In today’s action, I wrote a new Google Cloud Messaging (GCM) server interface to the GCM Cloud Connection Server (CCS) via XMPP. GCM CCS offers several benefits over GCM HTTP including one of my key requirements, bidirectional messaging.

My app server didn’t yet have a XMPP interface, so I followed Google’s sample and plugged in Smack. Then the fun began. I immediately started getting exceptions (see Smackdowns below). These varied based on state and configuration, but basically the result was the same: the GCM CCS server was abruptly closing the connection during authentication. How rude; Smack was getting smacked down.

I dug in but ran into several red herrings. For example, Smack’s stream headers didn’t match Google’s doc (no tag close); Google’s doc is wrong. I debugged Smack, tried different Smack versions, tried other XMPP clients, tweaked configurations, studied XMPP protocols and SASL authentication, and updated authentication parameters and allowed IPs. Ultimately, I had a minor error in one of the authentication parms. I found it by Base64-decoding the auth value in Google’s example and comparing it to my own traces.

This would have been a quick fix if CCS had just given an authentication error message rather than just slamming the door. It must be a security thing. Oh well, on to the next adventure.

Smackdowns 

No response from the server.: 
	at org.jivesoftware.smack.NonSASLAuthentication.authenticate(NonSASLAuthentication.java:73)
	at org.jivesoftware.smack.SASLAuthentication.authenticate(SASLAuthentication.java:357)
	at org.jivesoftware.smack.XMPPConnection.login(XMPPConnection.java:221)

java.net.SocketException: Connection closed by remote host
	at com.sun.net.ssl.internal.ssl.SSLSocketImpl.checkWrite(Unknown Source)
	at com.sun.net.ssl.internal.ssl.AppOutputStream.write(Unknown Source)
	at sun.nio.cs.StreamEncoder.writeBytes(Unknown Source)
	at sun.nio.cs.StreamEncoder.implFlushBuffer(Unknown Source)
	at sun.nio.cs.StreamEncoder.implFlush(Unknown Source)
	at sun.nio.cs.StreamEncoder.flush(Unknown Source)
	at java.io.OutputStreamWriter.flush(Unknown Source)
	at java.io.BufferedWriter.flush(Unknown Source)
	at org.jivesoftware.smack.util.ObservableWriter.flush(ObservableWriter.java:48)
	at org.jivesoftware.smack.PacketWriter.writePackets(PacketWriter.java:168)

java.io.EOFException: no more data available - expected end tag  to close start tag  from 
                                      line 1, parser stopped on END_TAG seen ...... @1:344
	at org.xmlpull.mxp1.MXParser.fillBuf(MXParser.java:3035)
	at org.xmlpull.mxp1.MXParser.more(MXParser.java:3046)
	at org.xmlpull.mxp1.MXParser.nextImpl(MXParser.java:1144)
	at org.xmlpull.mxp1.MXParser.next(MXParser.java:1093)
	at org.jivesoftware.smack.PacketReader.parsePackets(PacketReader.java:279)