AsyncSocket

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Socket描述了一个IP、端口对。它简化了程序员的操作，知道对方的IP以及PORT就可以给对方发送消息，再由服务器端来处理发送的这些消息。所以，Socket一定包含了通信的双发，即客户端（Client）与服务端（server）。

1）服务端利用Socket监听端口；

2）客户端发起连接；

3）服务端返回信息，建立连接，开始通信；

4）客户端，服务端断开连接。

1套接字（socket）概念

套接字（socket）是通信的基石，是支持TCP/IP协议的网络通信的基本操作单元。

应用层通过传输层进行数据通信时，TCP会遇到同时为多个应用程序进程提供并发服务的问题。多个TCP连接或多个应用程序进程可能需要通过同一个
TCP协议端口传输数据。为了**区别不同的应用程序进程和连接**，许多计算机操作系统为应用程序与TCP／IP协议交互提供了套接字(Socket)接口。应
用层可以和传输层通过Socket接口，区分来自不同应用程序进程或网络连接的通信，实现数据传输的并发服务。

2 建立socket连接

建立Socket连接至少需要一对套接字，其中一个运行于客户端，称为ClientSocket，另一个运行于服务器端，称为ServerSocket。

套接字之间的连接过程分为三个步骤：服务器监听，客户端请求，连接确认。

服务器监听：服务器端套接字并不定位具体的客户端套接字，而是处于等待连接的状态，实时监控网络状态，等待客户端的连接请求。

客户端请求：指客户端的套接字提出连接请求，要连接的目标是服务器端的套接字。为此，客户端的套接字必须首先描述它要连接的服务器的套接字，指出服务器端套接字的地址和端口号，然后就向服务器端套接字提出连接请求。

连接确认：当服务器端套接字监听到或者说接收到客户端套接字的连接请求时，就响应客户端套接字的请求，建立一个新的线程，把服务器端套接字的描述发
给客户端，一旦客户端确认了此描述，双方就正式建立连接。而服务器端套接字继续处于监听状态，继续接收其他客户端套接字的连接请求。

4、SOCKET连接与TCP连接

创建Socket连接时，可以指定使用的传输层协议，Socket可以支持不同的传输层协议（TCP或UDP），当使用TCP协议进行连接时，该Socket连接就是一个TCP连接。

5、Socket连接与HTTP连接

由于通常情况下Socket连接就是TCP连接，因此Socket连接一旦建立，通信双方即可开始相互发送数据内容，直到双方连接断开。但在实际网
络应用中，客户端到服务器之间的通信往往需要穿越多个中间节点，例如路由器、网关、防火墙等，大部分防火墙默认会关闭长时间处于非活跃状态的连接而导致
Socket 连接断连，因此需要通过轮询告诉网络，该连接处于活跃状态。

而HTTP连接使用的是“请求—响应”的方式，不仅在请求时需要先建立连接，而且需要客户端向服务器发出请求后，服务器端才能回复数据。

很多情况下，需要服务器端主动向客户端推送

iphone的标准推荐CFNetwork
C库编程.但是编程比较烦躁。在其它OS往往用类来封装的对Socket函数的处理。比如MFC的CAsysncSocket.在iphone也有类似于
开源项目.cocoa
AsyncSocket库, 官方网站:http://code.google.com/p/cocoaasyncsocket/ 它用来简化
CFnetwork的调用.

一.在项目引入ASyncSocket库

1.下载ASyncSocket库源码

2.把ASyncSocket库源码加入项目：只需要增加RunLoop目录中的AsyncSocket.h、AsyncSocket.m、AsyncUdpSocket.h和AsyncUdpSocket.m四个文件。

3.在项目增加CFNetwork框架

在Framework目录右健,选择Add-->Existing Files... ,
选择 CFNetwork.framework

二.TCP客户端

1. 在controller头文件定义AsyncSocket对象

import

import "AsyncSocket.h"

@interface HelloiPhoneViewController
: UIViewController {

UITextField * textField;

AsyncSocket * asyncSocket;

}

@property (retain, nonatomic) IBOutlet UITextField *textField;

(IBAction) buttonPressed: (id)sender;
(IBAction) textFieldDoneEditing: (id)sender;

@end

2.在需要联接地方使用connectToHost联接服务器

其中initWithDelegate的参数中self是必须。这个对象指针中的各个Socket响应的函数将被ASyncSocket所调用.

asyncSocket = [[AsyncSocket alloc] initWithDelegate:self];

NSError *err = nil;

if(![asyncSocket connectToHost:host on:port error:&err])

{

NSLog(@"Error: %@", err);

}

3.增加Socket响应事件

因为initWithDelegate把将当前对象传递进去，这样只要在当前对象方法实现相应方法.

4.关于NSData对象

无论SOCKET收发都采用NSData对象.它的定义是 http://developer.apple.com/library/mac
/#documentation/Cocoa/Reference/Foundation/Classes/NSData_Class/Reference/Reference.html

NSData主要是带一个(id)data指向的数据空间和长度 length.

NSString 转换成NSData 对象

NSData* xmlData = [@"testdata"
dataUsingEncoding:NSUTF8StringEncoding];

NSData 转换成NSString对象

NSData * data;

NSString *result = [[NSString alloc] initWithData:data
encoding:NSUTF8StringEncoding];

4.发送数据

AsyncSocket writeData 方法来发送数据，它有如下定义

- (void)writeData:(NSData *)data
withTimeout:(NSTimeInterval)timeout tag:(long)tag;

以下是一个实例语句.

NSData* aData= [@"test data" dataUsingEncoding:
NSUTF8StringEncoding];

[sock writeData:aData withTimeout:-1 tag:1];

在onSocket重载函数，有如定义采用是专门用来处理SOCKET的发送数据的：

-(void)onSocket(AsyncSocket *)sock didWriteDataWithTag:(long)tag

{

NSLog(@"thread(%),onSocket:%p didWriteDataWithTag:%d",[[NSThread
currentThread] name],

sock,tag);

}

5.接收Socket数据.

在onSocket重载函数，有如定义采用是专门用来处理SOCKET的接收数据的.

-(void) onSocket:(AsyncSocket *)sock didReadData:(NSData *)data
withTag:(long)tag

在中间将其转换成NSString进行显示.

NSString* aStr = [[NSString alloc] initWithData:data
encoding:NSUTF8StringEncoding];

NSLog(@"===%@",aStr);

[aStr release];

Asyncsocket的例子

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下面是用开源的库Asyncsocket的例子：////  SocketDemoViewController.h//  SocketDemo////  Created by xiang xiva on 10-7-10.//  Copyright 2010 __MyCompanyName__. All rights reserved.//#import <UIKit/UIKit.h>#import "AsyncSocket.h"#define SRV_CONNECTED 0#define SRV_CONNECT_SUC 1#define SRV_CONNECT_FAIL 2#define HOST_IP @"192.168.110.1"#define HOST_PORT 8080@interface SocketDemoViewController : UIViewController { UITextField *inputMsg; UILabel *outputMsg; AsyncSocket *client;}@property (nonatomic, retain) AsyncSocket *client;@property (nonatomic, retain) IBOutlet UITextField *inputMsg;@property (nonatomic, retain) IBOutlet UILabel *outputMsg;- (int) connectServer: (NSString *) hostIP port:(int) hostPort;- (void) showMessage:(NSString *) msg;- (IBAction) sendMsg;- (IBAction) reConnect;- (IBAction) textFieldDoneEditing:(id)sender;- (IBAction) backgroundTouch:(id)sender;@end////  SocketDemoViewController.m//  SocketDemo////  Created by xiang xiva on 10-7-10.//  Copyright 2010 __MyCompanyName__. All rights reserved.//#import "SocketDemoViewController.h"@implementation SocketDemoViewController@synthesize inputMsg, outputMsg;@synthesize client;/*// The designated initializer. Override to perform setup that is required before the view is loaded.- (id)initWithNibName:(NSString *)nibNameOrNil bundle:(NSBundle *)nibBundleOrNil {    self = [super initWithNibName:nibNameOrNil bundle:nibBundleOrNil];    if (self) {        // Custom initialization    }    return self;}*//*// Implement loadView to create a view hierarchy programmatically, without using a nib.- (void)loadView {}*/// Implement viewDidLoad to do additional setup after loading the view, typically from a nib.- (void)viewDidLoad {    //[super viewDidLoad]; [self connectServer:HOST_IP port:HOST_PORT]; //监听读取}// Override to allow orientations other than the default portrait orientation.- (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation {    return YES;}- (void)didReceiveMemoryWarning { // Releases the view if it doesn't have a superview.    [super didReceiveMemoryWarning]; // Release any cached data, images, etc that aren't in use.}- (void)viewDidUnload { self.client = nil; // Release any retained subviews of the main view. // e.g. self.myOutlet = nil;}- (int) connectServer: (NSString *) hostIP port:(int) hostPort{ if (client == nil) {  client = [[AsyncSocket alloc] initWithDelegate:self];  NSError *err = nil;  //192.168.110.128  if (![client connectToHost:hostIP onPort:hostPort error:&err]) {   NSLog(@"%@ %@", [err code], [err localizedDescription]);   UIAlertView *alert = [[UIAlertView alloc] initWithTitle:[@"Connection failed to host "           stringByAppendingString:hostIP]               message:[[[NSString alloc]initWithFormat:@"%@",[err code]] stringByAppendingString:[err localizedDescription]]                 delegate:self              cancelButtonTitle:@"OK"              otherButtonTitles:nil];   [alert show];   [alert release];   //client = nil;   return SRV_CONNECT_FAIL;  } else {   NSLog(@"Conectou!");   return SRV_CONNECT_SUC;  } } else {  [client readDataWithTimeout:-1 tag:0];  return SRV_CONNECTED; }}- (IBAction) reConnect{ int stat = [self connectServer:HOST_IP port:HOST_PORT]; switch (stat) {  case SRV_CONNECT_SUC:   [self showMessage:@"connect success"];   break;  case SRV_CONNECTED:   [self showMessage:@"It's connected,don't agian"];   break;  default:   break; }}- (IBAction) sendMsg{ NSString *inputMsgStr = self.inputMsg.text; NSString * content = [inputMsgStr stringByAppendingString:@"rn"]; NSLog(@"%a",content); NSData *data = [content dataUsingEncoding:NSISOLatin1StringEncoding]; [client writeData:data withTimeout:-1 tag:0]; //[data release]; //[content release]; //[inputMsgStr release]; //继续监听读取 //[client readDataWithTimeout:-1 tag:0];}#pragma mark -#pragma mark close Keyboard- (IBAction) textFieldDoneEditing:(id)sender{ [sender resignFirstResponder];}- (IBAction) backgroundTouch:(id)sender{ [inputMsg resignFirstResponder];}#pragma mark socket uitl- (void) showMessage:(NSString *) msg{ UIAlertView * alert = [[UIAlertView alloc]initWithTitle:@"Alert!"                                                    message:msg                                                   delegate:nil                                          cancelButtonTitle:@"OK"                                          otherButtonTitles:nil];    [alert show];    [alert release];}#pragma mark socket delegate- (void)onSocket:(AsyncSocket *)sock didConnectToHost:(NSString *)host port:(UInt16)port{ [client readDataWithTimeout:-1 tag:0];}- (void)onSocket:(AsyncSocket *)sock willDisconnectWithError:(NSError *)err{    NSLog(@"Error");}- (void)onSocketDidDisconnect:(AsyncSocket *)sock{ NSString *msg = @"Sorry this connect is failure"; [self showMessage:msg]; [msg release]; client = nil;}- (void)onSocketDidSecure:(AsyncSocket *)sock{}- (void)onSocket:(AsyncSocket *)sock didReadData:(NSData *)data withTag:(long)tag{ NSString* aStr = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding]; NSLog(@"Hava received datas is :%@",aStr); self.outputMsg.text = aStr; [aStr release]; [client readDataWithTimeout:-1 tag:0];}#pragma mark dealloc- (void)dealloc { [client release]; [inputMsg release]; [outputMsg release];    [super dealloc];}@end