MAC OS X上的客户端获得空响应（使用BSD套接字和Cocoa的NSFileHandle）

Question

I'm connecting a linux machine (acting as server) and a Mac machine (as the client) using bsd sockets. Because of Cocoa's improve I'm setting bsd sockets the usual way but then encapsulating it on a NSFileHandle object. I'm using this object to send and receive messages from the server.

The protocol goes as follow: Linux gets a message from the Mac, and immediately echoes that message back to Mac.

Everything goes well 'till I get the message back. My mac gets the message empty.

Here is what I do, when sending the message.

const char *toSend = [line cStringUsingEncoding:NSASCIIStringEncoding];
printf("message to send %s\n", toSend);
//[self writeData:[line dataUsingEncoding: encoding]];

[self writeData:[NSData dataWithBytes:toSend length:strlen(toSend)]];
[self readInBackgroundAndNotify];
NSNotificationCenter *nc = [NSNotificationCenter defaultCenter];
[nc addObserver:observer selector:@selector(process:) name:NSFileHandleReadCompletionNotification object:self];

As you can see I set "process" on "observer" to process the server respond. this method does the following.

NSFileHandle *fh = [notification object];
NSData *data = [fh availableData];
NSString *dataString = [[NSString alloc]
                        initWithData:data
                        encoding:NSASCIIStringEncoding];

printf("server says %s\n", [dataString cStringUsingEncoding:NSASCIIStringEncoding]);    
[dataString release];

On console I get: "server says " and that's all

On the Linux side I'm printing what I get, and before sending it back I check I there's something.

I know I can use bsd regular sockets on Mac but I really want to pull this of.

Answer 1

Shouldn't you add the observer before calling readInBackgroundAndNotify? Your message could be read and gone by the time your process gets around to doing that.