Question

我正在构建一个发送多播消息（SSDP）的iOS应用程序，并侦听来自实现该协议的设备的响应。我正在使用GCDAsyncUdpSocket创建UDP套接字来广播SSDP消息并接收响应。我遇到的问题是，应用程序从网络上的所有设备收到的消息是相同的：HTTP 412响应。

这是我的代码：

初始化套接字

@interface ViewController ()
{
    GCDAsyncUdpSocket *udpSocket;
}
@end

@implementation ViewController

- (void)viewDidLoad
{
    [super viewDidLoad];

    udpSocket = [[GCDAsyncUdpSocket alloc] initWithDelegate:self delegateQueue:dispatch_get_main_queue()];

    NSError *error = nil;

    if (![udpSocket bindToPort:0 error:&error])
    {
        NSLog(@"Error binding: %@", [error description]);
        return;
    }
    if (![udpSocket beginReceiving:&error])
    {
        NSLog(@"Error receiving: %@", [error description]);
        return;
    }

    [udpSocket enableBroadcast:YES error:&error];
    if (error != nil)
    {
        NSLog(@"Error enableing broadcast: %@", [error description]);
        return;
    }

    NSLog(@"Socket Created");
}

创建套接字

- (IBAction)socketFind:(id)sender
{
    NSString *str = [[NSString alloc] initWithString:@"M-SEARCH * HTTP/1.1\r\nHOST: 239.255.255.250:1900\r\nMAN: \"ssdp discover\"\r\nMX: 3\r\nST: ssdp:all\r\nUSER-AGENT: iOS UPnP/1.1 TestApp/1.0\r\n\r\n"];
    NSData *data = [str dataUsingEncoding:NSUTF8StringEncoding];
    [udpSocket sendData:data toHost:@"239.255.255.250" port:1900 withTimeout:-1 tag:0];

    NSLog(@"Sent Data");
}

数据已收到回拨

- (void)udpSocket:(GCDAsyncUdpSocket *)sock didReceiveData:(NSData *)data
      fromAddress:(NSData *)address
withFilterContext:(id)filterContext
{
    NSLog(@"Did Receive Data");
    NSString *msg = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
    if (msg)
    {
        NSLog(@"Message: %@",msg);
    }
    else
    {
        NSString *host = nil;
        uint16_t port = 0;
        [GCDAsyncUdpSocket getHost:&host port:&port fromAddress:address];

        NSLog(@"Unknown Message: %@:%hu", host, port);
    }
}

调用didReceiveData函数时，收到以下消息：

Message: HTTP/1.1 412 Precondition Failed

Connection:close

CONTENT-LENGTH:0

Answer 1

此问题与M-Search字符串有关。我错过了sspd和discover之间的冒号。如果您收到412响应，我会确保您正确格式化所有内容。事实证明，那是我的问题......

GCDAsyncUdpSocket组播获取HTTP 412响应

1 个答案: