>Is read guaranteed to return without blocking, if there is at least one byte in the internal TCP ringbuffer?

yes

> If there are NO bytes in the internal TCP ringbuffer, is read guaranteed to return immediately after at least one byte pops into the TCP ringbuffer (there could be more, but the point is, read is guaranteed NOT to wait for N bytes) and will return as soon as some bytes are available from the internal ringbuffer

yes