Hello TAPS,
In Montreal the topic of 0RTT and idempotent interfaces came up, I remember
there being interest in a summary of TCP Fast Open APIs. Michael Tuexen[1]
forwarded me a TFO test program for a different reason and this seemed like
a good starting point to attempt to summarise the APIs on different Operating
Systems.
I have included simplified APIs for Linux, FreeBSD, Mac Os and Windows[2][3].
I quickly searched for other Operating Systems none of the below had an easily
googlable API for TCP Fast Open:
NetBSD
OpenBSD
Dragonfly BSD
Haiku
React OS
Riot OS
If there are other platforms with TFO which I have missed I would
appreciate a pointer to documentation.
- Tom
A summary of TCP Fast Open Interfaces
Linux
socket(IPPROTO_TCP)
sendto(endpoint, MSG_FASTOPEN, data)
Perform a sendto() call on the socket with a flag to indicate fast
open and the idempotent data.
FreeBSD
socket(IPPROTO_TCP)
setsockopt(TCP_FASTOPEN)
sendto(endpoint, data)
Call setsockopt() to enable fast open. Call sendto() with the
idempotent data.
Mac OS
socket(IPPROTO_TCP)
connectx(endpoints, data)
Call to connectx() function with set of addresses and
idempotent data to send.
Windows
socket(IPPROTO_TCP)
setsockopt(TCP_FASTOPEN)
bind(local_addr)
ConnectEx(endpoint, data)
Set the fast open options on the socket.
ConnectEx() must be called bound to a local address, bind() the socket
to an address
Start the connection with the ConnectEx() call, pass in the idempotent
data.
Note:
This summary is deliberately a simplification of the API to aide comparison,
full details are in various platform documentation. All of these platforms
support binding to a local address before the call, the ConnectEx() API on
Windows requires it[2]. connectex() on Mac OS supports passing in a local
addresst to bind to.
[1]: https://github.com/nplab/test-programs/blob/master/tcp-fastopen.c
[2]:
https://docs.microsoft.com/en-us/windows/desktop/api/mswsock/nc-mswsock-lpfn_connectex
[3]: https://gist.github.com/krrr/8b5fec3c93dc332bc8109641206529b5
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