socket的简单使用概念socket通信过程，使用步骤：导入头文件创建socket函数connect连接到服务器发送数据接收服务器返回的数据关闭连接例子：请求百度

#import <sys/socket.h>
#import <netinet/in.h>
#import <arpa/inet.h>

int socket(int domain, int type, int protocol);

int clientSocket = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

int connect(int sockfd, const struct sockaddr * serv_addr, socklen_t addrlen);

struct sockaddr_in addr;
addr.sin_family = AF_INET;
addr.sin_addr.s_addr = inet_addr("127.0.0.1");
addr.sin_port = htons(12345);

int result = connect(clientSocket, (const struct sockaddr *) &addr, sizeof(addr));
if (result != 0) {
    NSLog(@"失败");
    return;
}

struct sockaddr_in {
__uint8_t sin_len;
sa_family_t sin_family;  //类型：IPV4类型
in_port_t sin_port;  //端口号，要使用大尾顺序（各个计算机CPU型号不同，存储的顺序也会不同，htons()函数会将各个计算机统一为网络需要的大尾顺序）
struct in_addr sin_addr;  //IP地址，无符号长整型数字，调用结构体中s_addr，通过inet_addr()函数可以转换字符串
char sin_zero[8];
};

#include < sys/socket.h >

ssize_t send(int s, const void * msg, size_t len, int flags);

const char *msg = "hello world";
ssize_t sendCount = send(clientSocket, msg, strlen(msg), 0);
NSLog(@"发送的字节数 %zd",sendCount);

NSString *request = @"GET / HTTP/1.1\r\n"
"Host: www.baidu.com\r\n"
"Connection: keep-alive\r\n\r\n";

ssize_t recv(int s, void * buf, size_t len, int flags);

//接收服务器返回的数据
//返回的是实际接收的字节个数
uint8_t buffer[1024];
ssize_t recvCount = recv(clientSocket, buffer, sizeof(buffer), 0);
NSLog(@"接收的字节数 %zd",recvCount);
//把字节数组转换成字符串
NSData *data = [NSData dataWithBytes:buffer length:recvCount];
NSString *recvMsg = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
NSLog(@“收到的字符串 : %@",recvMsg);

    //找到\r\n\r\n 的范围
NSRange range = [respose rangeOfString:@"\r\n\r\n"];
    //从\r\n\r\n之后的第一个位置开始截取字符串  响应体
NSString *html = [respose substringFromIndex:range.length + range.location ];

//发送和接收数据
- (NSString *)sendAndRecv:(NSString *)sendMsg {
    //3 向服务器发送数据
    //成功则返回实际传送出去的字符数，失败返回－1
    const char *msg = sendMsg.UTF8String;
    ssize_t sendCount = send(self.clientSocket, msg, strlen(msg), 0);
    NSLog(@"发送的字节数 %zd",sendCount);
    //4 接收服务器返回的数据
    //返回的是实际接收的字节个数
    uint8_t buffer[1024];
    NSMutableData *mData = [NSMutableData data];
    ssize_t recvCount = recv(self.clientSocket, buffer, sizeof(buffer), 0);;
    [mData appendBytes:buffer length:recvCount];
    //服务器会返回多次数据，等所有的数据都接收完成，再转换成字符串
    while (recvCount != 0) {
        recvCount = recv(self.clientSocket, buffer, sizeof(buffer), 0);
        NSLog(@"接收的字节数 %zd",recvCount);
        [mData appendBytes:buffer length:recvCount];
    }
    //把字节数组转换成字符串
    NSString *recvMsg = [[NSString alloc] initWithData:mData.copy encoding:NSUTF8StringEncoding];
    return recvMsg;
}