Overview of Networking

Over the next couple days we are going to look at how to write networking Apps, in Android, iPhone, and Phone 7.
A group of interconnected computers is a network.
The main network you are probably familiar with, the internet, is based on a layered architecture called the TCP/IP stack.
It consists of the following layers:
- Link Layer -- this layer is concerned with how the medium through which bits are actually sent is manipulated to send 1 and 0s (physical layer) as well as concerned with protocols to communicate between hosts in a local area network. For example, how signalling is done on a wire, radio, etc; you might use ARP and DHCP to map between IP and physical address of a host or to assign it.
- Internet Layer -- consists of the internet protocol (IP) used to send packets between hosts on the network.
- Transport Layer -- consists of a protocols such as UDP or TCP to allows connections over which data can be sent between hosts on the network. Uses IP underneath to implement the connections
- Application Layer -- consist of protocols like HTTP, FTP, SMTP, IMAP, POP, DNS, SSH, etc. which use TCP or UDP to give functionality to some application like a browser, mail client etc.

Clients and Servers

We will mainly be concerned with application protocol which are built on top of the transport layer.
One common model used in the transport layer is that of client and server machines on a network.
A server machine is identified on the internet by some IP address 130.65.86.46. Often we can find this IP by using a domain name lookup based on an easy to remember name such as www.cs.sjsu.edu. To do this we send this name to a domain name system (DNS) server that we know the IP address of, and that DNS server send back a record containing the IP address of the machine we are looking for.
In the server-client set-up, the server at a given IP address has processes running in the background called daemons which are listening all the time for connection requests from clients on a particular port number.
Port numbers are two bytes, some commonly used numbers are 80 (HTTP), 443 (HTTPS), 20 and 21 (FTP), 22 (SSH), 25 (SMTP).
Once a connection request comes into the server on a given port, the corresponding daemon can choose to accept it, and if so, a connection is established. Then the application layer protocol is typically used for the client to get or send data to the server.
For example if the client was a web browser, it might connect to port 80 on machine 130.65.86.46 and transmit to that server the following bytes:
```
GET / HTTP/1.0 newline
newline
```

The server might then respond by transmitting back to the client:

HTTP/1.1 200 OK
Date: Wed, 07 Oct 2009 18:11:01 GMT
Server: Apache/2.2.0 (Fedora)
Last-Modified: Mon, 17 Nov 2008 23:09:56 GMT
ETag: "f5678-2723-ad5ef900"
Accept-Ranges: bytes
Content-Length: 10019
Connection: close
Content-Type: text/html

...CS Department homepage

Checking Network Status

Android provides utilities for determining the device configuration and status of the network service.
This is typically done using the ConnectivityManager class which is used to determine whether there is any network connectivity and also to get notifications of changes to the network.

As an example, after importing android.net.*; android.content.*; android.util.*; the onStart() method of a subclass of Activity could use this class as follows:

@Override
public void onStart()
{
   super.onStart();
   ConnectivityManager cMgr = (ConnectivityManager)
      this.getSystemService(Context.CONNECTIVITY_SERVICE);
   NetworkInfo netInfo = cMgr.getActiveNetworkInfo();
   this.status.setText(netInfo.toString());
}

The output will say things like: type: Mobile, state: CONNECTED/CONNECTED, reason...
The netInfo object has methods like isAvailable, isConnected it also has a getState method.
Once you are connected you can use the IP network.

In order to get this to work you need to have the correct permissions set in the AndroidManifest.xml:

<uses-permission android:name="android.permission.INTERNET"></uses-permission>
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE">
The first is for general networking, the second is for the actual info we have above.

Creating a Server Socket

There are two devices involved in the client server architecture: the client and the server.
The mobile phone will typically be the client. So in order to test anything one typically wants to write a server as some Java program on the desktop.

The basic template for a server which listens on some port is:

import java.io.*;
import java.net.*;

public final class MyServer extends Thread
{
   private static final int PORT=8889;
   private static final int NUM_CONNECT=1;

   private MyServer() {}

   public static void main(String args[])
   {
      MyServer myServer = new MyServer();
      if(myServer !=null) {myServer.start();}
   }

   public void run()
   {
      try
      {
         ServerSocket server = new ServerSocket(PORT, NUM_CONNECT);
         Socket client = server.accept();
         
         BufferedReader reader = new BufferedReader(
            new InputStreamReader(client.getInputStream()));

         BufferedWriter writer = new BufferedWriter(
            new OutputStreamWriter(client.getOutputStream()));

         // do some reading and writing
      }
      catch(IOException ie)
      {
         ie.printStackTrace();
      }
   }
}

Quiz

Which of the following is true?

NSOpenTimer is used to schedule a callback at a particular time on iPhone.
Core Data is used to handle object relational mappings on iPhone.
To make a TCP connection it suffices to know the IP address of where you are connecting to.

Communicating with a Server

On your phone, you would then want code that could communicate with this server.

An example of how you might set this up is:

package org.pollett;

import android.app.Activity;
import android.os.Bundle;
import android.net.*;
import android.content.*;
import android.util.*;

public class MyClient extends Activity
{
   public void onCreate(Bundle savedInstanceState) 
   {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
 
        this.socketButton.setOnClickListener(new OnClickListener)() {
        public void onClick(final View v) {
           socketOutput.setText("");
           String output = callSocket(ipAddress.getText().toString(),
             port.getText().toString(),
             socketInput.getText().toString());
           socketOutput.setText(output);
        } 

       }
   }

   private String callSocket(String ip, String port, String socketData) {
      Socket socket = null;
      BufferedWriter writer = null;
      BufferedReader reader =null;
      String output = null;

      try{
         socket = new Socket(ip, Integer.parseInt(port));
         reader = new BufferedReader(
            new InputStreamReader(socket.getInputStream()));

         writer = new BufferedWriter(
            new OutputStreamWriter(socket.getOutputStream()));

         writer.write("hello world"+socketData+"\n");
         writer.flush();
         output = reader.readLine();
       
  
      }
      catch(Exception e){}
      return output;
   }

}

HTTP

One of the most common protocols implemented on top of TCP sockets is HTTP, the hypertext transfer protocol.
It is what is used to get web pages from a web server.
Today we begin by look at what facilities Android has for requesting web pages.

WebView

The easiest way to just view a web-page in Android is to:

Add the line:

 <uses-permission android:name="android.permission.INTERNET"></uses-permission>

to the manifest file

Add a WebView to our layout:

<WebView  
    android:id="@+id/webview"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
    />

Set the web page of the view in onCreate. (Need to import package android.webkit.*) :

webview = (WebView) findViewById(R.id.webview);
webview.getSettings().setJavaScriptEnabled(true);
webview.loadUrl("http://www.pollett.org/");

It should be noted that both the browsers in Android and iPhone are built off of webkit.

More on WebView

By default, links clicked on out of our WebView will be handled by the Android web browser.

To handle them ourselves, we could write a subclass of WebViewClient and override shouldOverrideUrlLoading:

private class MyWebViewClient extends WebViewClient {
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        view.loadUrl(url);
        return true;
    }
}

Then we set the WebViewClient of our WebView with a line like:
```
webview.setWebViewClient(new MyWebViewClient());
```

A Lower Level Way to Request a Page

One common reason to use HTTP is make use of a web service.
One might make a request of the form:
```
URL/service_name/method_name/?arg1=value1&arg2=value2...
```
which requests from the given URL the given method of the given web service with the given arguments.
The response is typically an XML or JSON document which is the output of calling the method.
We typically want to use data from this document, but we don't want to display it in a WebView.
This calls for a lower level way of dealing with the web.

Request a Page Using java.net

Using android.net, we could write code like:

String location="URL/service_name/method_name/?arg1=value1&arg2=value2";
String result = null;
try {
   URL url = new URL(location);
} catch (MalformedURLException e) {
  //handle somehow
}
if(url != null) {
   try {
      HttpURLConnection urlConn =
         (HttpURLConnection) url.openConnection();

      BufferedReader in =
         new BufferedReader(
            new InputStreamReader(
               urlConn.getInputStream()));
      String inputLine;
      while((inputLine = in.readLine()) != null)
      {
         result += "\n" + inputLine;
      }
   }
   catch (IOException e) {
   // handle somehow
   }

   return result;
}
return null;

Using a WebBrowser in Phone 7

We are next going to look at doing some of the analogous things for Android on Phone 7.
We are going to create an app that has a TextBox, two buttons and a WebBrowser.
When the Go button is clicked the url given in the TextBox is loaded into the WebBrowser. The contents of the TextBox are also saved to a file.
If someone clicks on Go Saved, it reloads the data from the flat file and goes to that web site.

MainPage.xaml

<phone:PhoneApplicationPage 
    x:Class="WindowsPhoneApplication4.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:phone="clr-namespace:Microsoft.Phone.Controls;assembly=Microsoft.Phone"
    xmlns:shell="clr-namespace:Microsoft.Phone.Shell;assembly=Microsoft.Phone"
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
    mc:Ignorable="d" d:DesignWidth="480" d:DesignHeight="768"
    FontFamily="{StaticResource PhoneFontFamilyNormal}"
    FontSize="{StaticResource PhoneFontSizeNormal}"
    Foreground="{StaticResource PhoneForegroundBrush}"
    SupportedOrientations="Portrait" Orientation="Portrait"
    shell:SystemTray.IsVisible="True">

    <!--LayoutRoot is the root grid where all page content is placed-->
    <Grid x:Name="LayoutRoot" Background="Transparent">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
        </Grid.RowDefinitions>

        <!--TitlePanel contains the name of the application and page title-->
        <StackPanel x:Name="TitlePanel" Grid.Row="0" Margin="12,17,0,28">
            <TextBlock x:Name="ApplicationTitle" Text="Browser Demo" Style="{StaticResource PhoneTextNormalStyle}"/>
        </StackPanel>

        <!--ContentPanel - place additional content here-->
        <Grid x:Name="ContentPanel" Grid.Row="1" Margin="12,0,12,0">
            <Button Content="Go" Height="72" HorizontalAlignment="Left" Margin="308,-16,0,0" Name="button1" VerticalAlignment="Top" Width="160" Click="button1_Click" />
            <phone:WebBrowser HorizontalAlignment="Left" Margin="12,116,0,0" Name="webBrowser1" VerticalAlignment="Top" Height="580" Width="444" />
            <Button Content="Go Saved" Height="72" HorizontalAlignment="Left" Margin="155,50,0,0" Name="button2" VerticalAlignment="Top" Width="160" Click="button2_Click" />
        </Grid>
        <TextBox Grid.RowSpan="2" Height="73" HorizontalAlignment="Left" Margin="12,56,0,0" Name="textBox1" Text="http://www.pollett.org" VerticalAlignment="Top" Width="330"  />
    </Grid>


</phone:PhoneApplicationPage>

MainPage.xaml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;
using Microsoft.Phone.Controls;
using System.IO.IsolatedStorage;
using System.IO;

namespace WindowsPhoneApplication4
{
    public partial class MainPage : PhoneApplicationPage
    {
        // Constructor
        public MainPage()
        {
            InitializeComponent();
        }

        /// 
        /// When the 'Go' button is clicked, navigate to the web site.
        /// Save url in storeurl.txt
        /// 
        private void button1_Click(object sender, RoutedEventArgs e)
        {
            string site;
            site = textBox1.Text;
            webBrowser1.Navigate(new Uri(site, UriKind.Absolute));
            using (var appStorage = IsolatedStorageFile.GetUserStoreForApplication())

            using (var file = appStorage.OpenFile("storeurl.txt", FileMode.OpenOrCreate))

            using (var writer = new StreamWriter(file))
            {
                writer.Write(site);
            }            
        }
        /// 
        /// When the 'Go Saved' button is clicked, read from
        /// storeurl.txt and navigate to the web site.
        /// 
        private void button2_Click(object sender, RoutedEventArgs e)
        {
            //using means we call Dispose() automatically when done with the object
            // if use var rather than a type compiler will use type inference
            using (var appStorage = IsolatedStorageFile.GetUserStoreForApplication())

            using (var file = appStorage.OpenFile("storeurl.txt", FileMode.Open))
            {

                using (var reader = new StreamReader(file))
                {
                    textBox1.Text = reader.ReadLine();
                    webBrowser1.Navigate(new Uri(textBox1.Text, UriKind.Absolute));
                }

            }
        }
    }
}

Networking Android, Phone7

Outline