{^/(\d\d\d\d/\d\d(/\d\d)?)$}, '/\1/', :permanent
              rewrite %r{^/\d\d\d\d/$}, '/', :redirect

              rewrite %r{^/view-img(/.+?)$}, '\1', :permanent
            end
          end

h2o の path はディレクトリの指定しかできないみたいなので (自動的に末尾スラッシュがついたりする)、rewrite で同時にパス決め打ちのディスパッチも行っています。

rewrite_rules.rb

class RewriteRules
	class RewriteRulesException < Exception
		attr_reader :response
		def initialize(response)
			@response = response
		end
	end

	attr_reader :env
	attr_reader :path

	def self.rewrite(env, &block)
		self.new(env).run(&block)
	end

	def initialize(env, &block)
		@env = env
		@path_orig = "#{env['SCRIPT_NAME']}#{env['PATH_INFO']}"
		@path = @path_orig.dup
	end

	def run(&block)
		begin
			instance_eval(&block)
			if @path != @path_orig
				return [ 307, { 'x-reproxy-url' => path }, [ ] ]
			else
				return [ 399, {}, [ ] ]
			end
		rescue RewriteRulesException => e
			return e.response
		end
	end

	def rewrite(regexp, replace, flag=:continue)
		if @path.gsub!(regexp, replace)
			case flag
			when :redirect
				raise RewriteRulesException.new([ 302, { 'Location' => @path }, [ ] ])
			when :permanent
				raise RewriteRulesException.new([ 301, { 'Location' => @path }, [ ] ])
			when :break
				raise RewriteRulesException.new([ 307, { 'x-reproxy-url' => @path }, [ ] ])
			when :continue
				# nothing
			else
				raise "unsupported flag: #{flag}"
			end
		end
	end
end

require 'rspec'

describe RewriteRules do
	it "should treat :permanent as 302 redirect" do
		env = {
			'PATH_INFO' => '/logs/latest'
		}
		expect(RewriteRules.rewrite(env) {
			rewrite %r{^/logs/latest$}, '/', :permanent
			rewrite %r{^/logs(/.+?)(\.(x?html|xml|txt))?$}, '\1', :permanent
			rewrite %r{^/foobar/}, '/bazbaz/'
		}).to eq( [301, {"Location"=>"/"}, []])
	end

	it "should treat :redirect as 301 redirect" do
		env = {
			'PATH_INFO' => '/logs/piyo.html'
		}
		expect(RewriteRules.rewrite(env) {
			rewrite %r{^/logs/latest$}, '/', :permanent
			rewrite %r{^/logs(/.+?)(\.(x?html|xml|txt))?$}, '\1', :redirect
			rewrite %r{^/foobar/}, '/bazbaz/'
		}).to eq([302, {"Location"=>"/piyo"}, []])
	end

	it "should treat as internal proxy by default" do
		env = {
			'PATH_INFO' => '/foobar/baz'
		}
		expect(RewriteRules.rewrite(env) {
			rewrite %r{^/logs/latest$}, '/', :permanent
			rewrite %r{^/logs(/.+?)(\.(x?html|xml|txt))?$}, '\1', :permanent
			rewrite %r{^/foobar/}, '/bazbaz/'
		}).to eq([307, {"x-reproxy-url"=>"/bazbaz/baz"}, []])
	end

	it "can write logic in dsl" do
		env = {
			'PATH_INFO' => '/foobar/baz',
			'XXX' => true,
		}
		expect(RewriteRules.rewrite(env) {
			if env['XXX']
				rewrite %r{^/foobar/}, '/bazbaz/'
			end
		}).to eq([307, {"x-reproxy-url"=>"/bazbaz/baz"}, []])

		env = {
			'PATH_INFO' => '/foobar/baz',
			'XXX' => false
		}
		expect(RewriteRules.rewrite(env) {
			if env['XXX']
				rewrite %r{^/foobar/}, '/bazbaz/'
			end
		}).to eq([399, {}, []])
	end
end

ところで

rewrite ルールが ruby で書けるということは、すなわち自由にテスト可能であることを意味します。Apache の RewriteRule や nginx の rewrite をテストするのはかなり面倒なので、かなり強力で嬉しい感じがします。