Creating CFSockets

Making sockets on the iPhone is a little bit harder than on Android.
We will only consider the case of writing a socket client not a server.
The socket API is based-off Berkeley sockets but with its own function names and not too many examples.
The basics steps we need are:
- Create a socket context
- Write a callback function
- Set up the address to connect to
- Connect and wait for the connection to complete in a run loop

Description of Our App

Our app connects to a server written in Java.
We send the message "Hello\n".
The Java server sends back a colon separated list of cities
The iPhone app displays these cities in a table.

Code of Server we will connect to

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()));

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

         String line = reader.readLine();

         System.out.println("Hello"+line);

         if(line.equals("HELLO"))
         {
            writer.print("Chicago:New York:San Francisco:");
            writer.print("Chicago:New York:San Francisco:");
            writer.println("Chicago:New York:San Francisco\n");
         }
         writer.flush();
      }
      catch(IOException ie)
      {
         ie.printStackTrace();
      }
   }
}

Quiz

Which of the following is true?

To handle links clicked in a WebView on Android we can create a subclass of WebViewClient and add an object of this subclass to our WebView using setViewClient.
Phone 7 exposes a socket API which looks like a C Sharp version of the Java Socket API.
LinQ syntax makes use of where from select clauses.

Set up the socket

Sockets on the iPhone are a C library, so the function calls are C.

Here is the code we use to set-up the socket:

CFSocketContext context = { 0, msg, NULL, NULL, NULL };
	
	
CFSocketRef client = CFSocketCreate(NULL, PF_INET, SOCK_STREAM, IPPROTO_TCP,
     kCFSocketConnectCallBack, (CFSocketCallBack)ConnectCallBack, &context);

The CFSocketContext struct looks like:

struct CFSocketContext {
   CFIndex version; // must be 0
   void *info; // data to send
   CFAllocatorRetainCallBack retain; // callback called when do CFRetain, CFRelease,CFCopy
   CFAllocatorReleaseCallBack release;
   CFAllocatorCopyDescriptionCallBack copyDescription;
};

The arguments to CFSocketCreate are:

CFSocketRef CFSocketCreate (
   CFAllocatorRef allocator,
   SInt32 protocolFamily, //PF_INET is IPv4
   SInt32 socketType, 
   SInt32 protocol,
   CFOptionFlags callBackTypes, //when we want to be called back
   CFSocketCallBack callout, //our callback
   const CFSocketContext *context
);

Set up the address to connect to:

Next we set up the address and port we want to connect to

struct sockaddr_in theName;
struct hostent *hp;
CFDataRef addressData;
	
theName.sin_port = htons(8889);
theName.sin_family = AF_INET; //what kind in internet addresses to use; want IP
	
hp = gethostbyname("pollett.org");
if( hp == NULL ) {
   return;
}

memcpy( &theName.sin_addr.s_addr, hp->h_addr_list[0], hp->h_length );
	
addressData = CFDataCreate( NULL, (UInt8 *)&theName, (CFIndex)sizeof( struct sockaddr_in ) );

Set up our Run Loop to wait for the connection to establish

We're ready to connect. But it might take a while for the connection to establish so we want to set up how we wait for this:

CFSocketConnectToAddress(client, addressData, 1); //connect; 1 second timeout

CFRunLoopSourceRef sourceRef =
		CFSocketCreateRunLoopSource(kCFAllocatorDefault, client, 0);
CFRunLoopAddSource(CFRunLoopGetCurrent(), sourceRef, kCFRunLoopCommonModes);
CFRelease(sourceRef);
CFRunLoopRun();

Our Callback Function

The callback is a C function so is not within a class definition. So we just put it outside of the implementation block of the class that is going to use it.

Here is the code:

CFSocketNativeHandle sock;
UInt8 buffer[1024];

void ConnectCallBack(
   CFSocketRef socket,
   CFSocketCallBackType type,
   CFDataRef address,
   const void *data,
   void *info)
{
    char *msg = info;
	
    NSLog(@"%s\n", msg);

    sock = CFSocketGetNative(socket);
	
    send(sock, msg, strlen(msg)+1, 0);
    recv(sock, buffer, sizeof(buffer), 0);
    NSLog(@"Got: %s \n", buffer);

	
    CFRunLoopStop(CFRunLoopGetCurrent()); //return execution to our program
    return;
}

Using Streams

Rather than use send and recv another way you can read and write from a socket connection is to use streams.

Using the native socket we had on the last slide, we could get a stream with code like:

CFReadStreamRef readStream = NULL;
CFWriteStreamRef writeStream = NULL;

CFStreamCreatePairWithSocket(kCFAllocatorDefault, sock, &readStream, &writeStream);

Then one can use methods like: CFReadStreamOpen, CFReadStreamClose, CFReadStreamRead, CFWriteStreamOpen, CFWriteStreamClose, CFWriteStreamWrite to read and write using streams.

One can also convert CFReadStreamRef's and CFWriteStreamRef's to Objective-C objects:

NSOutputStream *networkOutputStream = (NSOutputStream *) writeStream; 
NSInputStream *networkInputStream =(NSInputStream *) readStream;

and then work in Objective-C land.

Tables

Tables in iPhone development are used for several things:
- In Mail, to list our mail accounts, mail folders, and subfolders.
- In Settings, to display all the preferences you can change. Notice these are grouped and each group is viewed as a table row (section).
- etc.

Tables Interface Builder

Tables are defined using the class UITableView.
Each cell in a table is given by a UITableViewCell.
Tables get their configuration info by two objects set on them: an object implementing the UITableViewDelegate protocol and an object implementing the UITableViewDataSource protocol.
To start our project, we can create a view-based iPhone app.
Then fire up Interface Builder and drag a Table View over to the view.
There will seem to be default data populating the table (ignore this).
In the Connection Inspector, drag both the dataSource and delegate of the Table View to the File's Owner.

Tables Code

Aside: We can make the IDE and lines between methods it lists in its drop down by using lines like:
```
#pragma mark -
#pragma mark Table View Controller Methods
```

Here is our code to set up the data source for the table cells (from viewDidLoad)

NSString *data = [[NSString alloc] initWithCString: (char*)buffer encoding: NSASCIIStringEncoding];


NSArray *array = [data componentsSeparatedByString:@":"];
	
	
[array retain];
self.listData = array;
[array release];
[data release];

Tables Code

Lastly, we need to actually do the drawing in cells:

-(UITableViewCell *)tableView: (UITableView *)tableView
	cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
	static NSString *SimpleTableIdentifier = @"SimpleTableIdentifier";
	
	UITableViewCell *cell= [tableView dequeueReusableCellWithIdentifier:SimpleTableIdentifier];
	
	if(cell == nil) {
		cell = [[[UITableViewCell alloc] initWithFrame:CGRectZero
	   reuseIdentifier: SimpleTableIdentifier] autorelease];
	}
	
	NSUInteger row = [indexPath row];
	
	cell.textLabel.text = [listData objectAtIndex:row];
	return cell;
}

Rock'em Sock'em Sockets and Tables

Outline

Creating CFSockets

Description of Our App

Code of Server we will connect to

Quiz

Set up the socket

Set up the address to connect to:

Set up our Run Loop to wait for the connection to establish

Our Callback Function

Using Streams

Tables

Tables Interface Builder

Tables Code

Tables Code