Reads a sequence of bytes from this channel into the given buffer.
An attempt is made to read up to r bytes from the channel,
where r is the number of bytes remaining in the buffer, that is,
dst.remaining(), at the moment this method is invoked.
Suppose that a byte sequence of length n is read, where
0 <= n <= r.
This byte sequence will be transferred into the buffer so that the first
byte in the sequence is at index p and the last byte is at index
p + n - 1,
where p is the buffer's position at the moment this method is
invoked. Upon return the buffer's position will be equal to
p + n; its limit will not have changed.
A read operation might not fill the buffer, and in fact it might not
read any bytes at all. Whether or not it does so depends upon the
nature and state of the channel. A socket channel in non-blocking mode,
for example, cannot read any more bytes than are immediately available
from the socket's input buffer; similarly, a file channel cannot read
any more bytes than remain in the file. It is guaranteed, however, that
if a channel is in blocking mode and there is at least one byte
remaining in the buffer then this method will block until at least one
byte is read.
This method may be invoked at any time. If another thread has
already initiated a read operation upon this channel, however, then an
invocation of this method will block until the first operation is
complete.
