一、基本概念
在iOS中以NSStream(流)来发送和接收数据，可以设置流的代理，对流状态的变化做出相应。
1连接建立
2接收到数据
3连接关闭
NSStream：数据流的父类，用于定义抽象特性，例如：打开、关闭代理，NSStream继承自CFStream(CoreFoundation)
NSInputStream：NSStream的子类，用于读取输入
NSOutputStream：NSSTream的子类，用于写输出

二、开发步骤
1、网络连接设置
设置网络连接，绑定到主机和端口
设置输入流和输出流的代理，监听数据流的状态
将输入输出流添加至运行循环
打开输入流和输出流
2、发送消息给服务器
3、有可读取字节时，读取服务器返回的内容
4、到达流末尾时，关闭流，同时并从主运行循环中删除

#import "ViewController.h"

@interface ViewController ()<NSStreamDelegate>{
    NSInputStream *_inputStream;
    NSOutputStream *_outputSteam;
}

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
}


- (IBAction)connectToServer:(id)sender {
    //ios里实现sokcet的连接，使用C语言
    
    // 1.与服务器通过三次握手建立连接
    NSString *host = @"127.0.0.1";
    int port = 12345;
    
    // 2.定义输入输出流
    CFReadStreamRef readStream;
    CFWriteStreamRef writeStream;
    
    // 3.分配输入输出流的内存空间
    CFStreamCreatePairWithSocketToHost(NULL, (__bridge CFStringRef)host, port, &readStream, &writeStream);
    
    // 4.把C语言的输入输出流转成OC对象
    _inputStream = (__bridge NSInputStream *)readStream;
    _outputSteam = (__bridge NSOutputStream *)(writeStream);
    
    // 5.设置代理,监听数据接收的状态
    _outputSteam.delegate = self;
    _inputStream.delegate = self;
    
    // 把输入输入流添加到主运行循环(RunLoop)
    // 主运行循环是监听网络状态
    [_outputSteam scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
    [_inputStream scheduleInRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
    
    
    // 6.打开输入输出流
    [_inputStream open];
    [_outputSteam open];
}


//代理的回调是在主线程
//NSLog(@"%@",[NSThread currentThread]);
-(void)stream:(NSStream *)aStream handleEvent:(NSStreamEvent)eventCode{

//    NSStreamEventOpenCompleted = 1UL << 0,
//    NSStreamEventHasBytesAvailable = 1UL << 1,
//    NSStreamEventHasSpaceAvailable = 1UL << 2,
//    NSStreamEventErrorOccurred = 1UL << 3,
//    NSStreamEventEndEncountered = 1UL << 4
    
    switch (eventCode) {
        case NSStreamEventOpenCompleted:
            NSLog(@"%@",aStream);
            NSLog(@"成功连接建立，形成输入输出流的传输通道");
            break;
            
        case NSStreamEventHasBytesAvailable:
            NSLog(@"有数据可读");
            [self readData];
            break;
            
        case NSStreamEventHasSpaceAvailable:
            NSLog(@"可以发送数据");
            break;
            
         case NSStreamEventErrorOccurred:
            NSLog(@"有错误发生，连接失败");
            break;
            
         case NSStreamEventEndEncountered:
            NSLog(@"正常的断开连接");
            //把输入输入流关闭，而还要从主运行循环移除
            [_inputStream close];
            [_outputSteam close];
            [_inputStream removeFromRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];
            [_outputSteam removeFromRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];

            break;
        default:
            break;
    }

}

- (IBAction)loginBtnClick:(id)sender {
    //发送登录请求 使用输出流
    
    //拼接登录的指令 iam:zhangsan
    NSString *loginStr = @"iam:zhangsan";
    
    //uint8_t * 字符数组
    NSData *data = [loginStr dataUsingEncoding:NSUTF8StringEncoding];
    [_outputSteam write:data.bytes maxLength:data.length];
    
}


#pragma mark 读取服务器返回的数据
-(void)readData{
    
    //定义缓冲区 这个缓冲区只能存储1024字节
    uint8_t buf[1024];
    
    // 读取数据
    // len为从服务器读取到的实际字节数
    NSInteger len = [_inputStream read:buf maxLength:sizeof(buf)];
    
    // 把缓冲区里的实现字节数转成字符串
    NSString *receiverStr = [[NSString alloc] initWithBytes:buf length:len encoding:NSUTF8StringEncoding];
    NSLog(@"%@",receiverStr);

}
@end