Sockets: BufferedReader readLine() blocks

I am using BufferedReader.readLine() method to read a response from a remote server (which is written in C and I have no access to source code).

BufferedReader br = new BufferedReader(new InputStreamReader(in));
String line;
while((line = br.readLine())!=null){
    [...]
}

But it always blocks at the last line until it times out. So I used the following code:

int b;
while(true){
   b = in.read;
   [...]
}

and I found out that the last byte read has an integer value of 13, which I think it is a carriage return, right?

So why the readLine method blocks? How does the server usually signal an end of stream is reached? Thanks.