How to know if it is safe to keep reading from a socket inputStream (avoid read blocks) - sockets

Question

I'll give you a little bit of context first:
I have a class that is supposed to write in a socket some querys and then read the answers.
Here it is the code that is supposed to read from the inputStream:
private String getDataFromInputStream() throws IOException
{
StringBuilder sb = new StringBuilder();
InputStream stream = this.socket.getInputStream();
byte[] buff = new byte[1024];
int bytesRead = 0;
while(bytesRead >= 0)
{
bytesRead = stream.read(buff);
if (bytesRead > 0) sb.append(new String(buff, 0, bytesRead));
}
return sb.toString();
}
If the returned result is OK, this method works great, but if, for some reason, the InputStream.read keeps waiting for input it, of course, blocks.
So I changed that code to this one:
private String getDataFromInputStream() throws IOException
{
StringBuilder sb = new StringBuilder();
InputStream stream = this.socket.getInputStream();
byte[] buff = new byte[1024];
int bytesRead = 0;
while(stream.available() > 0)
{
bytesRead = stream.read(buff);
if (bytesRead > 0) sb.append(new String(buff, 0, bytesRead));
}
return sb.toString();
}
But here's the new problem: The second piece of code doesn't read the whole response. It just returns a fragment of the full response.
I know that the available() method returns 0 because the stream doesn't have more data to be read inside the buffer but there is more data to be read from the socket.
So how can I make a method flexible enought to read the whole thing even if it takes some time to the Stream to buffer the response and, also doesn't block when expecting input?
I need to get the whole response if the query succeeded and to close the input so it won't block, if the command failed and the socket is expecting any input.

Answer 1

Since you're using a socket, you'll need the source to tell you how much data it wants to send. That may be present in the first few bytes that is sent (in which case you wait for that specific number of bytes first) otherwise you'll have to modify the source to provide that information. This is what TCP and UDP packets do as well, where the header to the packets include the length of the data so that the client knows how many bytes to wait for.