目标C中的线程和套接字

Question

注意：我编辑了我的问题。我用它来连接并执行第一个回调，但是后续的回调根本不通过。

这是我第一次写目标-C(与GNUstep；这是一个家庭作业)。我已经找到了解决方案，但我正试图在其中添加更多内容。该应用程序是一个GUI客户端，连接到服务器并从中获取数据。多个客户端可以连接到同一台服务器。如果任何一个客户端更改了驻留在服务器上的数据，服务器将向所有注册客户端发送回调。这个解决方案最初是用Java (客户机和服务器)实现的，对于最近的任务，教授希望我们为它编写一个目标C客户机。他说我们不需要处理回调，但我还是想试一试。

我使用的是NSThread，我写的东西如下所示：

CallbackInterceptorThread.h

#import <Foundation/Foundation.h>
#import "AppDelegate.h"

@interface CallbackInterceptorThread : NSThread {
   @private
   NSString* clientPort;
   AppDelegate* appDelegate;
}

- (id) initWithClientPort: (NSString*) aClientPort
              appDelegate: (AppDelegate*) anAppDelegate;
- (void) main;
@end

CallbackInterceptorThread.m

#import <Foundation/Foundation.h>
#import "CallbackInterceptorThread.h"

#define MAXDATASIZE 4096

@implementation CallbackInterceptorThread

- (id) initWithClientPort: (NSString*) aClientPort
                appDelegate: (AppDelegate*) anAppDelegate {

   if((self = [super init])) {
      [clientPort autorelease];
      clientPort = [aClientPort retain];
      [appDelegate autorelease];
      appDelegate = [anAppDelegate retain];
   }

   return self;
}

- (void) main {

   GSRegisterCurrentThread();

   NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];

   char* buffer = malloc(MAXDATASIZE);
   Cst420ServerSocket* socket = [[Cst420ServerSocket alloc] initWithPort: clientPort];
   [socket retain];

   NSString* returnString;

   while(YES) {
      printf("Client waiting for callbacks on port %s\n", [clientPort cString]);

      if([socket accept]) {
         printf("Connection accepted!\n");
         while(YES) {
            printf("Inner loop\n");
            sleep(1);

            returnString = [socket receiveBytes: buffer maxBytes: MAXDATASIZE beginAt: 0];
            printf("Received from Server |%s|\n", [returnString cString]);
            if([returnString length] > 0) {
               printf("Got a callback from server\n");

               [appDelegate populateGui];
            }

            printf("Going to sleep now\n");
            sleep(1);
         }

         [socket close];
      }
   }
}

@end

Cst420ServerSocket是由老师提供给我们的。看起来是这样的：

#import "Cst420Socket.h"
#define PORT "4444"

/**
 * Cst420Socket.m - objective-c class for manipulating stream sockets.
 * Purpose: demonstrate stream sockets in Objective-C.
 * These examples are buildable on MacOSX and GNUstep on top of Windows7
 */

// get sockaddr, IPv4 or IPv6:
void *get_in_addr(struct sockaddr *sa){
    if (sa->sa_family == AF_INET) {
        return &(((struct sockaddr_in*)sa)->sin_addr);
    }
    return &(((struct sockaddr_in6*)sa)->sin6_addr);
}

@implementation Cst420ServerSocket

- (id) initWithPort: (NSString*) port{
   self = [super init];
   int ret = 0;
   memset(&hints, 0, sizeof hints);
   hints.ai_family = AF_INET;
   hints.ai_socktype = SOCK_STREAM;
   hints.ai_flags = AI_PASSIVE; // use my IP
   const char* portStr = [port UTF8String];
   if ((rv = getaddrinfo(NULL, portStr, &hints, &servinfo)) != 0) {
      fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
      ret = 1;
   }else{
      for(p = servinfo; p != NULL; p = p->ai_next) {
         if ((sockfd = socket(PF_INET, SOCK_STREAM, IPPROTO_TCP))==-1){
            perror("server: socket create error");
            continue;
         }
         if (bind(sockfd, p->ai_addr, p->ai_addrlen) == -1) {
#if defined(WINGS)
         closesocket(sockfd);
#else
         close(sockfd);
#endif
            perror("server: bind error");
            continue;
         }
         break;
      }
      if (p == NULL)  {
         fprintf(stderr, "server: failed to bind\n");
         ret = 2;
      }else{
         freeaddrinfo(servinfo); // all done with this structure
         if (listen(sockfd, BACKLOG) == -1) {
            perror("server: listen error");
            ret = 3;
         }
      }
      if (ret == 0){
         return self;
      } else {
         return nil;
      }
   }
}

- (BOOL) accept {
   BOOL ret = YES;
#if defined(WINGS)
   new_fd = accept(sockfd, NULL, NULL);
#else
   new_fd = accept(sockfd, (struct sockaddr *)&their_addr, &sin_size);
#endif
   if (new_fd == -1) {
      perror("server: accept error");
      ret = NO;
   }
   connected = ret;
   return ret;
}

- (int) sendBytes: (char*) byteMsg OfLength: (int) msgLength Index: (int) at{
   int ret = send(new_fd, byteMsg, msgLength, 0);
   if(ret == -1){
      NSLog(@"error sending bytes");
   }
   return ret;
}

- (NSString* ) receiveBytes: (char*) byteMsg
                   maxBytes: (int) max
                    beginAt: (int) at {
   int ret = recv(new_fd, byteMsg, max-1, at);
   if(ret == -1){
      NSLog(@"server error receiving bytes");
   }
   byteMsg[ret+at] = '\0';
   NSString * retStr = [NSString stringWithUTF8String: byteMsg];
   return retStr;
}

- (BOOL) close{
#if defined(WINGS)
   closesocket(new_fd);
#else
   close(new_fd);
#endif
   connected = NO;
   return YES;
}

- (void) dealloc {
#if defined(WINGS)
   closesocket(sockfd);
#else
   close(sockfd);
#endif
   [super dealloc];
}

@end

我们的教授还向我们提供了一个简单回显服务器和客户机的示例(服务器只会吐出客户机发送的任何内容)，我在线程中使用了相同的模式。

我最初的问题是我的回调拦截器线程不接受来自服务器的任何(回调)连接。服务器说它无法连接回客户端(ConnectException来自Java，它说“连接拒绝”)。我可以通过修改指导员的代码来解决这个问题。在connect函数中(未显示)，他将提示设置为使用AF_UNSPEC而不是AF_INET。因此，Java看到我的本地主机IP作为0:0:0:0:0:0:0:1 (以IPv6格式)出现。当Java试图连接回发送回调时，它会收到一个异常(不确定为什么不能连接到IPv6地址)。

在修复了这个问题之后，我再次试用了我的应用程序，这次来自服务器的回调被我的客户端接收到了。但是，随后的回调无法工作。在接收到第一个回调后，繁忙循环继续运行(正如它应该的那样)。但是，当服务器发送第二个回调时，客户端似乎无法读取它。在服务器端，我可以看到它成功地向客户端发送了回调。只是客户端在读取数据时遇到了困难。我添加了一些用于调试的打印语句(参见上文)，这就是我所得到的：

Client waiting for callbacks on port 2020
Connection accepted!
Inner loop
Received from Server |A callback from server to 127.0.0.1:2020|
Got a callback from server
Going to sleep now
Inner loop
Received from Server ||
Going to sleep now
Inner loop
Received from Server ||
Going to sleep now
Inner loop
... (and it keeps going regardless of the second callback being sent)

下面是我如何启动线程(从GUI)：

CallbackInterceptorThread* callbackInterceptorThread = [[CallbackInterceptorThread alloc] initWithClientPort: clientPort appDelegate: self];
[callbackInterceptorThread start];

Answer 1

我想我已经成功了。因此，在Java端(服务器)，这就是我所做的：

Socket socket = new Socket(clientAddress, clientPort);
BufferedOutputStream out = new BufferedOutputStream(socket.getOutputStream());
out.write(("A callback from server to " + clientAddress + ":" + clientPort).getBytes());
out.flush();
out.close();

我在教授的代码中放置了一些调试打印语句，并注意到在receiveBytes中，recv返回0。recv的返回值是它收到的消息的长度。所以它收到了一个零长度的字符串。但是，返回值为0也意味着对等方正确地关闭了连接(这正是我在out.close()方面所做的)。因此，我想，如果我需要响应第二个回调，我需要再次accept连接。所以我把繁忙的循环改为：

printf("Client waiting for callbacks on port %s\n", [clientPort cString]);
while([socket accept]) {
   printf("Connection accepted!\n");    

   returnString = [socket receiveBytes: buffer maxBytes: MAXDATASIZE beginAt: 0];
   printf("Received from Server |%s|\n", [returnString cString]);

   if([returnString length] > 0) {
      printf("Got a callback from server\n");
      [appDelegate populateGui];
   }
}

[socket close];

这似乎起了作用。我不确定这是否是正确的做法，所以我愿意接受改进的建议！