Crash during parsing socket message

[daryaklochkova]

Hi!

I have an issue with parsing a socket event message. My app crashes with error:
Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[__NSCFString appendString:]: nil argument' in function - (void)add:(NSData *)buffer SRChunkBuffer.

The buffer argument seems to be corrupt. I am sure I received the correct information because other clients parse it correctly. Could you help me, please?

Thank you,
Darya

[joeldart]

any chance this is signalr core? we dont have support for that yet. what version of signalr protocol are you using on the server?

[daryaklochkova]

We are using 2.3.0. Is it possible singnalr core if other clients are working fine? How can I check it?

[joeldart]

Signalr on dotnetcore is an entirely different protocol which is why I asked.

2.3 should be compatible though. what's the full stack trace and what data is being received?

[daryaklochkova]

I'm sorry, I made the mistake. The server uses asp net signalr(.net framework, not "core")

[daryaklochkova]

Stack trace after crash:
CrashStackTrace.txt

Stack trace after OBJ-C exception breakpoint
CrashStackTraceWithBreakpoint.txt

received data
receivedMessage.txt

Thanks for the help

[joeldart]

If I am reading your message correctly, it is crashing because it is trying to insert nil into the buffer here: https://github.com/DyKnow/SignalR-ObjC/blob/feature-dev/SignalR.Client/Transports/ServerSentEvents/SRChunkBuffer.m#L48

- (void)add:(NSData *)buffer {
    [_buffer appendString:[[NSString alloc] initWithData:buffer encoding:NSUTF8StringEncoding]];
}

but that should not be nil because the calling method checked that it had a greater-than-zero length here: https://github.com/DyKnow/SignalR-ObjC/blob/feature-dev/SignalR.Client/Transports/ServerSentEvents/SREventSourceStreamReader.m#L97-L102

                NSInteger read = [buffer length];
                if(read > 0) {
                    // Put chunks in the buffer
                    _offset = _offset + read;
                    
                    [_buffer add:buffer];
              ...

2 things:

1. what version of signalr-objc are you using
2. If you change the line in SRChunkBuffer.m to be

- (void)add:(NSData *)buffer {
    if (!buffer) return;
    [_buffer appendString:[[NSString alloc] initWithData:buffer encoding:NSUTF8StringEncoding]];
}

does it resolve the issue?

[daryaklochkova]

Yes, you are right, buffer not nil. But [[NSString alloc] initWithData:buffer encoding:NSUTF8StringEncoding]] return nil. I guess the buffer was corrupted. I need this message so I cannot ignore it.

I am using 2.0 version

[joeldart]

version: 2.0.2 is the latest, just to be sure there's nothing upstream that's been fixed.

data: interesting, what data type is the data that is returned. Im not sure ive seen eventsource return anything but string data.

could you write those bytes out to a file or something? I'd like to see if we could reproduce this in a unit test.

[daryaklochkova]

I tried to upgrade the library. I change my pod file to pod 'SignalR-ObjC', '~> 2.0.2' and run pod install. But I don't know how to verify that the library update was successful.
If the steps correct issue still reproduces on 2.0.2

SocketCrashReceivedData.txt
I collect this data in

SignalR-ObjC/SignalR.Client/Transports/ServerSentEvents/SREventSourceStreamReader.m

Line 90 in c412cc3

NSData *buffer = [stream propertyForKey:NSStreamDataWrittenToMemoryStreamKey];

NSData *buffer = [stream propertyForKey:NSStreamDataWrittenToMemoryStreamKey];
Is that what you asked for?

[joeldart]

The buffer for

SignalR-ObjC/SignalR.Client/Transports/ServerSentEvents/SREventSourceStreamReader.m

Line 95 in c412cc3

buffer = [buffer subdataWithRange:NSMakeRange(_offset, [buffer length] - _offset)];

on the line right after is the one that will get passed into the crashing line.

[daryaklochkova]

About the data format, my issue is reproduced in 50% of cases. I can not find any difference between the messages that we can parse and can not. So I think the data format is not the reason

[daryaklochkova]

data for line 95
CrashBufferData.txt

[joeldart]

thanks - I cant hop on this right now. To be sure I understand, when you pass that into [[NSString alloc] initWithData:buffer encoding:NSUTF8StringEncoding]] you found it returns nil?

[daryaklochkova]

Yes, that's right

[daryaklochkova]

I investigated the issue a bit. I get multiple socket events at the same time, so I believe multithreading may be the cause of the issue.

Also, I tried to skip the data writing if the function [[NSString alloc] initWithData:buffer encoding:NSUTF8StringEncoding]] returns nil as you suggested to me. In this case, I can reproduce a crash in this place

SignalR-ObjC/SignalR.Client/Transports/ServerSentEvents/SREventSourceStreamReader.m

Line 90 in c412cc3

NSData *buffer = [stream propertyForKey:NSStreamDataWrittenToMemoryStreamKey];

NSData *buffer = [stream propertyForKey:NSStreamDataWrittenToMemoryStreamKey]; Thread 1: EXC_BAD_ACCESS (code=1, address=0x1117b4000)
Stack traces
BadAccessStackTrace.txt

I hope it will be helpful