I just tried the exact same code in Linux. (It's an FTP client). In Linux, if sendfile() is called with 0 size, then it immediately returns zero. No traffic is generated on the network at all.
I think this is simple & sane behavior to adapt in NuttX. On Mon, Jun 19, 2023 at 4:02 AM Petro Karashchenko < petro.karashche...@gmail.com> wrote: > The sendfile() description across the OSes is not the same. The FreeBSD > version https://man.freebsd.org/cgi/man.cgi?sendfile(2) for example has > words "The nbytes argument specifies how many bytes of the file should be > sent, with 0 having the special meaning of send until the end of file has > been > reached" while Linux version does not states anything about zero count, so > this seems to be "system defined". We can try to experiment with the Linux > version to see how zero bytes count is handled. > > Best regards, > Petro > > On Sun, Jun 18, 2023, 11:10 PM Fotis Panagiotopoulos <f.j.pa...@gmail.com> > wrote: > > > Hi Alan, > > > > Thanks for checking this out. > > > > The resources you linked indicate (correctly) that a TCP segment may > have 0 > > data size. > > But also that usually this is not allowed for the users? I don't know, I > > don't intend to use this. > > > > However, sendfile (not the plain send) would be completely meaningless > with > > a 0 size, I think. > > Currently, NuttX will not send anything on the wire with size set to 0. > Not > > even an empty TCP segment. > > > > I don't really want to change the way it works, only improve its > behavior. > > As it is right now, resources are wasted, and the cryptic EAGAIN makes > > troubleshooting harder. > > > > But what's best? Return zero? Change errno? > > > > On Sun, Jun 18, 2023 at 10:13 PM Alan C. Assis <acas...@gmail.com> > wrote: > > > > > Suggest, try to run you same application with this issue on Linux. > > > > > > I'm expecting at least a similar error on Linux. > > > > > > BR, > > > > > > Alan > > > > > > On 6/18/23, Alan C. Assis <acas...@gmail.com> wrote: > > > > Hi Fotis, > > > > > > > > On 6/18/23, Fotis Panagiotopoulos <f.j.pa...@gmail.com> wrote: > > > >> Hello, > > > >> > > > >> Due to a bug in my application, the code tried to use sendfile() > with > > > >> zero > > > >> size. > > > >> > > > >> As I see, sendfile() will happily proceed, and it will block here: > > > >> > > https://github.com/apache/nuttx/blob/master/net/tcp/tcp_sendfile.c#L523 > > > >> > > > >> Obviously, it will never manage to send any data (as the requested > > size > > > >> is > > > >> 0), > > > >> and after the timeout expires, it will return EAGAIN. > > > >> > > > > > > > > Good finding! > > > > > > > > BTW, that is the default timeout value? > > > > > > > > I think conn->sconn.s_sndtimeo is only defined when people enable the > > > > CONFIG_NET_SOCKOPTS. > > > > > > > >> This seems a bit wrong to me. > > > >> Why not return immediately, but instead wait for the (inevitable) > > > >> timeout? > > > >> Why not return a more meaningful error code, or maybe just 0? > > > >> > > > > > > > > I was going to suggest avoid sending a packet with 0 byte, but it is > > > > supported: > > > > https://www.quora.com/Can-TCP-send-0-byte-packets > > > > https://github.com/golang/go/issues/10940 > > > > > > > > See, technically it is not an error! :-) > > > > > > > >> I couldn't find what the standards dictate for this edge case, so > > maybe > > > >> the > > > >> current behavior is correct. > > > >> > > > >> What do you think? > > > >> > > > > > > > > I think it is correct, but most servers will just ignore it and you > > > > will end-up with a timeout. > > > > > > > > BR, > > > > > > > > Alan > > > > > > > > > >
