iPhone ushers us back to heavy-weight apps

OK, if you can call an iPhone app, heavy weight… Just when you thought the rest of the cool apps would all run in a browser, here comes the iPhone. Before this, I thought mobile apps were pretty silly and too much of a pain to distribute. I tried my hand at J2ME, but the carriers have distribution of those really locked down and it is hard for anyone at a grass roots level to get a J2ME app distributed. All of the cool features require special signing certificates that are very carrier specific. (damn you, mobile carriers!!)
In comes the iPhone. Here is a mobile platform that offers a very consistent set of features and has a very large installed base. It has a huge cool factor (yes, even this long after it originally launched). The app store really changed the model for distributing mobile applications. Now, anyone (given a $99 entry fee) can become an iPhone developer. OK, I’m hearing people say $99 isn’t all, because you need to invest at least $1400 (rough figure) for a development box and device. This is exactly what I started with, and 20″ iMac and iPod touch. OK, but you don’t have to be anyone special to sign up, that’s the point. Anyone with about 1500 bucks and a little skill, creativity and ambition can become an iPhone developer. By all accounts, a lot of people have! 800 million app downloads to 30 million devices and 25,000 apps available in the app store! Holy cow! Now, that’s a markeplace! Developers keep 70% of the revenue. Good for Apple, good for us.
Today, I was watching a video on crunchgear about the NIN iPhone app and think this really drives home something I’ve been thinking about for a while. People don’t bother doing a really nice web app that runs on the iPhone, they write an iPhone app specifically for their service/movie/band, whatever. I recommend watching the video, just to see the really excellent integration of features on the iPhone and then in their regular web site. Very cool stuff!
I wonder, did the lack of Flash on the iPhone help boost iPhone apps? I certainly didn’t hurt. With Flash, there are a lot of developers who would have been ready to build apps sized for the iPhone. There would have been some really nifty, media-heavy/interactive apps built and deployed over the web (no need for the app store). The one thing that would have been missing is the tight integration with iPhone OS features. Things like geo-location, access to camera/photos/music, accelerometer, etc. I think Flash would have meant fewer native iPhone apps, but the native apps would have been built anyway.
I say, welcome back to the client applications! With a well-managed distribution/update system in place, client apps can be managed very easily. The app store does that reasonably well. I just hope I can build the next iShoot!

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Flash Socket Code and crossdomain Policy Serving

I’ve just spent the past day trying to get my flash app talking to another device on my network via socket 23. I found some sample telnet code (which operates on port 23) and allowed me to “talk” to the RFID reader. It worked fine as a new project in Flex Builder and being served from a local file. The moment I served the application from a web server (tomcat) on my laptop, I get crossdomain issues. Flash won’t open a socket that is different from the one that served your application unless that socket authorizes it. I will spare you the details that took many hours of my day. If you’re trying to talk to another web server on a different port, no problem.. just put the crossdomain.xml file on that server that authorizes the connection. In this case, I was trying to connect to another host and another port (which runs telnet, not http). The RFID reader can’t be modified to serve up a crossdomain.xml file, so I had to get creative.

My solution was to run a TCP proxy on my web server machine that proxied requests to the RFID reader. I made it listen on port 8023 and forward requests to 23 on the RFID reader. This was the start because I still got errors about that localhost:8023  not being authorized. It turns out that when you try the connection, flash connects to the socket and sends 23 bytes which contain “<policy-file-request/>”. Flash expects whatever is running at that port to respond with the policy string (that would have been in the crossdomain.xml file). So, I modified this little proxy class I got off the internet to recognize the proxy request and respond with a proxy string (null terminated.. that is very important!). Once I had this set up right, I was able to communicate from my flash app to my RFID reader. Not the most elegant solution, but this is something temporary for a demo.

 

To run the code below, compile with javac and invoke “java -classpath <class.file.location> ProxyThread 8023 192.168.1.39 23”. Those options are what I used to talk to my RFID reader, but you’ll likely use different values.

import java.net.*;
import java.io.*;
 
/*
  Java Transparent Proxy
  Copyright (C) 1999 by Didier Frick (http://www.dfr.ch/)
  This software is provided under the GNU general public license (http://www.gnu.org/copyleft/gpl.html).
*/

public class ProxyThread extends Thread {
     protected class StreamCopyThread extends Thread {
	private Socket inSock;
	private Socket outSock;
	private boolean done=false;
	private StreamCopyThread peer;
	private boolean inFromLocal;	// in from local port
	private OutputStream out;
 
	private String policy = "<cross-domain-policy>\n<allow-access-from domain=\"*\" to-ports=\"8023\"/>\n</cross-domain-policy>";
 
	public StreamCopyThread(Socket inSock, Socket outSock, boolean in) {
	    this.inSock=inSock;
	    this.outSock=outSock;
	    this.inFromLocal = in;
	}
 
	public void sendPolicy() {
		try {
			out.write(policy.getBytes());
			System.err.println("Sent policy");
		} catch (IOException ex) {
			System.err.println("Error sending policy file");
		}
	}
 
	public void run() {
	    byte[] buf=new byte[bufSize];
	    int count=-1;
	    try {
		InputStream in=inSock.getInputStream();
		out=outSock.getOutputStream();
		try {
		    while(((count=in.read(buf))>0)&&!isInterrupted()) {
		    	if (inFromLocal && count==23 && new String(buf).startsWith("<policy-file-request/>")) {
				// send policy file back.. don't forward this to other port
				System.err.println("Got policy request");
				peer.sendPolicy();
			}
			else {
				out.write(buf,0,count);
				//System.err.println(count+" bytes "+(inFromLocal?"sent":"received"));
			}
		    }
		} catch(Exception xc) {
		    if(debug) {
			// FIXME
			// It's very difficult to sort out between "normal"
			// exceptions (occuring when one end closes the connection
			// normally), and "exceptional" exceptions (when something
			// really goes wrong)
			// Therefore we only log exceptions occuring here if the debug flag
			// is true, in order to avoid cluttering up the log.
			err.println(header+":"+xc);
			xc.printStackTrace();
		    }
		} finally {
		    // The input and output streams will be closed when the sockets themselves
		    // are closed.
		    out.flush();
		}
	    } catch(Exception xc) {
		err.println(header+":"+xc);
		xc.printStackTrace();
	    }
	    synchronized(lock) {
		done=true;
		try {
		    if((peer==null)||peer.isDone()) {
			// Cleanup if there is only one peer OR
			// if _both_ peers are done
			inSock.close();
			outSock.close();
		    }
		    else 
			// Signal the peer (if any) that we're done on this side of the connection
			peer.interrupt();
		} catch(Exception xc) {
		    err.println(header+":"+xc);
		    xc.printStackTrace();
		} finally {
		    connections.removeElement(this);
		}
	    }
	}
 
	public boolean isDone() {
	    return done;
	}
    
	public void setPeer(StreamCopyThread peer) {
	    this.peer=peer;
	}
     }

    // Holds all the currently active StreamCopyThreads
    private java.util.Vector connections=new java.util.Vector();
    // Used to synchronize the connection-handling threads with this thread
    private Object lock=new Object();
    // The address to forward connections to
    private InetAddress dstAddr;
    // The port to forward connections to
    private int dstPort;
    // Backlog parameter used when creating the ServerSocket
    protected static final int backLog=100;
    // Timeout waiting for a StreamCopyThread to finish
    public static final int threadTimeout=2000; //ms
    // Linger time
    public static final int lingerTime=180; //seconds (?)
    // Size of receive buffer
    public static final int bufSize=2048;
    // Header to prepend to log messages
    private String header;
    // This proxy's server socket
    private ServerSocket srvSock;
    // Debug flag
    private boolean debug=false;
 
    // Log streams for output and error messages
    private PrintStream out;
    private PrintStream err;
 
    private static final String 
	argsMessage="Arguments: ( [source_address] source_port dest_address dest_port ) | config_file";
    private static final String 
	propertyPrefix="proxy";

 
    public ProxyThread(InetAddress srcAddr,int srcPort,
		       InetAddress dstAddr,int dstPort, PrintStream out, PrintStream err) 
	throws IOException {
	this.out=out;
	this.err=err;
	this.srvSock=(srcAddr==null) ? new ServerSocket(srcPort,backLog) :  
	    new ServerSocket(srcPort,backLog,srcAddr);
	this.dstAddr=dstAddr;
	this.dstPort=dstPort;
	this.header=(srcAddr==null ? "" : srcAddr.toString())+":"+srcPort+" <-> "+dstAddr+":"+dstPort;
	start();
    }
 
    public void run() {
	out.println(header+" : starting");
	try {
	    while(!isInterrupted()) {
		Socket serverSocket=srvSock.accept();
		try {
		    serverSocket.setSoLinger(true,lingerTime);
		    Socket clientSocket=new Socket(dstAddr,dstPort);
		    clientSocket.setSoLinger(true,lingerTime);
		    StreamCopyThread sToC=new StreamCopyThread(serverSocket,clientSocket, true);
		    StreamCopyThread cToS=new StreamCopyThread(clientSocket,serverSocket, false);
		    sToC.setPeer(cToS);
		    cToS.setPeer(sToC);
		    synchronized(lock) {
			connections.addElement(cToS);
			connections.addElement(sToC);
			sToC.start();
			cToS.start();
		    }
		} catch(Exception xc) {
		    err.println(header+":"+xc);
		    if(debug)
			xc.printStackTrace();
		}
	    }
	    srvSock.close();
	} catch(IOException xc) {
	    err.println(header+":"+xc);
	    if(debug)
		xc.printStackTrace();
	} finally {
	    cleanup();
	    out.println(header+" : stopped");
	}
    }
 
     private void cleanup() {
	synchronized(lock) {
	    try {
		while(connections.size()>0) {
		    StreamCopyThread sct=(StreamCopyThread)connections.elementAt(0);
		    sct.interrupt();
		    sct.join(threadTimeout);
		}
	    } catch(InterruptedException xc) {
	    }
	}
    }
 
    private static ProxyThread addProxy(String src,String srcPort, String dst, String dstPort,
					PrintStream out, PrintStream err) throws
					UnknownHostException, IOException
    {
	InetAddress srcAddr=(src==null) ? null : InetAddress.getByName(src);
	return new ProxyThread(srcAddr,Integer.parseInt(srcPort),
			       InetAddress.getByName(dst),Integer.parseInt(dstPort),out,err);
    }
 
    private static java.util.Vector parseConfigFile(String fileName,PrintStream out,PrintStream err) throws 
        FileNotFoundException, IOException, UnknownHostException
    {
	java.util.Vector result=new java.util.Vector();
	FileInputStream in=new FileInputStream(fileName);
	java.util.Properties props= new java.util.Properties();
	props.load(in);
	in.close();
	for(int i=0;;i++) {
	    String srcAddr=props.getProperty(propertyPrefix+"."+i+".sourceAddr");
	    String srcPort=props.getProperty(propertyPrefix+"."+i+".sourcePort");
	    if(srcPort==null)
		break;
	    String dstAddr=props.getProperty(propertyPrefix+"."+i+".destAddr");
	    String dstPort=props.getProperty(propertyPrefix+"."+i+".destPort");
	    if(dstAddr==null) {
		throw new IllegalArgumentException("Missing destination address for proxy "+i);
	    }
	    if(dstPort==null) {
		throw new IllegalArgumentException("Missing destination port for proxy "+i);
	    }
	    result.addElement(addProxy(srcAddr,srcPort,dstAddr,dstPort,out,err));
	}
	return result;
    }
 
    static java.util.Vector parseArguments(String[] argv,PrintStream out,PrintStream err) throws
        FileNotFoundException, IOException, UnknownHostException
    {
	java.util.Vector result=null;
	int argBase=0;
	String src=null;
	if(argv.length>1) {
	    if(argv.length>3) {
		argBase=1;
		src=argv[0];
	    }
	    result=new java.util.Vector();
	    result.addElement(addProxy(src,argv[argBase++],argv[argBase++],argv[argBase++],out,err));
	} else if(argv.length==1) {
	    result=parseConfigFile(argv[0],out,err);
	} else {
	    throw new IllegalArgumentException(argsMessage);
	}
	return result;
    }
 
    public static void main(String[] argv) throws Exception {
	System.out.println("Java Transparent Proxy");
	System.out.println("Copyright (C) 1999 by Didier Frick (http://www.dfr.ch/)");
	System.out.println("This software is provided under the GNU general public license"+
			   " (http://www.gnu.org/copyleft/gpl.html)");
	try {
	    parseArguments(argv,System.out,System.err);
	} catch(IllegalArgumentException xc) {
	    System.err.println(xc.getMessage());
	    System.exit(1);
	}
    }
}
The initial ProxyThread code came from here: http://www.dfr.ch/en/proxy.html