5 files changed, 77 insertions, 8 deletions

diff --git a/lib/unicorn/configurator.rb b/lib/unicorn/configurator.rb
index 89cbf5c..9752cdd 100644
--- a/lib/unicorn/configurator.rb
+++ b/lib/unicorn/configurator.rb
@@ -45,6 +45,7 @@ class Unicorn::Configurator
       },
     :pid => nil,
     :preload_app => false,
+    :check_client_connection => false,
     :rewindable_input => true, # for Rack 2.x: (Rack::VERSION[0] <= 1),
     :client_body_buffer_size => Unicorn::Const::MAX_BODY,
     :trust_x_forwarded => true,
@@ -96,6 +97,18 @@ class Unicorn::Configurator
     if ready_pipe = RACKUP.delete(:ready_pipe)
       server.ready_pipe = ready_pipe
     end
+    if set[:check_client_connection]
+      set[:listeners].each do |address|
+        if set[:listener_opts][address][:tcp_nopush] == true
+          raise ArgumentError,
+            "check_client_connection is incompatible with tcp_nopush:true"
+        end
+        if set[:listener_opts][address][:tcp_nodelay] == true
+          raise ArgumentError,
+            "check_client_connection is incompatible with tcp_nodelay:true"
+        end
+      end
+    end
     set.each do |key, value|
       value == :unset and next
       skip.include?(key) and next
@@ -454,6 +467,18 @@ class Unicorn::Configurator
     set_int(:client_body_buffer_size, bytes, 0)
   end
 
+  # When enabled, unicorn will check the client connection by writing
+  # the beginning of the HTTP headers before calling the application.
+  #
+  # This will prevent calling the application for clients who have
+  # disconnected while their connection was queued.
+  #
+  # This option cannot be used in conjunction with tcp_nodelay or
+  # tcp_nopush.
+  def check_client_connection(bool)
+    set_bool(:check_client_connection, bool)
+  end
+
   # Allow redirecting $stderr to a given path.  Unlike doing this from
   # the shell, this allows the unicorn process to know the path its
   # writing to and rotate the file if it is used for logging.  The
diff --git a/lib/unicorn/const.rb b/lib/unicorn/const.rb
index b3d8d71..f0c4c12 100644
--- a/lib/unicorn/const.rb
+++ b/lib/unicorn/const.rb
@@ -29,12 +29,16 @@ module Unicorn::Const
 
   # :stopdoc:
   # common errors we'll send back
-  ERROR_400_RESPONSE = "HTTP/1.1 400 Bad Request\r\n\r\n"
-  ERROR_414_RESPONSE = "HTTP/1.1 414 Request-URI Too Long\r\n\r\n"
-  ERROR_413_RESPONSE = "HTTP/1.1 413 Request Entity Too Large\r\n\r\n"
-  ERROR_500_RESPONSE = "HTTP/1.1 500 Internal Server Error\r\n\r\n"
+  ERROR_400_RESPONSE = "400 Bad Request\r\n\r\n"
+  ERROR_414_RESPONSE = "414 Request-URI Too Long\r\n\r\n"
+  ERROR_413_RESPONSE = "413 Request Entity Too Large\r\n\r\n"
+  ERROR_500_RESPONSE = "500 Internal Server Error\r\n\r\n"
+
   EXPECT_100_RESPONSE = "HTTP/1.1 100 Continue\r\n\r\n"
+  EXPECT_100_RESPONSE_SUFFIXED = "100 Continue\r\n\r\nHTTP/1.1 "
 
+  HTTP_RESPONSE_START = ['HTTP', '/1.1 ']
   HTTP_EXPECT = "HTTP_EXPECT"
+
   # :startdoc:
 end
diff --git a/lib/unicorn/http_request.rb b/lib/unicorn/http_request.rb
index a0435d6..79ead2e 100644
--- a/lib/unicorn/http_request.rb
+++ b/lib/unicorn/http_request.rb
@@ -22,11 +22,14 @@ class Unicorn::HttpParser
 
   NULL_IO = StringIO.new("")
 
+  attr_accessor :response_start_sent
+
   # :stopdoc:
   # A frozen format for this is about 15% faster
   REMOTE_ADDR = 'REMOTE_ADDR'.freeze
   RACK_INPUT = 'rack.input'.freeze
   @@input_class = Unicorn::TeeInput
+  @@check_client_connection = false
 
   def self.input_class
     @@input_class
@@ -35,6 +38,15 @@ class Unicorn::HttpParser
   def self.input_class=(klass)
     @@input_class = klass
   end
+
+  def self.check_client_connection
+    @@check_client_connection
+  end
+
+  def self.check_client_connection=(bool)
+    @@check_client_connection = bool
+  end
+
   # :startdoc:
 
   # Does the majority of the IO processing.  It has been written in
@@ -70,6 +82,13 @@ class Unicorn::HttpParser
       # an Exception thrown from the parser will throw us out of the loop
       false until add_parse(socket.kgio_read!(16384))
     end
+
+    # detect if the socket is valid by writing a partial response:
+    if @@check_client_connection && headers?
+      @response_start_sent = true
+      Unicorn::Const::HTTP_RESPONSE_START.each { |c| socket.write(c) }
+    end
+
     e[RACK_INPUT] = 0 == content_length ?
                     NULL_IO : @@input_class.new(socket, self)
     e.merge!(DEFAULTS)
diff --git a/lib/unicorn/http_response.rb b/lib/unicorn/http_response.rb
index b781e20..61563cd 100644
--- a/lib/unicorn/http_response.rb
+++ b/lib/unicorn/http_response.rb
@@ -18,11 +18,13 @@ module Unicorn::HttpResponse
   CRLF = "\r\n"
 
   # writes the rack_response to socket as an HTTP response
-  def http_response_write(socket, status, headers, body)
+  def http_response_write(socket, status, headers, body,
+                          response_start_sent=false)
     status = CODES[status.to_i] || status
 
+    http_response_start = response_start_sent ? '' : 'HTTP/1.1 '
     if headers
-      buf = "HTTP/1.1 #{status}\r\n" \
+      buf = "#{http_response_start}#{status}\r\n" \
             "Date: #{httpdate}\r\n" \
             "Status: #{status}\r\n" \
             "Connection: close\r\n"
diff --git a/lib/unicorn/http_server.rb b/lib/unicorn/http_server.rb
index 13df55a..ef1ea58 100644
--- a/lib/unicorn/http_server.rb
+++ b/lib/unicorn/http_server.rb
@@ -17,6 +17,7 @@ class Unicorn::HttpServer
                 :listener_opts, :preload_app,
                 :reexec_pid, :orig_app, :init_listeners,
                 :master_pid, :config, :ready_pipe, :user
+
   attr_reader :pid, :logger
   include Unicorn::SocketHelper
   include Unicorn::HttpResponse
@@ -355,6 +356,14 @@ class Unicorn::HttpServer
     Unicorn::HttpParser.trust_x_forwarded = bool
   end
 
+  def check_client_connection
+    Unicorn::HttpRequest.check_client_connection
+  end
+
+  def check_client_connection=(bool)
+    Unicorn::HttpRequest.check_client_connection = bool
+  end
+
   private
 
   # wait for a signal hander to wake us up and then consume the pipe
@@ -524,23 +533,33 @@ class Unicorn::HttpServer
       Unicorn.log_error(@logger, "app error", e)
       Unicorn::Const::ERROR_500_RESPONSE
     end
+    msg = "HTTP/1.1 #{msg}" unless @request.response_start_sent
     client.kgio_trywrite(msg)
     client.close
     rescue
   end
 
+  def expect_100_response
+    if @request.response_start_sent
+      Unicorn::Const::EXPECT_100_RESPONSE_SUFFIXED
+    else
+      Unicorn::Const::EXPECT_100_RESPONSE
+    end
+  end
+
   # once a client is accepted, it is processed in its entirety here
   # in 3 easy steps: read request, call app, write app response
   def process_client(client)
     status, headers, body = @app.call(env = @request.read(client))
 
     if 100 == status.to_i
-      client.write(Unicorn::Const::EXPECT_100_RESPONSE)
+      client.write(expect_100_response)
       env.delete(Unicorn::Const::HTTP_EXPECT)
       status, headers, body = @app.call(env)
     end
     @request.headers? or headers = nil
-    http_response_write(client, status, headers, body)
+    http_response_write(client, status, headers, body,
+                        @request.response_start_sent)
     client.shutdown # in case of fork() in Rack app
     client.close # flush and uncork socket immediately, no keepalive
   rescue => e