建立網(wǎng)絡(luò)通信連接至少要一對端口號(socket)碎浇。socket本質(zhì)是編程接口(API)讥裤，對TCP/IP的封裝宅静，TCP/IP也要提供可供程序員做網(wǎng)絡(luò)開發(fā)所用的接口，這就是Socket編程接口涌乳；HTTP是轎車蜻懦，提供了封裝或者顯示數(shù)據(jù)的具體形式;Socket是發(fā)動機(jī)，提供了網(wǎng)絡(luò)通信的能力夕晓。

http://www.cnblogs.com/purpleraintear/p/6403053.html 這里有一篇關(guān)于UDP疑難雜癥

創(chuàng)建 socket

    // 創(chuàng)建 socket
    // AF_INET IPv4; AF_INET6 IPv6
    // SOCK_STREAM TCP; SOCK_DGRAM UDP
    _socketFileDescriptor = socket(AF_INET, SOCK_DGRAM, 0);

發(fā)送廣播

發(fā)送廣播的時候宛乃，需要將socket設(shè)置為廣播：

    // 設(shè)置socket的屬性為廣播
    int value = 1;
    int error = setsockopt(_socketFileDescriptor, SOL_SOCKET, SO_BROADCAST, (const void *)&value, sizeof(value));

發(fā)送廣播數(shù)據(jù)：

dispatch_queue_t queue = dispatch_queue_create("net.qigge.socket", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(queue, ^{
        // 設(shè)置sendto 發(fā)送的地址
        struct sockaddr_in socketParameters;
        socketParameters.sin_family = AF_INET;
        socketParameters.sin_addr.s_addr = INADDR_BROADCAST;
        socketParameters.sin_port = htons([_port intValue]);
        sendto(_socketFileDescriptor, [data bytes], [data length], 0, (struct sockaddr *)&socketParameters22, sizeof(struct sockaddr));
        NSLog(@"sendto fail, errno=%d\n", errno); // errno 錯誤代碼
    });

注意：當(dāng)socket為阻塞模式時，sendto()和recvfrom()將會阻塞當(dāng)前線程蒸辆，應(yīng)當(dāng)將這個兩個方法放入子線程中烤惊。

接收廣播

接收廣播之前，需要先綁定端口:

struct sockaddr_in socketParameters;
socketParameters.sin_family = AF_INET;
socketParameters.sin_addr.s_addr = htonl(INADDR_ANY);
socketParameters.sin_port = htons([_port intValue]);
int b = bind(_socketFileDescriptor, (struct sockaddr *)&socketParameters, sizeof(socketParameters));
if ( b < 0) {
        NSLog(@"服務(wù)端綁定失敗");
        return;
    }
NSLog(@"服務(wù)端綁定成功吁朦！");

接收信息：

dispatch_queue_t queue = dispatch_queue_create("net.qigge.rec", DISPATCH_QUEUE_CONCURRENT);
    dispatch_async(queue, ^{
        while (1) {
            int                     err;
            struct sockaddr_storage addr;
            socklen_t               addrLen;
            uint8_t                 buffer[65536];
            ssize_t                 bytesRead;

            addrLen = sizeof(addr);
            
            bytesRead = recvfrom(_socketFileDescriptor, buffer, sizeof(buffer), 0, (struct sockaddr *) &addr, &addrLen);

            if (bytesRead < 0) {
                err = errno;
            } else if (bytesRead == 0) {
                err = EPIPE;
            } else {
                NSData *    dataObj;
                NSData *    addrObj;

                err = 0;

                dataObj = [NSData dataWithBytes:buffer length:(NSUInteger) bytesRead];
                addrObj = [NSData dataWithBytes:&addr  length:addrLen  ];
            }
        }
    });

服務(wù)端和客戶端都適用于發(fā)送UDP廣播和接收UDP廣播