iOS - BSDSocket 的使用

2016-08-13 725

1、BSDSocket

一套 unix 系统下的 socket API（纯 C）。
iOS 系统基于 unix，所以支持底层的 BSD Socket，在 Xcode 中可以直接使用。

2、基本使用

2.1 Client 客户端

TCP 客户端

包含头文件

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

创建 Socket

    // client Socket
    @property (nonatomic, assign) int clientSocket;

    self.clientSocket = socket(AF_INET, SOCK_STREAM, 0);

    if (self.clientSocket > 0) {
        NSLog(@"Socket 创建成功 %d", self.clientSocket);
    } else {
        NSLog(@"Socket 创建失败");
    }

连接到服务器

    // 创建服务器地址结构体
    struct sockaddr_in serverAddress;
    bzero(&serverAddress, sizeof(serverAddress));
    serverAddress.sin_family      = AF_INET;                        // 协议族
    serverAddress.sin_port        = htons(12345);                   // 端口 端口数据高位在前低位在后 12345 ＝> 3039 => 3930
    serverAddress.sin_addr.s_addr = inet_addr("192.168.88.100");    // inet_addr 函数可以把 ip 地址转换成一个整数

    int isConnected = connect(self.clientSocket, (const struct sockaddr *)&serverAddress, sizeof(serverAddress));

    if (isConnected) {
        NSLog(@"连接失败 %d", isConnected);
    } else {
        NSLog(@"连接成功");
    }

发送数据

    NSString *message = @"你好";

    ssize_t sendLen = send(self.clientSocket, message.UTF8String, strlen(message.UTF8String), 0);

    if (sendLen > 0) {
        NSLog(@"发送成功，发送 %ld 个字节数据", sendLen);
    } else {
        NSLog(@"发送失败 %zd", sendLen);
    }

接收数据

    // 接收字符串的数组，typedef unsigned char uint8_t;
    uint8_t buffer[1024];

    ssize_t recvLen = recv(self.clientSocket, buffer, sizeof(buffer), 0);

    if (recvLen > 0) {

        // 按照服务器返回的长度，从 buffer 中，读取二进制数据，建立 NSData 对象
        NSData *data = [NSData dataWithBytes:buffer length:recvLen];
        NSString *str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

        NSLog(@"接收成功，接收到 %ld 个字节数据\n 接收到：%@", recvLen, str);
    } else {
        NSLog(@"接收失败 %zd", recvLen);
    }

关闭连接

    // 数据传递完毕之后，关闭连接
    int isCloseed = close(self.clientSocket);

    NSLog(@"%d", isCloseed);

2.2 Server 服务端

TCP 服务端

包含头文件

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

创建 Socket

    // server Socket
    @property (nonatomic, assign) int serverSocket;

    // client Socket
    @property (nonatomic, assign) int clientSocket;

    self.serverSocket = socket(AF_INET, SOCK_STREAM, 0);

    if (self.serverSocket > 0) {
        NSLog(@"Socket 创建成功 %d", self.serverSocket);
    } else {
        NSLog(@"Socket 创建失败");
    }

开始监听

    // 创建服务器地址结构体
    struct sockaddr_in serverAddress;
    bzero(&serverAddress, sizeof(serverAddress));
    serverAddress.sin_family      = AF_INET;
    serverAddress.sin_port        = htons(12345);
    serverAddress.sin_addr.s_addr = inet_addr("192.168.88.100");

    int isBind = bind(self.serverSocket, (const struct sockaddr *)&serverAddress, sizeof(serverAddress));

    if (isBind) {
        NSLog(@"绑定失败 %d", isBind);
        return;
    } else {
        NSLog(@"绑定成功");
    }

    int isListen = listen(self.serverSocket, 10);

    if (isListen) {
        NSLog(@"监听失败 %d", isListen);
        return;
    } else {
        NSLog(@"监听成功");
    }

    // clientSocket
    struct sockaddr_in clientAddress;
    bzero(&clientAddress, sizeof(clientAddress));
    socklen_t len = sizeof(clientAddress);

    self.clientSocket = accept(self.serverSocket, (struct sockaddr *)&clientAddress, &len);

    if (self.clientSocket) {
        NSLog(@"接收成功 %d，client IP：%zd", self.clientSocket, clientAddress);
    } else {
        NSLog(@"接收失败");
    }

发送数据

    NSString *message = @"你好";

    // 使用 clientSocket
    ssize_t sendLen = send(self.clientSocket, message.UTF8String, strlen(message.UTF8String), 0);

    if (sendLen > 0) {
        NSLog(@"发送成功，发送 %ld 个字节数据", sendLen);
    } else {
        NSLog(@"发送失败 %zd", sendLen);
    }

接收数据

    // 接收字符串的数组，typedef unsigned char uint8_t;
    uint8_t buffer[1024];

    // 使用 clientSocket
    ssize_t recvLen = recv(self.clientSocket, buffer, sizeof(buffer), 0);

    if (recvLen > 0) {

        // 按照服务器返回的长度，从 buffer 中，读取二进制数据，建立 NSData 对象
        NSData *data = [NSData dataWithBytes:buffer length:recvLen];
        NSString *str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

        NSLog(@"接收成功，接收到 %ld 个字节数据\n 接收到：%@", recvLen, str);
    } else {
        NSLog(@"接收失败 %zd", recvLen);
    }

关闭连接

    // 数据传递完毕之后，关闭连接
    int isCloseed = close(self.serverSocket);

    NSLog(@"%d", isCloseed);

3、网络访问

1、请求：
- 1）请求行
  - GET / HTTP/1.1
  - 方法 GET
  - 路径 /
  - 协议 HTTP 1.1
- 2）请求头
  - Host: localhost 主机
  - User-Agent: 告诉服务器客户端的类型
  - Accept: 告诉服务器客户端支持的格式
  - Accept-Language: 告诉服务器客户端的语言
  - Accept-Encoding: 告诉服务器客户端支持的压缩格式
2、响应：
- 1）状态行
  - HTTP/1.1 200 OK
    - 协议 HTTP 1.1
    - 状态码:
      - 200 成功
      - 404 页面没找到
      - 301 内容没变化，用在缓存
- 2）响应头(主要在开发下载应用的时候使用的)
  - Date: Tue, 24 Mar 2015 01:52:25 GMT 访问日期
  - Server: Apache/2.4.9 (Unix) 访问服务器的类型
  - Content-Location: index.html.en 访问的文件名
  - Content-Length: 45 访问文件的大小
  - Content-Type: text/html 访问文件的类型
- 3）数据实体
  - <html><body><h1>It works!</h1></body></html>
  - 访问服务器最需的，相当于 NSURLConnection 异步方法回调中的 data。

TCP 客户端

    // 包含头文件
    #import <sys/socket.h>
    #import <netinet/in.h>
    #import <arpa/inet.h>
    #import <ifaddrs.h>

    @property (nonatomic, assign) int clientSocket;

    - (void)socketHttpRequest {

        // 连接到服务器，80 端口 apache 中就是 http 的协议
        if (![self connection:@"127.0.0.1" port:80]) {                                              
            return;
        }

        // 创建请求
        NSString *requestStr = @"GET / HTTP/1.1\n"                                                  
        "Host: localhost\n"
        "User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:36.0) Gecko/20100101 Firefox/36.0\n"
        "Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\n"
        "Accept-Language: zh-CN,zh;q=0.8,en-US;q=0.5,en;q=0.3\n"

        // \n 拼接换行，内容由 firefox 浏览器的网络控制面板的原始请求头信息中复制
        "Accept-Encoding: gzip, deflate\n"                                                          

        // 删除最后三行，最后一行加两个 \n\n
        "Connection: keep-alive\n\n";                                                               

        // 发送接收请求，发送给 web 服务器的请求需要遵守 http 协议
        NSString *recvStr = [self sendAndRecv:requestStr];                                          

        NSLog(@"%@", recvStr);
    }

    /// 创建连接
    - (BOOL)connection:(NSString *)hostText port:(int)port {

        // 创建 Socket

            self.clientSocket = socket(AF_INET, SOCK_STREAM, 0);

        // 连接到服务器

            struct sockaddr_in serverAddress;
            bzero(&serverAddress, sizeof(serverAddress));
            serverAddress.sin_family      = AF_INET;
            serverAddress.sin_port        = htons(port);
            serverAddress.sin_addr.s_addr = inet_addr(hostText.UTF8String);

            int isConnected = connect(self.clientSocket, (const struct sockaddr *)&serverAddress, sizeof(serverAddress));

            return (isConnected == 0);
    }

    /// 发送和接收字符串
    - (NSString *)sendAndRecv:(NSString *)message {

        // 发送数据

            send(self.clientSocket, message.UTF8String, strlen(message.UTF8String), 0);

        // 接收数据

            uint8_t buffer[1024];                                                                   

            ssize_t recvLen = recv(self.clientSocket, buffer, sizeof(buffer), 0);

            NSData *data = [NSData dataWithBytes:buffer length:recvLen];                            
            NSString *str = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];

            return str;
    }

4、客户端使用

TCP 客户端 & UDP

    // 包含头文件
    #import <sys/socket.h>
    #import <netinet/in.h>
    #import <arpa/inet.h>
    #import <ifaddrs.h>

    typedef NS_ENUM (NSInteger,ServerType) {
        ServerTypeTCP,
        ServerTypeUDP
    };

    @property (weak, nonatomic) IBOutlet UITextField *desIPTF;
    @property (weak, nonatomic) IBOutlet UITextField *desPortTF;

    @property (weak, nonatomic) IBOutlet UITextField *locIPTF;
    @property (weak, nonatomic) IBOutlet UITextField *locPortTF;

    @property (weak, nonatomic) IBOutlet UITextView *recvTextView;
    @property (weak, nonatomic) IBOutlet UITextField *sendTF;

    @property (nonatomic, assign) int clientSockfd;
    @property (nonatomic, assign) int udpSockfd;

    @property (nonatomic, assign) ServerType serType;

    - (void)viewDidLoad {
        [super viewDidLoad];

        NSString *ip_addr = [self getIPAddress];
        _locIPTF.text = ip_addr;
    }

    #pragma mark - 创建 TCP 连接

    - (IBAction)connectTCPServer:(id)sender {

        [NSThread detachNewThreadSelector:@selector(connectTCPSer) toTarget:self withObject:nil];
    }

    - (void)connectTCPSer {

        self.serType = ServerTypeTCP;

        BOOL success;
        int err;

        // 创建 socket
        self.clientSockfd = socket(AF_INET, SOCK_STREAM, 0);
        success = (self.clientSockfd != -1);

        NSString *logStr = nil;

        if (success == NO) {

            logStr = @"创建 socket 失败...\n";
            [self showMessage:logStr];

            return;

        } else {

            logStr = @"创建 socket 成功...\n";
            [self showMessage:logStr];

            // 服务器地址
            struct sockaddr_in ser_addr;
            memset(&ser_addr, 0, sizeof(ser_addr));
            ser_addr.sin_len         = sizeof(ser_addr);
            ser_addr.sin_family      = AF_INET;
            ser_addr.sin_port        = htons(_desPortTF.text.intValue);
            ser_addr.sin_addr.s_addr = inet_addr(_desIPTF.text.UTF8String);

            // 连接
            err = connect(self.clientSockfd, (struct sockaddr *)&ser_addr, sizeof(ser_addr));
            success = (err == 0);
        }

        if (success == NO) {

            logStr = @"socket 连接失败...\n";
            [self showMessage:logStr];

            return;

        } else {

            logStr = [NSString stringWithFormat:@"socket 连接 %@ 成功...\n", _desIPTF.text];
            [self showMessage:logStr];

            char buf[1024];
            do {
                // 接收数据
                ssize_t recvLen = recv(self.clientSockfd, buf, sizeof(buf), 0);

                if (recvLen > 0) {
                    logStr = [NSString stringWithFormat:@"recv：%@\n", [NSString stringWithUTF8String:buf]];
                    [self showMessage:logStr];
                }

            } while (strcmp(buf, "exit") != 0);
        }
    }

    #pragma mark - 创建 UDP 连接

    - (IBAction)connectUDP:(id)sender {

        [NSThread detachNewThreadSelector:@selector(connectUDP) toTarget:self withObject:nil];
    }

    - (void)connectUDP {

        self.serType = ServerTypeUDP;

        BOOL success;
        int err;

        // 创建 Socket
        self.udpSockfd = socket(AF_INET, SOCK_DGRAM, 0);
        success = (self.udpSockfd != -1);

        NSString *logStr = nil;

        if (success == NO) {

            logStr = @"创建 socket 失败...\n";
            [self showMessage:logStr];

            return;

        } else {

            logStr = @"创建 socket 成功...\n";
            [self showMessage:logStr];

            // 本地地址
            struct sockaddr_in loc_addr;
            bzero(&loc_addr, sizeof(loc_addr));
            loc_addr.sin_port        = htons(_locPortTF.text.intValue);
            loc_addr.sin_addr.s_addr = inet_addr(_locIPTF.text.UTF8String);

            // 绑定
            err = bind(self.udpSockfd, (const struct sockaddr *)&loc_addr, sizeof(loc_addr));
            success = (err == 0);
        }

        if (success == NO) {

            logStr = @"socket 绑定失败...\n";
            [self showMessage:logStr];

            return;

        } else {

            logStr = @"socket 绑定成功...\n";
            [self showMessage:logStr];

            // 目标地址
            struct sockaddr_in des_addr;
            bzero(&des_addr, sizeof(des_addr));
            des_addr.sin_family      = AF_INET;
            des_addr.sin_port        = htons(_desPortTF.text.intValue);
            des_addr.sin_addr.s_addr = inet_addr(_desIPTF.text.UTF8String);

            char buf[256];
            bzero(buf, sizeof(buf));

            while(1) {

                // 接收数据
                socklen_t des_addr_len = sizeof(des_addr);
                ssize_t recvLen = recvfrom(self.udpSockfd, buf, sizeof(buf), 0, (struct sockaddr*)&des_addr, &des_addr_len);

                if (recvLen > 0) {
                    logStr = [NSString stringWithFormat:@"recv：%@\n", [NSString stringWithUTF8String:buf]];
                    [self showMessage:logStr];
                }
            }
        }
    }

    #pragma mark - 发送数据

    - (IBAction)btnClick:(id)sender {

        if (_sendTF.text.length == 0) {
            return;
        } else {

            ssize_t sendLen;

            if (self.serType == ServerTypeTCP) {

                // 发送数据
                sendLen = send(self.clientSockfd, _sendTF.text.UTF8String, strlen(_sendTF.text.UTF8String), 0);

            } else if (self.serType == ServerTypeUDP) {

                // 目标地址
                struct sockaddr_in des_addr;
                bzero(&des_addr, sizeof(des_addr));
                des_addr.sin_family      = AF_INET;
                des_addr.sin_port        = htons(_desPortTF.text.intValue);
                des_addr.sin_addr.s_addr = inet_addr(_desIPTF.text.UTF8String);

                // 发送数据
                sendLen = sendto(self.udpSockfd, _sendTF.text.UTF8String, strlen(_sendTF.text.UTF8String), 0, 
                                 (struct sockaddr *)&des_addr, sizeof(des_addr));
            }

            if (sendLen > 0) {
                NSString *logStr = [NSString stringWithFormat:@"send：%@\n", _sendTF.text];
                [self showMessage:logStr];
            }
        }
    }

    #pragma mark - 获取本地 IP 地址

    - (NSString *)getIPAddress {

        NSString *address = @"error";
        struct ifaddrs *interfaces = NULL;
        struct ifaddrs *temp_addr = NULL;
        int success = 0;

        // retrieve the current interfaces - returns 0 on success
        success = getifaddrs(&interfaces);

        if (success == 0) {

            // Loop through linked list of interfaces
            temp_addr = interfaces;

            while (temp_addr != NULL) {

                if (temp_addr->ifa_addr->sa_family == AF_INET) {

                    // Check if interface is en0 which is the wifi connection on the iPhone
                    if ([[NSString stringWithUTF8String:temp_addr->ifa_name] isEqualToString:@"en0"]) {

                        // Get NSString from C String
                        address = [NSString stringWithUTF8String:inet_ntoa(((struct sockaddr_in *)temp_addr->ifa_addr)->sin_addr)];
                    }
                }
                temp_addr = temp_addr->ifa_next;
            }
        }

        // Free memory
        freeifaddrs(interfaces);
        return address;
    }

    // 显示信息
    - (void)showMessage:(NSString *)msg {

        dispatch_async(dispatch_get_main_queue(), ^{

            _recvTextView.text = [_recvTextView.text stringByAppendingString:msg];
        });
    }

5、服务端使用

TCP 服务端 & UDP

    // 包含头文件
    #import <sys/socket.h>
    #import <netinet/in.h>
    #import <arpa/inet.h>
    #import <ifaddrs.h>

    typedef NS_ENUM (NSInteger,ServerType) {
        ServerTypeTCP,
        ServerTypeUDP
    };

    @property (weak, nonatomic) IBOutlet UITextField *desIPTF;
    @property (weak, nonatomic) IBOutlet UITextField *desPortTF;

    @property (weak, nonatomic) IBOutlet UITextField *locIPTF;
    @property (weak, nonatomic) IBOutlet UITextField *locPortTF;

    @property (weak, nonatomic) IBOutlet UITextView *recvTextView;
    @property (weak, nonatomic) IBOutlet UITextField *sendTF;

    @property (nonatomic, assign) int serverSockfd;
    @property (nonatomic, assign) int clientSockfd;

    @property (nonatomic, assign) int udpSockfd;

    @property (nonatomic, assign) ServerType serType;

    - (void)viewDidLoad {
        [super viewDidLoad];

        NSString *ip_addr = [self getIPAddress];
        _locIPTF.text = ip_addr;
    }

    #pragma mark - 创建 TCP 监听

    - (IBAction)createdTCPServer:(id)sender {

        _desIPTF.enabled = NO;
        _desPortTF.enabled = NO;
        _locPortTF.enabled = NO;

        [NSThread detachNewThreadSelector:@selector(createdTCPSer) toTarget:self withObject:nil];
    }

    - (void)createdTCPSer {

        self.serType = ServerTypeTCP;

        BOOL success;
        int err;

        // 创建 socket
        self.serverSockfd = socket(AF_INET, SOCK_STREAM, 0);
        success = (self.serverSockfd != -1);

        NSString *logStr = nil;

        if (success == NO) {

            logStr = @"创建 socket 失败...\n";
            [self showMessage:logStr];

            return;

        } else {

            logStr = @"创建 socket 成功...\n";
            [self showMessage:logStr];

            // 本地地址
            struct sockaddr_in loc_addr;
            memset(&loc_addr, 0, sizeof(loc_addr));
            loc_addr.sin_family      = AF_INET;
            loc_addr.sin_port        = htons(_locPortTF.text.intValue);
            loc_addr.sin_addr.s_addr = inet_addr(_locIPTF.text.UTF8String);

            // 绑定
            err = bind(self.serverSockfd, (const struct sockaddr *)&loc_addr, sizeof(loc_addr));
            success = (err == 0);
        }

        if (success == NO) {

            logStr = @"socket 绑定失败...\n";
            [self showMessage:logStr];

            return;

        } else {

            logStr = @"socket 绑定成功...\n";
            [self showMessage:logStr];

            // 监听
            err = listen(self.serverSockfd, 5);     // 5：最大连接个数
            success = (err == 0);
        }

        if (success == NO) {

            logStr = @"socket 监听失败...\n";
            [self showMessage:logStr];

            return;

        } else {

            logStr = @"socket 监听成功...\n";
            [self showMessage:logStr];

            while (true) {      // 循环

                // 连接的客户端的地址
                struct sockaddr_in cli_addr;
                socklen_t cli_addr_Len = sizeof(cli_addr);

                // 接受客户端的请求，并建立连接
                self.clientSockfd = accept(self.serverSockfd, (struct sockaddr *)&cli_addr, &cli_addr_Len);
                success = (self.clientSockfd != -1);

                if (success) {

                    char *ip_addr = inet_ntoa(cli_addr.sin_addr);
                    int ip_port   = ntohs(cli_addr.sin_port);
                    dispatch_async(dispatch_get_main_queue(), ^{
                        _desIPTF.text = [NSString stringWithFormat:@"%s", ip_addr];
                        _desPortTF.text = [NSString stringWithFormat:@"%d", ip_port];
                    });

                    logStr = [NSString stringWithFormat:@"已连接：%s，port：%d\n", ip_addr, ip_port];
                    [self showMessage:logStr];

                    char buf[1024];
                    do {
                        // 返回读取的字节数
                        ssize_t recvLen = recv(self.clientSockfd, buf, sizeof(buf), 0);

                        if (recvLen > 0) {
                            logStr = [NSString stringWithFormat:@"recv：%@\n", [NSString stringWithUTF8String:buf]];
                            [self showMessage:logStr];
                        }

                    } while (strcmp(buf, "exit") != 0);
                }
            }
        }
    }

    #pragma mark - 创建 UDP 连接

    - (IBAction)connectUDP:(id)sender {

        [NSThread detachNewThreadSelector:@selector(connectUDP) toTarget:self withObject:nil];
    }

    - (void)connectUDP {

        self.serType = ServerTypeUDP;

        BOOL success;
        int err;

        // 创建 Socket
        self.udpSockfd = socket(AF_INET, SOCK_DGRAM, 0);
        success = (self.udpSockfd != -1);

        NSString *logStr = nil;

        if (success == NO) {

            logStr = @"创建 socket 失败...\n";
            [self showMessage:logStr];

            return;

        } else {

            logStr = @"创建 socket 成功...\n";
            [self showMessage:logStr];

            // 本地地址
            struct sockaddr_in loc_addr;
            bzero(&loc_addr, sizeof(loc_addr));
            loc_addr.sin_port        = htons(_locPortTF.text.intValue);
            loc_addr.sin_addr.s_addr = inet_addr(_locIPTF.text.UTF8String);

            // 绑定
            err = bind(self.udpSockfd, (const struct sockaddr *)&loc_addr, sizeof(loc_addr));
            success = (err == 0);
        }

        if (success == NO) {

            logStr = @"socket 绑定失败...\n";
            [self showMessage:logStr];

            return;

        } else {

            logStr = @"socket 绑定成功...\n";
            [self showMessage:logStr];

            // 目标地址
            struct sockaddr_in des_addr;
            bzero(&des_addr, sizeof(des_addr));
            des_addr.sin_family      = AF_INET;
            des_addr.sin_port        = htons(_desPortTF.text.intValue);
            des_addr.sin_addr.s_addr = inet_addr(_desIPTF.text.UTF8String);

            char buf[256];
            bzero(buf, sizeof(buf));

            while(1) {

                // 接收数据
                socklen_t des_addr_len = sizeof(des_addr);
                ssize_t recvLen = recvfrom(self.udpSockfd, buf, sizeof(buf), 0, (struct sockaddr*)&des_addr, &des_addr_len);

                if (recvLen > 0) {
                    logStr = [NSString stringWithFormat:@"recv：%@\n", [NSString stringWithUTF8String:buf]];
                    [self showMessage:logStr];
                }
            }
        }
    }

    #pragma mark - 发送数据

    - (IBAction)btnClick:(id)sender {

        if (_sendTF.text.length == 0) {
            return;
        } else {

            ssize_t sendLen;

            if (self.serType == ServerTypeTCP) {

                // 发送数据
                sendLen = send(self.clientSockfd, _sendTF.text.UTF8String, strlen(_sendTF.text.UTF8String), 0);

            } else if (self.serType == ServerTypeUDP) {

                // 目标地址
                struct sockaddr_in des_addr;
                bzero(&des_addr, sizeof(des_addr));
                des_addr.sin_family      = AF_INET;
                des_addr.sin_port        = htons(_desPortTF.text.intValue);
                des_addr.sin_addr.s_addr = inet_addr(_desIPTF.text.UTF8String);

                // 发送数据
                sendLen = sendto(self.udpSockfd, _sendTF.text.UTF8String, strlen(_sendTF.text.UTF8String), 0, 
                                 (struct sockaddr *)&des_addr, sizeof(des_addr));
            }

            if (sendLen > 0) {
                NSString *logStr = [NSString stringWithFormat:@"send：%@\n", _sendTF.text];
                [self showMessage:logStr];
            }
        }
    }

    #pragma mark - 获取本地 IP 地址

    - (NSString *)getIPAddress {

        NSString *address = @"error";
        struct ifaddrs *interfaces = NULL;
        struct ifaddrs *temp_addr = NULL;
        int success = 0;

        // retrieve the current interfaces - returns 0 on success
        success = getifaddrs(&interfaces);

        if (success == 0) {

            // Loop through linked list of interfaces
            temp_addr = interfaces;

            while (temp_addr != NULL) {

                if (temp_addr->ifa_addr->sa_family == AF_INET) {

                    // Check if interface is en0 which is the wifi connection on the iPhone
                    if ([[NSString stringWithUTF8String:temp_addr->ifa_name] isEqualToString:@"en0"]) {

                        // Get NSString from C String
                        address = [NSString stringWithUTF8String:inet_ntoa(((struct sockaddr_in *)temp_addr->ifa_addr)->sin_addr)];
                    }
                }
                temp_addr = temp_addr->ifa_next;
            }
        }

        // Free memory
        freeifaddrs(interfaces);
        return address;
    }

    // 显示信息
    - (void)showMessage:(NSString *)msg {

        dispatch_async(dispatch_get_main_queue(), ^{

            _recvTextView.text = [_recvTextView.text stringByAppendingString:msg];
        });
    }

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