On Sun, 7 Apr 2019, 04:24 John Dreystadt, <jdreyst...@gmail.com> wrote:
> I wrote some sample code (at the end of this message) to see how UDP
> worked in the Go environment. And I wound up with some issues because
> things did not seem to work as I expected. I am running go1.11.2 on both a
> Windows box and a Ubuntu box.
>
> Issue 1, when I call WriteMsgUDP with both a regular buffer and an out of
> band buffer, I get back the length as I expected. But I never see any out
> of band data on the read side. Is this a known error or am I just missing
> something?
>
> Issue 2, when I send a UDP message longer than the buffer at the receiving
> end I get an error on the Windows side along with a bit set in flags. The
> Ubuntu side does not report an error but does set a bit (but a different
> one). Even more odd, the Windows side does not return the address of the
> sending machine when this error occurs. While having one report an error
> while not the other is not unreasonable, losing the address of the sending
> machine seems really bad unless it just is not there on Windows.
>
> Issue 3, the documentation for the flags return from ReadMsgUDP just says
> "the flags set on the message" which is pretty short and does not even
> indicate who set the flags. Maybe something like "the flags are set on the
> message by the network stack and are operating system dependent".
>
> I used two copies of the following program running to see the issues. To
> replicate, first run one without any flags and then run the second with
> -mode=wr .
>
> package main
>
> import (
> "errors"
> "flag"
> "fmt"
> "net"
> )
>
> var rfserver = flag.String("RFS", "127.0.0.1:6000", "Read First Server
> Name:Port Number")
> var wfserver = flag.String("WFS", "127.0.0.1:6001", "Write First Server
> Name:Port Number")
>
> type modeValue string
>
> func (mode *modeValue) String() string {
> return string(*mode)
> }
>
> func (mode *modeValue) Set(s string) error {
> switch s {
> case "rw":
> *mode = modeValue(s)
> return nil
> case "wr":
> *mode = modeValue(s)
> return nil
> default:
> return errors.New("Mode must be rw or wr")
> }
> }
>
> var mode modeValue
>
> func main() {
> mode = modeValue("rw")
> flag.Var(&mode, "mode", "rw for read then write and wr for the reverse")
> flag.Parse()
> fmt.Println("Parameters", *rfserver, *wfserver, mode)
>
> rfudpaddr, err := net.ResolveUDPAddr("udp", *rfserver)
> if err != nil {
> panic(err)
> }
> wfudpaddr, err := net.ResolveUDPAddr("udp", *wfserver)
> if err != nil {
> panic(err)
> }
> var rudpaddr, wudpaddr *net.UDPAddr
> if mode == "rw" {
> rudpaddr, wudpaddr = rfudpaddr, wfudpaddr
> } else {
> wudpaddr, rudpaddr = rfudpaddr, wfudpaddr
> }
> pc, err := net.ListenUDP("udp", rudpaddr)
> if err != nil {
> panic(err)
> }
>
> if mode == "rw" {
> buffer := make([]byte, 5)
> oobbuffer := make([]byte, 5)
> n, oobn, flags, addr, err := pc.ReadMsgUDP(buffer, oobbuffer)
> fmt.Println("n,oobn,flags,addr,err", n, oobn, flags, addr, err)
> n, oobn, flags, addr, err = pc.ReadMsgUDP(buffer, oobbuffer)
>
Just quick note, I think you should reset both buffer and oobbuffer on
subsequence read.
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