网络：

服务器

客户端

网络架构：
CS:Client Server 客户端（Android iOSC、C++）和服务器
BS:Browser Server 浏览器（web前端）和服务器（Java）
长链接：客户端请求服务器建立链接，链接成功后理论上会一直保持链接可以随时客户端和服务器进行数据传输
短链接：客户端请求服务器建立链接并传输数据给服务器服务器接收到数据后给客服端返回数据返回之后链接断开
Socket:是基于TCP协议和 UDP协议数据传输的方法集

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端口：有0-25535个端口 1000以内是系统预留端口

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TCP协议：链接协议“三次握手”保证数据安全到达
UDP协议：非链接协议可以广播一对多不能保证数据安全性，传输效率高（省去了建立链接的过程）

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Socket详解

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AsyncSocket 框架

1.Socket创建TCP服务器

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2.Socket创建TCP客户端

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3.发送数据

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1. Socket服务器接收数据的协议方法
  
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5.文件传输

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6.简易的聊天工具

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ViewController.m

#import "ViewController.h"
#import "GCDAsyncSocket.h"
@interface ViewController ()<GCDAsyncSocketDelegate>
@property(nonatomic,strong)GCDAsyncSocket *serverSocket;
@property(nonatomic,strong)GCDAsyncSocket *clientSocket;
@property(nonatomic,strong)NSMutableArray *sockets;
@property (weak, nonatomic) IBOutlet UITextField *scoketTF;
@property (weak, nonatomic) IBOutlet UITextField *clientTF;
@property (weak, nonatomic) IBOutlet UITextView *textvView;
@property(nonatomic,strong)NSMutableData *fileData;
@property(nonatomic)NSInteger fileLength;
@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    self.fileData = [NSMutableData data];
    self.sockets = [NSMutableArray array];
    self.serverSocket = [[GCDAsyncSocket alloc]initWithDelegate:self delegateQueue:dispatch_get_main_queue()];
    //监听端口 等待被人链接
    [self.serverSocket acceptOnPort:8000 error:nil];
}
-(void)socket:(GCDAsyncSocket *)sock didAcceptNewSocket:(GCDAsyncSocket *)newSocket{
    NSLog(@"有新的socket链接进来");
    [self.sockets addObject:newSocket];
    //跟客户端要数据
    [newSocket readDataWithTimeout:-1 tag:self.sockets.count];
}
//已经读取到数据
-(void)socket:(GCDAsyncSocket *)sock didReadData:(NSData*)data withTag:(long)tag{
    NSString *text = [[NSString alloc]initWithData:data encoding:NSUTF8StringEncoding];
    if (text.length>0) {
        //得到对方的IP地址
        NSString *host = sock.connectedHost;
        self.textvView.text = [self.textvView.text stringByAppendingFormat:@"\n%@说：%@",host,text];
        //给客户端返回数据
        [sock writeData:[@"我是服务器 我收到了！"dataUsingEncoding:NSUTF8StringEncoding] withTimeout:-1 tag:0];
    }else{//接收到的是图片
        [self.fileData appendData:data];
        UIImage *image = [UIImage imageWithData:self.fileData];
        //判断如果数据接收完成才需要显示界面中
        NSLog(@"服务器接收到：%@",text);
        if(self.fileData.length == self.fileLength){
        UIImageView *iv = [[UIImageView alloc]initWithFrame:CGRectMake(100, 100, 100, 100)];
        iv.image = image;
        [self.view addSubview:iv];
      }
        
    }
    //跟客户端继续要数据
    [sock readDataWithTimeout:-1 tag:0];
}
-(void)socketDidDisconnect:(GCDAsyncSocket *)sock withError:(NSError *)err{
    NSLog(@"已经断开链接");
    [self.sockets removeObject:sock];
}
- (IBAction)senderAction:(UIButton*)sender {
    self.clientSocket = [[GCDAsyncSocket alloc]initWithDelegate:self delegateQueue:dispatch_get_main_queue()];
    [self.clientSocket connectToHost:self.scoketTF.text onPort:8000 error:nil];
    if (sender.tag == 0) {
        [self.clientSocket writeData:[self.clientTF.text dataUsingEncoding:NSUTF8StringEncoding] withTimeout:-1 tag:0];
        //显示自己说的内容
        self.textvView.text = [self.textvView.text stringByAppendingFormat:@"\n我说：%@",self.clientTF.text];
    }else{
        NSString *path = [[NSBundle mainBundle]pathForResource:@"timg2" ofType:@"jpg"];
        NSData *imageData = [NSData dataWithContentsOfFile:path];
        self.fileLength = imageData.length;
        [self.clientSocket writeData:imageData withTimeout:-1 tag:0];
    }
}