NSinputstream read data is returning null value? - ios

Question

In my app I'm using NSStreams for client server communication. In the delegate method in event hasbytesAvailable when I'm reading the data its returning null
Case: when the length is 4096 then read is fails and returns nil; Means when the length is equal to buffer size its failing to read, even if I put the maxlength to 4000 and buffer size to 4096, then also whenever 4000 bytes are read its failing. what to do?
Here is the code:
case NSStreamEventHasBytesAvailable:
if (aStream == inputStream) {
uint8_t buffer[4096];
int len;
while ([inputStream hasBytesAvailable]) {
len = (int)[inputStream read:buffer maxLength:sizeof(buffer)];
NSLog(#"\nThe length is -- %d\n",len);
if (len > 0) {
NSData *data = [[NSData alloc] initWithBytes:buffer length:len];
output = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
// output = [[NSString alloc] initWithBytes:buffer length:len encoding:NSUTF8StringEncoding];
}
}
}
NSLog(#"\n\n%#\n\n",output);

Answer 1

Data read from a network connection will not always be received in the same sized chunks it was sent in. This means the receiver needs to:
Know exactly how much data to expect in a message.
Remember any "left over" data from the current message as that belongs to the next message.
One of the easiest ways of doing this properly is to prefix the message with a byte-count and then only attempt to read that much data from the network connection. That leaves any remaining data in the "network buffer" until the client wants it.
Your code is receiving a string, which will be NUL-terminated, so that means you need to read the data in fixed-sized chunks, check every byte until you find the end-of-string and then tack together the chunks before converting it to a string. You then need to remember any "left over" data for the next message. Complicated stuff, eh?
I'd go with the message size prefix, as that is what pretty much everyone else does.

Answer 2

I think the code is absolutely fine and it should read the data, may be after you've read 4096 bytes there might be some more bytes available and loop continues, and you are initialising the output variable again, So you might be missing it.
Use the following snippet:
if (aStream == inputStream) {
uint8_t buffer[4096];
int len;
NSString* tempOutput = #"";
while ([inputStream hasBytesAvailable]) {
len = (int)[inputStream read:buffer maxLength:sizeof(buffer)];
NSLog(#"\nThe length is -- %d\n",len);
if (len > 0) {
NSData *data = [[NSData alloc] initWithBytes:buffer length:len];
output = [[NSString alloc] initWithData:data encoding:NSUTF8StringEncoding];
tempOutput = [tempOutput stringByAppendingString:output];
// output = [[NSString alloc] initWithBytes:buffer length:len encoding:NSUTF8StringEncoding];
}
}
output = tempOutput;
}