iOS 客户端/服务器实现和“操作正在进行中”错误答案

【问题标题】：iOS client/server implementation and "Operation now in progress" erroriOS 客户端/服务器实现和“操作正在进行中”错误
【发布时间】：2012-06-15 22:14:00
【问题描述】：

背景

我一直在通过各种示例代码和经典的 Unix 网络编程教科书自学有关套接字和网络编程的知识，同时尝试将这些知识应用到我正在开发的应用程序中现在。我目前正在处理需要简单的客户端-服务器设置的应用程序的一部分。

现在是这样的（嗯，应该是这样的）：

服务器使用NSNetService 发布自己并使用CFSocketCreateWithNative() 创建一个套接字
客户端找到NSNetServiceBrowser的服务器
客户端解析发现的服务
服务器从 CFSocket 获得一个回调，它创建一个新的类实例 (MyConnection) 来处理连接。通过CFStreamCreatePairWithSocket() 获得连接的读写流。
客户端向服务器发送消息 (@"hi")
服务器将从客户端接收到的数据发送回客户端（这是我的问题所在）
客户端在 UIAlertView 中显示字符串

两个问题

当我尝试让服务器将数据发送回客户端时，我收到“正在进行操作”错误，如下面的连接代码中所述。我相信这是因为NSOutputStream 没有可用空间。处理这个问题的最佳方法是什么？我知道它应该等待NSStreamEventHasSpaceAvailable 事件，但它似乎没有发生……
编辑：duh ...当我收到此错误时，我仅使用 iPhone 模拟器测试应用程序并让它充当服务器和客户端，因为我的新公寓还没有互联网：P 这似乎是一个使用两个真实设备时没有问题。
是否可以让这台服务器让每个连接对象的数据收发不阻塞其他连接对象的数据收发？每个新的连接对象是否需要在新的运行循环或线程或类似的东西上？我已经浏览了苹果并发文档，但没有任何东西跳出来......目标是尽可能快地向客户端发送回复，无论有多少其他客户端连接到服务器。
更新：我考虑只对连接进行排队并一次处理一个，而不是允许与该服务器的并发连接，因为需要发送到每个客户端的数据量非常小。这是最好的决定吗？如果队列中有数百个客户端怎么办？再想一想，这可能是个坏主意，因为在快速的本地网络上建立连接需要一两秒钟，而使用蓝牙则需要更长的时间......我希望得到一些关于这个问题的专家建议 :)

相关代码

注意：APNetService 和 APNetServiceBrowser 类似于 NSNetService 和 NSNetServiceBrowser

服务器代码

- (void) startServerForGroup:(NSString *)name
{
  self.groupName = name;

  NSInteger port = [self prepareListeningSocket];

  self.service = [[APNetService alloc] initWithDomain:@"local."
                                                 type:@"_example._tcp." 
                                                 name:self.groupName
                                                 port:port];
  self.service.delegate = self;
  [self.service publish];
}

- (NSInteger) prepareListeningSocket
{
  int     listenfd, err, junk, port;  
  BOOL    success;

  struct sockaddr_in addr;

  port = 0;

  listenfd = socket(AF_INET, SOCK_STREAM, 0);
  success = (listenfd != -1);

  if (success) {
    bzero(&addr, sizeof(addr));  
    addr.sin_len    = sizeof(addr);
    addr.sin_family = AF_INET;
    addr.sin_port   = 0;
    addr.sin_addr.s_addr = INADDR_ANY;
    err = bind(listenfd, (const struct sockaddr *) &addr, sizeof(addr));
    success = (err == 0);
  }
  if (success) {
    err = listen(listenfd, 5);
    success = (err == 0);
  }
  if (success) {
    socklen_t   addrLen;

    addrLen = sizeof(addr);
    err = getsockname(listenfd, (struct sockaddr *) &addr, &addrLen);
    success = (err == 0);

    if (success) {
      assert(addrLen == sizeof(addr));
      port = ntohs(addr.sin_port);
    }
  }
  if (success) {
    CFSocketContext context = { 0,(__bridge void*) self, NULL, NULL, NULL };

    CFSocketRef socket = CFSocketCreateWithNative(
                                                  NULL, 
                                                  listenfd, 
                                                  kCFSocketAcceptCallBack, 
                                                  AcceptCallback, 
                                                  &context
                                                  );
    if (socket) {
      self.listeningSocket = socket;
      CFRelease(socket);
      success = YES;
    }

    if (success) {
      CFRunLoopSourceRef  rls;

      listenfd = -1;

      rls = CFSocketCreateRunLoopSource(NULL, self.listeningSocket, 0);
      assert(rls != NULL);

      CFRunLoopAddSource(CFRunLoopGetCurrent(), rls, kCFRunLoopDefaultMode);

      CFRelease(rls);
    }
  }

  if ( success ) {
    return port;
  } 
  else {
    NSLog(@"FAILED TO START SERVER");

    if (listenfd != -1) {
      junk = close(listenfd);
      assert(junk == 0);
    }
    return -1;
  }
}

#pragma mark - Callback

// Called by CFSocket when someone connects to the listening socket
static void AcceptCallback(CFSocketRef s, CFSocketCallBackType type, CFDataRef address, const void *data, void *info)
{
  MyServer *  obj;

  obj = (__bridge MyServer *) info;

  assert(s == obj->_listeningSocket);

  MyConnection *newCon = [[MyConnection alloc] initWithFileDescriptor:*(int*)data];

  [newCon startReceive];

    //add the new connection object to the servers mutable array of connections
  [obj.connections addObject:newCon];

}

连接代码

- (void) startReceive
{
  CFReadStreamRef     readStream;
  CFWriteStreamRef    writeStream;

  CFStreamCreatePairWithSocket(NULL, self.fd, &readStream, &writeStream);

  self.inputStream =  (__bridge_transfer NSInputStream *) readStream;
  self.outputStream = (__bridge_transfer NSOutputStream*) writeStream;

  [self.inputStream setProperty:(id)kCFBooleanTrue forKey:(NSString *)kCFStreamPropertyShouldCloseNativeSocket];
  [self.outputStream setProperty:(id)kCFBooleanTrue forKey:(NSString *)kCFStreamPropertyShouldCloseNativeSocket];

  self.inputStream.delegate = self;
  self.outputStream.delegate = self;


  [self.inputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
  [self.outputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];

  [self.inputStream open];
  [self.outputStream open];
}


#pragma mark - NSStreamDelegate

- (void)stream:(NSStream *)aStream handleEvent:(NSStreamEvent)eventCode
{
  switch (eventCode) {

    case NSStreamEventHasBytesAvailable: {
      NSInteger       bytesRead;
      uint8_t         buffer[32768];

      bytesRead = [self.inputStream read:buffer maxLength:sizeof(buffer)];
      if (bytesRead == -1)...
      else if (bytesRead == 0)...
      else {
                NSData  *data = [NSData dataWithBytes:buffer length:bytesRead];
                [self didReceiveData:data];
      }
    } break;
    case NSStreamEventHasSpaceAvailable: {
      self.space = YES;
    } break;

    . . .
  }
}

- (void) didReceiveData:(NSData *)data
{
  if (self.space) 
    NSLog(@"SPACE");
  else
    NSLog(@"NO SPACE"); //this gets printed

  NSInteger i = [self.outputStream write:data.bytes maxLength:data.length];

  if (i < 0) {
    printf("%s",strerror(errno)); //"Operation now in progress" error
  }  
}

客户代码

#pragma mark - APNetServiceBrowserDelegate

- (void) browser:(APNetServiceBrowser *)browser didAddService:(APNetService *)service moreComing:(BOOL)moreComing
{
        //omitting checks that determine which server to connect to, if multiple

    service.delegate = self;
    [service resolveWithTimeout:20]; 
}


#pragma mark - APNetServiceDelegate

- (void) netServiceDidResolveAddress:(APNetService *)service
{    
  NSInputStream   *input; 
  NSOutputStream  *output;

  [service getInputStream:&input outputStream:&output];

  self.inputStream = input;
  self.outputStream = output;

  self.inputStream.delegate = self;
  self.outputStream.delegate = self;

  [self.inputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];
  [self.outputStream scheduleInRunLoop:[NSRunLoop currentRunLoop] forMode:NSRunLoopCommonModes];

  [self.inputStream open];
  [self.outputStream open];
}


#pragma mark - NSStreamDelegate

- (void) stream:(NSStream *)aStream handleEvent:(NSStreamEvent)eventCode
{
    switch (eventCode) {      

    case NSStreamEventHasBytesAvailable: {
      NSInteger       bytesRead;
      uint8_t         buffer[32768];

      bytesRead = [self.inputStream read:buffer maxLength:sizeof(buffer)];

      if (bytesRead == -1) NSLog(@"Error reading data");
      else if (bytesRead == 0) NSLog(@"no bytes read");
      else {
                NSData  *data = [NSData dataWithBytes:buffer length:bytesRead];
                [self didReceiveData:data];
      }
    } break;

    case NSStreamEventHasSpaceAvailable: {
      if (!self.isWaitingForReply) {
        [self sendHelloMessage];
      }
    } break;
        //omitted other NSStreamEvents    
  }
}

- (void) sendHelloMessage
{
  NSData *d = [NSKeyedArchiver archivedDataWithRootObject:@"hi"];

  [self.outputStream write:d.bytes maxLength:d.length];
  self.isWaiting = YES;
}


- (void) didReceiveData:(NSData *)data
{
  NSString  *string = [NSKeyedUnarchiver unarchiveObjectWithData:data];

  UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Message" 
                                                  message:string
                                                 delegate:self
                                        cancelButtonTitle:@"OK"
                                        otherButtonTitles:nil];
  [alert show];
}

【问题讨论】：

标签： objective-c ios network-programming client-server nsstream

【解决方案1】：

据我所见，您希望创建一个可以非常快速地处理许多连接的服务器。一个好的起点文档是 c10k 页面：http://www.kegel.com/c10k.html。是的，排队可能是个好主意，它消耗的资源比分叉少得多，而且响应速度更快。然而，这也意味着您的计算保持相对较小，以便您仍然能够快速回复。一个好的开始也许http://libevent.org/，检查它是如何做到的，它是为这种用途而设计的。

祝你好运。

【讨论】：