Support nonblocking socket read before select for MRI 1.9.3+ only

lib/mqtt/client.rb

@@ -167,6 +167,14 @@ def initialize(*args)
       @read_thread = nil
       @write_semaphore = Mutex.new
       @pubacks_semaphore = Mutex.new
+
+      @wait_for_read_func = method(
+        if OpenSSL::SSL::SSLSocket.method_defined?(:read_nonblock)
+          :nonblocking_read_before_select
+        else
+          :select_without_nonblocking_read
+        end
+      )
     end
 
     # Get the OpenSSL context, that is used if SSL/TLS is enabled
@@ -438,9 +446,12 @@ def unsubscribe(*topics)
 
     private
 
-    # Try to read a packet from the server
-    # Also sends keep-alive ping packets.
-    def receive_packet
+    def select_without_nonblocking_read
+      # Poll socket - is there data waiting?
+      [nil, !IO.select([@socket], [], [], SELECT_TIMEOUT).nil?]
+    end
+
+    def nonblocking_read_before_select
       first_byte_in_packet = nil
       data_available_to_read = false
       begin
@@ -456,6 +467,13 @@ def receive_packet
           [@socket], [], [], SELECT_TIMEOUT
         ).nil?
       end
+      [first_byte_in_packet, data_available_to_read]
+    end
+
+    # Try to read a packet from the server
+    # Also sends keep-alive ping packets.
+    def receive_packet
+      first_byte_in_packet, data_available_to_read = @wait_for_read_func.call
       if data_available_to_read
         # Yes - read in the packet
         packet = MQTT::Packet.read(@socket, first_byte_in_packet)

spec/mqtt_client_spec.rb

@@ -845,11 +845,9 @@
       expect(@read_queue.size).to eq(1)
     end
 
-    it "should put PUBLISH messages on to the read queue following a wait readable exception" do
-      wait_readable_exception = Class.new(StandardError) do
-        include IO::WaitReadable
-      end
-      allow(socket).to receive(:read_nonblock).and_raise(wait_readable_exception)
+    it "should put PUBLISH messages on to the read queue following an IO::WaitReadable exception",
+      :if => OpenSSL::SSL::SSLSocket.respond_to?(:read_nonblock) do
+      allow(socket).to receive(:read_nonblock).and_raise(IO::WaitReadable)
       socket.write("\x30\x0e\x00\x05topicpayload")
       socket.rewind
       client.send(:receive_packet)