Use a custom SSLContext in order to allow a specific SSL/TLS versio…

…ns to be configured.

 Closes owagner#12

README.md

@@ -129,14 +129,20 @@ Examples:
   Note that using SSL connections requires additional configuration at the JVM level. For example, the
   broker's certificate needs to be verifiable by the JVM using it's CA cert store.
 
+- mqtt.sslVersion
+
+  Optional, define the SSL version that should be used when connecting to the MQTT broker.
+  Possible values are limited by the executing JVM, but could be one of:
+  SSL, SSLv2, SSLv3, TLS, TLSv1, TLSv1.1, TLSv1.2
+
 - mqtt.clientid
 
   ClientID to use in the MQTT connection. Defaults to "hm2mqtt".
 
 - mqtt.topic
 
   The topic prefix used for publishing and subscribing. Defaults to "hm/".
-^
+
 - mqtt.username
 - mqtt.password
 

src/main/java/com/tellerulam/hm2mqtt/MQTTHandler.java

@@ -3,10 +3,13 @@
 import java.io.*;
 import java.math.*;
 import java.nio.charset.*;
+import java.security.*;
 import java.util.*;
 import java.util.concurrent.*;
 import java.util.logging.*;
 
+import javax.net.ssl.*;
+
 import org.eclipse.paho.client.mqttv3.*;
 import org.eclipse.paho.client.mqttv3.persist.*;
 
@@ -203,6 +206,25 @@ private void doConnect()
 			copts.setPassword(password.toCharArray());
 			L.fine("Using MQTT username "+username);
 		}
+		String sslVersion=System.getProperty("hm2mqtt.mqtt.sslVersion");
+		if (sslVersion!=null)
+		{
+			try
+			{
+				SSLContext context = SSLContext.getInstance(sslVersion);
+				// TODO Maybe use custom trust manager for CA certs https://gist.github.com/sharonbn/4104301
+				context.init(null, null, null);
+				copts.setSocketFactory(context.getSocketFactory());
+			}
+			catch(NoSuchAlgorithmException nsae)
+			{
+				L.log(Level.WARNING, "Error creating SSLContext, check your configuration", nsae);
+			}
+			catch(KeyManagementException kme)
+			{
+				L.log(Level.WARNING, "Error initializing SSLContext, check your configuration", kme);
+			}
+		}
 		try
 		{
 			mqttc.connect(copts);