Allow backlog parameter to be set with ssl_bind DSL (#2780)

Hint about backlog upper limit due to net.core.somaxconn
Guard against invalid backlog value

docs/architecture.md

@@ -31,10 +31,10 @@ _workers_, and we sometimes call the threads created by Puma's
 ![https://bit.ly/2zwzhEK](images/puma-connection-flow.png)
 
 * Upon startup, Puma listens on a TCP or UNIX socket.
-  * The backlog of this socket is configured (with a default of 1024). The
-    backlog determines the size of the queue for unaccepted connections.
-    Generally, you'll never hit the backlog cap in production. If the backlog is
-    full, the operating system refuses new connections.
+  * The backlog of this socket is configured with a default of 1024, but the
+    actual backlog value is capped by the `net.core.somaxconn` sysctl value.
+    The backlog determines the size of the queue for unaccepted connections. If
+    the backlog is full, the operating system is not accepting new connections.
   * This socket backlog is distinct from the `backlog` of work as reported by
     `Puma.stats` or the control server. The backlog that `Puma.stats` refers to
     represents the number of connections in the process' `todo` set waiting for

lib/puma/binder.rb

@@ -168,9 +168,9 @@ module Puma
             params = Util.parse_query uri.query
 
             opt = params.key?('low_latency') && params['low_latency'] != 'false'
-            bak = params.fetch('backlog', 1024).to_i
+            backlog = params.fetch('backlog', 1024).to_i
 
-            io = add_tcp_listener uri.host, uri.port, opt, bak
+            io = add_tcp_listener uri.host, uri.port, opt, backlog
 
             @ios[ios_len..-1].each do |i|
               addr = loc_addr_str i
@@ -255,7 +255,8 @@ module Puma
             logger.log "* Activated #{str}"
           else
             ios_len = @ios.length
-            io = add_ssl_listener uri.host, uri.port, ctx
+            backlog = params.fetch('backlog', 1024).to_i
+            io = add_ssl_listener uri.host, uri.port, ctx, optimize_for_latency = true, backlog
 
             @ios[ios_len..-1].each do |i|
               addr = loc_addr_str i

lib/puma/dsl.rb

@@ -48,6 +48,8 @@ module Puma
 
       ca_additions = "&ca=#{opts[:ca]}" if ['peer', 'force_peer'].include?(verify)
 
+      backlog_str = opts[:backlog] ? "&backlog=#{Integer(opts[:backlog])}" : ''
+
       if defined?(JRUBY_VERSION)
         ssl_cipher_list = opts[:ssl_cipher_list] ?
           "&ssl_cipher_list=#{opts[:ssl_cipher_list]}" : nil
@@ -55,7 +57,7 @@ module Puma
         keystore_additions = "keystore=#{opts[:keystore]}&keystore-pass=#{opts[:keystore_pass]}"
 
         "ssl://#{host}:#{port}?#{keystore_additions}#{ssl_cipher_list}" \
-          "&verify_mode=#{verify}#{tls_str}#{ca_additions}"
+          "&verify_mode=#{verify}#{tls_str}#{ca_additions}#{backlog_str}"
       else
         ssl_cipher_filter = opts[:ssl_cipher_filter] ?
           "&ssl_cipher_filter=#{opts[:ssl_cipher_filter]}" : nil
@@ -64,7 +66,7 @@ module Puma
           "&verification_flags=#{Array(ary).join ','}" : nil
 
         "ssl://#{host}:#{port}?cert=#{opts[:cert]}&key=#{opts[:key]}" \
-          "#{ssl_cipher_filter}&verify_mode=#{verify}#{tls_str}#{ca_additions}#{v_flags}"
+          "#{ssl_cipher_filter}&verify_mode=#{verify}#{tls_str}#{ca_additions}#{v_flags}#{backlog_str}"
       end
     end
 

test/test_binder.rb

@@ -275,6 +275,24 @@ class TestBinder < TestBinderBase
     assert_equal @events.stderr, env_hash["rack.errors"]
   end
 
+  def test_ssl_binder_sets_backlog
+    skip_unless :ssl
+
+    host = '127.0.0.1'
+    port = UniquePort.call
+    tcp_server = TCPServer.new(host, port)
+    tcp_server.define_singleton_method(:listen) do |backlog|
+      Thread.current[:backlog] = backlog
+      super(backlog)
+    end
+
+    TCPServer.stub(:new, tcp_server) do
+      @binder.parse ["ssl://#{host}:#{port}?#{ssl_query}&backlog=2048"], @events
+    end
+
+    assert_equal 2048, Thread.current[:backlog]
+  end
+
   def test_close_calls_close_on_ios
     @mocked_ios = [Minitest::Mock.new, Minitest::Mock.new]
     @mocked_ios.each { |m| m.expect(:close, true) }

test/test_config.rb

@@ -98,6 +98,21 @@ class TestConfigFile < TestConfigFileBase
     assert_equal [ssl_binding], conf.options[:binds]
   end
 
+  def test_ssl_bind_with_backlog
+    skip_unless :ssl
+
+    conf = Puma::Configuration.new do |c|
+      c.ssl_bind "0.0.0.0", "9292", {
+        backlog: "2048",
+      }
+    end
+
+    conf.load
+
+    ssl_binding = conf.options[:binds].first
+    assert ssl_binding.include?('&backlog=2048')
+  end
+
   def test_ssl_bind_jruby
     skip_unless :jruby
     skip_unless :ssl

test/test_thread_pool.rb

@@ -5,7 +5,7 @@ require "puma/thread_pool"
 class TestThreadPool < Minitest::Test
 
   def teardown
-    @pool.shutdown(1) if @pool
+    @pool.shutdown(1) if defined?(@pool)
   end
 
   def new_pool(min, max, &block)