<quote sender="Bryan K.">
> I am implementing a server-client tcp-ip application and I would like to
> know some things.
>
> a) When read(2) returns, is it sure that the other side has recieved the
> whole buffer passed to read(2)?
"On success, the number of bytes read is returned (zero indicates
end of file), and the file position is advanced by this number.
It is not an error if this number is smaller than the number of bytes
requested; this may happen for example because fewer bytes are actually
available right now (maybe because we were close to end-of-file, or
because we are reading from a pipe, or from a terminal), or because read()
was interrupted by a signal. On error, -1 is returned, and errno is set
appropriately. In this case it is left unspecified whether the file
position (if any) changes."
so, if the other side receive the whole buffer passed, read will return
the number of bytes.
> b) If i have a loop which write(2) one byte at each itteration, the kernel
> sends many tcp packets each one containing one byte of userfull data?
what if the other host cannot receive your packet? the way you write it
is quite high-level, so you have to take care of packet loss, and all
that... so that it can resend lost packets, etc. try reading the RFC for
TFTP.
> c) An ACK is sent when the kernel receives a tcp packet or when a userspace
> read(2) from the socket occurs?
when the kernel receive a packet, ip_rcv() captures it... but to know if
it is an ACK, then your application should check it. The kernel won't be
able to know because it depends on your data structure and
implementation of your user-land application.
Eugene
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