How to get the number of available bytes in NSInputStream class in iOS?

Question

Objective-C

Greetings!
Method Returns false, and len=1. And such a call returns the required number of bytes. How can I find out how many bytes are in the stream before the data is read by the read method?
[self.inputStream getBuffer:&buf1 length:&len];
[self.inputStream read:buf maxLength:1024];