crash while reading the socket data - recv() - in objective-c - ios

Question

I'm trying to read data from the socket and it works fine most of the time.
When I run the app for longer duration - app crashes and crashlytics points the crash to readingSocket() - this function just reads raw data from socket.
Below is code of readingSocket()
-(bool) readingSocket:(NSMutableData*)dataIn readBytes:(ssize_t)quantity error:(NSError **)error {
ssize_t readBytesNow = 0;
ssize_t grossRead= 0;
[dataIn setLength:0];
if (error != nil) {
*error = nil;
}
char *buffer = new char[6144];
do {
ssize_t readBytes = (quantity - grossRead);
readBytesNow = recv((int)raw_Socket, buffer, readBytes , MSG_DONTWAIT);
if (readBytesNow == 0) {
NSLog(#" read error");
delete[] buffer;
return false;
}
Else if (bytesRead < 0) {
if (errno == EAGAIN) {
[NSThread sleepForTimeInterval:0.5f];
NSLog(#" EAGAIN error");
continue;
}
else {
// if error != nil
delete[] buffer;
return false;
}
}
else if (readBytesNow > 0) {
grossRead += readBytesNow;
// doing some operations
}
} while (grossRead < quantity);
delete[] buffer;
return true;
}
I'm already doing so many checks after reading but not sure where could the probable cause for the crash or exception ??
any other better way to handle exception in my above code ?

Answer 1

I can't comment without 50 reputation (new user here), so here goes my comment as an answer.
Warning: I have no idea of the language your code is written, but I'm using my instincts as a C++ programmer (and probably mediocre one at it).
First thing I noticed was this piece of code:
if (error != nil) {
*error = nil;
}
In C world, this would be similar to checking if a pointer is null, but assigning null as its value afterwards.
Second thing to note is this construct:
-(bool) readingSocket:(NSMutableData*)dataIn readBytes:(ssize_t)quantity error:(NSError **)error {
...
char *buffer = new char[6144];
...
ssize_t readBytes = (quantity - grossRead);
When quantity > 6144 i.e. once in a blue moon, your network stack might read more than 6144 bytes which would result in a buffer overflow.
Tangential comments:
1) I think you should note that EAGAIN and EWOULDBLOCK may be the same value but not guaranteed. You might consider checking for both of them if you are not certain that your platform behaves exactly as you think.
An example link to Linux documentation
2) Your logic,
if (readBytesNow == 0) {
...
} Else if (bytesRead < 0) {
...
} else if (readBytesNow > 0) {
...
}
although being verbose, is unnecessary. You can use
if (readBytesNow == 0) {
...
} Else if (bytesRead < 0) {
...
} else {
...
}
to be sure you are not getting an additional comparison. This comparison might get optimised out anyway, but writing this way makes more sense. I had to look again to see "if I am missing something".
Hope these help.