On Fri, Aug 2, 2024 at 10:57 PM Niu Danny <danny...@hotmail.com> wrote:
> BAND data corresponds to out-of-band data bit mask for
> flags in `recv` and `send` calls, which in turn corresponds
> to TCP Urgent packet bit,
On what OS and where is that documented?
> and it's a (legacy) mechanism
> for dealing with head-of-line blocking. It's used by Telnet
> and FTP but not HTTP.
Where is that specified? It sure looks to me that TCP OOB data
matches the semantics in previous POSIX specs for the 'high-priority'
data checked for with POLLPRI. (At most one high-priority data was
permitted, and it was not subject to queuing/backpressure like the
priority bands)
That's how URG 'data' is reported on OpenBSD and is what is documented
by the Linux manual project at
https://man7.org/linux/man-pages/man2/poll.2.html
Indeed, that page currently documents that the values I suggest be
deprecated "convey no further information" on Linux.
> Windows has fully specifies behavior regarding TCP URG bit,
> OOB, and its own WSAPoll, which is a distant relative of ours.
I can believe that. Can you point us to the part of those docs which
you feel are relevant? What POLL* constant (or WSAPoll equivalent) do
they use for reporting not-yet-reached TCP URG pointer?
> Someone previously voiced their opinion that, since OOB is
> specified as protocol-specific by POSIX, OOB and band data
> cannot be portably used. Nonetheless, I believe the standard
> should note its history, and recommend developers to consult
> implementations' documents, as well as IETF RFCs if they
> insist on using it.
Last I checked, no IETF RFC provides any indication about poll() POLL*
values to use. Do you know of one that does?
I was careful in my request to suggest deprecation of the 'BAND' and
'NORM' values and *not* POLLPRI.
Philip Guenther
