diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index f1b5e6a8..87af470e 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -28,20 +28,21 @@ jobs:
           - ubuntu
 
         ruby:
-          - 2.5
           - 2.6
           - 2.7
           - 3.0
           - 3.1
           - 3.2
           - 3.3
+          - 3.4
 
-        gemfile: ["Gemfile"]
+        gemfile:
+          - gems/rack-v2.rb
 
         include:
           - experimental: false
             os: macos
-            ruby: 3.3
+            ruby: 3.4
             gemfile: gems/rack-v2.rb
           - experimental: true
             os: ubuntu
@@ -53,13 +54,16 @@ jobs:
             gemfile: gems/rack-v1.rb
           - experimental: true
             os: ubuntu
-            ruby: 3.2
+            ruby: 3.4
             gemfile: gems/rack-v2.rb
-          # enable when rack v3 is supported
-          # - experimental: true
-          #  os: ubuntu
-          #  ruby: 3.2
-          #  env: BUNDLE_GEMFILE=gems/rack-head.rb
+          - experimental: true
+            os: ubuntu
+            ruby: 3.4
+            gemfile: gems/rack-v3.rb
+          - experimental: true
+            os: ubuntu
+            ruby: 3.4
+            gemfile: gems/rack-head.rb
 
     steps:
     - uses: actions/checkout@v3
diff --git a/Gemfile b/Gemfile
index 7d8e9e86..0711ed08 100644
--- a/Gemfile
+++ b/Gemfile
@@ -4,6 +4,8 @@ gemspec
 
 group :development do
   gem "rake-compiler"
+  gem "rdoc"
+  gem "benchmark"
 end
 
 group :test do
diff --git a/benchmark/benchmarker.rb b/benchmark/benchmarker.rb
index 17378245..7929ba42 100644
--- a/benchmark/benchmarker.rb
+++ b/benchmark/benchmarker.rb
@@ -37,7 +37,7 @@ def start_server(handler_name)
         end
 
         app = proc do |env|
-          [200, {'Content-Type' => 'text/html', 'Content-Length' => '11'}, ['hello world']]
+          [200, {'content-type' => 'text/html', 'content-length' => '11'}, ['hello world']]
         end
 
         handler = Rack::Handler.const_get(handler_name)
diff --git a/example/adapter.rb b/example/adapter.rb
index 77375fdf..d583159e 100644
--- a/example/adapter.rb
+++ b/example/adapter.rb
@@ -8,7 +8,7 @@ def call(env)
     body = ["hello!"]
     [
       200,
-      { 'Content-Type' => 'text/plain' },
+      { 'content-type' => 'text/plain' },
       body
     ]
   end
@@ -20,13 +20,13 @@ def call(env)
     run SimpleAdapter.new
   end
   map '/files' do
-    run Rack::File.new('.')
+    run Rack::Files.new('.')
   end
 end
 
 # You could also start the server like this:
 #
 #   app = Rack::URLMap.new('/test'  => SimpleAdapter.new,
-#                          '/files' => Rack::File.new('.'))
+#                          '/files' => Rack::Files.new('.'))
 #   Thin::Server.start('0.0.0.0', 3000, app)
 #
diff --git a/example/async_app.ru b/example/async_app.ru
index 4e9be17b..8c5a2d8b 100755
--- a/example/async_app.ru
+++ b/example/async_app.ru
@@ -87,7 +87,7 @@ class AsyncApp
     body = DeferrableBody.new
     
     # Get the headers out there asap, let the client know we're alive...
-    EventMachine::next_tick { env['async.callback'].call [200, {'Content-Type' => 'text/plain'}, body] }
+    EventMachine::next_tick { env['async.callback'].call [200, {'content-type' => 'text/plain'}, body] }
     
     # Semi-emulate a long db request, instead of a timer, in reality we'd be 
     # waiting for the response data. Whilst this happens, other connections 
diff --git a/example/async_chat.ru b/example/async_chat.ru
index e9e3ddf8..55d12040 100755
--- a/example/async_chat.ru
+++ b/example/async_chat.ru
@@ -118,7 +118,7 @@ class Chat
         send_message = function(message_box) {
           xhr = XHR();
           xhr.open("POST", "/", true); 
-      		xhr.setRequestHeader("Content-Type", "application/x-www-form-urlencoded");
+      		xhr.setRequestHeader("content-type", "application/x-www-form-urlencoded");
       		xhr.setRequestHeader("X_REQUESTED_WITH", "XMLHttpRequest");
       		xhr.send("message="+escape(message_box.value));
           scroll();
@@ -161,7 +161,7 @@ class Chat
     body.callback { delete_user user_id }
     
     EventMachine::next_tick do
-      renderer.call [200, {'Content-Type' => 'text/html'}, body]
+      renderer.call [200, {'content-type' => 'text/html'}, body]
     end
   end
   
diff --git a/example/async_tailer.ru b/example/async_tailer.ru
index 467f0df6..eda6be9d 100755
--- a/example/async_tailer.ru
+++ b/example/async_tailer.ru
@@ -70,7 +70,7 @@ class AsyncTailer
     
     EventMachine::next_tick do
       
-      env['async.callback'].call [200, {'Content-Type' => 'text/html'}, body]
+      env['async.callback'].call [200, {'content-type' => 'text/html'}, body]
       
       body.call ["<h1>Async Tailer</h1><pre>"]
       
diff --git a/example/config.ru b/example/config.ru
index bc655f85..8a530fd2 100644
--- a/example/config.ru
+++ b/example/config.ru
@@ -14,7 +14,7 @@ app = proc do |env|
   
   [
     200,                                        # Status code
-    { 'Content-Type' => 'text/html' },          # Reponse headers
+    { 'content-type' => 'text/html' },          # Reponse headers
     body                                        # Body of the response
   ]
 end
diff --git a/ext/thin_parser/common.rl b/ext/thin_parser/common.rl
index 08877036..ad9ba529 100644
--- a/ext/thin_parser/common.rl
+++ b/ext/thin_parser/common.rl
@@ -43,7 +43,7 @@
   Method = ( upper | digit | safe ){1,20} >mark %request_method;
 
   http_number = ( digit+ "." digit+ ) ;
-  HTTP_Version = ( "HTTP/" http_number ) >mark %http_version ;
+  HTTP_Version = ( "HTTP/" http_number ) >mark %request_http_version ;
   Request_Line = ( Method " " Request_URI ("#" Fragment){0,1} " " HTTP_Version CRLF ) ;
 
   field_name = ( token -- ":" )+ >start_field %write_field;
diff --git a/ext/thin_parser/parser.c b/ext/thin_parser/parser.c
index 42832de4..7005d083 100644
--- a/ext/thin_parser/parser.c
+++ b/ext/thin_parser/parser.c
@@ -295,8 +295,8 @@ case 13:
 tr17:
 #line 59 "parser.rl"
 	{	
-    if (parser->http_version != NULL) {
-      parser->http_version(parser->data, PTR_TO(mark), LEN(mark, p));
+    if (parser->request_http_version != NULL) {
+      parser->request_http_version(parser->data, PTR_TO(mark), LEN(mark, p));
     }
   }
 	goto st14;
diff --git a/ext/thin_parser/parser.h b/ext/thin_parser/parser.h
index f80d40f6..6a587e3a 100644
--- a/ext/thin_parser/parser.h
+++ b/ext/thin_parser/parser.h
@@ -33,7 +33,7 @@ typedef struct http_parser {
   element_cb fragment;
   element_cb request_path;
   element_cb query_string;
-  element_cb http_version;
+  element_cb request_http_version;
   element_cb header_done;
   
 } http_parser;
diff --git a/ext/thin_parser/parser.rl b/ext/thin_parser/parser.rl
index 05c8eb62..eb0db63c 100644
--- a/ext/thin_parser/parser.rl
+++ b/ext/thin_parser/parser.rl
@@ -56,9 +56,9 @@
     }
   }
 
-  action http_version {	
-    if (parser->http_version != NULL) {
-      parser->http_version(parser->data, PTR_TO(mark), LEN(mark, fpc));
+  action request_http_version {
+    if (parser->request_http_version != NULL) {
+      parser->request_http_version(parser->data, PTR_TO(mark), LEN(mark, fpc));
     }
   }
 
diff --git a/ext/thin_parser/thin.c b/ext/thin_parser/thin.c
index b3e777cc..082d7bd5 100644
--- a/ext/thin_parser/thin.c
+++ b/ext/thin_parser/thin.c
@@ -21,7 +21,7 @@ static VALUE global_request_method;
 static VALUE global_request_uri;
 static VALUE global_fragment;
 static VALUE global_query_string;
-static VALUE global_http_version;
+static VALUE global_request_http_version;
 static VALUE global_content_length;
 static VALUE global_http_content_length;
 static VALUE global_request_path;
@@ -150,11 +150,12 @@ static void query_string(void *data, const char *at, size_t length)
   rb_hash_aset(req, global_query_string, val);
 }
 
-static void http_version(void *data, const char *at, size_t length)
+static void request_http_version(void *data, const char *at, size_t length)
 {
   VALUE req = (VALUE)data;
   VALUE val = rb_str_new(at, length);
-  rb_hash_aset(req, global_http_version, val);
+  rb_hash_aset(req, global_request_http_version, val);
+  rb_hash_aset(req, global_server_protocol, val);
 }
 
 /** Finalizes the request header to have a bunch of stuff that's
@@ -211,7 +212,6 @@ static void header_done(void *data, const char *at, size_t length)
   }
   
   /* set some constants */
-  rb_hash_aset(req, global_server_protocol, global_server_protocol_value);
   rb_hash_aset(req, global_url_scheme, global_url_scheme_value);
   rb_hash_aset(req, global_script_name, global_empty);
 }
@@ -237,7 +237,7 @@ VALUE Thin_HttpParser_alloc(VALUE klass)
   hp->fragment = fragment;
   hp->request_path = request_path;
   hp->query_string = query_string;
-  hp->http_version = http_version;
+  hp->request_http_version = request_http_version;
   hp->header_done = header_done;
   thin_http_parser_init(hp);
 
@@ -401,7 +401,7 @@ void Init_thin_parser()
   DEF_GLOBAL(request_uri, "REQUEST_URI");
   DEF_GLOBAL(fragment, "FRAGMENT");
   DEF_GLOBAL(query_string, "QUERY_STRING");
-  DEF_GLOBAL(http_version, "HTTP_VERSION");
+  DEF_GLOBAL(request_http_version, "thin.request_http_version");
   DEF_GLOBAL(request_path, "REQUEST_PATH");
   DEF_GLOBAL(content_length, "CONTENT_LENGTH");
   DEF_GLOBAL(http_content_length, "HTTP_CONTENT_LENGTH");
diff --git a/gems/rack-head.rb b/gems/rack-head.rb
index e79a8585..d3001cbe 100644
--- a/gems/rack-head.rb
+++ b/gems/rack-head.rb
@@ -1,16 +1,5 @@
 # frozen_string_literal: true
 
-source 'https://rubygems.org'
-
-gemspec path: "../"
+eval_gemfile "../Gemfile"
 
 gem 'rack', github: 'rack/rack'
-
-group :development do
-  gem "rake-compiler"
-end
-
-group :test do
-  gem "rake", ">= 12.3.3"
-  gem "rspec", "~> 3.5"
-end
diff --git a/gems/rack-v1.rb b/gems/rack-v1.rb
index a77be550..e5be601e 100644
--- a/gems/rack-v1.rb
+++ b/gems/rack-v1.rb
@@ -1,17 +1,5 @@
 # frozen_string_literal: true
 
-source 'https://rubygems.org'
-
-gemspec path: "../"
+eval_gemfile "../Gemfile"
 
 gem 'rack', '~> 1.0'
-
-group :development do
-  gem "rake-compiler"
-end
-
-group :test do
-  gem "rake", ">= 12.3.3"
-  gem "rspec", "~> 3.5"
-end
-
diff --git a/gems/rack-v2.rb b/gems/rack-v2.rb
index 498d17c4..8dfecd29 100644
--- a/gems/rack-v2.rb
+++ b/gems/rack-v2.rb
@@ -1,16 +1,5 @@
 # frozen_string_literal: true
 
-source 'https://rubygems.org'
+eval_gemfile "../Gemfile"
 
-gemspec path: "../"
-
-gem 'rack', '~> 2.0'
-
-group :development do
-  gem "rake-compiler"
-end
-
-group :test do
-  gem "rake", ">= 12.3.3"
-  gem "rspec", "~> 3.5"
-end
+gem 'rack', "~> 2.0"
diff --git a/gems/rack-v3.rb b/gems/rack-v3.rb
new file mode 100644
index 00000000..01923819
--- /dev/null
+++ b/gems/rack-v3.rb
@@ -0,0 +1,5 @@
+# frozen_string_literal: true
+
+eval_gemfile "../Gemfile"
+
+gem 'rack', "~> 3.0"
diff --git a/lib/rack/adapter/loader.rb b/lib/rack/adapter/loader.rb
index 4574f284..c05968ed 100644
--- a/lib/rack/adapter/loader.rb
+++ b/lib/rack/adapter/loader.rb
@@ -15,6 +15,13 @@ class AdapterNotFound < RuntimeError; end
     [:file,    nil]
   ]
   
+  # Rack v1 compatibility...
+  unless const_defined?(:Files)
+    require 'rack/file'
+    
+    Files = File
+  end
+  
   module Adapter
     # Guess which adapter to use based on the directory structure
     # or file content.
@@ -64,7 +71,7 @@ def self.for(name, options={})
         return Merb::Rack::Application.new
         
       when :file
-        return Rack::File.new(options[:chdir])
+        return Rack::Files.new(options[:chdir])
         
       else
         raise AdapterNotFound, "Adapter not found: #{name}"
diff --git a/lib/rack/adapter/rails.rb b/lib/rack/adapter/rails.rb
index 0da1b98b..31113e20 100644
--- a/lib/rack/adapter/rails.rb
+++ b/lib/rack/adapter/rails.rb
@@ -23,7 +23,7 @@ def initialize(options = {})
         load_application
 
         @rails_app = self.class.rack_based? ? ActionController::Dispatcher.new : CgiApp.new
-        @file_app  = Rack::File.new(::File.join(RAILS_ROOT, "public"))
+        @file_app  = Rack::Files.new(::File.join(RAILS_ROOT, "public"))
       end
 
       def load_application
diff --git a/lib/thin/request.rb b/lib/thin/request.rb
index b5efe24b..4b3fe4df 100644
--- a/lib/thin/request.rb
+++ b/lib/thin/request.rb
@@ -22,7 +22,7 @@ class Request
     SERVER_NAME       = 'SERVER_NAME'.freeze
     REQUEST_METHOD    = 'REQUEST_METHOD'.freeze
     LOCALHOST         = 'localhost'.freeze
-    HTTP_VERSION      = 'HTTP_VERSION'.freeze
+    REQUEST_HTTP_VERSION      = 'thin.request_http_version'.freeze
     HTTP_1_0          = 'HTTP/1.0'.freeze
     REMOTE_ADDR       = 'REMOTE_ADDR'.freeze
     CONTENT_LENGTH    = 'CONTENT_LENGTH'.freeze
@@ -114,7 +114,7 @@ def persistent?
       # Clients and servers SHOULD NOT assume that a persistent connection
       # is maintained for HTTP versions less than 1.1 unless it is explicitly
       # signaled. (http://www.w3.org/Protocols/rfc2616/rfc2616-sec8.html)
-      if @env[HTTP_VERSION] == HTTP_1_0
+      if @env[REQUEST_HTTP_VERSION] == HTTP_1_0
         @env[CONNECTION] =~ KEEP_ALIVE_REGEXP
 
       # HTTP/1.1 client intends to maintain a persistent connection unless
diff --git a/lib/thin/response.rb b/lib/thin/response.rb
index 7a5ce93c..f5ff806e 100644
--- a/lib/thin/response.rb
+++ b/lib/thin/response.rb
@@ -1,18 +1,64 @@
 module Thin
   # A response sent to the client.
   class Response
-    CONNECTION     = 'Connection'.freeze
+    class Stream
+      def initialize(writer)
+        @read_closed = true
+        @write_closed = false
+        @writer = writer
+      end
+
+      def read(length = nil, outbuf = nil)
+        raise ::IOError, 'not opened for reading' if @read_closed
+      end
+
+      def write(chunk)
+        raise ::IOError, 'not opened for writing' if @write_closed
+
+        @writer.call(chunk)
+      end
+
+      alias :<< :write
+
+      def close
+        @read_closed = @write_closed = true
+
+        nil
+      end
+
+      def closed?
+        @read_closed && @write_closed
+      end
+
+      def close_read
+        @read_closed = true
+
+        nil
+      end
+
+      def close_write
+        @write_closed = true
+
+        nil
+      end
+
+      def flush
+        self
+      end
+    end
+
+    CONNECTION     = 'connection'.freeze
     CLOSE          = 'close'.freeze
     KEEP_ALIVE     = 'keep-alive'.freeze
-    SERVER         = 'Server'.freeze
-    CONTENT_LENGTH = 'Content-Length'.freeze
+    SERVER         = 'server'.freeze
+    CONTENT_LENGTH = 'content-length'.freeze
 
     PERSISTENT_STATUSES  = [100, 101].freeze
 
     #Error Responses
-    ERROR            = [500, {'Content-Type' => 'text/plain'}, ['Internal server error']].freeze
-    PERSISTENT_ERROR = [500, {'Content-Type' => 'text/plain', 'Connection' => 'keep-alive', 'Content-Length' => "21"}, ['Internal server error']].freeze
-    BAD_REQUEST      = [400, {'Content-Type' => 'text/plain'}, ['Bad Request']].freeze
+    ERROR            = [500, {'content-type' => 'text/plain'}, ['Internal server error']].freeze
+    PERSISTENT_ERROR = [500, {'content-type' => 'text/plain', 'connection' => 'keep-alive', 'content-length' => "21"}, ['Internal server error']].freeze
+    BAD_REQUEST      = [400, {'content-type' => 'text/plain'}, ['Bad Request']].freeze
 
     # Status code
     attr_accessor :status
@@ -86,14 +132,16 @@ def close
     # Yields each chunk of the response.
     # To control the size of each chunk
     # define your own +each+ method on +body+.
-    def each
+    def each(&block)
       yield head
 
       unless @skip_body
         if @body.is_a?(String)
           yield @body
-        else
+        elsif @body.respond_to?(:each)
           @body.each { |chunk| yield chunk }
+        else
+          @body.call(Stream.new(block))
         end
       end
     end
@@ -104,7 +152,7 @@ def persistent!
     end
 
     # Persistent connection must be requested as keep-alive
-    # from the server and have a Content-Length, or the response
+    # from the server and have a content-length, or the response
     # status must require that the connection remain open.
     def persistent?
       (@persistent && @headers.has_key?(CONTENT_LENGTH)) || PERSISTENT_STATUSES.include?(@status)
diff --git a/lib/thin/stats.rb b/lib/thin/stats.rb
index 57252363..385b0887 100644
--- a/lib/thin/stats.rb
+++ b/lib/thin/stats.rb
@@ -43,7 +43,7 @@ def serve(env)
         
         [
           200,
-          { 'Content-Type' => 'text/html' },
+          { 'content-type' => 'text/html' },
           [body]
         ]
       end
diff --git a/script/profile b/script/profile
index 87045277..6bc81fdb 100755
--- a/script/profile
+++ b/script/profile
@@ -9,7 +9,7 @@ require 'thin'
 
 class Adapter
   def call(env)
-    [200, {'Content-Type' => 'text/html', 'Content-Length' => '11'}, ['hello world']]
+    [200, {'content-type' => 'text/html', 'content-length' => '11'}, ['hello world']]
   end
 end
 
diff --git a/site/rdoc.rb b/site/rdoc.rb
index aca0e339..9652805f 100644
--- a/site/rdoc.rb
+++ b/site/rdoc.rb
@@ -169,7 +169,7 @@ module Page
   %realtitle%
 ENDIF:title
   </title>
-  <meta http-equiv="Content-Type" content="text/html; charset=%charset%" />
+  <meta http-equiv="content-type" content="text/html; charset=%charset%" />
   <link rel="stylesheet" href="%style_url%" type="text/css" media="screen" />
   <script language="JavaScript" type="text/javascript">
     // <![CDATA[
@@ -371,7 +371,7 @@ module Page
 FILE_INDEX = %{
 <html>
 <head>
-<meta http-equiv="Content-Type" content="text/html; charset=%charset%">
+<meta http-equiv="content-type" content="text/html; charset=%charset%">
 <style>
 <!--
   body {
diff --git a/site/thin.rb b/site/thin.rb
index 25827bcc..9a0c226d 100644
--- a/site/thin.rb
+++ b/site/thin.rb
@@ -127,8 +127,8 @@ def usage_page
         [
           200,          # Status code
           {             # Response headers
-            'Content-Type' => 'text/html',
-            'Content-Length' => '2',
+            'content-type' => 'text/html',
+            'content-length' => '2',
           },
           ['hi']        # Response body
         ]
diff --git a/spec/daemonizing_spec.rb b/spec/daemonizing_spec.rb
index 6a716801..6b4a0675 100644
--- a/spec/daemonizing_spec.rb
+++ b/spec/daemonizing_spec.rb
@@ -94,6 +94,7 @@ def name
       subject.kill(1)
     end
 
+    sleep(1)
     expect(File.exist?(subject.pid_file)).to be_falsey
   end
   
diff --git a/spec/perf/server_perf_spec.rb b/spec/perf/server_perf_spec.rb
index 000f520e..c74dadab 100644
--- a/spec/perf/server_perf_spec.rb
+++ b/spec/perf/server_perf_spec.rb
@@ -4,7 +4,7 @@
   before do
     start_server do |env|
       body = env.inspect + env['rack.input'].read
-      [200, { 'Content-Length' => body.size.to_s }, body]
+      [200, { 'content-length' => body.size.to_s }, body]
     end
   end
   
@@ -25,7 +25,7 @@
   before do
     start_server('/tmp/thin_test.sock') do |env|
       body = env.inspect + env['rack.input'].read
-      [200, { 'Content-Length' => body.size.to_s }, body]
+      [200, { 'content-length' => body.size.to_s }, body]
     end
   end
   
diff --git a/spec/rack/loader_spec.rb b/spec/rack/loader_spec.rb
index e1e6efbe..e35b691b 100644
--- a/spec/rack/loader_spec.rb
+++ b/spec/rack/loader_spec.rb
@@ -32,7 +32,7 @@
   end
   
   it "should load File adapter" do
-    expect(Rack::File).to receive(:new)
+    expect(Rack::Files).to receive(:new)
     Rack::Adapter.for(:file)
   end
   
diff --git a/spec/request/parser_spec.rb b/spec/request/parser_spec.rb
index 2e11e2a0..7be5cac6 100644
--- a/spec/request/parser_spec.rb
+++ b/spec/request/parser_spec.rb
@@ -12,7 +12,7 @@
     request = R("GET / HTTP/1.1\r\nHost: localhost\r\n\r\n")
     expect(request.env['SERVER_PROTOCOL']).to eq('HTTP/1.1')
     expect(request.env['REQUEST_PATH']).to eq('/')
-    expect(request.env['HTTP_VERSION']).to eq('HTTP/1.1')
+    expect(request.env['thin.request_http_version']).to eq('HTTP/1.1')
     expect(request.env['REQUEST_URI']).to eq('/')
     expect(request.env['GATEWAY_INTERFACE']).to eq('CGI/1.2')
     expect(request.env['REQUEST_METHOD']).to eq('GET')
@@ -195,7 +195,6 @@
     expect(request.env['PATH_INFO']).to eq('/hi')
     expect(request.env['REQUEST_PATH']).to eq('/hi')
     expect(request.env['REQUEST_URI']).to eq('/hi?qs')
-    expect(request.env['HTTP_VERSION']).to eq('HTTP/1.1')
     expect(request.env['REQUEST_METHOD']).to eq('GET')
     expect(request.env["rack.url_scheme"]).to eq('http')
     expect(request.env['FRAGMENT'].to_s).to eq("f")
@@ -276,4 +275,4 @@
 
     expect(request.env['REQUEST_URI']).to eq("/H%uFFFDhnchenbrustfilet")
   end
-end
\ No newline at end of file
+end
diff --git a/spec/request/persistent_spec.rb b/spec/request/persistent_spec.rb
index 2419c082..f86a46d4 100644
--- a/spec/request/persistent_spec.rb
+++ b/spec/request/persistent_spec.rb
@@ -6,30 +6,30 @@
   end
   
   it "should not assume that a persistent connection is maintained for HTTP version 1.0" do
-    @request.env['HTTP_VERSION'] = 'HTTP/1.0'
+    @request.env['thin.request_http_version'] = 'HTTP/1.0'
     expect(@request).not_to be_persistent
   end
 
   it "should assume that a persistent connection is maintained for HTTP version 1.0 when specified" do
-    @request.env['HTTP_VERSION'] = 'HTTP/1.0'
+    @request.env['thin.request_http_version'] = 'HTTP/1.0'
     @request.env['HTTP_CONNECTION'] = 'Keep-Alive'
     expect(@request).to be_persistent
   end
   
   it "should maintain a persistent connection for HTTP/1.1 client" do
-    @request.env['HTTP_VERSION'] = 'HTTP/1.1'
+    @request.env['thin.request_http_version'] = 'HTTP/1.1'
     @request.env['HTTP_CONNECTION'] = 'Keep-Alive'
     expect(@request).to be_persistent
   end
 
   it "should maintain a persistent connection for HTTP/1.1 client by default" do
-    @request.env['HTTP_VERSION'] = 'HTTP/1.1'
+    @request.env['thin.request_http_version'] = 'HTTP/1.1'
     expect(@request).to be_persistent
   end
 
   it "should not maintain a persistent connection for HTTP/1.1 client when Connection header include close" do
-    @request.env['HTTP_VERSION'] = 'HTTP/1.1'
+    @request.env['thin.request_http_version'] = 'HTTP/1.1'
     @request.env['HTTP_CONNECTION'] = 'close'
     expect(@request).not_to be_persistent
   end
-end
\ No newline at end of file
+end
diff --git a/spec/response_spec.rb b/spec/response_spec.rb
index ba1df5a3..d96d66a6 100644
--- a/spec/response_spec.rb
+++ b/spec/response_spec.rb
@@ -3,22 +3,22 @@
 describe Response do
   before do
     @response = Response.new
-    @response.headers['Content-Type'] = 'text/html'
-    @response.headers['Content-Length'] = '0'
+    @response.headers['content-type'] = 'text/html'
+    @response.headers['content-length'] = '0'
     @response.body = ''
   end
   
   it 'should output headers' do
-    expect(@response.headers_output).to include("Content-Type: text/html", "Content-Length: 0", "Connection: close")
+    expect(@response.headers_output).to include("content-type: text/html", "content-length: 0", "connection: close")
   end
   
   it 'should include server name header' do
-    expect(@response.headers_output).to include("Server: thin")
+    expect(@response.headers_output).to include("server: thin")
   end
   
   it 'should output head' do
-    expect(@response.head).to include("HTTP/1.1 200 OK", "Content-Type: text/html", "Content-Length: 0",
-                                  "Connection: close", "\r\n\r\n")
+    expect(@response.head).to include("HTTP/1.1 200 OK", "content-type: text/html", "content-length: 0",
+                                      "connection: close", "\r\n\r\n")
   end
   
   it 'should allow duplicates in headers' do
@@ -71,18 +71,18 @@
     expect(@response).not_to be_persistent
   end
   
-  it "should not be persistent when no Content-Length" do
+  it "should not be persistent when no content-length" do
     @response = Response.new
-    @response.headers = {'Content-Type' => 'text/html'}
+    @response.headers = {'content-type' => 'text/html'}
     @response.body = ''
     
     @response.persistent!
     expect(@response).not_to be_persistent
   end
 
-  it "should ignore Content-Length case" do
+  it "should ignore content-length case" do
     @response = Response.new
-    @response.headers = {'Content-Type' => 'text/html', 'content-length' => '0'}
+    @response.headers = {'content-type' => 'text/html', 'content-length' => '0'}
     @response.body = ''
 
     @response.persistent!
diff --git a/spec/server/robustness_spec.rb b/spec/server/robustness_spec.rb
index 7f18a109..df6af14a 100644
--- a/spec/server/robustness_spec.rb
+++ b/spec/server/robustness_spec.rb
@@ -4,7 +4,7 @@
   before do
     start_server do |env|
       body = 'hello!'
-      [200, { 'Content-Type' => 'text/html' }, body]
+      [200, { 'content-type' => 'text/html' }, body]
     end
   end
   
diff --git a/spec/server/stopping_spec.rb b/spec/server/stopping_spec.rb
index 67d4c61e..90a18233 100644
--- a/spec/server/stopping_spec.rb
+++ b/spec/server/stopping_spec.rb
@@ -5,7 +5,7 @@
 describe Server, "stopping" do
   before do
     start_server do |env|
-      [200, { 'Content-Type' => 'text/html' }, ['ok']]
+      [200, { 'content-type' => 'text/html' }, ['ok']]
     end
     @done = false
   end
diff --git a/spec/server/swiftiply_spec.rb b/spec/server/swiftiply_spec.rb
index 56e6d6c7..263d214b 100644
--- a/spec/server/swiftiply_spec.rb
+++ b/spec/server/swiftiply_spec.rb
@@ -12,7 +12,7 @@
       sleep 2 # HACK ooh boy, I wish I knew how to make those specs more stable...
       start_server('0.0.0.0', 5555, :backend => Backends::SwiftiplyClient, :wait_for_socket => false) do |env|
         body = env.inspect + env['rack.input'].read
-        [200, { 'Content-Type' => 'text/html' }, body]
+        [200, { 'content-type' => 'text/html' }, body]
       end
     end
     
diff --git a/spec/server/tcp_spec.rb b/spec/server/tcp_spec.rb
index 48d82d7b..f7051978 100644
--- a/spec/server/tcp_spec.rb
+++ b/spec/server/tcp_spec.rb
@@ -4,7 +4,7 @@
   before do
     start_server do |env|
       body = env.inspect + env['rack.input'].read
-      [200, { 'Content-Type' => 'text/html' }, body]
+      [200, { 'content-type' => 'text/html' }, body]
     end
   end
   
@@ -15,8 +15,8 @@
   it 'should GET from TCPSocket' do
     status, headers, body = parse_response(send_data("GET /?this HTTP/1.0\r\nConnection: close\r\n\r\n"))
     expect(status).to eq(200)
-    expect(headers['Content-Type']).to eq('text/html')
-    expect(headers['Connection']).to eq('close')
+    expect(headers['content-type']).to eq('text/html')
+    expect(headers['connection']).to eq('close')
     expect(body).to include('this')
   end
   
diff --git a/spec/server/threaded_spec.rb b/spec/server/threaded_spec.rb
index 71e3e2e5..1067a370 100644
--- a/spec/server/threaded_spec.rb
+++ b/spec/server/threaded_spec.rb
@@ -6,7 +6,7 @@
     start_server DEFAULT_TEST_ADDRESS, DEFAULT_TEST_PORT, :threaded => true do |env|
       sleep env['PATH_INFO'].delete('/').to_i
       @requests += 1
-      [200, { 'Content-Type' => 'text/html' }, 'hi']
+      [200, { 'content-type' => 'text/html' }, 'hi']
     end
   end
   
diff --git a/spec/server/unix_socket_spec.rb b/spec/server/unix_socket_spec.rb
index 856950cc..776787c4 100644
--- a/spec/server/unix_socket_spec.rb
+++ b/spec/server/unix_socket_spec.rb
@@ -3,7 +3,7 @@
 describe Server, "on UNIX domain socket" do
   before do
     start_server('/tmp/thin_test.sock') do |env|
-      [200, { 'Content-Type' => 'text/html' }, [env.inspect]]
+      [200, { 'content-type' => 'text/html' }, [env.inspect]]
     end
   end
   
diff --git a/spec/spec_helper.rb b/spec/spec_helper.rb
index 3819f04a..d92ae73a 100644
--- a/spec/spec_helper.rb
+++ b/spec/spec_helper.rb
@@ -66,7 +66,7 @@ def failure_message_when_negated
   class ValidateWithLint
     def matches?(request)
       @request = request
-      Rack::Lint.new(proc{[200, {'Content-Type' => 'text/html', 'Content-Length' => '0'}, []]}).call(@request.env)
+      Rack::Lint.new(proc{[200, {'content-type' => 'text/html', 'content-length' => '0'}, []]}).call(@request.env)
       true
     rescue Rack::Lint::LintError => e
       @message = e.message
diff --git a/thin.gemspec b/thin.gemspec
index d5faf34e..6c2a50c1 100644
--- a/thin.gemspec
+++ b/thin.gemspec
@@ -20,11 +20,12 @@ Thin::GemSpec ||= Gem::Specification.new do |s|
     'changelog_uri'   => 'https://github.com/macournoyer/thin/blob/master/CHANGELOG'
   }
 
-  s.required_ruby_version = '>= 1.8.5'
+  s.required_ruby_version = '>= 2.6'
   
-  s.add_dependency        'rack',         '>= 1', '< 3'
+  s.add_dependency        'rack',         '>= 1', '< 4'
   s.add_dependency        'eventmachine', '~> 1.0', '>= 1.0.4'
   s.add_dependency        'daemons',      '~> 1.0', '>= 1.0.9'  unless Thin.win?
+  s.add_dependency        'logger' 
 
   s.files                 = %w(CHANGELOG README.md Rakefile) +
                             Dir["{bin,doc,example,lib}/**/*"] - Dir["lib/thin_parser.*"] +