It is now possible to specify a timeout when opening a TCPSocket.

README.md

@@ -89,6 +89,15 @@ client.ca_file   = path_to('root-ca.pem')
 client.connect()
 ~~~
 
+The default timeout when opening a TCP Socket is 30 seconds. To specify it explicitly, use 'connect_timeout =>':
+
+~~~ ruby
+client = MQTT::Client.connect(
+  :host => 'myserver.example.com',
+  :connect_timeout => 15
+)
+~~~
+
 The connection can either be made without the use of a block:
 
 ~~~ ruby

lib/mqtt/client.rb

@@ -39,6 +39,9 @@ class Client
     # Number of seconds to wait for acknowledgement packets (default is 5 seconds)
     attr_accessor :ack_timeout
 
+    # Number of seconds to connect to the server (default is 90 seconds)
+    attr_accessor :connect_timeout
+
     # Username to authenticate to the server with
     attr_accessor :username
 
@@ -72,6 +75,7 @@ class Client
       :clean_session => true,
       :client_id => nil,
       :ack_timeout => 5,
+      :connect_timeout => 30,
       :username => nil,
       :password => nil,
       :will_topic => nil,
@@ -239,7 +243,7 @@ def connect(clientid = nil)
 
       unless connected?
         # Create network socket
-        tcp_socket = TCPSocket.new(@host, @port)
+        tcp_socket = open_tcp_socket
 
         if @ssl
           # Set the protocol version
@@ -600,6 +604,19 @@ def next_packet_id
       @last_packet_id
     end
 
+    def open_tcp_socket
+      return TCPSocket.new @host, @port, connect_timeout: @connect_timeout if RUBY_VERSION.to_f >= 3.0
+
+      begin
+        Timeout.timeout(@connect_timeout) do
+          return TCPSocket.new(@host, @port)
+        end
+      rescue Timeout::Error
+        raise IO::TimeoutError, "Connection timed out for \"#{@host}\" port #{@port}" if defined? IO::TimeoutError
+        raise Errno::ETIMEDOUT, "Connection timed out for \"#{@host}\" port #{@port}"
+      end
+    end
+
     # ---- Deprecated attributes and methods  ---- #
     public
 

spec/mqtt_client_spec.rb

@@ -655,6 +655,19 @@ def wait_for_puback(id)
       client.instance_variable_set('@socket', socket)
     end
 
+    it "should respect connect_timeout" do
+      client = MQTT::Client.new(:host => '198.51.100.1', :connect_timeout => 0.1)
+      expect {
+        client.connect
+      }.to raise_error( 
+        if defined? IO::TimeoutError
+          IO::TimeoutError
+        else
+          Errno::ETIMEDOUT
+        end
+      )
+    end
+
     it "should respect timeouts" do
       require "socket"
       rd, wr = UNIXSocket.pair