NSOutputStream crashing with Bad Access after write (Objective-c)

Question

I have been trying to get a basic TCP client up and running for my iOS application but have run into a block which i cannot seem to work my head around.

So far i can connect, send a message which is received on the server side but then my app crashes.

Client.h

#import <Foundation/Foundation.h>
@interface Client : NSObject <NSStreamDelegate>
{
    NSInputStream *inputStream;
    NSOutputStream *outputStream;
}

-(void)initNetworkCommunication;
-(void)send:(NSString*)message;
@end

Client.m

#import "Client.h"

@implementation Client

- (void)initNetworkCommunication {
    CFReadStreamRef readStream;
    CFWriteStreamRef writeStream;
    CFStreamCreatePairWithSocketToHost(NULL, (CFStringRef)@"10.0.1.51", 7769, &readStream, &writeStream);
    inputStream = ( NSInputStream *)CFBridgingRelease(readStream);
    outputStream = ( NSOutputStream *)CFBridgingRelease(writeStream);

    [inputStream setDelegate:self];
    [outputStream setDelegate:self];

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

    [inputStream open];
    [outputStream open];
}

- (void)send:(NSString*)message
{
    NSData *data = [[NSData alloc] initWithData:[message dataUsingEncoding:NSUTF8StringEncoding]];
    [outputStream write:[data bytes] maxLength:[data length]];
}

- (void)stream:(NSStream *)theStream handleEvent:(NSStreamEvent)streamEvent {
    NSLog(@"stream event %i", streamEvent);

    switch (streamEvent) {

        case NSStreamEventOpenCompleted:
            NSLog(@"Stream opened");
            break;

        case NSStreamEventHasBytesAvailable:
            if (theStream == inputStream) {

                uint8_t buffer[1024];
                int len;

                while ([inputStream hasBytesAvailable]) {
                    len = [inputStream read:buffer maxLength:sizeof(buffer)];
                    if (len > 0) {

                        NSString *output = [[NSString alloc] initWithBytes:buffer length:len encoding:NSASCIIStringEncoding];

                        if (nil != output) {
                            NSLog(@"server said: %@", output);
                        }
                    }
                }
            }
            break;

        case NSStreamEventErrorOccurred:
            NSLog(@"Can not connect to the host!");
            break;

        case NSStreamEventEndEncountered:
            NSLog(@"End Encountered!");
            [theStream close];
            [theStream removeFromRunLoop:[NSRunLoop currentRunLoop] forMode:NSDefaultRunLoopMode];
            theStream = nil;
            break;

        default:
            NSLog(@"Unknown event");
    }
}

@end

The output in the console is

2013-10-03 17:01:38.542 MMORPG[6076:70b] stream event 1
2013-10-03 17:01:38.543 MMORPG[6076:70b] Stream opened
2013-10-03 17:01:43.495 MMORPG[6076:70b] stream event 4
2013-10-03 17:01:43.495 MMORPG[6076:70b] Unknown event

It seems like, my message is sent, i receive stream event #4 and then i get a bad access crash. The problem is i have no idea what its having trouble accessing?

Any help would be greatly appreciated!

Can you post the stack trace for the crash? An EXC_BAD_ACCESS crash typically indicates a memory management error. Using the NSZombies instrument might help you track the problem down. — Andrew Madsen, Oct 03 '13 at 16:43
With Zombies enabled i get this extra message in my output 2013-10-03 17:48:43.989 MMORPG[6332:70b] *** -[Client respondsToSelector:]: message sent to deallocated instance 0x8ecffc0 Could this be something to do with the NSStreamDelegate which my object implements? — Jarmez De La Rocha, Oct 03 '13 at 16:53
Yes, if your NSStream's delegate (a Client instance) is deallocated while the stream is still around and open, you'd get a crash like you describe. You need to make sure something has a strong reference to the client, or else make sure you close and release the stream before Client is deallocated. — Andrew Madsen, Oct 03 '13 at 17:11
How very stupid of me! Good call, was missing a strong reference in my view controller. I really do not know how i overlooked that!! — Jarmez De La Rocha, Oct 03 '13 at 17:17
Glad to hear it. I turned my comment into a real answer, in case you'd like to accept it. — Andrew Madsen, Oct 03 '13 at 17:19

score 9 · Accepted Answer · answered Oct 03 '13 at 17:19

The problem is that NSStream keeps an assign/unsafe_unretained reference to its delegate. If the delegate is released before the stream is closed and released, the stream will try to call methods on its now deallocated delegate, causing a crash. The solution is to either make sure some other object has a strong reference to the client, preventing its early deallocation, or else make sure you close and release the stream before its delegate is deallocated.

NSOutputStream crashing with Bad Access after write (Objective-c)

1 Answers1